Sample records for halo occupation framework

  1. THE HALO OCCUPATION DISTRIBUTION OF SDSS QUASARS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Richardson, Jonathan; Chatterjee, Suchetana; Nagai, Daisuke

    2012-08-10

    We present an estimate of the projected two-point correlation function (2PCF) of quasars in the Sloan Digital Sky Survey (SDSS) over the full range of one- and two-halo scales, 0.02 h{sup -1} Mpc < r{sub p} < 120 h{sup -1} Mpc. This was achieved by combining data from SDSS DR7 on large scales and Hennawi et al. (with appropriate statistical corrections) on small scales. Our combined clustering sample is the largest spectroscopic quasar clustering sample to date, containing {approx}48, 000 quasars in the redshift range 0.4 {approx}< z {approx}< 2.5 with median redshift 1.4. We interpret these precise 2PCF measurementsmore » within the halo occupation distribution (HOD) framework and constrain the occupation functions of central and satellite quasars in dark matter halos. In order to explain the small-scale clustering, the HOD modeling requires that a small fraction of z {approx} 1.4 quasars, f{sub sat} = (7.4 {+-} 1.4) Multiplication-Sign 10{sup -4}, be satellites in dark matter halos. At z {approx} 1.4, the median masses of the host halos of central and satellite quasars are constrained to be M{sub cen} = 4.1{sup +0.3}{sub -0.4} Multiplication-Sign 10{sup 12} h{sup -1} M{sub Sun} and M{sub sat} = 3.6{sup +0.8}{sub -1.0} Multiplication-Sign 10{sup 14} h{sup -1} M{sub Sun }, respectively. To investigate the redshift evolution of the quasar-halo relationship, we also perform HOD modeling of the projected 2PCF measured by Shen et al. for SDSS quasars with median redshift 3.2. We find tentative evidence for an increase in the mass scale of quasar host halos-the inferred median mass of halos hosting central quasars at z {approx} 3.2 is M{sub cen} = 14.1{sup +5.8}{sub -6.9} Multiplication-Sign 10{sup 12} h{sup -1} M{sub Sun }. The cutoff profiles of the mean occupation functions of central quasars reveal that quasar luminosity is more tightly correlated with halo mass at higher redshifts. The average quasar duty cycle around the median host halo mass is inferred to be f

  2. Redshift-space distortions with the halo occupation distribution - II. Analytic model

    NASA Astrophysics Data System (ADS)

    Tinker, Jeremy L.

    2007-01-01

    We present an analytic model for the galaxy two-point correlation function in redshift space. The cosmological parameters of the model are the matter density Ωm, power spectrum normalization σ8, and velocity bias of galaxies αv, circumventing the linear theory distortion parameter β and eliminating nuisance parameters for non-linearities. The model is constructed within the framework of the halo occupation distribution (HOD), which quantifies galaxy bias on linear and non-linear scales. We model one-halo pairwise velocities by assuming that satellite galaxy velocities follow a Gaussian distribution with dispersion proportional to the virial dispersion of the host halo. Two-halo velocity statistics are a combination of virial motions and host halo motions. The velocity distribution function (DF) of halo pairs is a complex function with skewness and kurtosis that vary substantially with scale. Using a series of collisionless N-body simulations, we demonstrate that the shape of the velocity DF is determined primarily by the distribution of local densities around a halo pair, and at fixed density the velocity DF is close to Gaussian and nearly independent of halo mass. We calibrate a model for the conditional probability function of densities around halo pairs on these simulations. With this model, the full shape of the halo velocity DF can be accurately calculated as a function of halo mass, radial separation, angle and cosmology. The HOD approach to redshift-space distortions utilizes clustering data from linear to non-linear scales to break the standard degeneracies inherent in previous models of redshift-space clustering. The parameters of the occupation function are well constrained by real-space clustering alone, separating constraints on bias and cosmology. We demonstrate the ability of the model to separately constrain Ωm,σ8 and αv in models that are constructed to have the same value of β at large scales as well as the same finger-of-god distortions at

  3. The Halo Occupation Distribution of Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Chatterjee, Suchetana; Nagai, D.; Richardson, J.; Zheng, Z.; Degraf, C.; DiMatteo, T.

    2011-05-01

    We investigate the halo occupation distribution of active galactic nuclei (AGN) using a state-of-the-art cosmological hydrodynamic simulation that self-consistently incorporates the growth and feedback of supermassive black holes and the physics of galaxy formation (DiMatteo et al. 2008). We show that the mean occupation function can be modeled as a softened step function for central AGN and a power law for the satellite population. The satellite occupation is consistent with weak redshift evolution and a power law index of unity. The number of satellite black holes at a given halo mass follows a Poisson distribution. We show that at low redshifts (z=1.0) feedback from AGN is responsible for higher suppression of black hole growth in higher mass halos. This effect introduces a bias in the correlation between instantaneous AGN luminosity and the host halo mass, making AGN clustering depend weakly on luminosity at low redshifts. We show that the radial distribution of AGN follows a power law which is fundamentally different from those of galaxies and dark matter. The best-fit power law index is -2.26 ± 0.23. The power law exponent do not show any evolution with redshift, host halo mass and AGN luminosity within statistical limits. Incorporating the environmental dependence of supermassive black hole accretion and feedback, our formalism provides the most complete theoretical tool for interpreting current and future measurements of AGN clustering.

  4. Exploring the squeezed three-point galaxy correlation function with generalized halo occupation distribution models

    NASA Astrophysics Data System (ADS)

    Yuan, Sihan; Eisenstein, Daniel J.; Garrison, Lehman H.

    2018-04-01

    We present the GeneRalized ANd Differentiable Halo Occupation Distribution (GRAND-HOD) routine that generalizes the standard 5 parameter halo occupation distribution model (HOD) with various halo-scale physics and assembly bias. We describe the methodology of 4 different generalizations: satellite distribution generalization, velocity bias, closest approach distance generalization, and assembly bias. We showcase the signatures of these generalizations in the 2-point correlation function (2PCF) and the squeezed 3-point correlation function (squeezed 3PCF). We identify generalized HOD prescriptions that are nearly degenerate in the projected 2PCF and demonstrate that these degeneracies are broken in the redshift-space anisotropic 2PCF and the squeezed 3PCF. We also discuss the possibility of identifying degeneracies in the anisotropic 2PCF and further demonstrate the extra constraining power of the squeezed 3PCF on galaxy-halo connection models. We find that within our current HOD framework, the anisotropic 2PCF can predict the squeezed 3PCF better than its statistical error. This implies that a discordant squeezed 3PCF measurement could falsify the particular HOD model space. Alternatively, it is possible that further generalizations of the HOD model would open opportunities for the squeezed 3PCF to provide novel parameter measurements. The GRAND-HOD Python package is publicly available at https://github.com/SandyYuan/GRAND-HOD.

  5. The 6dF Galaxy Survey: dependence of halo occupation on stellar mass

    NASA Astrophysics Data System (ADS)

    Beutler, Florian; Blake, Chris; Colless, Matthew; Jones, D. Heath; Staveley-Smith, Lister; Campbell, Lachlan; Parker, Quentin; Saunders, Will; Watson, Fred

    2013-03-01

    In this paper we study the stellar mass dependence of galaxy clustering in the 6dF Galaxy Survey (6dFGS). The near-infrared selection of 6dFGS allows more reliable stellar mass estimates compared to optical bands used in other galaxy surveys. Using the halo occupation distribution model, we investigate the trend of dark matter halo mass and satellite fraction with stellar mass by measuring the projected correlation function, wp(rp). We find that the typical halo mass (M1) as well as the satellite power-law index (α) increases with stellar mass. This indicates (1) that galaxies with higher stellar mass sit in more massive dark matter haloes and (2) that these more massive dark matter haloes accumulate satellites faster with growing mass compared to haloes occupied by low stellar mass galaxies. Furthermore, we find a relation between M1 and the minimum dark matter halo mass (Mmin) of M1 ≈ 22 Mmin, in agreement with similar findings for Sloan Digital Sky Survey galaxies. The satellite fraction of 6dFGS galaxies declines with increasing stellar mass from 21 per cent at Mstellar = 2.6 × 1010 h-2 M⊙ to 12 per cent at Mstellar = 5.4 × 1010 h-2 M⊙ indicating that high stellar mass galaxies are more likely to be central galaxies. We compare our results to two different semi-analytic models derived from the Millennium Simulation, finding some disagreement. Our results can be used for placing new constraints on semi-analytic models in the future, particularly the behaviour of luminous red satellites. Finally, we compare our results to studies of halo occupation using galaxy-galaxy weak lensing. We find good overall agreement, representing a valuable cross-check for these two different tools of studying the matter distribution in the Universe.

  6. Modelling galaxy clustering: halo occupation distribution versus subhalo matching.

    PubMed

    Guo, Hong; Zheng, Zheng; Behroozi, Peter S; Zehavi, Idit; Chuang, Chia-Hsun; Comparat, Johan; Favole, Ginevra; Gottloeber, Stefan; Klypin, Anatoly; Prada, Francisco; Rodríguez-Torres, Sergio A; Weinberg, David H; Yepes, Gustavo

    2016-07-01

    We model the luminosity-dependent projected and redshift-space two-point correlation functions (2PCFs) of the Sloan Digital Sky Survey (SDSS) Data Release 7 Main galaxy sample, using the halo occupation distribution (HOD) model and the subhalo abundance matching (SHAM) model and its extension. All the models are built on the same high-resolution N -body simulations. We find that the HOD model generally provides the best performance in reproducing the clustering measurements in both projected and redshift spaces. The SHAM model with the same halo-galaxy relation for central and satellite galaxies (or distinct haloes and subhaloes), when including scatters, has a best-fitting χ 2 /dof around 2-3. We therefore extend the SHAM model to the subhalo clustering and abundance matching (SCAM) by allowing the central and satellite galaxies to have different galaxy-halo relations. We infer the corresponding halo/subhalo parameters by jointly fitting the galaxy 2PCFs and abundances and consider subhaloes selected based on three properties, the mass M acc at the time of accretion, the maximum circular velocity V acc at the time of accretion, and the peak maximum circular velocity V peak over the history of the subhaloes. The three subhalo models work well for luminous galaxy samples (with luminosity above L * ). For low-luminosity samples, the V acc model stands out in reproducing the data, with the V peak model slightly worse, while the M acc model fails to fit the data. We discuss the implications of the modelling results.

  7. Unveiling Galaxy Bias via the Halo Model, KiDS and GAMA

    NASA Astrophysics Data System (ADS)

    Dvornik, Andrej; Hoekstra, Henk; Kuijken, Konrad; Schneider, Peter; Amon, Alexandra; Nakajima, Reiko; Viola, Massimo; Choi, Ami; Erben, Thomas; Farrow, Daniel J.; Heymans, Catherine; Hildebrandt, Hendrik; Sifón, Cristóbal; Wang, Lingyu

    2018-06-01

    We measure the projected galaxy clustering and galaxy-galaxy lensing signals using the Galaxy And Mass Assembly (GAMA) survey and Kilo-Degree Survey (KiDS) to study galaxy bias. We use the concept of non-linear and stochastic galaxy biasing in the framework of halo occupation statistics to constrain the parameters of the halo occupation statistics and to unveil the origin of galaxy biasing. The bias function Γgm(rp), where rp is the projected comoving separation, is evaluated using the analytical halo model from which the scale dependence of Γgm(rp), and the origin of the non-linearity and stochasticity in halo occupation models can be inferred. Our observations unveil the physical reason for the non-linearity and stochasticity, further explored using hydrodynamical simulations, with the stochasticity mostly originating from the non-Poissonian behaviour of satellite galaxies in the dark matter haloes and their spatial distribution, which does not follow the spatial distribution of dark matter in the halo. The observed non-linearity is mostly due to the presence of the central galaxies, as was noted from previous theoretical work on the same topic. We also see that overall, more massive galaxies reveal a stronger scale dependence, and out to a larger radius. Our results show that a wealth of information about galaxy bias is hidden in halo occupation models. These models should therefore be used to determine the influence of galaxy bias in cosmological studies.

  8. Analytical halo model of galactic conformity

    NASA Astrophysics Data System (ADS)

    Pahwa, Isha; Paranjape, Aseem

    2017-09-01

    We present a fully analytical halo model of colour-dependent clustering that incorporates the effects of galactic conformity in a halo occupation distribution framework. The model, based on our previous numerical work, describes conformity through a correlation between the colour of a galaxy and the concentration of its parent halo, leading to a correlation between central and satellite galaxy colours at fixed halo mass. The strength of the correlation is set by a tunable 'group quenching efficiency', and the model can separately describe group-level correlations between galaxy colour (1-halo conformity) and large-scale correlations induced by assembly bias (2-halo conformity). We validate our analytical results using clustering measurements in mock galaxy catalogues, finding that the model is accurate at the 10-20 per cent level for a wide range of luminosities and length-scales. We apply the formalism to interpret the colour-dependent clustering of galaxies in the Sloan Digital Sky Survey (SDSS). We find good overall agreement between the data and a model that has 1-halo conformity at a level consistent with previous results based on an SDSS group catalogue, although the clustering data require satellites to be redder than suggested by the group catalogue. Within our modelling uncertainties, however, we do not find strong evidence of 2-halo conformity driven by assembly bias in SDSS clustering.

  9. The Halo Occupation Distribution of obscured quasars: revisiting the unification model

    NASA Astrophysics Data System (ADS)

    Mitra, Kaustav; Chatterjee, Suchetana; DiPompeo, Michael A.; Myers, Adam D.; Zheng, Zheng

    2018-06-01

    We model the projected angular two-point correlation function (2PCF) of obscured and unobscured quasars selected using the Wide-field Infrared Survey Explorer (WISE), at a median redshift of z ˜ 1 using a five parameter Halo Occupation Distribution (HOD) parametrization, derived from a cosmological hydrodynamic simulation by Chatterjee et al. The HOD parametrization was previously used to model the 2PCF of optically selected quasars and X-ray bright active galactic nuclei (AGNs) at z ˜ 1. The current work shows that a single HOD parametrization can be used to model the population of different kinds of AGN in dark matter haloes suggesting the universality of the relationship between AGN and their host dark matter haloes. Our results show that the median halo mass of central quasar hosts increases from optically selected (4.1^{+0.3}_{-0.4} × 10^{12} h^{-1} M_{⊙}) and infra-red (IR) bright unobscured populations (6.3^{+6.2}_{-2.3} × 10^{12} h^{-1} M_{⊙}) to obscured quasars (10.0^{+2.6}_{-3.7} × 10^{12} h^{-1} M_{⊙}), signifying an increase in the degree of clustering. The projected satellite fractions also increase from optically bright to obscured quasars and tend to disfavour a simple `orientation only' theory of active galactic nuclei unification. Our results also show that future measurements of the small-scale clustering of obscured quasars can constrain current theories of galaxy evolution where quasars evolve from an IR-bright obscured phase to the optically bright unobscured phase.

  10. Accurate mass and velocity functions of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Comparat, Johan; Prada, Francisco; Yepes, Gustavo; Klypin, Anatoly

    2017-08-01

    N-body cosmological simulations are an essential tool to understand the observed distribution of galaxies. We use the MultiDark simulation suite, run with the Planck cosmological parameters, to revisit the mass and velocity functions. At redshift z = 0, the simulations cover four orders of magnitude in halo mass from ˜1011M⊙ with 8783 874 distinct haloes and 532 533 subhaloes. The total volume used is ˜515 Gpc3, more than eight times larger than in previous studies. We measure and model the halo mass function, its covariance matrix w.r.t halo mass and the large-scale halo bias. With the formalism of the excursion-set mass function, we explicit the tight interconnection between the covariance matrix, bias and halo mass function. We obtain a very accurate (<2 per cent level) model of the distinct halo mass function. We also model the subhalo mass function and its relation to the distinct halo mass function. The set of models obtained provides a complete and precise framework for the description of haloes in the concordance Planck cosmology. Finally, we provide precise analytical fits of the Vmax maximum velocity function up to redshift z < 2.3 to push for the development of halo occupation distribution using Vmax. The data and the analysis code are made publicly available in the Skies and Universes data base.

  11. The Impact of Assembly Bias on the Galaxy Content of Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Zehavi, Idit; Contreras, Sergio; Padilla, Nelson; Smith, Nicholas J.; Baugh, Carlton M.; Norberg, Peder

    2018-01-01

    We study the dependence of the galaxy content of dark matter halos on large-scale environment and halo formation time using semi-analytic galaxy models applied to the Millennium simulation. We analyze subsamples of halos at the extremes of these distributions and measure the occupation functions for the galaxies they host. We find distinct differences among these occupation functions. The main effect with environment is that central galaxies (and in one model, also the satellites) in denser regions start populating lower-mass halos. A similar, but significantly stronger, trend exists with halo age, where early-forming halos are more likely to host central galaxies at lower halo mass. We discuss the origin of these trends and the connection to the stellar mass–halo mass relation. We find that, at fixed halo mass, older halos and to some extent also halos in dense environments tend to host more massive galaxies. Additionally, we see a reverse trend for the occupation of satellite galaxies where early-forming halos have fewer satellites, likely due to having more time for them to merge with the central galaxy. We describe these occupancy variations in terms of the changes in the occupation function parameters, which can aid in constructing realistic mock galaxy samples. Finally, we study the corresponding galaxy auto- and cross-correlation functions of the different samples and elucidate the impact of assembly bias on galaxy clustering. Our results can inform theoretical modeling of galaxy assembly bias and attempts to detect it in the real universe.

  12. Analytic halo approach to the bispectrum of galaxies in redshift space

    NASA Astrophysics Data System (ADS)

    Yamamoto, Kazuhiro; Nan, Yue; Hikage, Chiaki

    2017-02-01

    We present an analytic formula for the galaxy bispectrum in redshift space on the basis of the halo approach description with the halo occupation distribution of central galaxies and satellite galaxies. This work is an extension of a previous work on the galaxy power spectrum, which illuminated the significant contribution of satellite galaxies to the higher multipole spectrum through the nonlinear redshift space distortions of their random motions. Behaviors of the multipoles of the bispectrum are compared with results of numerical simulations assuming a halo occupation distribution of the low-redshift (LOWZ) sample of the Sloan Digital Sky Survey (SDSS) III baryon oscillation spectroscopic survey (BOSS) survey. Also presented are analytic approximate formulas for the multipoles of the bispectrum, which is useful to understanding their characteristic properties. We demonstrate that the Fingers of God effect is quite important for the higher multipoles of the bispectrum in redshift space, depending on the halo occupation distribution parameters.

  13. The XMM Cluster Survey: the halo occupation number of BOSS galaxies in X-ray clusters

    NASA Astrophysics Data System (ADS)

    Mehrtens, Nicola; Romer, A. Kathy; Nichol, Robert C.; Collins, Chris A.; Sahlén, Martin; Rooney, Philip J.; Mayers, Julian A.; Bermeo-Hernandez, A.; Bristow, Martyn; Capozzi, Diego; Christodoulou, L.; Comparat, Johan; Hilton, Matt; Hoyle, Ben; Kay, Scott T.; Liddle, Andrew R.; Mann, Robert G.; Masters, Karen; Miller, Christopher J.; Parejko, John K.; Prada, Francisco; Ross, Ashley J.; Schneider, Donald P.; Stott, John P.; Streblyanska, Alina; Viana, Pedro T. P.; White, Martin; Wilcox, Harry; Zehavi, Idit

    2016-12-01

    We present a direct measurement of the mean halo occupation distribution (HOD) of galaxies taken from the eleventh data release (DR11) of the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey (BOSS). The HOD of BOSS low-redshift (LOWZ: 0.2 < z < 0.4) and Constant-Mass (CMASS: 0.43 < z < 0.7) galaxies is inferred via their association with the dark matter haloes of 174 X-ray-selected galaxy clusters drawn from the XMM Cluster Survey (XCS). Halo masses are determined for each galaxy cluster based on X-ray temperature measurements, and range between log10(M180/M⊙) = 13 and 15. Our directly measured HODs are consistent with the HOD-model fits inferred via the galaxy-clustering analyses of Parejko et al. for the BOSS LOWZ sample and White et al. for the BOSS CMASS sample. Under the simplifying assumption that the other parameters that describe the HOD hold the values measured by these authors, we have determined a best-fitting alpha-index of 0.91 ± 0.08 and 1.27^{+0.03}_{-0.04} for the CMASS and LOWZ HOD, respectively. These alpha-index values are consistent with those measured by White et al. and Parejko et al. In summary, our study provides independent support for the HOD models assumed during the development of the BOSS mock-galaxy catalogues that have subsequently been used to derive BOSS cosmological constraints.

  14. Re-imagining occupational therapy clients as communities: Presenting the community-centred practice framework.

    PubMed

    Hyett, Nerida; Kenny, Amanda; Dickson-Swift, Virginia

    2018-01-09

    Occupational therapists' are increasingly working with communities and providing services at the community level. There is, however, a lack of conceptual frameworks to guide this work. The aim of this article is to present a new conceptual framework for community-centered practice in occupational therapy. The conceptual framework was developed from qualitative multi-case research on exemplars of community participation. The first was, a network of Canadian food security programs, and the second, a rural Australian community banking initiative. Key themes were identified from across the case studies, and cross-case findings interpreted using occupational therapy and occupational science knowledge, and relevant social theory. The outcome is a four-stage, occupation-focused, community-centered practice framework. The Community-Centred Practice Framework can be used by occupational therapists to understand and apply a community-centered practice approach. The four stages are: (1) Community Identity, (2) Community Occupations, (3) Community Resources and Barriers, and (4) Participation Enablement. Further research is needed to trial and critically evaluate the framework, to assess its usefulness as a robust, occupation-focused, frame of reference to guide community-centered practice in occupational therapy. The proposed framework should assist occupational therapists to conceptualize community-centered practice, and to utilize and apply theory.

  15. Spatial clustering and halo occupation distribution modelling of local AGN via cross-correlation measurements with 2MASS galaxies

    NASA Astrophysics Data System (ADS)

    Krumpe, Mirko; Miyaji, Takamitsu; Coil, Alison L.; Aceves, Hector

    2018-02-01

    We present the clustering properties and halo occupation distribution (HOD) modelling of very low redshift, hard X-ray-detected active galactic nuclei (AGN) using cross-correlation function measurements with Two-Micron All Sky Survey galaxies. Spanning a redshift range of 0.007 < z < 0.037, with a median z = 0.024, we present a precise AGN clustering study of the most local AGN in the Universe. The AGN sample is drawn from the SWIFT/BAT 70-month and INTEGRAL/IBIS eight year all-sky X-ray surveys and contains both type I and type II AGN. We find a large-scale bias for the full AGN sample of b=1.04^{+0.10}_{-0.11}, which corresponds to a typical host dark matter halo mass of M_h^typ=12.84^{+0.22}_{-0.30} h^{-1} M_{⊙}. When split into low and high X-ray luminosity and type I and type II AGN subsamples, we detect no statistically significant differences in the large-scale bias parameters. However, there are differences in the small-scale clustering, which are reflected in the full HOD model results. We find that low and high X-ray luminosity AGN, as well as type I and type II AGN, occupy dark matter haloes differently, with 3.4σ and 4.0σ differences in their mean halo masses, respectively, when split by luminosity and type. The latter finding contradicts a simple orientation-based AGN unification model. As a by-product of our cross-correlation approach, we also present the first HOD model of 2MASS galaxies.

  16. Revealing the Cosmic Web-dependent Halo Bias

    NASA Astrophysics Data System (ADS)

    Yang, Xiaohu; Zhang, Youcai; Lu, Tianhuan; Wang, Huiyuan; Shi, Feng; Tweed, Dylan; Li, Shijie; Luo, Wentao; Lu, Yi; Yang, Lei

    2017-10-01

    Halo bias is the one of the key ingredients of the halo models. It was shown at a given redshift to be only dependent, to the first order, on the halo mass. In this study, four types of cosmic web environments—clusters, filaments, sheets, and voids—are defined within a state-of-the-art high-resolution N-body simulation. Within these environments, we use both halo-dark matter cross correlation and halo-halo autocorrelation functions to probe the clustering properties of halos. The nature of the halo bias differs strongly between the four different cosmic web environments described here. With respect to the overall population, halos in clusters have significantly lower biases in the {10}11.0˜ {10}13.5 {h}-1 {M}⊙ mass range. In other environments, however, halos show extremely enhanced biases up to a factor 10 in voids for halos of mass ˜ {10}12.0 {h}-1 {M}⊙ . Such a strong cosmic web environment dependence in the halo bias may play an important role in future cosmological and galaxy formation studies. Within this cosmic web framework, the age dependency of halo bias is found to be only significant in clusters and filaments for relatively small halos ≲ {10}12.5 {h}-1 {M}⊙ .

  17. Effective Dark Matter Halo Catalog in f(R) Gravity.

    PubMed

    He, Jian-Hua; Hawken, Adam J; Li, Baojiu; Guzzo, Luigi

    2015-08-14

    We introduce the idea of an effective dark matter halo catalog in f(R) gravity, which is built using the effective density field. Using a suite of high resolution N-body simulations, we find that the dynamical properties of halos, such as the distribution of density, velocity dispersion, specific angular momentum and spin, in the effective catalog of f(R) gravity closely mimic those in the cold dark matter model with a cosmological constant (ΛCDM). Thus, when using effective halos, an f(R) model can be viewed as a ΛCDM model. This effective catalog therefore provides a convenient way for studying the baryonic physics, the galaxy halo occupation distribution and even semianalytical galaxy formation in f(R) cosmologies.

  18. Independence: proposing an initial framework for occupational therapy.

    PubMed

    Collins, Bethan

    2017-11-01

    The concept of independence is common in occupational therapy theory and practice but has rarely been clearly defined or conceptualized within in occupational therapy literature and there seems to be no standard definition. This can result in ambiguity, which potentially jeopardizes client-centred practice. This paper proposes an occupational therapy independence framework (OTIF) that synthesizes the range of characterizations of independence in a practically useful and occupation-centred manner. A review of literature, clinical experience, doctoral research and conversations with occupational therapists and disabled people, in particular those involved in a disability activism group and people with physical disabilities, has led to the development of the OTIF. Independence and interdependence, as characterized in the OTIF, occur when an individual exerts choice over occupational performance and can engage in occupations in a manner acceptable to the individual. Interdependence results when occupations are performed with another person whereas independence involves solitary occupational performance. Dependence typically results from inability to choose occupations or a mismatch between performance capacity and environmental factors. The OTIF has the potential to clarify the conceptualization of independence within occupational therapy theory and practice. This initial proposal is presented to stimulate debate and discussion.

  19. Remapping dark matter halo catalogues between cosmological simulations

    NASA Astrophysics Data System (ADS)

    Mead, A. J.; Peacock, J. A.

    2014-05-01

    We present and test a method for modifying the catalogue of dark matter haloes produced from a given cosmological simulation, so that it resembles the result of a simulation with an entirely different set of parameters. This extends the method of Angulo & White, which rescales the full particle distribution from a simulation. Working directly with the halo catalogue offers an advantage in speed, and also allows modifications of the internal structure of the haloes to account for non-linear differences between cosmologies. Our method can be used directly on a halo catalogue in a self-contained manner without any additional information about the overall density field; although the large-scale displacement field is required by the method, this can be inferred from the halo catalogue alone. We show proof of concept of our method by rescaling a matter-only simulation with no baryon acoustic oscillation (BAO) features to a more standard Λ cold dark matter model containing a cosmological constant and a BAO signal. In conjunction with the halo occupation approach, this method provides a basis for the rapid generation of mock galaxy samples spanning a wide range of cosmological parameters.

  20. On the scatter in the relation between stellar mass and halo mass: random or halo formation time dependent?

    NASA Astrophysics Data System (ADS)

    Wang, Lan; De Lucia, Gabriella; Weinmann, Simone M.

    2013-05-01

    The empirical traditional halo occupation distribution (HOD) model of Wang et al. fits, by construction, both the stellar mass function and correlation function of galaxies in the local Universe. In contrast, the semi-analytical models of De Lucia & Blazoit (hereafter DLB07) and Guo et al. (hereafter Guo11), built on the same dark matter halo merger trees than the empirical model, still have difficulties in reproducing these observational data simultaneously. We compare the relations between the stellar mass of galaxies and their host halo mass in the three models, and find that they are different. When the relations are rescaled to have the same median values and the same scatter as in Wang et al., the rescaled DLB07 model can fit both the measured galaxy stellar mass function and the correlation function measured in different galaxy stellar mass bins. In contrast, the rescaled Guo11 model still overpredicts the clustering of low-mass galaxies. This indicates that the detail of how galaxies populate the scatter in the stellar mass-halo mass relation does play an important role in determining the correlation functions of galaxies. While the stellar mass of galaxies in the Wang et al. model depends only on halo mass and is randomly distributed within the scatter, galaxy stellar mass depends also on the halo formation time in semi-analytical models. At fixed value of infall mass, galaxies that lie above the median stellar mass-halo mass relation reside in haloes that formed earlier, while galaxies that lie below the median relation reside in haloes that formed later. This effect is much stronger in Guo11 than in DLB07, which explains the overclustering of low mass galaxies in Guo11. Assembly bias in Guo11 model might be overly strong. Nevertheless, in case that a significant assembly bias indeed exists in the real Universe, one needs to use caution when applying current HOD and abundance matching models that employ the assumption of random scatter in the relation

  1. A technical framework to describe occupant behavior for building energy simulations

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Turner, William; Hong, Tianzhen

    2013-12-20

    Green buildings that fail to meet expected design performance criteria indicate that technology alone does not guarantee high performance. Human influences are quite often simplified and ignored in the design, construction, and operation of buildings. Energy-conscious human behavior has been demonstrated to be a significant positive factor for improving the indoor environment while reducing the energy use of buildings. In our study we developed a new technical framework to describe energy-related human behavior in buildings. The energy-related behavior includes accounting for individuals and groups of occupants and their interactions with building energy services systems, appliances and facilities. The technical frameworkmore » consists of four key components: i. the drivers behind energy-related occupant behavior, which are biological, societal, environmental, physical, and economical in nature ii. the needs of the occupants are based on satisfying criteria that are either physical (e.g. thermal, visual and acoustic comfort) or non-physical (e.g. entertainment, privacy, and social reward) iii. the actions that building occupants perform when their needs are not fulfilled iv. the systems with which an occupant can interact to satisfy their needs The technical framework aims to provide a standardized description of a complete set of human energy-related behaviors in the form of an XML schema. For each type of behavior (e.g., occupants opening/closing windows, switching on/off lights etc.) we identify a set of common behaviors based on a literature review, survey data, and our own field study and analysis. Stochastic models are adopted or developed for each type of behavior to enable the evaluation of the impact of human behavior on energy use in buildings, during either the design or operation phase. We will also demonstrate the use of the technical framework in assessing the impact of occupancy behavior on energy saving technologies. The technical framework

  2. HALO--a Java framework for precise transcript half-life determination.

    PubMed

    Friedel, Caroline C; Kaufmann, Stefanie; Dölken, Lars; Zimmer, Ralf

    2010-05-01

    Recent improvements in experimental technologies now allow measurements of de novo transcription and/or RNA decay at whole transcriptome level and determination of precise transcript half-lives. Such transcript half-lives provide important insights into the regulation of biological processes and the relative contributions of RNA decay and de novo transcription to differential gene expression. In this article, we present HALO (Half-life Organizer), the first software for the precise determination of transcript half-lives from measurements of RNA de novo transcription or decay determined with microarrays or RNA-seq. In addition, methods for quality control, filtering and normalization are supplied. HALO provides a graphical user interface, command-line tools and a well-documented Java application programming interface (API). Thus, it can be used both by biologists to determine transcript half-lives fast and reliably with the provided user interfaces as well as software developers integrating transcript half-life analysis into other gene expression profiling pipelines. Source code, executables and documentation are available at http://www.bio.ifi.lmu.de/software/halo.

  3. The halo model in a massive neutrino cosmology

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Massara, Elena; Villaescusa-Navarro, Francisco; Viel, Matteo, E-mail: emassara@sissa.it, E-mail: villaescusa@oats.inaf.it, E-mail: viel@oats.inaf.it

    2014-12-01

    We provide a quantitative analysis of the halo model in the context of massive neutrino cosmologies. We discuss all the ingredients necessary to model the non-linear matter and cold dark matter power spectra and compare with the results of N-body simulations that incorporate massive neutrinos. Our neutrino halo model is able to capture the non-linear behavior of matter clustering with a ∼20% accuracy up to very non-linear scales of k = 10 h/Mpc (which would be affected by baryon physics). The largest discrepancies arise in the range k = 0.5 – 1 h/Mpc where the 1-halo and 2-halo terms are comparable and are present also inmore » a massless neutrino cosmology. However, at scales k < 0.2 h/Mpc our neutrino halo model agrees with the results of N-body simulations at the level of 8% for total neutrino masses of < 0.3 eV. We also model the neutrino non-linear density field as a sum of a linear and clustered component and predict the neutrino power spectrum and the cold dark matter-neutrino cross-power spectrum up to k = 1 h/Mpc with ∼30% accuracy. For masses below 0.15 eV the neutrino halo model captures the neutrino induced suppression, casted in terms of matter power ratios between massive and massless scenarios, with a 2% agreement with the results of N-body/neutrino simulations. Finally, we provide a simple application of the halo model: the computation of the clustering of galaxies, in massless and massive neutrinos cosmologies, using a simple Halo Occupation Distribution scheme and our halo model extension.« less

  4. Dark matter haloes: a multistream view

    NASA Astrophysics Data System (ADS)

    Ramachandra, Nesar S.; Shandarin, Sergei F.

    2017-09-01

    Mysterious dark matter constitutes about 85 per cent of all masses in the Universe. Clustering of dark matter plays a dominant role in the formation of all observed structures on scales from a fraction to a few hundreds of Mega-parsecs. Galaxies play a role of lights illuminating these structures so they can be observed. The observations in the last several decades have unveiled opulent geometry of these structures currently known as the cosmic web. Haloes are the highest concentrations of dark matter and host luminous galaxies. Currently the most accurate modelling of dark matter haloes is achieved in cosmological N-body simulations. Identifying the haloes from the distribution of particles in N-body simulations is one of the problems attracting both considerable interest and efforts. We propose a novel framework for detecting potential dark matter haloes using the field unique for dark matter-multistream field. The multistream field emerges at the non-linear stage of the growth of perturbations because the dark matter is collisionless. Counting the number of velocity streams in gravitational collapses supplements our knowledge of spatial clustering. We assume that the virialized haloes have convex boundaries. Closed and convex regions of the multistream field are hence isolated by imposing a positivity condition on all three eigenvalues of the Hessian estimated on the smoothed multistream field. In a single-scale analysis of high multistream field resolution and low softening length, the halo substructures with local multistream maxima are isolated as individual halo sites.

  5. Cosmic Vorticity and the Origin Halo Spins

    NASA Astrophysics Data System (ADS)

    Libeskind, Noam I.; Hoffman, Yehuda; Steinmetz, Matthias; Gottlöber, Stefan; Knebe, Alexander; Hess, Steffen

    2013-04-01

    In the standard model of cosmology, structure emerges out of a non-rotational flow and the angular momentum of collapsing halos is induced by tidal torques. The growth of angular momentum in the linear and quasi-linear phases is associated with a shear, curl-free, flow and it is well described within the linear framework of tidal torque theory (TTT). However, TTT ceases to be applicable as halos approach turnaround when their ambient flow field becomes rotational. Subsequently, halos become embedded in a vortical flow field and the growth of their angular momentum is affected by the vorticity of their ambient velocity field. Using a cosmological simulation, we have examined the importance of the curl of the velocity field in determining halo spin, finding a significant alignment between the two: the vorticity tends to be perpendicular to the axis of the fastest collapse of the velocity shear tensor (e 1). This is independent of halo masses and cosmic web environment. Our results agree with previous findings on the tendency of halo spin to be perpendicular to e 1, and of the spin of (simulated) halos and (observed) galaxies to be aligned with the large-scale structure. It follows that angular momentum growth proceeds in two distinct phases. First, the angular momentum emerges out of a shear, curl-free, potential flow, as described by TTT. In the second phase, in which halos approach virialization, the angular momentum emerges out of a vortical flow and halo spin becomes partially aligned with the vorticity of the ambient flow field.

  6. Occupancy schedules learning process through a data mining framework

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    D'Oca, Simona; Hong, Tianzhen

    Building occupancy is a paramount factor in building energy simulations. Specifically, lighting, plug loads, HVAC equipment utilization, fresh air requirements and internal heat gain or loss greatly depends on the level of occupancy within a building. Developing the appropriate methodologies to describe and reproduce the intricate network responsible for human-building interactions are needed. Extrapolation of patterns from big data streams is a powerful analysis technique which will allow for a better understanding of energy usage in buildings. A three-step data mining framework is applied to discover occupancy patterns in office spaces. First, a data set of 16 offices with 10more » minute interval occupancy data, over a two year period is mined through a decision tree model which predicts the occupancy presence. Then a rule induction algorithm is used to learn a pruned set of rules on the results from the decision tree model. Finally, a cluster analysis is employed in order to obtain consistent patterns of occupancy schedules. Furthermore, the identified occupancy rules and schedules are representative as four archetypal working profiles that can be used as input to current building energy modeling programs, such as EnergyPlus or IDA-ICE, to investigate impact of occupant presence on design, operation and energy use in office buildings.« less

  7. Occupancy schedules learning process through a data mining framework

    DOE PAGES

    D'Oca, Simona; Hong, Tianzhen

    2014-12-17

    Building occupancy is a paramount factor in building energy simulations. Specifically, lighting, plug loads, HVAC equipment utilization, fresh air requirements and internal heat gain or loss greatly depends on the level of occupancy within a building. Developing the appropriate methodologies to describe and reproduce the intricate network responsible for human-building interactions are needed. Extrapolation of patterns from big data streams is a powerful analysis technique which will allow for a better understanding of energy usage in buildings. A three-step data mining framework is applied to discover occupancy patterns in office spaces. First, a data set of 16 offices with 10more » minute interval occupancy data, over a two year period is mined through a decision tree model which predicts the occupancy presence. Then a rule induction algorithm is used to learn a pruned set of rules on the results from the decision tree model. Finally, a cluster analysis is employed in order to obtain consistent patterns of occupancy schedules. Furthermore, the identified occupancy rules and schedules are representative as four archetypal working profiles that can be used as input to current building energy modeling programs, such as EnergyPlus or IDA-ICE, to investigate impact of occupant presence on design, operation and energy use in office buildings.« less

  8. COSMIC VORTICITY AND THE ORIGIN HALO SPINS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Libeskind, Noam I.; Steinmetz, Matthias; Gottloeber, Stefan

    2013-04-01

    In the standard model of cosmology, structure emerges out of a non-rotational flow and the angular momentum of collapsing halos is induced by tidal torques. The growth of angular momentum in the linear and quasi-linear phases is associated with a shear, curl-free, flow and it is well described within the linear framework of tidal torque theory (TTT). However, TTT ceases to be applicable as halos approach turnaround when their ambient flow field becomes rotational. Subsequently, halos become embedded in a vortical flow field and the growth of their angular momentum is affected by the vorticity of their ambient velocity field.more » Using a cosmological simulation, we have examined the importance of the curl of the velocity field in determining halo spin, finding a significant alignment between the two: the vorticity tends to be perpendicular to the axis of the fastest collapse of the velocity shear tensor (e{sub 1}). This is independent of halo masses and cosmic web environment. Our results agree with previous findings on the tendency of halo spin to be perpendicular to e{sub 1}, and of the spin of (simulated) halos and (observed) galaxies to be aligned with the large-scale structure. It follows that angular momentum growth proceeds in two distinct phases. First, the angular momentum emerges out of a shear, curl-free, potential flow, as described by TTT. In the second phase, in which halos approach virialization, the angular momentum emerges out of a vortical flow and halo spin becomes partially aligned with the vorticity of the ambient flow field.« less

  9. Sensitivity of the halo nuclei-12C elastic scattering at incident nucleon energy 800 MeV to the halo density distribution

    NASA Astrophysics Data System (ADS)

    Hassan, M. A. M.; Nour El-Din, M. S. M.; Ellithi, A.; Hosny, H.; Salama, T. N. E.

    2017-10-01

    In the framework of Glauber optical limit approximation where Coulomb effect is taken into account, the elastic scattering differential cross section for halo nuclei with {}^{12}{C} at 800 MeV/N has been calculated. Its sensitivity to the halo densities and the root mean square of the core and halo is the main goal of the current study. The projectile nuclei are taken to be one-neutron and two-neutron halo. The calculations are carried out for Gaussian-Gaussian, Gaussian-Oscillator and Gaussian-2 s phenomenological densities for each considered projectile in the mass number range 6-29. Also included a comparison between the obtained results of phenomenological densities and the results within the microscopic densities LSSM of {}6{He} and {}^{11}{Li} and microscopic densities GCM of {}^{11}{Be} where the density of the target nucleus {}^{12}{C} obtained from electron-{}^{12}{C} scattering is used. The zero range approximation is considered in the calculations. We found that the sensitivity of elastic scattering differential cross section to the halo density is clear if the nucleus appears as two clear different clusters, core and halo.

  10. The Excursion Set Theory of Halo Mass Functions, Halo Clustering, and Halo Growth

    NASA Astrophysics Data System (ADS)

    Zentner, Andrew R.

    I review the excursion set theory with particular attention toward applications to cold dark matter halo formation and growth, halo abundance, and halo clustering. After a brief introduction to notation and conventions, I begin by recounting the heuristic argument leading to the mass function of bound objects given by Press and Schechter. I then review the more formal derivation of the Press-Schechter halo mass function that makes use of excursion sets of the density field. The excursion set formalism is powerful and can be applied to numerous other problems. I review the excursion set formalism for describing both halo clustering and bias and the properties of void regions. As one of the most enduring legacies of the excursion set approach and one of its most common applications, I spend considerable time reviewing the excursion set theory of halo growth. This section of the review culminates with the description of two Monte Carlo methods for generating ensembles of halo mass accretion histories. In the last section, I emphasize that the standard excursion set approach is the result of several simplifying assumptions. Dropping these assumptions can lead to more faithful predictions and open excursion set theory to new applications. One such assumption is that the height of the barriers that define collapsed objects is a constant function of scale. I illustrate the implementation of the excursion set approach for barriers of arbitrary shape. One such application is the now well-known improvement of the excursion set mass function derived from the "moving" barrier for ellipsoidal collapse. I also emphasize that the statement that halo accretion histories are independent of halo environment in the excursion set approach is not a general prediction of the theory. It is a simplifying assumption. I review the method for constructing correlated random walks of the density field in the more general case. I construct a simple toy model to illustrate that excursion set

  11. Beyond assembly bias: exploring secondary halo biases for cluster-size haloes

    DOE PAGES

    Mao, Yao-Yuan; Zentner, Andrew R.; Wechsler, Risa H.

    2017-12-01

    Secondary halo bias, commonly known as ‘assembly bias’, is the dependence of halo clustering on a halo property other than mass. This prediction of the Λ Cold Dark Matter cosmology is essential to modelling the galaxy distribution to high precision and interpreting clustering measurements. As the name suggests, different manifestations of secondary halo bias have been thought to originate from halo assembly histories. We show conclusively that this is incorrect for cluster-size haloes. We present an up-to-date summary of secondary halo biases of high-mass haloes due to various halo properties including concentration, spin, several proxies of assembly history, and subhalomore » properties. While concentration, spin, and the abundance and radial distribution of subhaloes exhibit significant secondary biases, properties that directly quantify halo assembly history do not. In fact, the entire assembly histories of haloes in pairs are nearly identical to those of isolated haloes. In general, a global correlation between two halo properties does not predict whether or not these two properties exhibit similar secondary biases. For example, assembly history and concentration (or subhalo abundance) are correlated for both paired and isolated haloes, but follow slightly different conditional distributions in these two cases. Lastly, this results in a secondary halo bias due to concentration (or subhalo abundance), despite the lack of assembly bias in the strict sense for cluster-size haloes. Due to this complexity, caution must be exercised in using any one halo property as a proxy to study the secondary bias due to another property.« less

  12. Beyond assembly bias: exploring secondary halo biases for cluster-size haloes

    NASA Astrophysics Data System (ADS)

    Mao, Yao-Yuan; Zentner, Andrew R.; Wechsler, Risa H.

    2018-03-01

    Secondary halo bias, commonly known as `assembly bias', is the dependence of halo clustering on a halo property other than mass. This prediction of the Λ Cold Dark Matter cosmology is essential to modelling the galaxy distribution to high precision and interpreting clustering measurements. As the name suggests, different manifestations of secondary halo bias have been thought to originate from halo assembly histories. We show conclusively that this is incorrect for cluster-size haloes. We present an up-to-date summary of secondary halo biases of high-mass haloes due to various halo properties including concentration, spin, several proxies of assembly history, and subhalo properties. While concentration, spin, and the abundance and radial distribution of subhaloes exhibit significant secondary biases, properties that directly quantify halo assembly history do not. In fact, the entire assembly histories of haloes in pairs are nearly identical to those of isolated haloes. In general, a global correlation between two halo properties does not predict whether or not these two properties exhibit similar secondary biases. For example, assembly history and concentration (or subhalo abundance) are correlated for both paired and isolated haloes, but follow slightly different conditional distributions in these two cases. This results in a secondary halo bias due to concentration (or subhalo abundance), despite the lack of assembly bias in the strict sense for cluster-size haloes. Due to this complexity, caution must be exercised in using any one halo property as a proxy to study the secondary bias due to another property.

  13. Beyond assembly bias: exploring secondary halo biases for cluster-size haloes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Mao, Yao-Yuan; Zentner, Andrew R.; Wechsler, Risa H.

    Secondary halo bias, commonly known as ‘assembly bias’, is the dependence of halo clustering on a halo property other than mass. This prediction of the Λ Cold Dark Matter cosmology is essential to modelling the galaxy distribution to high precision and interpreting clustering measurements. As the name suggests, different manifestations of secondary halo bias have been thought to originate from halo assembly histories. We show conclusively that this is incorrect for cluster-size haloes. We present an up-to-date summary of secondary halo biases of high-mass haloes due to various halo properties including concentration, spin, several proxies of assembly history, and subhalomore » properties. While concentration, spin, and the abundance and radial distribution of subhaloes exhibit significant secondary biases, properties that directly quantify halo assembly history do not. In fact, the entire assembly histories of haloes in pairs are nearly identical to those of isolated haloes. In general, a global correlation between two halo properties does not predict whether or not these two properties exhibit similar secondary biases. For example, assembly history and concentration (or subhalo abundance) are correlated for both paired and isolated haloes, but follow slightly different conditional distributions in these two cases. Lastly, this results in a secondary halo bias due to concentration (or subhalo abundance), despite the lack of assembly bias in the strict sense for cluster-size haloes. Due to this complexity, caution must be exercised in using any one halo property as a proxy to study the secondary bias due to another property.« less

  14. Accurate Modeling of Galaxy Clustering on Small Scales: Testing the Standard ΛCDM + Halo Model

    NASA Astrophysics Data System (ADS)

    Sinha, Manodeep; Berlind, Andreas A.; McBride, Cameron; Scoccimarro, Roman

    2015-01-01

    The large-scale distribution of galaxies can be explained fairly simply by assuming (i) a cosmological model, which determines the dark matter halo distribution, and (ii) a simple connection between galaxies and the halos they inhabit. This conceptually simple framework, called the halo model, has been remarkably successful at reproducing the clustering of galaxies on all scales, as observed in various galaxy redshift surveys. However, none of these previous studies have carefully modeled the systematics and thus truly tested the halo model in a statistically rigorous sense. We present a new accurate and fully numerical halo model framework and test it against clustering measurements from two luminosity samples of galaxies drawn from the SDSS DR7. We show that the simple ΛCDM cosmology + halo model is not able to simultaneously reproduce the galaxy projected correlation function and the group multiplicity function. In particular, the more luminous sample shows significant tension with theory. We discuss the implications of our findings and how this work paves the way for constraining galaxy formation by accurate simultaneous modeling of multiple galaxy clustering statistics.

  15. Painting galaxies into dark matter halos using machine learning

    NASA Astrophysics Data System (ADS)

    Agarwal, Shankar; Davé, Romeel; Bassett, Bruce A.

    2018-05-01

    We develop a machine learning (ML) framework to populate large dark matter-only simulations with baryonic galaxies. Our ML framework takes input halo properties including halo mass, environment, spin, and recent growth history, and outputs central galaxy and halo baryonic properties including stellar mass (M*), star formation rate (SFR), metallicity (Z), neutral (H I) and molecular (H_2) hydrogen mass. We apply this to the MUFASA cosmological hydrodynamic simulation, and show that it recovers the mean trends of output quantities with halo mass highly accurately, including following the sharp drop in SFR and gas in quenched massive galaxies. However, the scatter around the mean relations is under-predicted. Examining galaxies individually, at z = 0 the stellar mass and metallicity are accurately recovered (σ ≲ 0.2 dex), but SFR and H I show larger scatter (σ ≳ 0.3 dex); these values improve somewhat at z = 1, 2. Remarkably, ML quantitatively recovers second parameter trends in galaxy properties, e.g. that galaxies with higher gas content and lower metallicity have higher SFR at a given M*. Testing various ML algorithms, we find that none perform significantly better than the others, nor does ensembling improve performance, likely because none of the algorithms reproduce the large observed scatter around the mean properties. For the random forest algorithm, we find that halo mass and nearby (˜200 kpc) environment are the most important predictive variables followed by growth history, while halo spin and ˜Mpc scale environment are not important. Finally we study the impact of additionally inputting key baryonic properties M*, SFR, and Z, as would be available e.g. from an equilibrium model, and show that particularly providing the SFR enables H I to be recovered substantially more accurately.

  16. The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: modelling the clustering and halo occupation distribution of BOSS CMASS galaxies in the Final Data Release

    NASA Astrophysics Data System (ADS)

    Rodríguez-Torres, Sergio A.; Chuang, Chia-Hsun; Prada, Francisco; Guo, Hong; Klypin, Anatoly; Behroozi, Peter; Hahn, Chang Hoon; Comparat, Johan; Yepes, Gustavo; Montero-Dorta, Antonio D.; Brownstein, Joel R.; Maraston, Claudia; McBride, Cameron K.; Tinker, Jeremy; Gottlöber, Stefan; Favole, Ginevra; Shu, Yiping; Kitaura, Francisco-Shu; Bolton, Adam; Scoccimarro, Román; Samushia, Lado; Schlegel, David; Schneider, Donald P.; Thomas, Daniel

    2016-08-01

    We present a study of the clustering and halo occupation distribution of Baryon Oscillation Spectroscopic Survey (BOSS) CMASS galaxies in the redshift range 0.43 < z < 0.7 drawn from the Final SDSS-III Data Release. We compare the BOSS results with the predictions of a halo abundance matching (HAM) clustering model that assigns galaxies to dark matter haloes selected from the large BigMultiDark N-body simulation of a flat Λ cold dark matter Planck cosmology. We compare the observational data with the simulated ones on a light cone constructed from 20 subsequent outputs of the simulation. Observational effects such as incompleteness, geometry, veto masks and fibre collisions are included in the model, which reproduces within 1σ errors the observed monopole of the two-point correlation function at all relevant scales: from the smallest scales, 0.5 h-1 Mpc, up to scales beyond the baryon acoustic oscillation feature. This model also agrees remarkably well with the BOSS galaxy power spectrum (up to k ˜ 1 h Mpc-1), and the three-point correlation function. The quadrupole of the correlation function presents some tensions with observations. We discuss possible causes that can explain this disagreement, including target selection effects. Overall, the standard HAM model describes remarkably well the clustering statistics of the CMASS sample. We compare the stellar-to-halo mass relation for the CMASS sample measured using weak lensing in the Canada-France-Hawaii Telescope Stripe 82 Survey with the prediction of our clustering model, and find a good agreement within 1σ. The BigMD-BOSS light cone including properties of BOSS galaxies and halo properties is made publicly available.

  17. Haloes gone MAD: The Halo-Finder Comparison Project

    NASA Astrophysics Data System (ADS)

    Knebe, Alexander; Knollmann, Steffen R.; Muldrew, Stuart I.; Pearce, Frazer R.; Aragon-Calvo, Miguel Angel; Ascasibar, Yago; Behroozi, Peter S.; Ceverino, Daniel; Colombi, Stephane; Diemand, Juerg; Dolag, Klaus; Falck, Bridget L.; Fasel, Patricia; Gardner, Jeff; Gottlöber, Stefan; Hsu, Chung-Hsing; Iannuzzi, Francesca; Klypin, Anatoly; Lukić, Zarija; Maciejewski, Michal; McBride, Cameron; Neyrinck, Mark C.; Planelles, Susana; Potter, Doug; Quilis, Vicent; Rasera, Yann; Read, Justin I.; Ricker, Paul M.; Roy, Fabrice; Springel, Volker; Stadel, Joachim; Stinson, Greg; Sutter, P. M.; Turchaninov, Victor; Tweed, Dylan; Yepes, Gustavo; Zemp, Marcel

    2011-08-01

    We present a detailed comparison of fundamental dark matter halo properties retrieved by a substantial number of different halo finders. These codes span a wide range of techniques including friends-of-friends, spherical-overdensity and phase-space-based algorithms. We further introduce a robust (and publicly available) suite of test scenarios that allow halo finder developers to compare the performance of their codes against those presented here. This set includes mock haloes containing various levels and distributions of substructure at a range of resolutions as well as a cosmological simulation of the large-scale structure of the universe. All the halo-finding codes tested could successfully recover the spatial location of our mock haloes. They further returned lists of particles (potentially) belonging to the object that led to coinciding values for the maximum of the circular velocity profile and the radius where it is reached. All the finders based in configuration space struggled to recover substructure that was located close to the centre of the host halo, and the radial dependence of the mass recovered varies from finder to finder. Those finders based in phase space could resolve central substructure although they found difficulties in accurately recovering its properties. Through a resolution study we found that most of the finders could not reliably recover substructure containing fewer than 30-40 particles. However, also here the phase-space finders excelled by resolving substructure down to 10-20 particles. By comparing the halo finders using a high-resolution cosmological volume, we found that they agree remarkably well on fundamental properties of astrophysical significance (e.g. mass, position, velocity and peak of the rotation curve). We further suggest to utilize the peak of the rotation curve, vmax, as a proxy for mass, given the arbitrariness in defining a proper halo edge. Airport code for Madrid, Spain

  18. Halo Nuclei

    NASA Astrophysics Data System (ADS)

    Al-Khalili, Jim

    2017-10-01

    While neutron halos were discovered 30 years ago, this is the first book written on the subject of this exotic form of nuclei that typically contain many more neutrons than stable isotopes of those elements. It provides an introductory description of the halo and outlines the discovery and evidence for its existence. It also discusses different theoretical models of the halo's structure as well as models and techniques in reaction theory that have allowed us to study the halo. This is written at the graduate student (starting at PhD) level. The author of the book, Jim Al-Khalili, is a theoretician who published some of the key papers on the structure of the halo in the mid and late 90s and was the first to determine its true size. This monograph is based on review articles he has written on the mathematical models used to determine the halo structure and the reactions used to model that structure.

  19. Semi-empirical catalog of early-type galaxy-halo systems: dark matter density profiles, halo contraction and dark matter annihilation strength

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chae, Kyu-Hyun; Kravtsov, Andrey V.; Frieman, Joshua A.

    With Sloan Digital Sky Survey galaxy data and halo data from up-to-date N-body simulations within the ΛCDM framework we construct a semi-empirical catalog (SEC) of early-type galaxy-halo systems by making a self-consistent bivariate statistical match of stellar mass (M{sub *}) and velocity dispersion (σ) with halo virial mass (M{sub vir}) as demonstrated here for the first time. We then assign stellar mass profile and velocity dispersion profile parameters to each system in the SEC using their observed correlations with M{sub *} and σ. Simultaneously, we solve for dark matter density profile of each halo using the spherical Jeans equation. Themore » resulting dark matter density profiles deviate in general from the dissipationless profile of Navarro-Frenk-White or Einasto and their mean inner density slope and concentration vary systematically with M{sub vir}. Statistical tests of the distribution of profiles at fixed M{sub vir} rule out the null hypothesis that it follows the distribution predicted by dissipationless N-body simulations for M{sub vir}∼<10{sup 13.5} {sup –} {sup 14.5} M{sub s}un. These dark matter profiles imply that dark matter density is, on average, enhanced significantly in the inner region of halos with M{sub vir}∼<10{sup 13.5} {sup –} {sup 14.5} M{sub s}un supporting halo contraction. The main characteristics of halo contraction are: (1) the mean dark matter density within the effective radius has increased by a factor varying systematically up to ≈ 3–4 at M{sub vir} = 10{sup 12} M{sub s}un, and (2) the inner density slope has a mean of (α) ≈ 1.3 with ρ{sub dm}(r)∝r{sup −α} and a halo-to-halo rms scatter of rms(α) ∼ 0.4–0.5 for 10{sup 12} M{sub s}un∼« less

  20. The Galaxy-Halo Connection in High-redshift Universe: Details and Evolution of Stellar-to-halo Mass Ratios of Lyman Break Galaxies on CFHTLS Deep Fields

    NASA Astrophysics Data System (ADS)

    Ishikawa, Shogo; Kashikawa, Nobunari; Toshikawa, Jun; Tanaka, Masayuki; Hamana, Takashi; Niino, Yuu; Ichikawa, Kohei; Uchiyama, Hisakazu

    2017-05-01

    We present the results of clustering analyses of Lyman break galaxies (LBGs) at z˜ 3, 4, and 5 using the final data release of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). Deep- and wide-field images of the CFHTLS Deep Survey enable us to obtain sufficiently accurate two-point angular correlation functions to apply a halo occupation distribution analysis. The mean halo masses, calculated as < {M}h> ={10}11.7{--}{10}12.8 {h}-1 {M}⊙ , increase with the stellar-mass limit of LBGs. The threshold halo mass to have a central galaxy, {M}\\min , follows the same increasing trend as the low-z results, whereas the threshold halo mass to have a satellite galaxy, M 1, shows higher values at z=3{--}5 than z=0.5{--}1.5, over the entire stellar mass range. Satellite fractions of dropout galaxies, even at less massive halos, are found to drop sharply, from z = 2 down to less than 0.04, at z=3{--}5. These results suggest that satellite galaxies form inefficiently within dark halos at z=3{--}5, even for less massive satellites with {M}\\star < {10}10 {M}⊙ . We compute stellar-to-halo mass ratios (SHMRs) assuming a main sequence of galaxies, which is found to provide SHMRs consistent with those derived from a spectral energy distribution fitting method. The observed SHMRs are in good agreement with model predictions based on the abundance-matching method, within 1σ confidence intervals. We derive observationally, for the first time, {M}{{h}}{pivot}, which is the halo mass at a peak in the star-formation efficiency, at 3< z< 5, and it shows a small increasing trend with cosmic time at z> 3. In addition, {M}{{h}}{pivot} and its normalization are found to be almost unchanged during 0< z< 5. Our study provides observational evidence that galaxy formation is ubiquitously most efficient near a halo mass of {M}{{h}}˜ {10}12 {M}⊙ over cosmic time.

  1. The MICE Grand Challenge lightcone simulation - II. Halo and galaxy catalogues

    NASA Astrophysics Data System (ADS)

    Crocce, M.; Castander, F. J.; Gaztañaga, E.; Fosalba, P.; Carretero, J.

    2015-10-01

    This is the second in a series of three papers in which we present an end-to-end simulation from the MICE collaboration, the MICE Grand Challenge (MICE-GC) run. The N-body contains about 70 billion dark-matter particles in a (3 h-1 Gpc)3 comoving volume spanning five orders of magnitude in dynamical range. Here, we introduce the halo and galaxy catalogues built upon it, both in a wide (5000 deg2) and deep (z < 1.4) lightcone and in several comoving snapshots. Haloes were resolved down to few 1011 h-1 M⊙. This allowed us to model galaxies down to absolute magnitude Mr < -18.9. We used a new hybrid halo occupation distribution and abundance matching technique for galaxy assignment. The catalogue includes the spectral energy distributions of all galaxies. We describe a variety of halo and galaxy clustering applications. We discuss how mass resolution effects can bias the large-scale two-pt clustering amplitude of poorly resolved haloes at the ≲5 per cent level, and their three-pt correlation function. We find a characteristic scale-dependent bias of ≲6 per cent across the BAO feature for haloes well above M⋆ ˜ 1012 h-1 M⊙ and for luminous red galaxy like galaxies. For haloes well below M⋆ the scale dependence at 100 h-1 Mpc is ≲2 per cent. Lastly, we discuss the validity of the large-scale Kaiser limit across redshift and departures from it towards non-linear scales. We make the current version of the lightcone halo and galaxy catalogue (MICECATv1.0) publicly available through a dedicated web portal to help develop and exploit the new generation of astronomical surveys.

  2. What is the Milky Way outer halo made of?

    NASA Astrophysics Data System (ADS)

    Jablonka, Pascale; Battaglia, G.

    2018-06-01

    In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in-situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this talk I will focus on the outer regions of the Milky Way stellar halo, and present results from a program aimed at determining chemical abundances of halo stars with large present-day Galactocentric distances, $>$15 kpc. The data-set consists of high resolution spectra for 28 red giant branch stars covering a wide metallicity range.We show that the ratio of $\\alpha$-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H]$\\gtrsim -1.5$ when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples.

  3. Halo assembly bias and the tidal anisotropy of the local halo environment

    NASA Astrophysics Data System (ADS)

    Paranjape, Aseem; Hahn, Oliver; Sheth, Ravi K.

    2018-05-01

    We study the role of the local tidal environment in determining the assembly bias of dark matter haloes. Previous results suggest that the anisotropy of a halo's environment (i.e. whether it lies in a filament or in a more isotropic region) can play a significant role in determining the eventual mass and age of the halo. We statistically isolate this effect, using correlations between the large-scale and small-scale environments of simulated haloes at z = 0 with masses between 1011.6 ≲ (m/h-1 M⊙) ≲ 1014.9. We probe the large-scale environment, using a novel halo-by-halo estimator of linear bias. For the small-scale environment, we identify a variable αR that captures the tidal anisotropy in a region of radius R = 4R200b around the halo and correlates strongly with halo bias at fixed mass. Segregating haloes by αR reveals two distinct populations. Haloes in highly isotropic local environments (αR ≲ 0.2) behave as expected from the simplest, spherically averaged analytical models of structure formation, showing a negative correlation between their concentration and large-scale bias at all masses. In contrast, haloes in anisotropic, filament-like environments (αR ≳ 0.5) tend to show a positive correlation between bias and concentration at any mass. Our multiscale analysis cleanly demonstrates how the overall assembly bias trend across halo mass emerges as an average over these different halo populations, and provides valuable insights towards building analytical models that correctly incorporate assembly bias. We also discuss potential implications for the nature and detectability of galaxy assembly bias.

  4. A framework for quantifying the impact of occupant behavior on energy savings of energy conservation measures

    DOE PAGES

    Sun, K; Hong, T

    2017-07-01

    © 2017 Elsevier B.V. To improve energy efficiency—during new buildings design or during a building retrofit—evaluating the energy savings potential of energy conservation measures (ECMs) is a critical task. In building retrofits, occupant behavior significantly impacts building energy use and is a leading factor in uncertainty when determining the effectiveness of retrofit ECMs. Current simulation-based assessment methods simplify the representation of occupant behavior by using a standard or representative set of static and homogeneous assumptions ignoring the dynamics, stochastics, and diversity of occupant's energy-related behavior in buildings. The simplification contributes to significant gaps between the simulated and measured actual energymore » performance of buildings. This study presents a framework for quantifying the impact of occupant behaviors on ECM energy savings using building performance simulation. During the first step of the study, three occupant behavior styles (austerity, normal, and wasteful) were defined to represent different levels of energy consciousness of occupants regarding their interactions with building energy systems (HVAC, windows, lights and plug-in equipment). Next, a simulation workflow was introduced to determine a range of the ECM energy savings. Then, guidance was provided to interpret the range of ECM savings to support ECM decision making. Finally, a pilot study was performed in a real building to demonstrate the application of the framework. Simulation results show that the impact of occupant behaviors on ECM savings vary with the type of ECM. Occupant behavior minimally affects energy savings for ECMs that are technology-driven (the relative savings differ by less than 2%) and have little interaction with the occupants; for ECMs with strong occupant interaction, such as the use of zonal control variable refrigerant flow system and natural ventilation, energy savings are significantly affected by occupant behavior

  5. A framework for quantifying the impact of occupant behavior on energy savings of energy conservation measures

    DOE PAGES

    Sun, Kaiyu; Hong, Tianzhen

    2017-04-27

    To improve energy efficiency—during new buildings design or during a building retrofit—evaluating the energy savings potential of energy conservation measures (ECMs) is a critical task. In building retrofits, occupant behavior significantly impacts building energy use and is a leading factor in uncertainty when determining the effectiveness of retrofit ECMs. Current simulation-based assessment methods simplify the representation of occupant behavior by using a standard or representative set of static and homogeneous assumptions ignoring the dynamics, stochastics, and diversity of occupant's energy-related behavior in buildings. The simplification contributes to significant gaps between the simulated and measured actual energy performance of buildings. Thismore » paper presents a framework for quantifying the impact of occupant behaviors on ECM energy savings using building performance simulation. During the first step of the study, three occupant behavior styles (austerity, normal, and wasteful) were defined to represent different levels of energy consciousness of occupants regarding their interactions with building energy systems (HVAC, windows, lights and plug-in equipment). Next, a simulation workflow was introduced to determine a range of the ECM energy savings. Then, guidance was provided to interpret the range of ECM savings to support ECM decision making. Finally, a pilot study was performed in a real building to demonstrate the application of the framework. Simulation results show that the impact of occupant behaviors on ECM savings vary with the type of ECM. Occupant behavior minimally affects energy savings for ECMs that are technology-driven (the relative savings differ by less than 2%) and have little interaction with the occupants; for ECMs with strong occupant interaction, such as the use of zonal control variable refrigerant flow system and natural ventilation, energy savings are significantly affected by occupant behavior (the relative savings

  6. A framework for quantifying the impact of occupant behavior on energy savings of energy conservation measures

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sun, Kaiyu; Hong, Tianzhen

    To improve energy efficiency—during new buildings design or during a building retrofit—evaluating the energy savings potential of energy conservation measures (ECMs) is a critical task. In building retrofits, occupant behavior significantly impacts building energy use and is a leading factor in uncertainty when determining the effectiveness of retrofit ECMs. Current simulation-based assessment methods simplify the representation of occupant behavior by using a standard or representative set of static and homogeneous assumptions ignoring the dynamics, stochastics, and diversity of occupant's energy-related behavior in buildings. The simplification contributes to significant gaps between the simulated and measured actual energy performance of buildings. Thismore » paper presents a framework for quantifying the impact of occupant behaviors on ECM energy savings using building performance simulation. During the first step of the study, three occupant behavior styles (austerity, normal, and wasteful) were defined to represent different levels of energy consciousness of occupants regarding their interactions with building energy systems (HVAC, windows, lights and plug-in equipment). Next, a simulation workflow was introduced to determine a range of the ECM energy savings. Then, guidance was provided to interpret the range of ECM savings to support ECM decision making. Finally, a pilot study was performed in a real building to demonstrate the application of the framework. Simulation results show that the impact of occupant behaviors on ECM savings vary with the type of ECM. Occupant behavior minimally affects energy savings for ECMs that are technology-driven (the relative savings differ by less than 2%) and have little interaction with the occupants; for ECMs with strong occupant interaction, such as the use of zonal control variable refrigerant flow system and natural ventilation, energy savings are significantly affected by occupant behavior (the relative savings

  7. Strong bimodality in the host halo mass of central galaxies from galaxy-galaxy lensing

    NASA Astrophysics Data System (ADS)

    Mandelbaum, Rachel; Wang, Wenting; Zu, Ying; White, Simon; Henriques, Bruno; More, Surhud

    2016-04-01

    We use galaxy-galaxy lensing to study the dark matter haloes surrounding a sample of locally brightest galaxies (LBGs) selected from the Sloan Digital Sky Survey. We measure mean halo mass as a function of the stellar mass and colour of the central galaxy. Mock catalogues constructed from semi-analytic galaxy formation simulations demonstrate that most LBGs are the central objects of their haloes, greatly reducing interpretation uncertainties due to satellite contributions to the lensing signal. Over the full stellar mass range, 10.3 < log [M*/M⊙] < 11.6, we find that passive central galaxies have haloes that are at least twice as massive as those of star-forming objects of the same stellar mass. The significance of this effect exceeds 3σ for log [M*/M⊙] > 10.7. Tests using the mock catalogues and on the data themselves clarify the effects of LBG selection and show that it cannot artificially induce a systematic dependence of halo mass on LBG colour. The bimodality in halo mass at fixed stellar mass is reproduced by the astrophysical model underlying our mock catalogue, but the sign of the effect is inconsistent with recent, nearly parameter-free age-matching models. The sign and magnitude of the effect can, however, be reproduced by halo occupation distribution models with a simple (few-parameter) prescription for type dependence.

  8. The Accountability-Well-Being-Ethics framework: a new philosophical foundation for occupational therapy.

    PubMed

    Taff, Steven D; Bakhshi, Parul; Babulal, Ganesh M

    2014-12-01

    The context that supported occupational therapy's inception has been replaced with new challenges brought on by globalization and dramatic changes in health care. Thus, the profession's philosophical grounding needs to be reframed to (a) achieve balance between science-driven and holistic elements, (b) operate within larger contexts on problems brought on by sociopolitical and natural determinants of health, and (c) maintain an ethical identity across all arenas of practice. This paper presents a brief discussion of the philosophical underpinnings in occupational therapy's history, outlines new global challenges for the profession, and proposes a new framework to address these challenges through education, practice, and research. Occupational therapy finds itself practising in a growing number of middle- and low-income countries where its roles and values need to be context and culture specific. The Accountability-Well-Being-Ethics framework guides the three domains of education, research, and practice to be relevant in an increasingly complex world.

  9. Ab initio calculation of one-nucleon halo states

    NASA Astrophysics Data System (ADS)

    Rodkin, D. M.; Tchuvil'sky, Yu M.

    2018-02-01

    We develop an approach to microscopic and ab initio description of clustered systems, states with halo nucleon and one-nucleon resonances. For these purposes a basis combining ordinary shell-model components and cluster-channel terms is built up. The transformation of clustered wave functions to the uniform Slater-determinant type is performed using the concept of cluster coefficients. The resulting basis of orthonormalized wave functions is used for calculating the eigenvalues and the eigenvectors of Hamiltonians built in the framework of ab initio approaches. Calculations of resonance and halo states of 5He, 9Be and 9B nuclei demonstrate that the approach is workable and labor-saving.

  10. Galaxy power spectrum in redshift space: Combining perturbation theory with the halo model

    NASA Astrophysics Data System (ADS)

    Okumura, Teppei; Hand, Nick; Seljak, Uroš; Vlah, Zvonimir; Desjacques, Vincent

    2015-11-01

    Theoretical modeling of the redshift-space power spectrum of galaxies is crucially important to correctly extract cosmological information from galaxy redshift surveys. The task is complicated by the nonlinear biasing and redshift space distortion (RSD) effects, which change with halo mass, and by the wide distribution of halo masses and their occupations by galaxies. One of the main modeling challenges is the existence of satellite galaxies that have both radial distribution inside the halos and large virial velocities inside halos, a phenomenon known as the Finger-of-God (FoG) effect. We present a model for the redshift-space power spectrum of galaxies in which we decompose a given galaxy sample into central and satellite galaxies and relate different contributions to the power spectrum to 1-halo and 2-halo terms in a halo model. Our primary goal is to ensure that any parameters that we introduce have physically meaningful values, and are not just fitting parameters. For the lowest order 2-halo terms we use the previously developed RSD modeling of halos in the context of distribution function and perturbation theory approach. This term needs to be multiplied by the effect of radial distances and velocities of satellites inside the halo. To this one needs to add the 1-halo terms, which are nonperturbative. We show that the real space 1-halo terms can be modeled as almost constant, with the finite extent of the satellites inside the halo inducing a small k2R2 term over the range of scales of interest, where R is related to the size of the halo given by its halo mass. We adopt a similar model for FoG in redshift space, ensuring that FoG velocity dispersion is related to the halo mass. For FoG k2 type expansions do not work over the range of scales of interest and FoG resummation must be used instead. We test several simple damping functions to model the velocity dispersion FoG effect. Applying the formalism to mock galaxies modeled after the "CMASS" sample of the

  11. Galaxy power spectrum in redshift space: Combining perturbation theory with the halo model

    DOE PAGES

    Okumura, Teppei; Hand, Nick; Seljak, Uros; ...

    2015-11-19

    Theoretical modeling of the redshift-space power spectrum of galaxies is crucially important to correctly extract cosmological information from galaxy redshift surveys. The task is complicated by the nonlinear biasing and redshift space distortion (RSD) effects, which change with halo mass, and by the wide distribution of halo masses and their occupations by galaxies. One of the main modeling challenges is the existence of satellite galaxies that have both radial distribution inside the halos and large virial velocities inside halos, a phenomenon known as the Finger-of-God (FoG) effect. We present a model for the redshift-space power spectrum of galaxies in whichmore » we decompose a given galaxy sample into central and satellite galaxies and relate different contributions to the power spectrum to 1-halo and 2-halo terms in a halo model. Our primary goal is to ensure that any parameters that we introduce have physically meaningful values, and are not just fitting parameters. For the lowest order 2-halo terms we use the previously developed RSD modeling of halos in the context of distribution function and perturbation theory approach. This term needs to be multiplied by the effect of radial distances and velocities of satellites inside the halo. To this one needs to add the 1-halo terms, which are nonperturbative. We show that the real space 1-halo terms can be modeled as almost constant, with the finite extent of the satellites inside the halo inducing a small k 2R 2 term over the range of scales of interest, where R is related to the size of the halo given by its halo mass. Furthermore, we adopt a similar model for FoG in redshift space, ensuring that FoG velocity dispersion is related to the halo mass. For FoG k 2 type expansions do not work over the range of scales of interest and FoG resummation must be used instead. We test several simple damping functions to model the velocity dispersion FoG effect. Applying the formalism to mock galaxies modeled after the

  12. The Splashback Radius of Halos from Particle Dynamics. I. The SPARTA Algorithm

    NASA Astrophysics Data System (ADS)

    Diemer, Benedikt

    2017-07-01

    Motivated by the recent proposal of the splashback radius as a physical boundary of dark-matter halos, we present a parallel computer code for Subhalo and PARticle Trajectory Analysis (SPARTA). The code analyzes the orbits of all simulation particles in all host halos, billions of orbits in the case of typical cosmological N-body simulations. Within this general framework, we develop an algorithm that accurately extracts the location of the first apocenter of particles after infall into a halo, or splashback. We define the splashback radius of a halo as the smoothed average of the apocenter radii of individual particles. This definition allows us to reliably measure the splashback radii of 95% of host halos above a resolution limit of 1000 particles. We show that, on average, the splashback radius and mass are converged to better than 5% accuracy with respect to mass resolution, snapshot spacing, and all free parameters of the method.

  13. The halo Boltzmann equation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Biagetti, Matteo; Desjacques, Vincent; Kehagias, Alex

    2016-04-01

    Dark matter halos are the building blocks of the universe as they host galaxies and clusters. The knowledge of the clustering properties of halos is therefore essential for the understanding of the galaxy statistical properties. We derive an effective halo Boltzmann equation which can be used to describe the halo clustering statistics. In particular, we show how the halo Boltzmann equation encodes a statistically biased gravitational force which generates a bias in the peculiar velocities of virialized halos with respect to the underlying dark matter, as recently observed in N-body simulations.

  14. The Faber–Jackson relation and Fundamental Plane from halo abundance matching

    DOE PAGES

    Desmond, Harry; Wechsler, Risa H.

    2016-11-02

    The Fundamental Plane (FP) describes the relation between the stellar mass, size, and velocity dispersion of elliptical galaxies; the Faber–Jackson relation (FJR) is its projection on to {mass, velocity} space. In this work, we re-deploy and expand the framework of Desmond & Wechsler to ask whether abundance matching-based Λ-cold dark matter models which have shown success in matching the spatial distribution of galaxies are also capable of explaining key properties of the FJR and FP, including their scatter. Within our framework, agreement with the normalization of the FJR requires haloes to expand in response to disc formation. We find thatmore » the tilt of the FP may be explained by a combination of the observed non-homology in galaxy structure and the variation in mass-to-light ratio produced by abundance matching with a universal initial mass function, provided that the anisotropy of stellar motions is taken into account. However, the predicted scatter around the FP is considerably increased by situating galaxies in cosmologically motivated haloes due to the variations in halo properties at fixed stellar mass and appears to exceed that of the data. Finally, this implies that additional correlations between galaxy and halo variables may be required to fully reconcile these models with elliptical galaxy scaling relations.« less

  15. HaloSat - A CubeSat to Study the Hot Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    2017-01-01

    Observations of the nearby universe fail to locate about half of the baryons observed in the early universe. The missing baryons may be in hot galactic halos. HaloSat is a CubeSat designed to map oxygen line emission (O VII and O VIII) around the Milky Way in order to constrain the mass and spatial distribution of hot gas in the halo. HaloSat has a grasp competitive with current X-ray observatories. Its observing program will be optimized to minimize contributions from solar wind charge exchange (SWCX) emission that limit the accuracy of current measurements. We will describe the HaloSat mission concept, progress towards its implementation, and plans for archiving and distribution of the data.

  16. DO NOT FORGET THE FOREST FOR THE TREES: THE STELLAR-MASS HALO-MASS RELATION IN DIFFERENT ENVIRONMENTS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tonnesen, Stephanie; Cen, Renyue, E-mail: stonnes@gmail.com, E-mail: cen@astro.princeton.edu

    2015-10-20

    The connection between dark matter halos and galactic baryons is often not well constrained nor well resolved in cosmological hydrodynamical simulations. Thus, halo occupation distribution models that assign galaxies to halos based on halo mass are frequently used to interpret clustering observations, even though it is well known that the assembly history of dark matter halos is related to their clustering. In this paper we use high-resolution hydrodynamical cosmological simulations to compare the halo and stellar mass growth of galaxies in a large-scale overdensity to those in a large-scale underdensity (on scales of about 20 Mpc). The simulation reproduces assemblymore » bias, in which halos have earlier formation times in overdense environments than in underdense regions. We find that the ratio of stellar mass to halo mass is larger in overdense regions in central galaxies residing in halos with masses between 10{sup 11} and 10{sup 12.9} M{sub ⊙}. When we force the local density (within 2 Mpc) at z = 0 to be the same for galaxies in the large-scale over- and underdensities, we find the same results. We posit that this difference can be explained by a combination of earlier formation times, more interactions at early times with neighbors, and more filaments feeding galaxies in overdense regions. This result puts the standard practice of assigning stellar mass to halos based only on their mass, rather than considering their larger environment, into question.« less

  17. HaloSat- A CubeSat to Study the Hot Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    We propose to develop, build, and fly HaloSat, a CubeSat capable of measuring the oxygen line emission from the hot Galactic halo. A dedicated CubeSat enables an instrument design and observing strategy to maximize the halo signal while minimizing foregrounds from solar wind charge exchange interactions within the solar system. We will use HaloSat to map the distribution of hot gas in the Milky Way and determine whether it fills an extended, and thus massive halo, or whether the halo is compact, and thus does not contribute significantly to the total mass of the Milky Way. HaloSat can be accomplished at modest cost using a CubeSat, a novel platform for space astrophysics missions. We will use a commercially available CubeSat bus and commercially available X-ray detectors to reduce development risk and minimize overall mission cost. HaloSat builds on the initiatives of GSFC/Wallops Flight Facility (WFF) in the development of CubeSats for low cost access to space and relies on the technical expertise of WFF personnel for spacecraft and mission design and operations. The team, from University of Iowa (UI), GSFC, Johns Hopkins, and CNRS (France), contains experts in X-ray detector development and data analysis and the astrophysics of hot plasmas and Galactic structure. The UI team will include a number of junior researchers (undergraduates, graduate students, and a postdoc) and help train them for future leadership roles on NASA space flight missions.

  18. Halo vest instrumentation

    NASA Astrophysics Data System (ADS)

    Huston, Dryver R.; Krag, Martin

    1996-05-01

    The halo vest is a head and neck immobilization system that is often used on patients that are recovering from cervical trauma or surgery. The halo vest system consists of a rigid halo that is firmly attached to the skull, an upright support structure for stabilization and immobilization, and a torso-enveloping vest. The main purpose of this study was to measure the forces that are carried by the halo-vest structure as the subject undergoes various activities of daily living and external loading for different vest designs. A tethered strain gage load cell based instrumentation system was used to take these load measurements on ten different subjects. Three different halo-vest systems were evaluated. The primary difference between the vests was the amount of torso coverage and the use of shoulder straps. The loads were measured, analyzed and used to compare the vests and to create a model of halo-vest-neck mechanics. Future applications of this technology to standalone data logging, pin-load measuring and biofeedback applications are discussed.

  19. The Milky Way, the Galactic halo, and the Halos of Galaxies

    NASA Astrophysics Data System (ADS)

    Gerhard, Ortwin

    2015-08-01

    The Milky Way, "our" Galaxy, is currently the subject of intense study with many ground-based surveys, in anticipation of upcoming results from the GAIA mission. From this work we have been learning about the full three-dimensional structure of the Galactic box/peanut bulge, the distribution of stars in the bar and disk, and the many streams in the Galactic halo. The data tell us that most of the Galactic bulge formed from the disk, and that a large fraction of the Galactic halo has been accreted from outside. Similarly, in many external galaxy halos there is now evidence for tidal streams and accretion of satellites. To see these features requires exquisite data - mostly very deep photometry, but some halo substructures have also been found with kinematic data. These observations illustrate how galaxy halos are still growing, and sometimes can be used to "time" the accretion events. In comparison with cosmological simulations, the structure of galaxy halos gives us a vivid illustration of the hierarchical nature of our Universe.

  20. Galaxy and Mass Assembly (GAMA): halo formation times and halo assembly bias on the cosmic web

    NASA Astrophysics Data System (ADS)

    Tojeiro, Rita; Eardley, Elizabeth; Peacock, John A.; Norberg, Peder; Alpaslan, Mehmet; Driver, Simon P.; Henriques, Bruno; Hopkins, Andrew M.; Kafle, Prajwal R.; Robotham, Aaron S. G.; Thomas, Peter; Tonini, Chiara; Wild, Vivienne

    2017-09-01

    We present evidence for halo assembly bias as a function of geometric environment (GE). By classifying Galaxy and Mass Assembly (GAMA) galaxy groups as residing in voids, sheets, filaments or knots using a tidal tensor method, we find that low-mass haloes that reside in knots are older than haloes of the same mass that reside in voids. This result provides direct support to theories that link strong halo tidal interactions with halo assembly times. The trend with GE is reversed at large halo mass, with haloes in knots being younger than haloes of the same mass in voids. We find a clear signal of halo downsizing - more massive haloes host galaxies that assembled their stars earlier. This overall trend holds independently of GE. We support our analysis with an in-depth exploration of the L-Galaxies semi-analytic model, used here to correlate several galaxy properties with three different definitions of halo formation time. We find a complex relationship between halo formation time and galaxy properties, with significant scatter. We confirm that stellar mass to halo mass ratio, specific star formation rate (SFR) and mass-weighed age are reasonable proxies of halo formation time, especially at low halo masses. Instantaneous SFR is a poor indicator at all halo masses. Using the same semi-analytic model, we create mock spectral observations using complex star formation and chemical enrichment histories, which approximately mimic GAMA's typical signal-to-noise ratio and wavelength range. We use these mocks to assert how well potential proxies of halo formation time may be recovered from GAMA-like spectroscopic data.

  1. [The 20th century legal framework regarding risk at work and occupational health in Colombia].

    PubMed

    Arango-Soler, Juan M; Luna-García, Jairo E; Correa-Moreno, Yerson A; Campos, Adriana C

    2013-01-01

    Analyzing the 20th century Colombian legal framework from the point of view of labor law, social security and public health for identifying concepts regarding occupational health and professional risk and trying to establish convergence and differences between such foci and whether they fulfilled a complementary view. This work involved documentary research by means of thematic categorical analysis of the laws and statutes promulgated in 20th century Colombia, considering the main element or entity which should have regulated that related to professional risk or occupational health. The development of the 20th century Colombian legal framework regarding health at work was periodized, revealing the predominance of a view of social law focused on protecting dependent workers' work-related risks, as part of a tendency extending to the Colombian Sistema General de Riesgos Laborales. The proposed stages used for organizing the legal framework concerning social security regarding professional risk and occupational health facilitated some important elements being recognized concerning the social, legal and institutional context from which workers' health laws emerged. Tension was noted concerning statutes orientated towards redress and compensation regarding accidents at work and legislation emphasizing prevention.

  2. Galactic Warps in Triaxial Halos

    NASA Astrophysics Data System (ADS)

    Jeon, Myoungwon; Kim, Sungsoo S.; Ann, Hong Bae

    2009-05-01

    We study the behavior of galactic disks in triaxial halos both numerically and analytically to see if warps can be excited and sustained in triaxial potentials. We consider the following two scenarios: (1) galactic disks that are initially tilted relative to the equatorial plane of the halo (for a pedagogical purpose), and (2) tilted infall of dark matter relative to the equatorial plane of the disk and the halo. With numerical simulations of 100,000 disk particles in a fixed halo potential, we find that in triaxial halos, warps can be excited and sustained just as in spherical or axisymmetric halos but they show some oscillatory behavior and even can be transformed to a polar-ring system if the halo has a prolate-like triaxiality. The nonaxisymmetric component of the halo causes the disk to nutate, and the differential nutation between the inner and outer parts of the disk generally makes the magnitude of the warp slightly diminish and fluctuate. We also find that warps are relatively weaker in oblate and oblate-like triaxial halos, and since these halos are the halo configurations of disk galaxies inferred by cosmological simulations, our results are consistent with the fact that most of the observed warps are quite weak. We derive approximate formulae for the torques exerted on the disk by the triaxial halo and the dark matter torus, and with these formulae we successfully describe the behavior of the disks in our simulations. The techniques used in deriving these formulae could be applied for realistic halos with more complex structures.

  3. Conserved actions, maximum entropy and dark matter haloes

    NASA Astrophysics Data System (ADS)

    Pontzen, Andrew; Governato, Fabio

    2013-03-01

    We use maximum entropy arguments to derive the phase-space distribution of a virialized dark matter halo. Our distribution function gives an improved representation of the end product of violent relaxation. This is achieved by incorporating physically motivated dynamical constraints (specifically on orbital actions) which prevent arbitrary redistribution of energy. We compare the predictions with three high-resolution dark matter simulations of widely varying mass. The numerical distribution function is accurately predicted by our argument, producing an excellent match for the vast majority of particles. The remaining particles constitute the central cusp of the halo (≲4 per cent of the dark matter). They can be accounted for within the presented framework once the short dynamical time-scales of the centre are taken into account.

  4. The Milky Way, the Galactic Halo, and the Halos of Galaxies

    NASA Astrophysics Data System (ADS)

    Gerhard, Ortwin

    2016-08-01

    The Milky Way, ``our'' Galaxy, is currently the subject of intense study with many ground-based surveys, in anticipation of upcoming results from the Gaia mission. From this work we have been learning about the full three-dimensional structure of the Galactic box/peanut bulge, the distribution of stars in the bar and disk, and the many streams and substructures in the Galactic halo. The data indicate that a large fraction of the Galactic halo has been accreted from outside. Similarly, in many external galaxy halos there is now evidence for tidal streams and accretion of satellites. To study these features requires exquisite, deep photometry and spectroscopy. These observations illustrate how galaxy halos are still growing, and sometimes can be used to ``time'' the accretion events. In comparison with cosmological simulations, the structure of galaxy halos gives us a vivid illustration of the hierarchical nature of our Universe.

  5. HALOE Science Investigation

    NASA Technical Reports Server (NTRS)

    Benner, D. Chris

    1998-01-01

    This cooperative agreement has investigated a number of spectroscopic problems of interest to the Halogen Occultation Experiment (HALOE). The types of studies performed are in two parts, namely, those that involve the testing and characterization of correlation spectrometers and those that provide basic molecular spectroscopic information. In addition, some solar studies were performed with the calibration data returned by HALOE from orbit. In order to accomplish this a software package was written as part of this cooperative agreement. The HALOE spectroscopic instrument package was used in various tests of the HALOE flight instrument. These included the spectral response test, the early stages of the gas response test and various spectral response tests of the detectors and optical elements of the instruments. Considerable effort was also expended upon the proper laboratory setup for many of the prelaunch tests of the HALOE flight instrument, including the spectral response test and the gas response test. These tests provided the calibration and the assurance that the calibration was performed correctly.

  6. Group galaxy number density profiles far out: Is the `one-halo' term NFW out to >10 virial radii?

    NASA Astrophysics Data System (ADS)

    Trevisan, M.; Mamon, G. A.; Stalder, D. H.

    2017-10-01

    While the density profiles (DPs) of Lambda cold dark matter haloes obey the Navarro, Frenk & White (NFW) law out to roughly one virial radius, rvir, the structure of their outer parts is still poorly understood, because the one-halo term describing the halo itself is dominated by the two-halo term representing the other haloes picked up. Using a semi-analytical model, we measure the real-space one-halo number DP of groups out to 20rvir by assigning each galaxy to its nearest group above mass Ma, in units of the group rvir. If Ma is small (large), the outer DP of groups falls rapidly (slowly). We find that there is an optimal Ma for which the stacked DP resembles the NFW model to 0.1 dex accuracy out to 13 virial radii. We find similar long-range NFW surface DPs (out to 10rvir) in the Sloan Digital Sky Survey observations using a galaxy assignment scheme that combines the non-linear virialized regions of groups with their linear outer parts. The optimal Ma scales as the minimum mass of the groups that are stacked to a power 0.25-0.3. The NFW model thus does not solely originate from violent relaxation. Moreover, populating haloes with galaxies using halo occupation distribution models must proceed out to much larger radii than usually done.

  7. The concentration dependence of the galaxy–halo connection: Modeling assembly bias with abundance matching

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lehmann, Benjamin V.; Mao, Yao -Yuan; Becker, Matthew R.

    Empirical methods for connecting galaxies to their dark matter halos have become essential for interpreting measurements of the spatial statistics of galaxies. In this work, we present a novel approach for parameterizing the degree of concentration dependence in the abundance matching method. Furthermore, this new parameterization provides a smooth interpolation between two commonly used matching proxies: the peak halo mass and the peak halo maximal circular velocity. This parameterization controls the amount of dependence of galaxy luminosity on halo concentration at a fixed halo mass. Effectively this interpolation scheme enables abundance matching models to have adjustable assembly bias in the resulting galaxy catalogs. With the newmore » $$400\\,\\mathrm{Mpc}\\,{h}^{-1}$$ DarkSky Simulation, whose larger volume provides lower sample variance, we further show that low-redshift two-point clustering and satellite fraction measurements from SDSS can already provide a joint constraint on this concentration dependence and the scatter within the abundance matching framework.« less

  8. The concentration dependence of the galaxy–halo connection: Modeling assembly bias with abundance matching

    DOE PAGES

    Lehmann, Benjamin V.; Mao, Yao -Yuan; Becker, Matthew R.; ...

    2016-12-28

    Empirical methods for connecting galaxies to their dark matter halos have become essential for interpreting measurements of the spatial statistics of galaxies. In this work, we present a novel approach for parameterizing the degree of concentration dependence in the abundance matching method. Furthermore, this new parameterization provides a smooth interpolation between two commonly used matching proxies: the peak halo mass and the peak halo maximal circular velocity. This parameterization controls the amount of dependence of galaxy luminosity on halo concentration at a fixed halo mass. Effectively this interpolation scheme enables abundance matching models to have adjustable assembly bias in the resulting galaxy catalogs. With the newmore » $$400\\,\\mathrm{Mpc}\\,{h}^{-1}$$ DarkSky Simulation, whose larger volume provides lower sample variance, we further show that low-redshift two-point clustering and satellite fraction measurements from SDSS can already provide a joint constraint on this concentration dependence and the scatter within the abundance matching framework.« less

  9. Statistical Aspects of X-Class Halo and Non-Halo Events, 1996-2014

    NASA Technical Reports Server (NTRS)

    Wilson, Robert M.

    2016-01-01

    Of the 166 X-class events that occurred during the interval 1996-2014, 80 had associations with halo events, 68 had no associations with halo events, and 18 occurred during LASCO (Large Angle and Spectrometric COronagraph) data gaps. Both the duration and location of the X-class halo events proved to be statistically important parameters with respect to the geo-effectiveness of the events. Forty-four of the 80 X-class halo events occurred within 45 degrees of the Sun's central meridian and 47 of the 80 had duration greater than or equal to 30 minutes, whereas only 28 of the 68 X-class non-halo events occurred within 45 degrees of the Sun's central meridian (2 events have unknown location) and 22 of the 68 had duration greater than or equal to 30 minutes. Ignoring the 4 largest X-class flares greater than or equal to X4.0 during the LASCO data gaps, 17 of the remaining 20 were associated with halo events, and 14 of the 17 had at least one geo-magnetically disturbed day (Ap (i.e. NOAA's Ap* (ApStar)index: the major magnetic storms going back to 1932) greater than or equal to 25 nanotesias) within 1-5 days following the X-class halo event. Based on the hourly Dst (Disturbance storm time) index, the most geo-effective X-class halo event during the interval 1996-2014 was that of an X1.7 flare that occurred on 2001 March 29 at 0957, having an hourly Disturbance storm time minimum equal to minus 387 nanotesias. On average, the X-class halo events (80 events) were found to have a mean duration (42 minutes) slightly longer than the mean duration (29 minutes) of the X-class non-halo events (68 events) with the difference in the means being statistically important at the 1 percent level of significance.

  10. Comparison of halo of 11Be, 15C, and 19C

    NASA Astrophysics Data System (ADS)

    Kharab, R.; Kumar, R.; Singh, P.; Sharma, H. C.

    2007-12-01

    We have compared the halo of 11Be, 15C, and 19C nuclei by analyzing the one-neutron stripping reaction data on the Be target at 60-, 54-, and 57-MeV/ A beam energies, respectively, within the framework of the eikonal approximation approach. The determination of effective range through the comparison of the total cross section data and prediction has revealed that the halo of 19C is the well developed, while that of 15C is the least and that of 11Be lies in between these two. The longitudinal momentum distribution data also strengthen these observations.

  11. Cosmic web type dependence of halo clustering

    NASA Astrophysics Data System (ADS)

    Fisher, J. D.; Faltenbacher, A.

    2018-01-01

    We use the Millennium Simulation to show that halo clustering varies significantly with cosmic web type. Haloes are classified as node, filament, sheet and void haloes based on the eigenvalue decomposition of the velocity shear tensor. The velocity field is sampled by the peculiar velocities of a fixed number of neighbouring haloes, and spatial derivatives are computed using a kernel borrowed from smoothed particle hydrodynamics. The classification scheme is used to examine the clustering of haloes as a function of web type for haloes with masses larger than 1011 h- 1 M⊙. We find that node haloes show positive bias, filament haloes show negligible bias and void and sheet haloes are antibiased independent of halo mass. Our findings suggest that the mass dependence of halo clustering is rooted in the composition of web types as a function of halo mass. The substantial fraction of node-type haloes for halo masses ≳ 2 × 1013 h- 1 M⊙ leads to positive bias. Filament-type haloes prevail at intermediate masses, 1012-1013 h- 1 M⊙, resulting in unbiased clustering. The large contribution of sheet-type haloes at low halo masses ≲ 1012 h- 1 M⊙ generates antibiasing.

  12. "Invisible" Galactic Halos.

    ERIC Educational Resources Information Center

    Lugt, Karel Vander

    1993-01-01

    Develops a simple core-halo model of a galaxy that exhibits the main features of observed rotation curves and quantitatively illustrates the need to postulate halos of dark matter. Uses only elementary mechanics. (Author/MVL)

  13. Hot Gas Halos in Galaxies

    NASA Astrophysics Data System (ADS)

    Mulchaey, John

    Most galaxy formation models predict that massive low-redshift disk galaxies are embedded in extended hot halos of externally accreted gas. Such gas appears necessary to maintain ongoing star formation in isolated spirals like the Milky Way. To explain the large population of red galaxies in rich groups and clusters, most galaxy evolution models assume that these hot gas halos are stripped completely when a galaxy enters a denser environment. This simple model has been remarkably successful at reproducing many observed properties of galaxies. Although theoretical arguments suggest hot gas halos are an important component in galaxies, we know very little about this gas from an observational standpoint. In fact, previous observations have failed to detect soft X-ray emission from such halos in disk galaxies. Furthermore, the assumption that hot gas halos are stripped completely when a galaxy enters a group or cluster has not been verified. We propose to combine proprietary and archival XMM-Newton observations of galaxies in the field, groups and clusters to study how hot gas halos are impacted by environment. Our proposed program has three components: 1) The deepest search to date for a hot gas halo in a quiescent spiral galaxy. A detection will confirm a basic tenet of disk galaxy formation models, whereas a non-detection will seriously challenge these models and impose new constraints on the growth mode and feedback history of disk galaxies. 2) A detailed study of the hot gas halos properties of field early-type galaxies. As environmental processes such as stripping are not expected to be important in the field, a study of hot gas halos in this environment will allow us to better understand how feedback and other internal processes impact hot gas halos. 3) A study of hot gas halos in the outskirts of groups and clusters. By comparing observations with our suite of simulations we can begin to understand what role the stripping of hot gas halos plays in galaxy

  14. Spatial clustering of dark matter haloes: secondary bias, neighbour bias, and the influence of massive neighbours on halo properties

    NASA Astrophysics Data System (ADS)

    Salcedo, Andrés N.; Maller, Ariyeh H.; Berlind, Andreas A.; Sinha, Manodeep; McBride, Cameron K.; Behroozi, Peter S.; Wechsler, Risa H.; Weinberg, David H.

    2018-04-01

    We explore the phenomenon commonly known as halo assembly bias, whereby dark matter haloes of the same mass are found to be more or less clustered when a second halo property is considered, for haloes in the mass range 3.7 × 1011-5.0 × 1013 h-1 M⊙. Using the Large Suite of Dark Matter Simulations (LasDamas) we consider nine commonly used halo properties and find that a clustering bias exists if haloes are binned by mass or by any other halo property. This secondary bias implies that no single halo property encompasses all the spatial clustering information of the halo population. The mean values of some halo properties depend on their halo's distance to a more massive neighbour. Halo samples selected by having high values of one of these properties therefore inherit a neighbour bias such that they are much more likely to be close to a much more massive neighbour. This neighbour bias largely accounts for the secondary bias seen in haloes binned by mass and split by concentration or age. However, haloes binned by other mass-like properties still show a secondary bias even when the neighbour bias is removed. The secondary bias of haloes selected by their spin behaves differently than that for other halo properties, suggesting that the origin of the spin bias is different than of other secondary biases.

  15. Institutional Variables, Collegial Relationships, and Occupational Satisfaction: Testing the Conceptual Framework of Faculty Job Satisfaction among Counselor Educators

    ERIC Educational Resources Information Center

    Michel, Rebecca E.

    2012-01-01

    Occupational satisfaction is the extent to which individuals are fulfilled by their employment. The Conceptual Framework of Faculty Job Satisfaction (Hagedorn, 2000) describes how aspects of work impact occupational satisfaction, yet researchers have not previously used this model with counselor educators. This study investigated the applicability…

  16. Spatial clustering of dark matter haloes: secondary bias, neighbour bias, and the influence of massive neighbours on halo properties

    DOE PAGES

    Salcedo, Andres N.; Maller, Ariyeh H.; Berlind, Andreas A.; ...

    2018-01-15

    Here, we explore the phenomenon commonly known as halo assembly bias, whereby dark matter haloes of the same mass are found to be more or less clustered when a second halo property is considered, for haloes in the mass range 3.7 × 10 11–5.0 × 10 13 h –1 M ⊙. Using the Large Suite of Dark Matter Simulations (LasDamas) we consider nine commonly used halo properties and find that a clustering bias exists if haloes are binned by mass or by any other halo property. This secondary bias implies that no single halo property encompasses all the spatial clusteringmore » information of the halo population. The mean values of some halo properties depend on their halo's distance to a more massive neighbour. Halo samples selected by having high values of one of these properties therefore inherit a neighbour bias such that they are much more likely to be close to a much more massive neighbour. This neighbour bias largely accounts for the secondary bias seen in haloes binned by mass and split by concentration or age. However, haloes binned by other mass-like properties still show a secondary bias even when the neighbour bias is removed. The secondary bias of haloes selected by their spin behaves differently than that for other halo properties, suggesting that the origin of the spin bias is different than of other secondary biases.« less

  17. Spatial clustering of dark matter haloes: secondary bias, neighbour bias, and the influence of massive neighbours on halo properties

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Salcedo, Andres N.; Maller, Ariyeh H.; Berlind, Andreas A.

    Here, we explore the phenomenon commonly known as halo assembly bias, whereby dark matter haloes of the same mass are found to be more or less clustered when a second halo property is considered, for haloes in the mass range 3.7 × 10 11–5.0 × 10 13 h –1 M ⊙. Using the Large Suite of Dark Matter Simulations (LasDamas) we consider nine commonly used halo properties and find that a clustering bias exists if haloes are binned by mass or by any other halo property. This secondary bias implies that no single halo property encompasses all the spatial clusteringmore » information of the halo population. The mean values of some halo properties depend on their halo's distance to a more massive neighbour. Halo samples selected by having high values of one of these properties therefore inherit a neighbour bias such that they are much more likely to be close to a much more massive neighbour. This neighbour bias largely accounts for the secondary bias seen in haloes binned by mass and split by concentration or age. However, haloes binned by other mass-like properties still show a secondary bias even when the neighbour bias is removed. The secondary bias of haloes selected by their spin behaves differently than that for other halo properties, suggesting that the origin of the spin bias is different than of other secondary biases.« less

  18. Sun-Earth L1 Region Halo-To-Halo Orbit and Halo-To-LisaJous Orbit Transfers

    NASA Technical Reports Server (NTRS)

    Roberts, Craig E.; DeFazio, Robert

    2004-01-01

    Practical techniques for designing transfer trajectories between Libration Point Orbits (LPOs) are presented. Motivation for development of these techniques was provided by a hardware contingency experienced by the Solar Heliospheric Observatory (SOHO), a joint mission of the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) orbiting the L1 point of the Sun-Earth system. A potential solution to the problem involved a transfer from SOHO s periodic halo orbit to a new LPO of substantially different dimensions. Assuming the SOHO halo orbit as the departure orbit, several practical LPO transfer techniques were developed to obtain new Lissajous or periodic halo orbits that satisfy mission requirements and constraints. While not implemented for the SOHO mission, practical LPO transfer techniques were devised that are generally applicable to current and future LPO missions.

  19. The Dual Origin Of Stellar Halos

    NASA Astrophysics Data System (ADS)

    Zolotov, Adi

    In the dominant Lambda+Cold Dark Matter cosmological paradigm, galaxy stellar halos are thought to form hierarchically from multiple accretion events, starting from the first structures to collapse in the Universe. This dissertation aims to make the first detailed theoretical predictions for the origin of galactic stellar halos. We focus on understanding the physical processes involved in halo formation using high-resolution, N-body + Smooth Particle Hydrodynamic simulations of disk galaxies in a cosmological context. These self-consistent simulations are used to study the competing importance of dissipative processes and dissipationless mergers in the formation of stellar halos. The relative contribution of each mechanism, and its specific role in assembling the inner and outer regions of halos is explored, as a function of galaxy mass and merging history. We show that the presence of both accreted and in situ stars in halos is a generic feature of galaxy formation. For L* galaxies, the relative contribution of each stellar population to a halo is shown to be a function of a galaxy's accretion history. Galaxies with recent mergers, like M31, will host relatively few in situ stars, while galaxies with more quiescent recent histories, like the Milky Way, will likely have a larger relative contribution from an in situ population. We show that in situ halo stars are more [alpha/Fe]-rich than accreted stars at the high [Fe/H] end of a halo's metallicity distribution function. In lower mass galaxies, M ˜ 1010 M, in situ stars dominate the stellarmass of halos. In these galaxies, in situ halo stars are, on average, younger and more metal-rich than accreted halo stars. Because in situ stars are dominant, these trends result in halos that are more metal-rich than simple accretion models predict. The halos of low mass galaxies do not extend out to the virial radii of the primary, as they do in more massive galaxies. We find that the ratio of luminous-halo mass to total

  20. The halo current in ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Pautasso, G.; Giannone, L.; Gruber, O.; Herrmann, A.; Maraschek, M.; Schuhbeck, K. H.; ASDEX Upgrade Team

    2011-04-01

    Due to the complexity of the phenomena involved, a self-consistent physical model for the prediction of the halo current is not available. Therefore the ITER specifications of the spatial distribution and evolution of the halo current rely on empirical assumptions. This paper presents the results of an extensive analysis of the halo current measured in ASDEX Upgrade with particular emphasis on the evolution of the halo region, on the magnitude and time history of the halo current, and on the structure and duration of its toroidal and poloidal asymmetries. The effective length of the poloidal path of the halo current in the vessel is found to be rather insensitive to plasma parameters. Large values of the toroidally averaged halo current are observed in both vertical displacement events and centred disruptions but last a small fraction of the current quench; they coincide typically with a large but short-lived MHD event.

  1. The effect of halo nuclear density on reaction cross-section for light ion collision

    NASA Astrophysics Data System (ADS)

    Hassan, M. A. M.; Nour El-Din, M. S. M.; Ellithi, A.; Ismail, E.; Hosny, H.

    2015-08-01

    In the framework of the optical limit approximation (OLA), the reaction cross-section for halo nucleus — stable nucleus collision at intermediate energy, has been studied. The projectile nuclei are taken to be one-neutron halo (1NHP) and two-neutron halo (2NHP). The calculations are carried out for Gaussian-Gaussian (GG), Gaussian-Oscillator (GO), and Gaussian-2S (G2S) densities for each considered projectile. As a target, the stable nuclei in the range 4-28 of the mass number are used. An analytic expression of the phase shift function has been derived. The zero range approximation is considered in the calculations. Also, the in-medium effect is studied. The obtained results are analyzed and compared with the geometrical reaction cross-section and the available experimental data.

  2. A Multidisciplinary Research Framework on Green Schools: Infrastructure, Social Environment, Occupant Health, and Performance

    ERIC Educational Resources Information Center

    Magzamen, Sheryl; Mayer, Adam P.; Barr, Stephanie; Bohren, Lenora; Dunbar, Brian; Manning, Dale; Reynolds, Stephen J.; Schaeffer, Joshua W.; Suter, Jordan; Cross, Jennifer E.

    2017-01-01

    Background: Sustainable school buildings hold much promise to reducing operating costs, improve occupant well-being and, ultimately, teacher and student performance. However, there is a scarcity of evidence on the effects of sustainable school buildings on health and performance indicators. We sought to create a framework for a multidisciplinary…

  3. Simulating Halos with the Caterpillar Project

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    The Caterpillar Project is a beautiful series of high-resolution cosmological simulations. The goal of this project is to examine the evolution of dark-matter halos like the Milky Ways, to learn about how galaxies like ours formed. This immense computational project is still in progress, but the Caterpillar team is already providing a look at some of its first results.Lessons from Dark-Matter HalosWhy simulate the dark-matter halos of galaxies? Observationally, the formation history of our galaxy is encoded in galactic fossil record clues, like the tidal debris from disrupted satellite galaxies in the outer reaches of our galaxy, or chemical abundance patterns throughout our galactic disk and stellar halo.But to interpret this information in a way that lets us learn about our galaxys history, we need to first test galaxy formation and evolution scenarios via cosmological simulations. Then we can compare the end result of these simulations to what we observe today.This figure illustrates the difference that mass resolution makes. In the left panel, the mass resolution is 1.5*10^7 solar masses per particle. In the right panel, the mass resolution is 3*10^4 solar masses per particle [Griffen et al. 2016]A Computational ChallengeDue to how computationally expensive such simulations are, previous N-body simulations of the growth of Milky-Way-like halos have consisted of only one or a few halos each. But in order to establish a statistical understanding of how galaxy halos form and find out whether the Milky Ways halo is typical or unusual! it is necessary to simulate a larger number of halos.In addition, in order to accurately follow the formation and evolution of substructure within the dark-matter halos, these simulations must be able to resolve the smallest dwarf galaxies, which are around a million solar masses. This requires an extremely high mass resolution, which adds to the computational expense of the simulation.First OutcomesThese are the challenges faced by

  4. Dependence of Halo Bias and Kinematics on Assembly Variables

    NASA Astrophysics Data System (ADS)

    Xu, Xiaoju; Zheng, Zheng

    2018-06-01

    Using dark matter haloes identified in a large N-body simulation, we study halo assembly bias, with halo formation time, peak maximum circular velocity, concentration, and spin as the assembly variables. Instead of grouping haloes at fixed mass into different percentiles of each assembly variable, we present the joint dependence of halo bias on the values of halo mass and each assembly variable. In the plane of halo mass and one assembly variable, the joint dependence can be largely described as halo bias increasing outward from a global minimum. We find it unlikely to have a combination of halo variables to absorb all assembly bias effects. We then present the joint dependence of halo bias on two assembly variables at fixed halo mass. The gradient of halo bias does not necessarily follow the correlation direction of the two assembly variables and it varies with halo mass. Therefore in general for two correlated assembly variables one cannot be used as a proxy for the other in predicting halo assembly bias trend. Finally, halo assembly is found to affect the kinematics of haloes. Low-mass haloes formed earlier can have much higher pairwise velocity dispersion than those of massive haloes. In general, halo assembly leads to a correlation between halo bias and halo pairwise velocity distribution, with more strongly clustered haloes having higher pairwise velocity and velocity dispersion. However, the correlation is not tight, and the kinematics of haloes at fixed halo bias still depends on halo mass and assembly variables.

  5. Testing galaxy quenching theories with scatter in the stellar-to-halo mass relation

    NASA Astrophysics Data System (ADS)

    Tinker, Jeremy L.

    2017-05-01

    We use the scatter in the stellar-to-halo mass relation to constrain galaxy evolution models. If the efficiency of converting accreted baryons into stars varies with time, haloes of the same present-day mass but different formation histories will have different z = 0 galaxy stellar mass. This is one of the sources of scatter in stellar mass at fixed halo mass, σlog M*. For massive haloes that undergo rapid quenching of star formation at z ˜ 2, different mechanisms that trigger this quenching yield different values of σlog M*. We use this framework to test various models in which quenching begins after a galaxy crosses a threshold in one of the following physical quantities: redshift, halo mass, stellar mass and stellar-to-halo mass ratio. Our model is highly idealized, with other sources of scatter likely to arise as more physics is included. Thus, our test is whether a model can produce scatter lower than observational bounds, leaving room for other sources. Recent measurements find σlog M* = 0.16 dex for 1011 M⊙ galaxies. Under the assumption that the threshold is constant with time, such a low value of σlog M* rules out all of these models with the exception of quenching by a stellar mass threshold. Most physical quantities, such as metallicity, will increase scatter if they are uncorrelated with halo formation history. Thus, to decrease the scatter of a given model, galaxy properties would correlate tightly with formation history, creating testable predictions for their clustering. Understanding why σlog M* is so small may be key to understanding the physics of galaxy formation.

  6. SPHERES HALO

    NASA Image and Video Library

    2017-06-23

    iss052e006482 (6/23/2017) --- Astronaut Peggy Whitson is photographed during a test session of the Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) Halo investigation in the Kibo module. The SPHERES Halo investigation studies the possibility of launching several separate components and then attaching them once they are in space. The investigation upgrades the International Space Station’s fleet of SPHERES to enable each SPHERE to communicate with six external objects at the same time, testing new control and remote assembly methods.

  7. Predicting weak lensing statistics from halo mass reconstructions - Final Paper

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Everett, Spencer

    2015-08-20

    As dark matter does not absorb or emit light, its distribution in the universe must be inferred through indirect effects such as the gravitational lensing of distant galaxies. While most sources are only weakly lensed, the systematic alignment of background galaxies around a foreground lens can constrain the mass of the lens which is largely in the form of dark matter. In this paper, I have implemented a framework to reconstruct all of the mass along lines of sight using a best-case dark matter halo model in which the halo mass is known. This framework is then used to makemore » predictions of the weak lensing of 3,240 generated source galaxies through a 324 arcmin² field of the Millennium Simulation. The lensed source ellipticities are characterized by the ellipticity-ellipticity and galaxy-mass correlation functions and compared to the same statistic for the intrinsic and ray-traced ellipticities. In the ellipticity-ellipticity correlation function, I and that the framework systematically under predicts the shear power by an average factor of 2.2 and fails to capture correlation from dark matter structure at scales larger than 1 arcminute. The model predicted galaxy-mass correlation function is in agreement with the ray-traced statistic from scales 0.2 to 0.7 arcminutes, but systematically underpredicts shear power at scales larger than 0.7 arcminutes by an average factor of 1.2. Optimization of the framework code has reduced the mean CPU time per lensing prediction by 70% to 24 ± 5 ms. Physical and computational shortcomings of the framework are discussed, as well as potential improvements for upcoming work.« less

  8. The Anemic Stellar Halo of M101

    NASA Astrophysics Data System (ADS)

    Holwerda, Benne

    2014-10-01

    Models of galaxy formation in a cosmological context predict that massive disk galaxies should have richly-structured extended stellar halos, containing ~10% of a galaxy's stars, originating in large part from the tidal disruption of dwarf galaxies. Observations of a number of nearby disk galaxies have generally agreed with these expectations. Recent new observations in integrated light with a novel array of low scattered-light telephoto lenses have failed to convincingly detect a stellar halo in the nearby massive face-on disk galaxy M101 (van Dokkum et al. 2014). They argue that any halo has to have <0.3% of the mass of the galaxy. This halo would be the least massive of any massive disk galaxy in the local Universe (by factors of several) -- such a halo is not predicted or naturally interpreted by the models, and would present a critical challenge to the picture of ubiquitous stellar halos formed from the debris of disrupting dwarf galaxies.We propose to resolve the stellar populations of this uniquely anemic stellar halo for 6 orbits with HST (ACS and WFC3), allowing us to reach surface brightness limits sufficient to clearly detect and characterize M101's stellar halo if it carries more than 0.1% of M101's mass. With resolved stellar populations, we can use the gradient of stellar populations as a function of radius to separate stellar halo from disk, which is impossible using integrated light observations. The resolved stellar populations will reveal the halo mass to much greater accuracy, measure the halo radial profile, constrain any halo lopsidedness, estimate the halo's stellar metallicity, and permit an analysis of outer disk stellar populations.

  9. Testing the Self-Consistency of the Excursion Set Approach to Predicting the Dark Matter Halo Mass Function

    NASA Astrophysics Data System (ADS)

    Achitouv, I.; Rasera, Y.; Sheth, R. K.; Corasaniti, P. S.

    2013-12-01

    The excursion set approach provides a framework for predicting how the abundance of dark matter halos depends on the initial conditions. A key ingredient of this formalism is the specification of a critical overdensity threshold (barrier) which protohalos must exceed if they are to form virialized halos at a later time. However, to make its predictions, the excursion set approach explicitly averages over all positions in the initial field, rather than the special ones around which halos form, so it is not clear that the barrier has physical motivation or meaning. In this Letter we show that once the statistical assumptions which underlie the excursion set approach are considered a drifting diffusing barrier model does provide a good self-consistent description both of halo abundance as well as of the initial overdensities of the protohalo patches.

  10. Framework for continuous assessment and improvement of occupational health and safety issues in construction companies.

    PubMed

    Mahmoudi, Shahram; Ghasemi, Fakhradin; Mohammadfam, Iraj; Soleimani, Esmaeil

    2014-09-01

    Construction industry is among the most hazardous industries, and needs a comprehensive and simple-to-administer tool to continuously assess and promote its health and safety performance. Through the study of various standard systems (mainly Health, Safety, and Environment Management System; Occupational Health and Safety Assessment Series 180001; and British Standard, occupational health and safety management systems-Guide 8800), seven main elements were determined for the desired framework, and then, by reviewing literature, factors affecting these main elements were determined. The relative importance of each element and its related factors was calculated at organizational and project levels. The provided framework was then implemented in three construction companies, and results were compared together. THE RESULTS OF THE STUDY SHOW THAT THE RELATIVE IMPORTANCE OF THE MAIN ELEMENTS AND THEIR RELATED FACTORS DIFFER BETWEEN ORGANIZATIONAL AND PROJECT LEVELS: leadership and commitment are the most important elements at the organization level, whereas risk assessment and management are most important at the project level. The present study demonstrated that the framework is easy to administer, and by interpreting the results, the main factors leading to the present condition of companies can be determined.

  11. Comparative analysis of proton- and neutron-halo breakups

    NASA Astrophysics Data System (ADS)

    Mukeru, B.

    2018-06-01

    A detailed analysis of the proton- and neutron-halo breakup cross sections is presented. Larger neutron-halo breakup cross sections than proton-halo breakup cross sections are obtained. This is found to be mainly due to the projectile structure, namely the ground state wave function and the dipole electric response function. It is also found that the continuum–continuum couplings are stronger in the proton-halo breakup than in the neutron-halo breakup. The increase of proton- and neutron-halo ground state separation energy slightly strengthens these couplings in the proton- and neutron-halo total and nuclear breakups, while they are weakened in the proton- and neutron-halo Coulomb breakups. The Coulomb-nuclear interference remains strongly destructive in both proton- and neutron-halo breakups and this is independent of the ground state separation energy. The results also show that the increase of the neutron-halo ground state separation energy decreases significantly the agreement between the proton- and neutron-halo breakup cross sections, both qualitatively and quantitatively. It is obtained that when the proton-halo ground state separation energy is increased by a factor of 4.380, the proton-halo breakup cross section is reduced by a factor of 4.392, indicating a clear proportionality. However, when the neutron-halo ground state separation energy is increased by the same factor, the neutron-halo total breakup cross section is reduced by a factor of 8.522.

  12. Observing halos through airplane windows

    NASA Astrophysics Data System (ADS)

    Shaw, Joseph A.

    2017-09-01

    A halo is one of the most frequent and impressive optical phenomena easily observable in the sky. It is also one of the natural optical phenomena most often visible through an airplane window. Halos and related phenomena vary from a single spot of light formed by reflection of the sun from the tops of plate-shaped ice crystals to large rings with splashes of colors, caused by a combination of reflection and refraction in ice crystals. Even with extreme heat at the ground, an airplane quickly rises through sufficient altitude to find ice crystals in the clouds, enabling an alert passenger (or pilot) to see ice-crystal optical phenomena. This paper briefly reviews these phenomena with photographs and diagrams. Photographs include commonly seen halos, as well as Bottlinger's rings, a rare halo that is still not fully explained. Tips are given for enhancing your chances of seeing and understanding halos.

  13. Halo-free Phase Contrast Microscopy

    NASA Astrophysics Data System (ADS)

    Nguyen, Tan H.; Kandel, Mikhail; Shakir, Haadi M.; Best-Popescu, Catherine; Arikkath, Jyothi; Do, Minh N.; Popescu, Gabriel

    2017-03-01

    We present a new approach for retrieving halo-free phase contrast microscopy (hfPC) images by upgrading the conventional PC microscope with an external interferometric module, which generates sufficient data for reversing the halo artifact. Acquiring four independent intensity images, our approach first measures haloed phase maps of the sample. We solve for the halo-free sample transmission function by using a physical model of the image formation under partial spatial coherence. Using this halo-free sample transmission, we can numerically generate artifact-free PC images. Furthermore, this transmission can be further used to obtain quantitative information about the sample, e.g., the thickness with known refractive indices, dry mass of live cells during their cycles. We tested our hfPC method on various control samples, e.g., beads, pillars and validated its potential for biological investigation by imaging live HeLa cells, red blood cells, and neurons.

  14. Halo modelling in chameleon theories

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lombriser, Lucas; Koyama, Kazuya; Li, Baojiu, E-mail: lucas.lombriser@port.ac.uk, E-mail: kazuya.koyama@port.ac.uk, E-mail: baojiu.li@durham.ac.uk

    2014-03-01

    We analyse modelling techniques for the large-scale structure formed in scalar-tensor theories of constant Brans-Dicke parameter which match the concordance model background expansion history and produce a chameleon suppression of the gravitational modification in high-density regions. Thereby, we use a mass and environment dependent chameleon spherical collapse model, the Sheth-Tormen halo mass function and linear halo bias, the Navarro-Frenk-White halo density profile, and the halo model. Furthermore, using the spherical collapse model, we extrapolate a chameleon mass-concentration scaling relation from a ΛCDM prescription calibrated to N-body simulations. We also provide constraints on the model parameters to ensure viability on localmore » scales. We test our description of the halo mass function and nonlinear matter power spectrum against the respective observables extracted from large-volume and high-resolution N-body simulations in the limiting case of f(R) gravity, corresponding to a vanishing Brans-Dicke parameter. We find good agreement between the two; the halo model provides a good qualitative description of the shape of the relative enhancement of the f(R) matter power spectrum with respect to ΛCDM caused by the extra attractive gravitational force but fails to recover the correct amplitude. Introducing an effective linear power spectrum in the computation of the two-halo term to account for an underestimation of the chameleon suppression at intermediate scales in our approach, we accurately reproduce the measurements from the N-body simulations.« less

  15. Assessing colour-dependent occupation statistics inferred from galaxy group catalogues

    NASA Astrophysics Data System (ADS)

    Campbell, Duncan; van den Bosch, Frank C.; Hearin, Andrew; Padmanabhan, Nikhil; Berlind, Andreas; Mo, H. J.; Tinker, Jeremy; Yang, Xiaohu

    2015-09-01

    We investigate the ability of current implementations of galaxy group finders to recover colour-dependent halo occupation statistics. To test the fidelity of group catalogue inferred statistics, we run three different group finders used in the literature over a mock that includes galaxy colours in a realistic manner. Overall, the resulting mock group catalogues are remarkably similar, and most colour-dependent statistics are recovered with reasonable accuracy. However, it is also clear that certain systematic errors arise as a consequence of correlated errors in group membership determination, central/satellite designation, and halo mass assignment. We introduce a new statistic, the halo transition probability (HTP), which captures the combined impact of all these errors. As a rule of thumb, errors tend to equalize the properties of distinct galaxy populations (i.e. red versus blue galaxies or centrals versus satellites), and to result in inferred occupation statistics that are more accurate for red galaxies than for blue galaxies. A statistic that is particularly poorly recovered from the group catalogues is the red fraction of central galaxies as a function of halo mass. Group finders do a good job in recovering galactic conformity, but also have a tendency to introduce weak conformity when none is present. We conclude that proper inference of colour-dependent statistics from group catalogues is best achieved using forward modelling (i.e. running group finders over mock data) or by implementing a correction scheme based on the HTP, as long as the latter is not too strongly model dependent.

  16. The Average Star Formation Histories of Galaxies in Dark Matter Halos from z = 0-8

    NASA Astrophysics Data System (ADS)

    Behroozi, Peter S.; Wechsler, Risa H.; Conroy, Charlie

    2013-06-01

    We present a robust method to constrain average galaxy star formation rates (SFRs), star formation histories (SFHs), and the intracluster light (ICL) as a function of halo mass. Our results are consistent with observed galaxy stellar mass functions, specific star formation rates (SSFRs), and cosmic star formation rates (CSFRs) from z = 0 to z = 8. We consider the effects of a wide range of uncertainties on our results, including those affecting stellar masses, SFRs, and the halo mass function at the heart of our analysis. As they are relevant to our method, we also present new calibrations of the dark matter halo mass function, halo mass accretion histories, and halo-subhalo merger rates out to z = 8. We also provide new compilations of CSFRs and SSFRs; more recent measurements are now consistent with the buildup of the cosmic stellar mass density at all redshifts. Implications of our work include: halos near 1012 M ⊙ are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z ~ 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z ~ 1-1.5, and dwarf galaxies at low redshifts have higher stellar mass to halo mass ratios than previous expectations and form later than in most theoretical models. Finally, we provide new fitting formulae for SFHs that are more accurate than the standard declining tau model. Our approach places a wide variety of observations relating to the SFH of galaxies into a self-consistent framework based on the modern understanding of structure formation in ΛCDM. Constraints on the stellar mass-halo mass relationship and SFRs are available for download online.

  17. Mapping stellar content to dark matter haloes - III. Environmental dependence and conformity of galaxy colours

    NASA Astrophysics Data System (ADS)

    Zu, Ying; Mandelbaum, Rachel

    2018-05-01

    Recent studies suggest that the quenching properties of galaxies are correlated over several megaparsecs. The large-scale `galactic conformity' phenomenon around central galaxies has been regarded as a potential signature of `galaxy assembly bias' or `pre-heating', both of which interpret conformity as a result of direct environmental effects acting on galaxy formation. Building on the iHOD halo quenching framework developed in Zu and Mandelbaum, we discover that our fiducial halo mass quenching model, without any galaxy assembly bias, can successfully explain the overall environmental dependence and the conformity of galaxy colours in Sloan Digital Sky Survey, as measured by the mark correlation functions of galaxy colours and the red galaxy fractions around isolated primaries, respectively. Our fiducial iHOD halo quenching mock also correctly predicts the differences in the spatial clustering and galaxy-galaxy lensing signals between the more versus less red galaxy subsamples, split by the red-sequence ridge line at fixed stellar mass. Meanwhile, models that tie galaxy colours fully or partially to halo assembly bias have difficulties in matching all these observables simultaneously. Therefore, we demonstrate that the observed environmental dependence of galaxy colours can be naturally explained by the combination of (1) halo quenching and (2) the variation of halo mass function with environment - an indirect environmental effect mediated by two separate physical processes.

  18. A general framework to test gravity using galaxy clusters - I. Modelling the dynamical mass of haloes in f(R) gravity

    NASA Astrophysics Data System (ADS)

    Mitchell, Myles A.; He, Jian-hua; Arnold, Christian; Li, Baojiu

    2018-06-01

    We propose a new framework for testing gravity using cluster observations, which aims to provide an unbiased constraint on modified gravity models from Sunyaev-Zel'dovich (SZ) and X-ray cluster counts and the cluster gas fraction, among other possible observables. Focusing on a popular f(R) model of gravity, we propose a novel procedure to recalibrate mass scaling relations from Λ cold dark matter (ΛCDM) to f(R) gravity for SZ and X-ray cluster observables. We find that the complicated modified gravity effects can be simply modelled as a dependence on a combination of the background scalar field and redshift, fR(z)/(1 + z), regardless of the f(R) model parameter. By employing a large suite of N-body simulations, we demonstrate that a theoretically derived tanh fitting formula is in excellent agreement with the dynamical mass enhancement of dark matter haloes for a large range of background field parameters and redshifts. Our framework is sufficiently flexible to allow for tests of other models and inclusion of further observables, and the one-parameter description of the dynamical mass enhancement can have important implications on the theoretical modelling of observables and on practical tests of gravity.

  19. Historical halo displays as past weather indicator

    NASA Astrophysics Data System (ADS)

    Neuhäuser, Dagmar; Neuhäuser, Ralph

    2017-04-01

    Certain halo displays like the 22° circle were known to indicate specific weather pattern since millennia - as specified in Babylonian omina, Aristotle's Meteorology, farmers' weather lore, etc. Today, it is known that halo phenomena are due to refraction and reflection of sun and moon light in ice crystals in cirrus and cirrostratus, so that halo observations do indicate atmospheric conditions like temperature, humidity, pressure etc. in a few km height. The Astronomical Diaries of Babylonia have recorded both halo phenomena (circles, parhelia, etc.) and weather conditions (rain, clouds, etc.), so that we can use them to show statistically, whether, which and how fast halo phenomena are related to weather - for the last few centuries BC for Babylonia. We can then also compare the observations of Babylonian priests in the given BC epoch (without air and light pollution) with the last few decades of the modern epoch (with air and light pollution), where amateur halo observers have systematically recorded such phenomena (in Europe). Weather and climate are known to be partly driven by solar activity. Hence, one could also consider whether there is an indirect relation between halo displays as weather proxy and aurorae as solar activity proxy - if low solar activity leads to low pressure systems, one could expect more halos, preliminary studies show such a hint. For the last few decades, we have many halo observations, satellite imaging of the aurora oval, and many data on solar activity. A statistically sufficient amount of aurora and halo observations should be available for the historic time to investigate such a possible connection: halos were recorded very often in antiquity and the medieval times (as found in chronicles etc.), and modern scholarly catalogs of aurorae also often contain unrecognized halo displays.

  20. Probing the shape and internal structure of dark matter haloes with the halo-shear-shear three-point correlation function

    NASA Astrophysics Data System (ADS)

    Shirasaki, Masato; Yoshida, Naoki

    2018-04-01

    Weak lensing three-point statistics are powerful probes of the structure of dark matter haloes. We propose to use the correlation of the positions of galaxies with the shapes of background galaxy pairs, known as the halo-shear-shear correlation (HSSC), to measure the mean halo ellipticity and the abundance of subhaloes in a statistical manner. We run high-resolution cosmological N-body simulations and use the outputs to measure the HSSC for galaxy haloes and cluster haloes. Non-spherical haloes cause a characteristic azimuthal variation of the HSSC, and massive subhaloes in the outer region near the virial radius contribute to ˜ 10 per cent of the HSSC amplitude. Using the HSSC and its covariance estimated from our N-body simulations, we make forecast for constraining the internal structure of dark matter haloes with future galaxy surveys. With 1000 galaxy groups with mass greater than 1013.5 h-1M⊙, the average halo ellipticity can be measured with an accuracy of 10 percent. A spherical, smooth mass distribution can be ruled out at a ˜5σ significance level. The existence of subhaloes whose masses are in 1-10 percent of the main halo mass can be detected with ˜104 galaxies/clusters. We conclude that the HSSC provides valuable information on the structure of dark haloes and hence on the nature of dark matter.

  1. How do stars affect ψDM halos?

    NASA Astrophysics Data System (ADS)

    Chan, James H. H.; Schive, Hsi-Yu; Woo, Tak-Pong; Chiueh, Tzihong

    2018-04-01

    Wave dark matter (ψDM) predicts a compact soliton core and a granular halo in every galaxy. This work presents the first simulation study of an elliptical galaxy by including both stars and ψDM, focusing on the systematic changes of the central soliton and halo granules. With the addition of stars in the inner halo, we find the soliton core consistently becomes more prominent by absorbing mass from the host halo than that without stars, and the halo granules become "non-isothermal", "hotter" in the inner halo and "cooler" in the outer halo, as opposed to the isothermal halo in pure ψDM cosmological simulations. Moreover, the composite (star+ψDM) mass density is found to follow a r-2 isothermal profile near the half-light radius in most cases. Most striking is the velocity dispersion of halo stars that increases rapidly toward the galactic center by a factor of at least 2 inside the half-light radius caused by the deepened soliton gravitational potential, a result that compares favorably with observations of elliptical galaxies and bulges in spiral galaxies. However in some rare situations we find a phase segregation turning a compact distribution of stars into two distinct populations with high and very low velocity dispersions; while the high-velocity component mostly resides in the halo, the very low-velocity component is bound to the interior of the soliton core, resembling stars in faint dwarf spheroidal galaxies.

  2. Probing the galaxy-halo connection in UltraVISTA to z ˜ 2

    NASA Astrophysics Data System (ADS)

    McCracken, H. J.; Wolk, M.; Colombi, S.; Kilbinger, M.; Ilbert, O.; Peirani, S.; Coupon, J.; Dunlop, J.; Milvang-Jensen, B.; Caputi, K.; Aussel, H.; Béthermin, M.; Le Fèvre, O.

    2015-05-01

    We use percent-level precision photometric redshifts in the UltraVISTA-DR1 near-infrared survey to investigate the changing relationship between galaxy stellar mass and the dark matter haloes hosting them to z ˜ 2. We achieve this by measuring the clustering properties and abundances of a series of volume-limited galaxy samples selected by stellar mass and star formation activity. We interpret these results in the framework of a phenomenological halo model and numerical simulations. Our measurements span a uniquely large range in stellar mass and redshift and reach below the characteristic stellar mass to z ˜ 2. Our results are: (1) at fixed redshift and scale, clustering amplitude depends monotonically on sample stellar mass threshold; (2) at fixed angular scale, the projected clustering amplitude decreases with redshift but the comoving correlation length remains constant; (3) characteristic halo masses and galaxy bias increase with increasing median stellar mass of the sample; (4) the slope of these relationships is modified in lower mass haloes; (5) concerning the passive galaxy population, characteristic halo masses are consistent with a simply less-abundant version of the full galaxy sample, but at lower redshifts the fraction of satellite galaxies in the passive population is very different from the full galaxy sample; (6) finally, we find that the ratio between the characteristic halo mass and median stellar mass at each redshift bin reaches a peak at log (Mh/M⊙) ˜ 12.2 and the position of this peak remains constant out to z ˜ 2. The behaviour of the full and passively evolving galaxy samples can be understood qualitatively by considering the slow evolution of the characteristic stellar mass in the redshift range probed by our survey.

  3. Charge radius of the 13N* proton halo nucleus with Halo Effective Field Theory

    NASA Astrophysics Data System (ADS)

    Mosavi Khansari, M.; Khalili, H.; Sadeghi, H.

    2018-02-01

    We evaluated the charge radius of the first excited state of 13N with halo Effective Field Theory (hEFT) at the low energies. The halo effective field theory without pion is used to examine the halo nucleus bound state with a large S-wave scattering length. We built Lagrangian from the effective core and the valence proton of the fields and obtained the charge form factor at Leading-Order (LO). The charge radius at leading order for the first excited state of the proton halo nucleus, 13N, has been estimated as rc = 2.52 fm. This result is without any finite-size contributions included from the core and the proton. If we consider the contributions of the charge radius of the proton and the core, the result will be [rC]13N* = 5.85 fm.

  4. ULTRAVIOLET HALOS AROUND SPIRAL GALAXIES. I. MORPHOLOGY

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hodges-Kluck, Edmund; Cafmeyer, Julian; Bregman, Joel N., E-mail: hodgeskl@umich.edu

    2016-12-10

    We examine ultraviolet halos around a sample of highly inclined galaxies within 25 Mpc to measure their morphology and luminosity. Despite contamination from galactic light scattered into the wings of the point-spread function, we find that ultraviolet (UV) halos occur around each galaxy in our sample. Around most galaxies the halos form a thick, diffuse disk-like structure, but starburst galaxies with galactic superwinds have qualitatively different halos that are more extensive and have filamentary structure. The spatial coincidence of the UV halos above star-forming regions, the lack of consistent association with outflows or extraplanar ionized gas, and the strong correlationmore » between the halo and galaxy UV luminosity suggest that the UV light is an extragalactic reflection nebula. UV halos may thus represent 10{sup 6}–10{sup 7} M {sub ⊙} of dust within 2–10 kpc of the disk, whose properties may change with height in starburst galaxies.« less

  5. THE DUAL ORIGIN OF STELLAR HALOS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zolotov, Adi; Hogg, David W.; Willman, Beth

    2009-09-10

    We investigate the formation of the stellar halos of four simulated disk galaxies using high-resolution, cosmological SPH + N-body simulations. These simulations include a self-consistent treatment of all the major physical processes involved in galaxy formation. The simulated galaxies presented here each have a total mass of {approx}10{sup 12} M{sub sun}, but span a range of merger histories. These simulations allow us to study the competing importance of in situ star formation (stars formed in the primary galaxy) and accretion of stars from subhalos in the building of stellar halos in a {lambda}CDM universe. All four simulated galaxies are surroundedmore » by a stellar halo, whose inner regions (r < 20 kpc) contain both accreted stars, and an in situ stellar population. The outer regions of the galaxies' halos were assembled through pure accretion and disruption of satellites. Most of the in situ halo stars formed at high redshift out of smoothly accreted cold gas in the inner 1 kpc of the galaxies' potential wells, possibly as part of their primordial disks. These stars were displaced from their central locations into the halos through a succession of major mergers. We find that the two galaxies with recently quiescent merger histories have a higher fraction of in situ stars ({approx}20%-50%) in their inner halos than the two galaxies with many recent mergers ({approx}5%-10% in situ fraction). Observational studies concentrating on stellar populations in the inner halo of the Milky Way will be the most affected by the presence of in situ stars with halo kinematics, as we find that their existence in the inner few tens of kpc is a generic feature of galaxy formation.« less

  6. A Multidisciplinary Research Framework on Green Schools: Infrastructure, Social Environment, Occupant Health, and Performance.

    PubMed

    Magzamen, Sheryl; Mayer, Adam P; Barr, Stephanie; Bohren, Lenora; Dunbar, Brian; Manning, Dale; Reynolds, Stephen J; Schaeffer, Joshua W; Suter, Jordan; Cross, Jennifer E

    2017-05-01

    Sustainable school buildings hold much promise to reducing operating costs, improve occupant well-being and, ultimately, teacher and student performance. However, there is a scarcity of evidence on the effects of sustainable school buildings on health and performance indicators. We sought to create a framework for a multidisciplinary research agenda that links school facilities, health, and educational outcomes. We conducted a nonsystematic review of peer review publications, government documents, organizational documents, and school climate measurement instruments. We found that studies on the impact of physical environmental factors (air, lighting, and thermal comfort) on health and occupant performance are largely independent of research on the social climate. The current literature precludes the formation of understanding the causal relation among school facilities, social climate, occupant health, and occupant performance. Given the average age of current school facilities in the United States, construction of new school facilities or retrofits of older facilities will be a major infrastructure investment for many municipalities over the next several decades. Multidisciplinary research that seeks to understand the impact of sustainable design on the health and performance of occupants will need to include both an environmental science and social science perspective to inform best practices and quantification of benefits that go beyond general measures of costs savings from energy efficiencies. © 2017, American School Health Association.

  7. An order statistics approach to the halo model for galaxies

    NASA Astrophysics Data System (ADS)

    Paul, Niladri; Paranjape, Aseem; Sheth, Ravi K.

    2017-04-01

    We use the halo model to explore the implications of assuming that galaxy luminosities in groups are randomly drawn from an underlying luminosity function. We show that even the simplest of such order statistics models - one in which this luminosity function p(L) is universal - naturally produces a number of features associated with previous analyses based on the 'central plus Poisson satellites' hypothesis. These include the monotonic relation of mean central luminosity with halo mass, the lognormal distribution around this mean and the tight relation between the central and satellite mass scales. In stark contrast to observations of galaxy clustering; however, this model predicts no luminosity dependence of large-scale clustering. We then show that an extended version of this model, based on the order statistics of a halo mass dependent luminosity function p(L|m), is in much better agreement with the clustering data as well as satellite luminosities, but systematically underpredicts central luminosities. This brings into focus the idea that central galaxies constitute a distinct population that is affected by different physical processes than are the satellites. We model this physical difference as a statistical brightening of the central luminosities, over and above the order statistics prediction. The magnitude gap between the brightest and second brightest group galaxy is predicted as a by-product, and is also in good agreement with observations. We propose that this order statistics framework provides a useful language in which to compare the halo model for galaxies with more physically motivated galaxy formation models.

  8. Characteristic time for halo current growth and rotation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Boozer, Allen H., E-mail: ahb17@columbia.edu

    2015-10-15

    A halo current flows for part of its path through the plasma edge and for part through the chamber walls and during tokamak disruptions can be as large as tenths of the plasma current. The primary interest in halo currents is the large force that they can exert on machine components particularly if the toriodal rotation of the halo current resonates with a natural oscillation frequency of the tokamak device. Halo currents arise when required to slow down the growth of a kink that is too unstable to be stabilized by the chamber walls. The width of the current channelmore » in the halo plasma is comparable to the amplitude of the kink, and the halo current grows linearly, not exponentially, in time. The current density in the halo is comparable to that of the main plasma body. The rocket force due to plasma flowing out of the halo and recombining on the chamber walls can cause the non-axisymmetric magnetic structure produced by the kink to rotate toroidally at a speed comparable to the halo speed of sound. Gerhardt's observations of the halo current in NSTX shot 141 687 [Nucl. Fusion 53, 023005 (2013)] illustrate many features of the theory of halo currents and are discussed as a summary of the theory.« less

  9. Reconstruction of halo power spectrum from redshift-space galaxy distribution: cylinder-grouping method and halo exclusion effect

    NASA Astrophysics Data System (ADS)

    Okumura, Teppei; Takada, Masahiro; More, Surhud; Masaki, Shogo

    2017-07-01

    The peculiar velocity field measured by redshift-space distortions (RSD) in galaxy surveys provides a unique probe of the growth of large-scale structure. However, systematic effects arise when including satellite galaxies in the clustering analysis. Since satellite galaxies tend to reside in massive haloes with a greater halo bias, the inclusion boosts the clustering power. In addition, virial motions of the satellite galaxies cause a significant suppression of the clustering power due to non-linear RSD effects. We develop a novel method to recover the redshift-space power spectrum of haloes from the observed galaxy distribution by minimizing the contamination of satellite galaxies. The cylinder-grouping method (CGM) we study effectively excludes satellite galaxies from a galaxy sample. However, we find that this technique produces apparent anisotropies in the reconstructed halo distribution over all the scales which mimic RSD. On small scales, the apparent anisotropic clustering is caused by exclusion of haloes within the anisotropic cylinder used by the CGM. On large scales, the misidentification of different haloes in the large-scale structures, aligned along the line of sight, into the same CGM group causes the apparent anisotropic clustering via their cross-correlation with the CGM haloes. We construct an empirical model for the CGM halo power spectrum, which includes correction terms derived using the CGM window function at small scales as well as the linear matter power spectrum multiplied by a simple anisotropic function at large scales. We apply this model to a mock galaxy catalogue at z = 0.5, designed to resemble Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey (BOSS) CMASS galaxies, and find that our model can predict both the monopole and quadrupole power spectra of the host haloes up to k < 0.5 {{h Mpc^{-1}}} to within 5 per cent.

  10. WEIGHING THE GALACTIC DARK MATTER HALO: A LOWER MASS LIMIT FROM THE FASTEST HALO STAR KNOWN

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Przybilla, Norbert; Tillich, Alfred; Heber, Ulrich

    2010-07-20

    The mass of the Galactic dark matter halo is under vivid discussion. A recent study by Xue et al. revised the Galactic halo mass downward by a factor of {approx}2 relative to previous work, based on the line-of-sight velocity distribution of {approx}2400 blue horizontal-branch (BHB) halo stars. The observations were interpreted with a statistical approach using cosmological galaxy formation simulations, as only four of the six-dimensional phase-space coordinates were determined. Here we concentrate on a close investigation of the stars with the highest negative radial velocity from that sample. For one star, SDSSJ153935.67+023909.8 (J1539+0239 for short), we succeed in measuringmore » a significant proper motion, i.e., full phase-space information is obtained. We confirm the star to be a Population II BHB star from an independent quantitative analysis of the Sloan Digital Sky Survey (SDSS) spectrum-providing the first non-LTE (NLTE) study of any halo BHB star-and reconstruct its three-dimensional trajectory in the Galactic potential. J1539+0239 turns out to be the fastest halo star known to date, with a Galactic rest-frame velocity of 694{sup +300}{sub -221} km s{sup -1} (full uncertainty range from Monte Carlo error propagation) at its current position. The extreme kinematics of the star allows a significant lower limit to be put on the halo mass in order to keep it bound, of M {sub halo} {>=} 1.7{sup +2.3}{sub -1.1} x 10{sup 12} M{sub sun}. We conclude that the Xue et al. results tend to underestimate the true halo mass as their most likely mass value is consistent with our analysis only at a level of 4%. However, our result confirms other studies that make use of the full phase-space information.« less

  11. Is the Milky Way's hot halo convectively unstable?

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Henley, David B.; Shelton, Robin L., E-mail: dbh@physast.uga.edu

    2014-03-20

    We investigate the convective stability of two popular types of model of the gas distribution in the hot Galactic halo. We first consider models in which the halo density and temperature decrease exponentially with height above the disk. These halo models were created to account for the fact that, on some sight lines, the halo's X-ray emission lines and absorption lines yield different temperatures, implying that the halo is non-isothermal. We show that the hot gas in these exponential models is convectively unstable if γ < 3/2, where γ is the ratio of the temperature and density scale heights. Usingmore » published measurements of γ and its uncertainty, we use Bayes' theorem to infer posterior probability distributions for γ, and hence the probability that the halo is convectively unstable for different sight lines. We find that, if these exponential models are good descriptions of the hot halo gas, at least in the first few kiloparsecs from the plane, the hot halo is reasonably likely to be convectively unstable on two of the three sight lines for which scale height information is available. We also consider more extended models of the halo. While isothermal halo models are convectively stable if the density decreases with distance from the Galaxy, a model of an extended adiabatic halo in hydrostatic equilibrium with the Galaxy's dark matter is on the boundary between stability and instability. However, we find that radiative cooling may perturb this model in the direction of convective instability. If the Galactic halo is indeed convectively unstable, this would argue in favor of supernova activity in the Galactic disk contributing to the heating of the hot halo gas.« less

  12. Stabilizing properties of the halo apparatus.

    PubMed

    Mirza, S K; Moquin, R R; Anderson, P A; Tencer, A F; Steinmann, J; Varnau, D

    1997-04-01

    A cadaveric cervical spine specimen fixed between a fiberglass torso and a plastic skull was used as a model to determine the effect of halo structural parameters on motion at a lesion simulated at C5-C6. In a second part, nine commercially available halo devices were compared. To define the contributions of the various components of the halo apparatus to reducing motion in an injured cervical spine and to compare the stability offered by a sample of commercially available halo devices. Controversy exists concerning the ability of the halo apparatus to stabilize the injured cervical spine. The halo apparatus has been shown to be the most effective nonsurgical method for stabilizing the fractured spine. Nonetheless, several clinical studies have demonstrated that unacceptably large motions can occur at the injured spinal segment stabilized with a halo apparatus. Each cadaveric cervical spine was mounted onto a fiberglass torso and a rigid plastic skull was attached to the base of the occiput. A posterior ligamentous lesion was created between C5 and C6. The halo ring was fitted to the skull and a vest to the torso. Loads were applied to the skull in flexion, extension, and lateral bending, and relative angulation between C5 and C6 was measured with electroinclinometers. In the first part, the effect of parameters such as vest tightness, vest-thorax friction, vest deformation, and connecting bar rigidity on spinal angulation were measured using one vest. In the second part, the stability offered by each of nine commercially available halo devices was compared. Increasing chest strap tightness and decreasing vest deformation reduced angulation at the spinal lesion. Once connecting bar joints were tightened to 25% of their recommended torque, increased tightening or adding additional bars had no effect on rigidity. Although specific vests permitted significantly greater motion in specific directions, no vest allowed greater angulation consistently in all loading planes

  13. Concentrations of Simulated Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Child, Hillary

    2017-01-01

    We present the concentration-mass (c-M) relation of dark matter halos in two new high-volume high-resolution cosmological N-body simulations, Q Continuum and Outer Rim. Concentration describes the density of the central regions of halos; it is highest for low-mass halos at low redshift, decreasing at high mass and redshift. The shape of the c-M relation is an important probe of cosmology. We discuss the redshift dependence of the c-M relation, several different methods to determine concentrations of simulated halos, and potential sources of bias in concentration measurements. To connect to lensing observations, we stack halos, which also allows us to assess the suitability of the Navarro-Frenk-White profile and other profiles, such as Einasto, with an additional shape parameter. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144082.

  14. Unbound particles in dark matter halos

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Behroozi, Peter S.; Wechsler, Risa H.; Loeb, Abraham, E-mail: behroozi@stanford.edu, E-mail: aloeb@cfa.harvard.edu, E-mail: rwechsler@stanford.edu

    2013-06-01

    We investigate unbound dark matter particles in halos by tracing particle trajectories in a simulation run to the far future (a = 100). We find that the traditional sum of kinetic and potential energies is a very poor predictor of which dark matter particles will eventually become unbound from halos. We also study the mass fraction of unbound particles, which increases strongly towards the edges of halos, and decreases significantly at higher redshifts. We discuss implications for dark matter detection experiments, precision calibrations of the halo mass function, the use of baryon fractions to constrain dark energy, and searches formore » intergalactic supernovae.« less

  15. Unbound particles in dark matter halos

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Behroozi, Peter S.; Loeb, Abraham; Wechsler, Risa H.

    2013-06-13

    We investigate unbound dark matter particles in halos by tracing particle trajectories in a simulation run to the far future (a = 100). We find that the traditional sum of kinetic and potential energies is a very poor predictor of which dark matter particles will eventually become unbound from halos. We also study the mass fraction of unbound particles, which increases strongly towards the edges of halos, and decreases significantly at higher redshifts. We discuss implications for dark matter detection experiments, precision calibrations of the halo mass function, the use of baryon fractions to constrain dark energy, and searches formore » intergalactic supernovae.« less

  16. Effective field theory description of halo nuclei

    NASA Astrophysics Data System (ADS)

    Hammer, H.-W.; Ji, C.; Phillips, D. R.

    2017-10-01

    Nuclear halos emerge as new degrees of freedom near the neutron and proton driplines. They consist of a core and one or a few nucleons which spend most of their time in the classically-forbidden region outside the range of the interaction. Individual nucleons inside the core are thus unresolved in the halo configuration, and the low-energy effective interactions are short-range forces between the core and the valence nucleons. Similar phenomena occur in clusters of 4He atoms, cold atomic gases near a Feshbach resonance, and some exotic hadrons. In these weakly-bound quantum systems universal scaling laws for s-wave binding emerge that are independent of the details of the interaction. Effective field theory (EFT) exposes these correlations and permits the calculation of non-universal corrections to them due to short-distance effects, as well as the extension of these ideas to systems involving the Coulomb interaction and/or binding in higher angular-momentum channels. Halo nuclei exhibit all these features. Halo EFT, the EFT for halo nuclei, has been used to compute the properties of single-neutron, two-neutron, and single-proton halos of s-wave and p-wave type. This review summarizes these results for halo binding energies, radii, Coulomb dissociation, and radiative capture, as well as the connection of these properties to scattering parameters, thereby elucidating the universal correlations between all these observables. We also discuss how Halo EFT's encoding of the long-distance physics of halo nuclei can be used to check and extend ab initio calculations that include detailed modeling of their short-distance dynamics.

  17. The HALO / HALO-2 Supernova Neutrino Detectors

    NASA Astrophysics Data System (ADS)

    Yen, Stanley; HALO Collaboration; HALO-2 Collaboration

    2016-09-01

    The Helium and Lead Observatory (HALO) is a dedicated supernova neutrino detector in SNOLAB, which is built from 79 tons of surplus lead and the helium-3 neutron detectors from the SNO experiment. It is sensitive primarily to electron neutrinos, and is thus complementary to water Cerenkov and organic scintillation detectors which are primarily sensitive to electron anti-neutrinos. A comparison of the rates in these complementary detectors will enable a flavor decomposition of the neutrino flux from the next galactic core-collapse supernova. We have tentative ideas to build a 1000-ton HALO-2 detector in the Gran Sasso laboratory by using the lead from the decommissioned OPERA detector. We are exploring several neutron detector technologies to supplement the existing helium-3 detectors. We welcome new collaborators to join us. This research is supported by the NRC and NSERC (Canada), the US DOE and NSF, and the German RISE program.

  18. Smooth halos in the cosmic web

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gaite, José, E-mail: jose.gaite@upm.es

    Dark matter halos can be defined as smooth distributions of dark matter placed in a non-smooth cosmic web structure. This definition of halos demands a precise definition of smoothness and a characterization of the manner in which the transition from smooth halos to the cosmic web takes place. We introduce entropic measures of smoothness, related to measures of inequality previously used in economy and with the advantage of being connected with standard methods of multifractal analysis already used for characterizing the cosmic web structure in cold dark matter N-body simulations. These entropic measures provide us with a quantitative description ofmore » the transition from the small scales portrayed as a distribution of halos to the larger scales portrayed as a cosmic web and, therefore, allow us to assign definite sizes to halos. However, these ''smoothness sizes'' have no direct relation to the virial radii. Finally, we discuss the influence of N-body discreteness parameters on smoothness.« less

  19. Towards inclusive occupational therapy: Introducing the CORE approach for inclusive and occupation-focused practice.

    PubMed

    Pereira, Robert B

    2017-12-01

    Occupation is a human right and a social determinant of health. It is also taken for granted. Having access to, and participating in, occupation, is intricately linked to positive health and wellbeing. Despite theory and evidence to support the link between occupation, health and wellbeing, occupational therapists can struggle with applying an occupation focus in practice and knowing how to use occupational frameworks to enable occupation. The purpose of this paper is to introduce the Capabilities, Opportunities, Resources and Environments (CORE) approach for inclusive and occupation-focused practice. It provides occupational therapists with a means of operationalising occupational enablement and facilitating social inclusion. The CORE approach is introduced by linking its main ideas to Economist and Nobel Prize Laureate Amartya Sen's capabilities approach, as well as findings from the author's doctoral research into entrenched disadvantage and social inclusion. Practical questions guided by the CORE approach's acronym are given to explore how the approach can be utilised alongside other occupational models and frameworks to encourage strategies for effective enablement through occupation for social inclusion. As experts in enabling occupation, occupational therapists can use the CORE approach to design occupation-focused interventions and promote inclusive occupational therapy. © 2017 Occupational Therapy Australia.

  20. The Halo mass function from Excursion Set Theory. II. The Diffusing Barrier

    NASA Astrophysics Data System (ADS)

    Maggiore, Michele; Riotto, Antonio

    2010-07-01

    In excursion set theory, the computation of the halo mass function is mapped into a first-passage time process in the presence of a barrier, which in the spherical collapse model is a constant and in the ellipsoidal collapse model is a fixed function of the variance of the smoothed density field. However, N-body simulations show that dark matter halos grow through a mixture of smooth accretion, violent encounters, and fragmentations, and modeling halo collapse as spherical, or even as ellipsoidal, is a significant oversimplification. In addition, the very definition of what is a dark matter halo, both in N-body simulations and observationally, is a difficult problem. We propose that some of the physical complications inherent to a realistic description of halo formation can be included in the excursion set theory framework, at least at an effective level, by taking into account that the critical value for collapse is not a fixed constant δ c , as in the spherical collapse model, nor a fixed function of the variance σ of the smoothed density field, as in the ellipsoidal collapse model, but rather is itself a stochastic variable, whose scatter reflects a number of complicated aspects of the underlying dynamics. Solving the first-passage time problem in the presence of a diffusing barrier we find that the exponential factor in the Press-Schechter mass function changes from exp{-δ2 c /2σ2} to exp{-aδ2 c /2σ2}, where a = 1/(1 + DB ) and DB is the diffusion coefficient of the barrier. The numerical value of DB , and therefore the corresponding value of a, depends among other things on the algorithm used for identifying halos. We discuss the physical origin of the stochasticity of the barrier and, from recent N-body simulations that studied the properties of the collapse barrier, we deduce a value DB ~= 0.25. Our model then predicts a ~= 0.80, in excellent agreement with the exponential fall off of the mass function found in N-body simulations, for the same halo

  1. Halo Intrinsic Alignment: Dependence on Mass, Formation Time, and Environment

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Xia, Qianli; Kang, Xi; Wang, Peng

    In this paper we use high-resolution cosmological simulations to study halo intrinsic alignment and its dependence on mass, formation time, and large-scale environment. In agreement with previous studies using N -body simulations, it is found that massive halos have stronger alignment. For the first time, we find that for a given halo mass older halos have stronger alignment and halos in cluster regions also have stronger alignment than those in filaments. To model these dependencies, we extend the linear alignment model with inclusion of halo bias and find that the halo alignment with its mass and formation time dependence canmore » be explained by halo bias. However, the model cannot account for the environment dependence, as it is found that halo bias is lower in clusters and higher in filaments. Our results suggest that halo bias and environment are independent factors in determining halo alignment. We also study the halo alignment correlation function and find that halos are strongly clustered along their major axes and less clustered along the minor axes. The correlated halo alignment can extend to scales as large as 100 h {sup −1} Mpc, where its feature is mainly driven by the baryon acoustic oscillation effect.« less

  2. Studying generalised dark matter interactions with extended halo-independent methods

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kahlhoefer, Felix; Wild, Sebastian

    2016-10-20

    The interpretation of dark matter direct detection experiments is complicated by the fact that neither the astrophysical distribution of dark matter nor the properties of its particle physics interactions with nuclei are known in detail. To address both of these issues in a very general way we develop a new framework that combines the full formalism of non-relativistic effective interactions with state-of-the-art halo-independent methods. This approach makes it possible to analyse direct detection experiments for arbitrary dark matter interactions and quantify the goodness-of-fit independent of astrophysical uncertainties. We employ this method in order to demonstrate that the degeneracy between astrophysicalmore » uncertainties and particle physics unknowns is not complete. Certain models can be distinguished in a halo-independent way using a single ton-scale experiment based on liquid xenon, while other models are indistinguishable with a single experiment but can be separated using combined information from several target elements.« less

  3. Halo vest effect on balance.

    PubMed

    Richardson, J K; Ross, A D; Riley, B; Rhodes, R L

    2000-03-01

    To determine the effect of a halo vest, a cervical orthosis, on clinically relevant balance parameters. Subjects performed unipedal stance (with eyes open and closed, on both firm and soft surfaces) and functional reach, with and without the application of a halo vest. A convenience sample of 12 healthy young subjects, with an equal number of men and women. Seconds for unipedal stance (maximum 45); inches for functional reach. Both unipedal stance times and functional reach (mean +/- standard deviation) were significantly decreased with the halo vest as compared to without it (29.1+/-5.8 vs. 32.8+/-6.4 seconds, p = .002; 12.9+/-1.4 vs. 15.1+/-2.1 inches, p<.01). A halo vest causes an acute impairment in balance in the healthy young. It is likely that the impairment would be greater in older or injured patients, thus increasing their risk for a fall, which could have devastating consequences.

  4. The Outer Halos of Early-Type Galaxies

    NASA Astrophysics Data System (ADS)

    Gerhard, Ortwin; Arnaboldi, Magda; Longobardi, Alessia

    2015-04-01

    The outer halos of massive early-type galaxies (ETGs) are dark matter dominated and may have formed by accretion of smaller systems during galaxy evolution. Here a brief report is given of some recent work on the kinematics, angular momentum, and mass distributions of simulated ETG halos, and of corresponding properties of observed halos measured with planetary nebulae (PNe) as tracers. In the outermost regions of the Virgo-central galaxy M87, the PN data show that the stellar halo and the co-spatial intracluster light are distinct kinematic components.

  5. Framework for Assessing the ICT Competency in Teachers up to the Requirements of "Teacher" Occupational Standard

    ERIC Educational Resources Information Center

    Avdeeva, Svetlana; Zaichkina, Olga; Nikulicheva, Nataliya; Khapaeva, Svetlana

    2016-01-01

    The paper deals with problems of working out a test framework for the assessment of teachers' ICT competency in line with the requirements of "Teacher" occupational standard. The authors have analyzed the known approaches to assessing teachers' ICT competency--ISTE Standards and UNESCO ICT CFT and have suggested their own approach to…

  6. Simulation of halo particles with Simpsons

    NASA Astrophysics Data System (ADS)

    Machida, Shinji

    2003-12-01

    Recent code improvements and some simulation results of halo particles with Simpsons will be presented. We tried to identify resonance behavior of halo particles by looking at tune evolution of individual macro particle.

  7. Self-consistent construction of virialized wave dark matter halos

    NASA Astrophysics Data System (ADS)

    Lin, Shan-Chang; Schive, Hsi-Yu; Wong, Shing-Kwong; Chiueh, Tzihong

    2018-05-01

    Wave dark matter (ψ DM ), which satisfies the Schrödinger-Poisson equation, has recently attracted substantial attention as a possible dark matter candidate. Numerical simulations have, in the past, provided a powerful tool to explore this new territory of possibility. Despite their successes in revealing several key features of ψ DM , further progress in simulations is limited, in that cosmological simulations so far can only address formation of halos below ˜2 ×1011 M⊙ and substantially more massive halos have become computationally very challenging to obtain. For this reason, the present work adopts a different approach in assessing massive halos by constructing wave-halo solutions directly from the wave distribution function. This approach bears certain similarities with the analytical construction of the particle-halo (cold dark matter model). Instead of many collisionless particles, one deals with one single wave that has many noninteracting eigenstates. The key ingredient in the wave-halo construction is the distribution function of the wave power, and we use several halos produced by structure formation simulations as templates to determine the wave distribution function. Among different models, we find the fermionic King model presents the best fits and we use it for our wave-halo construction. We have devised an iteration method for constructing the nonlinear halo and demonstrate its stability by three-dimensional simulations. A Milky Way-sized halo has also been constructed, and the inner halo is found to be flatter than the NFW profile. These wave-halos have small-scale interferences both in space and time producing time-dependent granules. While the spatial scale of granules varies little, the correlation time is found to increase with radius by 1 order of magnitude across the halo.

  8. THE STELLAR-TO-HALO MASS RELATION OF LOCAL GALAXIES SEGREGATES BY COLOR

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Rodríguez-Puebla, Aldo; Yang, Xiaohu; Foucaud, Sebastien

    By means of a statistical approach that combines different semi-empirical methods of galaxy-halo connection, we derive the stellar-to-halo mass relations (SHMR) of local blue and red central galaxies. We also constrain the fraction of halos hosting blue/red central galaxies and the occupation statistics of blue and red satellites as a function of halo mass, M {sub h}. For the observational input we use the blue and red central/satellite galaxy stellar mass functions and two-point correlation functions in the stellar mass range of 9 < log(M {sub *}/M {sub ☉}) <12. We find that: (1) the SHMR of central galaxies is segregated bymore » color, with blue centrals having a SHMR above that of red centrals; at log(M {sub h}/M {sub ☉}) ∼12, the M {sub *}-to-M {sub h} ratio of the blue centrals is ≈0.05, which is ∼1.7 times larger than the value of red centrals. (2) The constrained scatters around the SHMRs of red and blue centrals are ≈0.14 and ≈0.11 dex, respectively. The scatter of the average SHMR of all central galaxies changes from ∼0.20 dex to ∼0.14 dex in the 11.3 < log(M {sub h}/M {sub ☉}) <15 range. (3) The fraction of halos hosting blue centrals at M{sub h}=10{sup 11} M {sub ☉} is 87%, but at 2 × 10{sup 12} M {sub ☉} decays to ∼20%, approaching a few percent at higher masses. The characteristic mass at which this fraction is the same for blue and red galaxies is M{sub h}≈7×10{sup 11} M {sub ☉}. Our results suggest that the SHMR of central galaxies at large masses is shaped by mass quenching. At low masses processes that delay star formation without invoking too strong supernova-driven outflows could explain the high M {sub *}-to-M {sub h} ratios of blue centrals as compared to those of the scarce red centrals.« less

  9. [Halos and multifocal intraocular lenses: origin and interpretation].

    PubMed

    Alba-Bueno, F; Vega, F; Millán, M S

    2014-10-01

    To present the theoretical and experimental characterization of the halo in multifocal intraocular lenses (MIOL). The origin of the halo in a MIOL is the overlaying of 2 or more images. Using geometrical optics, it can be demonstrated that the diameter of each halo depends on the addition of the lens (ΔP), the base power (P(d)), and the diameter of the IOL that contributes to the «non-focused» focus. In the image plane that corresponds to the distance focus, the halo diameter (δH(d)) is given by: δH(d)=d(pn) ΔP/P(d), where d(pn) is the diameter of the IOL that contributes to the near focus. Analogously, in the near image plane the halo diameter (δH(n)) is: δH(n)=d(pd) ΔP/P(d), where d(pd) is the diameter of the IOL that contributes to the distance focus. Patients perceive halos when they see bright objects over a relatively dark background. In vitro, the halo can be characterized by analyzing the intensity profile of the image of a pinhole that is focused by each of the foci of a MIOL. A comparison has been made between the halos induced by different MIOL of the same base power (20D) in an optical bench. As predicted by theory, the larger the addition of the MIOL, the larger the halo diameter. For large pupils and with MIOL with similar aspheric designs and addition (SN6AD3 vs ZMA00), the apodized MIOL has a smaller halo diameter than a non-apodized one in distance vision, while in near vision the size is very similar, but the relative intensity is higher in the apodized MIOL. When comparing lenses with the same diffractive design, but with different spherical-aspheric base design (SN60D3 vs SN6AD3), the halo in distance vision of the spherical MIOL is larger, while in near vision the spherical IOL induces a smaller halo, but with higher intensity due to the spherical aberration of the distance focus in the near image. In the case of a trifocal-diffractive IOL (AT LISA 839MP) the most noticeable characteristic is the double-halo formation due to the 2 non

  10. On physical scales of dark matter halos

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zemp, Marcel, E-mail: mzemp@pku.edu.cn

    2014-09-10

    It is common practice to describe formal size and mass scales of dark matter halos as spherical overdensities with respect to an evolving density threshold. Here, we critically investigate the evolutionary effects of several such commonly used definitions and compare them to the halo evolution within fixed physical scales as well as to the evolution of other intrinsic physical properties of dark matter halos. It is shown that, in general, the traditional way of characterizing sizes and masses of halos dramatically overpredicts the degree of evolution in the last 10 Gyr, especially for low-mass halos. This pseudo-evolution leads to themore » illusion of growth even though there are no major changes within fixed physical scales. Such formal size definitions also serve as proxies for the virialized region of a halo in the literature. In general, those spherical overdensity scales do not coincide with the virialized region. A physically more precise nomenclature would be to simply characterize them by their very definition instead of calling such formal size and mass definitions 'virial'. In general, we find a discrepancy between the evolution of the underlying physical structure of dark matter halos seen in cosmological structure formation simulations and pseudo-evolving formal virial quantities. We question the importance of the role of formal virial quantities currently ubiquitously used in descriptions, models, and relations that involve properties of dark matter structures. Concepts and relations based on pseudo-evolving formal virial quantities do not properly reflect the actual evolution of dark matter halos and lead to an inaccurate picture of the physical evolution of our universe.« less

  11. The global dark halo structure of the Andromeda galaxy

    NASA Astrophysics Data System (ADS)

    Hayashi, Kohei; Chiba, Masashi

    2014-01-01

    We set new limits on the global shape of the dark halo in the Andromeda galaxy based on axisymmetric mass models constructed by Hayashi & Chiba (2012). This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Based on the application of our models to latest kinematical data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield not a spherical but a prolate shape for its dark halo. We also find that the prolate dark halo is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their galactic host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web.

  12. Research Progresses of Halo Streams in the Solar Neighborhood

    NASA Astrophysics Data System (ADS)

    Xi-long, Liang; Jing-kun, Zhao; Yu-qin, Chen; Gang, Zhao

    2018-01-01

    The stellar streams originated from the Galactic halo may be detected when they pass by the solar neighborhood, and they still keep some information at their birth times. Thus, the investigation of halo streams in the solar neighborhood is very important for understanding the formation and evolution of our Galaxy. In this paper, the researches of halo streams in the solar neighborhood are briefly reviewed. We have introduced the methods how to detect the halo streams and identify their member stars, summarized the progresses in the observation of member stars of halo streams and in the study of their origins, introduced in detail how to analyze the origins of halo streams in the solar neighborhood by means of numerical simulation and chemical abundance, and finally discussed the prospects of the LAMOST and GAIA in the research of halo streams in the solar neighborhood.

  13. A look into the inside of haloes: a characterization of the halo shape as a function of overdensity in the Planck cosmology

    NASA Astrophysics Data System (ADS)

    Despali, Giulia; Giocoli, Carlo; Bonamigo, Mario; Limousin, Marceau; Tormen, Giuseppe

    2017-04-01

    In this paper, we study the triaxial properties of dark matter haloes of a wide range of masses extracted from a set of cosmological N-body simulations. We measure the shape at different distances from the halo centre (characterized by different overdensity thresholds), both in three and in two dimensions. We discuss how halo triaxiality increases with mass, redshift and distance from the halo centre. We also examine how the orientations of the different ellipsoids are aligned with each other and what is the gradient in internal shapes for haloes with different virial configurations. Our findings highlight that the internal part of the halo retains memory of the violent formation process keeping the major axis oriented towards the preferential direction of the infalling material while the outer part becomes rounder due to continuous isotropic merging events. This effect is clearly evident in high-mass haloes - which formed more recently - while it is more blurred in low-mass haloes. We present simple distributions that may be used as priors for various mass reconstruction algorithms, operating in different wavelengths, in order to recover a more complex and realistic dark matter distribution of isolated and relaxed systems.

  14. Halo correlations in nonlinear cosmic density fields

    NASA Astrophysics Data System (ADS)

    Bernardeau, F.; Schaeffer, R.

    1999-09-01

    The question we address in this paper is the determination of the correlation properties of the dark matter halos appearing in cosmic density fields once they underwent a strongly nonlinear evolution induced by gravitational dynamics. A series of previous works have given indications that kind of non-Gaussian features are induced by nonlinear evolution in term of the high-order correlation functions. Assuming such patterns for the matter field, i.e. that the high-order correlation functions behave as products of two-body correlation functions, we derive the correlation properties of the halos, that are assumed to represent the correlation properties of galaxies or clusters. The hierarchical pattern originally induced by gravity is shown to be conserved for the halos. The strength of their correlations at any order varies, however, but is found to depend only on their internal properties, namely on the parameter x~ m/r(3-gamma ) where m is the mass of the halo, r its size and gamma is the power law index of the two-body correlation function. This internal parameter is seen to be close to the depth of the internal potential well of virialized objects. We were able to derive the explicit form of the generating function of the moments of the halo counts probability distribution function. In particular we show explicitly that, generically, S_P(x)-> P(P-2) in the rare halo limit. Various illustrations of our general results are presented. As a function of the properties of the underlying matter field, we construct the count probabilities for halos and in particular discuss the halo void probability. We evaluate the dependence of the halo mass function on the environment: within clusters, hierarchical clustering implies the higher masses are favored. These properties solely arise from what is a natural bias (ie, naturally induced by gravity) between the observed objects and the unseen matter field, and how it manifests itself depending on which selection effects are

  15. Alignment of Outcome Instruments Used in Hand Therapy With the Occupational Therapy Practice Framework: Domain and Process and the International Classification of Functioning, Disability and Health: A Scoping Review.

    PubMed

    Lesher, Danielle Ann-Marie; Mulcahey, M J; Hershey, Peter; Stanton, Donna Breger; Tiedgen, Andrea C

    We sought to identify outcome instruments used in rehabilitation of the hand and upper extremity; to determine their alignment with the constructs of the International Classification of Functioning, Disability and Health (ICF) and the Occupational Therapy Practice Framework: Domain and Process; and to report gaps in the constructs measured by outcome instruments as a basis for future research. We searched CINAHL, MEDLINE, OTseeker, and the Cochrane Central Register of Controlled Trials using scoping review methodology and evaluated outcome instruments for concordance with the ICF and the Framework. We identified 18 outcome instruments for analysis. The findings pertain to occupational therapists' focus on body functions, body structures, client factors, and activities of daily living; a gap in practice patterns in use of instruments; and overestimation of the degree to which instruments used are occupationally based. Occupational therapy practitioners should use outcome instruments that embody conceptual frameworks for classifying function and activity. Copyright © 2017 by the American Occupational Therapy Association, Inc.

  16. Water quality, health, and human occupations.

    PubMed

    Blakeney, Anne B; Marshall, Amy

    2009-01-01

    To introduce evidence of the critical link between water quality and human occupations. A participatory action research design was used to complete a three-phase project. Phase 1 included mapping the watershed of Letcher County, Kentucky. Phase 2 consisted of surveying 122 Letcher County health professionals. Phase 3, the primary focus of this article, consisted of interviews with Letcher County adults regarding their lived experiences with water. The Occupational Therapy Practice Framework: Domain and Process (American Occupational Therapy Association, 2002) was used to structure questions. The Model of Occupational Justice provided the theoretical framework for presentation of the results. The watershed in Letcher County, Kentucky, is polluted as a result of specific coal mining practices and a lack of adequate infrastructure. As a result, citizens experience occupational injustice in the forms of occupational imbalance, occupational deprivation, and occupational alienation.

  17. Abundances and Evolution of Lithium in the Galactic Halo and Disk

    NASA Astrophysics Data System (ADS)

    Ryan, Sean G.; Kajino, Toshitaka; Beers, Timothy C.; Suzuki, Takeru Ken; Romano, Donatella; Matteucci, Francesca; Rosolankova, Katarina

    2001-03-01

    We have measured the Li abundance of 18 stars with -2<~[Fe/H]<~-1 and 6000<~Teff<~6400 K, a parameter range that was poorly represented in previous studies. We examine the Galactic chemical evolution (GCE) of this element, combining these data with previous samples of turnoff stars over the full range of halo metallicities. We find that A(Li) increases from a level of ~2.10 at [Fe/H]=-3.5 to ~2.40 at [Fe/H]=-1.0, where A(Li)=log10(n(Li)/n(H))+12.00. We compare the observations with several GCE calculations, including existing one-zone models and a new model developed in the framework of inhomogeneous evolution of the Galactic halo. We show that Li evolved at a constant rate relative to iron throughout the halo and old disk epochs but that during the formation of young disk stars, the production of Li relative to iron increased significantly. These observations can be understood in the context of models in which postprimordial Li evolution during the halo and old disk epochs is dominated by Galactic cosmic-ray fusion and spallation reactions, with some contribution from the ν-process in supernovae. The onset of more efficient Li production (relative to iron) in the young disk coincides with the appearance of Li from novae and asymptotic giant branch (AGB) stars. The major challenge facing the models is to reconcile the mild evolution of Li during the halo and old disk phases with the more efficient production (relative to iron) at [Fe/H]>-0.5. We speculate that cool-bottom processing (production) of Li in low-mass stars may provide an important late-appearing source of Li, without attendant Fe production, that might explain the Li production in the young disk. Based on observations obtained with the University College London échelle spectrograph (UCLES) on the Anglo-Australian Telescope (AAT) and the Utrecht échelle spectrograph (UES) on the William Herschel Telescope (WHT).

  18. Squeezing the halo bispectrum: a test of bias models

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Dizgah, Azadeh Moradinezhad; Chan, Kwan Chuen; Noreña, Jorge

    We study the halo-matter cross bispectrum in the presence of primordial non-Gaussianity of the local type. We restrict ourselves to the squeezed limit, for which the calculation are straightforward, and perform the measurements in the initial conditions of N-body simulations, to mitigate the contamination induced by nonlinear gravitational evolution. Interestingly, the halo-matter cross bispectrum is not trivial even in this simple limit as it is strongly sensitive to the scale-dependence of the quadratic and third-order halo bias. Therefore, it can be used to test biasing prescriptions. We consider three different prescription for halo clustering: excursion set peaks (ESP), local biasmore » and a model in which the halo bias parameters are explicitly derived from a peak-background split. In all cases, the model parameters are fully constrained with statistics other than the cross bispectrum. We measure the cross bispectrum involving one halo fluctuation field and two mass overdensity fields for various halo masses and collapse redshifts. We find that the ESP is in reasonably good agreement with the numerical data, while the other alternatives we consider fail in various cases. This suggests that the scale-dependence of halo bias also is a crucial ingredient to the squeezed limit of the halo bispectrum.« less

  19. HALOE test and evaluation software

    NASA Technical Reports Server (NTRS)

    Edmonds, W.; Natarajan, S.

    1987-01-01

    Computer programming, system development and analysis efforts during this contract were carried out in support of the Halogen Occultation Experiment (HALOE) at NASA/Langley. Support in the major areas of data acquisition and monitoring, data reduction and system development are described along with a brief explanation of the HALOE project. Documented listings of major software are located in the appendix.

  20. Disc-halo interactions in ΛCDM

    NASA Astrophysics Data System (ADS)

    Bauer, Jacob S.; Widrow, Lawrence M.; Erkal, Denis

    2018-05-01

    We present a new method for embedding a stellar disc in a cosmological dark matter halo and provide a worked example from a Λ cold dark matter zoom-in simulation. The disc is inserted into the halo at a redshift z = 3 as a zero-mass rigid body. Its mass and size are then increased adiabatically while its position, velocity, and orientation are determined from rigid-body dynamics. At z = 1, the rigid disc (RD) is replaced by an N-body disc whose particles sample a three-integral distribution function (DF). The simulation then proceeds to z = 0 with live disc (LD) and halo particles. By comparison, other methods assume one or more of the following: the centre of the RD during the growth phase is pinned to the minimum of the halo potential, the orientation of the RD is fixed, or the live N-body disc is constructed from a two rather than three-integral DF. In general, the presence of a disc makes the halo rounder, more centrally concentrated, and smoother, especially in the innermost regions. We find that methods in which the disc is pinned to the minimum of the halo potential tend to overestimate the amount of adiabatic contraction. Additionally, the effect of the disc on the subhalo distribution appears to be rather insensitive to the disc insertion method. The LD in our simulation develops a bar that is consistent with the bars seen in late-type spiral galaxies. In addition, particles from the disc are launched or `kicked up' to high galactic latitudes.

  1. Halo-free phase contrast microscopy (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Nguyen, Tan H.; Kandel, Mikhail E.; Shakir, Haadi M.; Best, Catherine; Do, Minh N.; Popescu, Gabriel

    2017-02-01

    The phase contrast (PC) method is one of the most impactful developments in the four-century long history of microscopy. It allows for intrinsic, nondestructive contrast of transparent specimens, such as live cells. However, PC is plagued by the halo artifact, a result of insufficient spatial coherence in the illumination field, which limits its applicability. We present a new approach for retrieving halo-free phase contrast microscopy (hfPC) images by upgrading the conventional PC microscope with an external interferometric module, which generates sufficient data for reversing the halo artifact. Measuring four independent intensity images, our approach first measures haloed phase maps of the sample. We solve for the halo-free sample transmission function by using a physical model of the image formation under partial spatial coherence. Using this halo-free sample transmission, we can numerically generate artifact-free PC images. Furthermore, this transmission can be further used to obtain quantitative information about the sample, e.g., the thickness with known refractive indices, dry mass of live cells during their cycles. We tested our hfPC method on various control samples, e.g., beads, pillars and validated its potential for biological investigation by imaging live HeLa cells, red blood cells, and neurons.

  2. The Structure of Dark Matter Halos in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Burkert, A.

    1995-07-01

    Recent observations indicate that dark matter halos have flat central density profiles. Cosmological simulations with nonbaryonic dark matter, however, predict self-similar halos with central density cusps. This contradiction has lead to the conclusion that dark matter must be baryonic. Here it is shown that the dark matter halos of dwarf spiral galaxies represent a one-parameter family with self-similar density profiles. The observed global halo parameters are coupled with each other through simple scaling relations which can be explained by the standard cold dark matter model if one assumes that all the halos formed from density fluctuations with the same primordial amplitude. We find that the finite central halo densities correlate with the other global parameters. This result rules out scenarios where the flat halo cores formed subsequently through violent dynamical processes in the baryonic component. These cores instead provide important information on the origin and nature of dark matter in dwarf galaxies.

  3. Subhalo demographics in the Illustris simulation: effects of baryons and halo-to-halo variation

    NASA Astrophysics Data System (ADS)

    Chua, Kun Ting Eddie; Pillepich, Annalisa; Rodriguez-Gomez, Vicente; Vogelsberger, Mark; Bird, Simeon; Hernquist, Lars

    2017-12-01

    We study the abundance of subhaloes in the hydrodynamical cosmological simulation Illustris, which includes both baryons and dark matter in a cold dark matter volume 106.5 Mpc a side. We compare Illustris to its dark-matter only (DMO) analogue, Illustris-Dark and quantify the effects of baryonic processes on the demographics of subhaloes in the host mass range 1011-3 × 1014 M⊙. We focus on both the evolved (z = 0) subhalo cumulative mass functions (SHMF) and the statistics of subhaloes ever accreted, i.e. infall SHMF. We quantify the variance in subhalo abundance at fixed host mass and investigate the physical reasons responsible for such scatter. We find that in Illustris, baryonic physics impacts both the infall and z = 0 subhalo abundance by tilting the DMO function and suppressing the abundance of low-mass subhaloes. The breaking of self-similarity in the subhalo abundance at z = 0 is enhanced by the inclusion of baryonic physics. The non-monotonic alteration of the evolved subhalo abundances can be explained by the modification of the concentration-mass relation of Illustris hosts compared to Illustris-Dark. Interestingly, the baryonic implementation in Illustris does not lead to an increase in the halo-to-halo variation compared to Illustris-Dark. In both cases, the normalized intrinsic scatter today is larger for Milky Way-like haloes than for cluster-sized objects. For Milky Way-like haloes, it increases from about eight per cent at infall to about 25 per cent at the current epoch. In both runs, haloes of fixed mass formed later host more subhaloes than early formers.

  4. The Prolate Dark Matter Halo of the Andromeda Galaxy

    NASA Astrophysics Data System (ADS)

    Hayashi, Kohei; Chiba, Masashi

    2014-07-01

    We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi & Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for its dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.

  5. The growth and structure of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Zhao, D. H.; Mo, H. J.; Jing, Y. P.; Börner, G.

    2003-02-01

    In this paper, we analyse in detail the mass-accretion histories and structural properties of dark haloes in high-resolution N-body simulations. We model the density distribution in individual haloes using the Navarro-Frenk-White (NFW) profile. For a given halo, there is a tight correlation between its inner-scale radius rs and the mass within it, Ms, for all its main progenitors. Using this correlation, one can predict quite well the structural properties of a dark halo at any time in its history from its mass-accretion history, implying that the structure properties and the mass-accretion history are closely correlated. The predicted growing rate of concentration c with time tends to increase with decreasing mass-accretion rate. The build-up of dark haloes in cold dark matter (CDM) models generally consists of an early phase of fast accretion (where the halo mass Mh increases with time much faster than the expansion rate of the Universe) and a late phase of slow accretion (where Mh increases with time approximately as the expansion rate). These two phases are separated at a time when c~ 4 and the typical binding energy of the halo is approximately equal to that of a singular isothermal sphere with the same circular velocity. Haloes in the two accretion phases show systematically different properties, for example, the circular velocity vh increases rapidly with time in the fast accretion phase but remains almost constant in the slow accretion phase, the inner properties of a halo, such as rs and Ms increase rapidly with time in the fast accretion phase but change only slowly in the slow accretion phase, the inner circular velocity vs is approximately equal to vh in the fast accretion phase but is larger in the slow accretion phase. The potential well associated with a halo is built up mainly in the fast accretion phase, while a large amount of mass can be accreted in the slow accretion phase without changing the potential well significantly. We discuss our results

  6. N-body dark matter haloes with simple hierarchical histories

    NASA Astrophysics Data System (ADS)

    Jiang, Lilian; Helly, John C.; Cole, Shaun; Frenk, Carlos S.

    2014-05-01

    We present a new algorithm which groups the subhaloes found in cosmological N-body simulations by structure finders such as SUBFIND into dark matter haloes whose formation histories are strictly hierarchical. One advantage of these `Dhaloes' over the commonly used friends-of-friends (FoF) haloes is that they retain their individual identity in the cases when FoF haloes are artificially merged by tenuous bridges of particles or by an overlap of their outer diffuse haloes. Dhaloes are thus well suited for modelling galaxy formation and their merger trees form the basis of the Durham semi-analytic galaxy formation model, GALFORM. Applying the Dhalo construction to the Λ cold dark matter Millennium II Simulation, we find that approximately 90 per cent of Dhaloes have a one-to-one, bijective match with a corresponding FoF halo. The remaining 10 per cent are typically secondary components of large FoF haloes. Although the mass functions of both types of haloes are similar, the mass of Dhaloes correlates much more tightly with the virial mass, M200, than FoF haloes. Approximately 80 per cent of FoF and bijective and non-bijective Dhaloes are relaxed according to standard criteria. For these relaxed haloes, all three types have similar concentration-M200 relations and, at fixed mass, the concentration distributions are described accurately by log-normal distributions.

  7. The Origin of the Milky Way's Halo Age Distribution

    NASA Astrophysics Data System (ADS)

    Carollo, Daniela; Tissera, Patricia B.; Beers, Timothy C.; Gudin, Dmitrii; Gibson, Brad K.; Freeman, Ken C.; Monachesi, Antonela

    2018-05-01

    We present an analysis of the radial age gradients for the stellar halos of five Milky Way (MW) mass-sized systems simulated as part of the Aquarius Project. The halos show a diversity of age trends, reflecting their different assembly histories. Four of the simulated halos possess clear negative age gradients, ranging from approximately ‑7 to ‑19 Myr kpc‑1, shallower than those determined by recent observational studies of the Milky Way’s stellar halo. However, when restricting the analysis to the accreted component alone, all of the stellar halos exhibit a steeper negative age gradient with values ranging from ‑8 to ‑32 Myr kpc‑1, closer to those observed in the Galaxy. Two of the accretion-dominated simulated halos show a large concentration of old stars in the center, in agreement with the Ancient Chronographic Sphere reported observationally. The stellar halo that best reproduces the current observed characteristics of the age distributions of the Galaxy is that formed principally by the accretion of small satellite galaxies. Our findings suggest that the hierarchical clustering scenario can reproduce the MW’s halo age distribution if the stellar halo was assembled from accretion and the disruption of satellite galaxies with dynamical masses less than ∼109.5 M ⊙, and a minimal in situ contribution.

  8. Empowerment and occupation: A new perspective.

    PubMed

    Hammell, Karen R Whalley

    2016-12-01

    The idea of empowerment permeates the occupational therapy literature yet has received little critical reflection from occupational therapy's theorists. This paper aims to explore the concept of empowerment and highlight a recent definition that resonates with occupational therapists' core values. Empowerment is generally understood to be a process of bestowing power and giving ability to someone deficient in both. However, a new definition provides a framework for understanding how empowerment might enhance people's capabilities. The World Bank's depiction of empowerment fits well with occupational therapists' beliefs in the importance of the ability and opportunity to "do," providing a framework for action. This framework focuses on people's capabilities: their freedom-or opportunity-to choose what they wish to do and to be and their ability to act on these wishes. Moreover, the World Bank's assertion that empowered people have freedom of both choice and action suggests empowerment is a relevant concept for occupational therapists.

  9. Exploring Occupational and Behavioral Risk Factors for Obesity in Firefighters: A Theoretical Framework and Study Design

    PubMed Central

    Schnall, Peter; Dobson, Marnie; Israel, Leslie; Landsbergis, Paul; Galassetti, Pietro; Pontello, Andria; Kojaku, Stacey; Baker, Dean

    2011-01-01

    Firefighters and police officers have the third highest prevalence of obesity among 41 male occupational groups in the United States (US). However, few studies have examined the relationship of firefighter working conditions and health behaviors with obesity. This paper presents a theoretical framework describing the relationship between working conditions, health behaviors, and obesity in firefighters. In addition, the paper describes a detailed study plan for exploring the role of occupational and behavioral risk factors in the development of obesity in firefighters enrolled in the Orange County Fire Authority Wellness Fitness Program. The study plan will be described with emphasis on its methodological merits: adopting a participatory action research approach, developing a firefighter-specific work and health questionnaire, conducting both a cross-sectional epidemiological study using the questionnaire and a sub-study to assess the validity of the questionnaire with dietary intake and physical activity measures, and evaluating the strengths and weaknesses of the body mass index as an obesity measure in comparison to skinfold-based percent body fat. The study plan based on a theoretical framework can be an essential first step for establishing effective intervention programs for obesity among professional and voluntary firefighters. PMID:22953214

  10. Exploring occupational and behavioral risk factors for obesity in firefighters: a theoretical framework and study design.

    PubMed

    Choi, Bongkyoo; Schnall, Peter; Dobson, Marnie; Israel, Leslie; Landsbergis, Paul; Galassetti, Pietro; Pontello, Andria; Kojaku, Stacey; Baker, Dean

    2011-12-01

    Firefighters and police officers have the third highest prevalence of obesity among 41 male occupational groups in the United States (US). However, few studies have examined the relationship of firefighter working conditions and health behaviors with obesity. This paper presents a theoretical framework describing the relationship between working conditions, health behaviors, and obesity in firefighters. In addition, the paper describes a detailed study plan for exploring the role of occupational and behavioral risk factors in the development of obesity in firefighters enrolled in the Orange County Fire Authority Wellness Fitness Program. The study plan will be described with emphasis on its methodological merits: adopting a participatory action research approach, developing a firefighter-specific work and health questionnaire, conducting both a cross-sectional epidemiological study using the questionnaire and a sub-study to assess the validity of the questionnaire with dietary intake and physical activity measures, and evaluating the strengths and weaknesses of the body mass index as an obesity measure in comparison to skinfold-based percent body fat. The study plan based on a theoretical framework can be an essential first step for establishing effective intervention programs for obesity among professional and voluntary firefighters.

  11. Isobar analog states (IAS), double isobar analog states (DIAS), configuration states (CS), and double configuration states (DCS) in halo nuclei. Halo isomers

    NASA Astrophysics Data System (ADS)

    Izosimov, I. N.

    2015-10-01

    It has been shown that IAS, DIAS, CS, and DCS can simultaneously have n-n, n-p, and p-p halo components in their wave functions. Differences in halo structure of the excited and ground states can result in the formation of isomers (halo-isomers). Both the Borromean and tango halo types can be observed for n-p configurations of atomic nuclei. The structure of the ground and excited states with different isospin quantum number in halo like nuclei is discussed. B(Mλ) and B(Eλ) for γ-transitions in 6,7,8Li, 8,9,10Be, 8,10,11B, 10,11,12,13,14C, 13,14,15,16,17N, 15,16,17,19O, and 17F are analyzed. Special attention is given to nuclei whose ground state does not exhibit halo structure but the excited state may have one.

  12. An improved catalog of halo wide binary candidates

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Allen, Christine; Monroy-Rodríguez, Miguel A., E-mail: chris@astro.unam.mx

    2014-08-01

    We present an improved catalog of halo wide binaries compiled from an extensive literature search. Most of our binaries stem from the common proper motion binary catalogs by Allen et al. and Chanamé and Gould, but we have also included binaries from the lists of Ryan and Zapatero-Osorio and Martín. All binaries were carefully checked and their distances and systemic radial velocities are included when available. Probable membership to the halo population was tested by means of reduced proper motion diagrams for 251 candidate halo binaries. After eliminating obvious disk binaries, we ended up with 211 probable halo binaries, 150more » of which have radial velocities available. We compute galactic orbits for these 150 binaries and calculate the time they spend within the galactic disk. Considering the full sample of 251 candidate halo binaries as well as several subsamples, we find that the distribution of angular separations (or expected major semiaxes) follows a power law f(a) ∼ a {sup –1} (Oepik's relation) up to different limits. For the 50 most disk-like binaries, those that spend their entire lives within z = ±500 pc, this limit is found to be 19,000 AU (0.09 pc), while for the 50 most halo-like binaries, those that spend on average only 18% of their lives within z = ±500 pc, the limit is 63,000 AU (0.31 pc). In a companion paper, we employ this catalog to establish limits on the masses of the halo massive perturbers (massive compact halo objects).« less

  13. The Phase-space Density Distribution of Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Williams, Liliya L. R.; Austin, Crystal; Barnes, Eric; Babul, Arif; Dalcanton, Julianne

    2004-12-01

    High resolution N-body simulations have all but converged on a common empirical form for the shape of the density profiles of halos, but the full understanding of the underlying physics of halo formation has eluded them so far. We investigate the formation and structure of dark matter halos using analytical and semi-analytical techniques. Our halos are formed via an extended secondary infall model (ESIM); they contain secondary perturbations and hence random tangential and ra- dial motions which affect the halo’s evolution at it undergoes shell-crossing and virialization. Even though the density profiles of NFW and ESIM halos are different their phase-space density distributions are the same: ρ σ3 ∝ r α , with α 1 875 over 3 decades in radius. We use two approaches to try to explain this “universal” slope: (1) The Jeans equation analysis yields many insights, however, does not answer why α 1 875. (2) The secondary infall model of the 1960’s £ ¤ and 1970’s, augmented by “thermal motions” of particles does predict that halos should have α 1 875. However, this relies on assumptions of spherical symmetry and slow accretion. While £ ¤ for ESIM halos these assumptions are justified, they most certainly break down for simulated halos which forms hierarchically. We speculate that our argument may apply to an “on-average” formation scenario of halos within merger-driven numerical simulations, and thereby explain why α 1 875 for NFW halos. Thus, ρ σ3 ∝ r 1 875 may be a generic feature of violent relaxation.

  14. Bimodal Formation Time Distribution for Infall Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Shi, Jingjing; Wang, Huiyuan; Mo, H. J.; Xie, Lizhi; Wang, Xiaoyu; Lapi, Andrea; Sheth, Ravi K.

    2018-04-01

    We use a 200 {h}-1 {Mpc} a-side N-body simulation to study the mass accretion history (MAH) of dark matter halos to be accreted by larger halos, which we call infall halos. We define a quantity {a}nf}\\equiv (1+{z}{{f}})/(1+{z}peak}) to characterize the MAH of infall halos, where {z}peak} and {z}{{f}} are the accretion and formation redshifts, respectively. We find that, at given {z}peak}, their MAH is bimodal. Infall halos are dominated by a young population at high redshift and by an old population at low redshift. For the young population, the {a}nf} distribution is narrow and peaks at about 1.2, independent of {z}peak}, while for the old population, the peak position and width of the {a}nf} distribution both increase with decreasing {z}peak} and are both larger than those of the young population. This bimodal distribution is found to be closely connected to the two phases in the MAHs of halos. While members of the young population are still in the fast accretion phase at z peak, those of the old population have already entered the slow accretion phase at {z}peak}. This bimodal distribution is not found for the whole halo population, nor is it seen in halo merger trees generated with the extended Press–Schechter formalism. The infall halo population at {z}peak} are, on average, younger than the whole halo population of similar masses identified at the same redshift. We discuss the implications of our findings in connection to the bimodal color distribution of observed galaxies and to the link between central and satellite galaxies.

  15. What sets the central structure of dark matter haloes?

    NASA Astrophysics Data System (ADS)

    Ogiya, Go; Hahn, Oliver

    2018-02-01

    Dark matter (DM) haloes forming near the thermal cut-off scale of the density perturbations are unique, since they are the smallest objects and form through monolithic gravitational collapse, while larger haloes contrastingly have experienced mergers. While standard cold dark matter (CDM) simulations readily produce haloes that follow the universal Navarro-Frenk-White (NFW) density profile with an inner slope, ρ ∝ r-α, with α = 1, recent simulations have found that when the free-streaming cut-off expected for the CDM model is resolved, the resulting haloes follow nearly power-law density profiles of α ∼ 1.5. In this paper, we study the formation of density cusps in haloes using idealized N-body simulations of the collapse of proto-haloes. When the proto-halo profile is initially cored due to particle free-streaming at high redshift, we universally find ∼r-1.5 profiles irrespective of the proto-halo profile slope outside the core and large-scale non-spherical perturbations. Quite in contrast, when the proto-halo has a power-law profile, then we obtain profiles compatible with the NFW shape when the density slope of the proto-halo patch is shallower than a critical value, αini ∼ 0.3, while the final slope can be steeper for αini ≳ 0.3. We further demonstrate that the r-1.5 profiles are sensitive to small-scale noise, which gradually drives them towards an inner slope of -1, where they become resilient to such perturbations. We demonstrate that the r-1.5 solutions are in hydrostatic equilibrium, largely consistent with a simple analytic model, and provide arguments that angular momentum appears to determine the inner slope.

  16. A Universal Angular Momentum Profile for Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Liao, Shihong; Chen, Jianxiong; Chu, M.-C.

    2017-07-01

    The angular momentum distribution in dark matter halos and galaxies is a key ingredient in understanding their formation. Specifically, the internal distribution of angular momenta is closely related to the formation of disk galaxies. In this article, we use halos identified from a high-resolution simulation, the Bolshoi simulation, to study the spatial distribution of specific angular momenta, j(r,θ ). We show that by stacking halos with similar masses to increase the signal-to-noise ratio, the profile can be fitted as a simple function, j{(r,θ )={j}s{\\sin }2{(θ /{θ }s)(r/{r}s)}2/(1+r/{r}s)}4, with three free parameters, {j}s,{r}s, and {θ }s. Specifically, j s correlates with the halo mass M vir as {j}s\\propto {M}{vir}2/3, r s has a weak dependence on the halo mass as {r}s\\propto {M}{vir}0.040, and {θ }s is independent of M vir. This profile agrees with that from a rigid shell model, though its origin is unclear. Our universal specific angular momentum profile j(r,θ ) is useful in modeling the angular momenta of halos. Furthermore, by using an empirical stellar mass-halo mass relation, we can infer the average angular momentum distribution of a dark matter halo. The specific angular momentum-stellar mass relation within a halo computed from our profile is shown to share a similar shape as that from the observed disk galaxies.

  17. Halo abundance matching: accuracy and conditions for numerical convergence

    NASA Astrophysics Data System (ADS)

    Klypin, Anatoly; Prada, Francisco; Yepes, Gustavo; Heß, Steffen; Gottlöber, Stefan

    2015-03-01

    Accurate predictions of the abundance and clustering of dark matter haloes play a key role in testing the standard cosmological model. Here, we investigate the accuracy of one of the leading methods of connecting the simulated dark matter haloes with observed galaxies- the halo abundance matching (HAM) technique. We show how to choose the optimal values of the mass and force resolution in large volume N-body simulations so that they provide accurate estimates for correlation functions and circular velocities for haloes and their subhaloes - crucial ingredients of the HAM method. At the 10 per cent accuracy, results converge for ˜50 particles for haloes and ˜150 particles for progenitors of subhaloes. In order to achieve this level of accuracy a number of conditions should be satisfied. The force resolution for the smallest resolved (sub)haloes should be in the range (0.1-0.3)rs, where rs is the scale radius of (sub)haloes. The number of particles for progenitors of subhaloes should be ˜150. We also demonstrate that the two-body scattering plays a minor role for the accuracy of N-body simulations thanks to the relatively small number of crossing-times of dark matter in haloes, and the limited force resolution of cosmological simulations.

  18. The prolate dark matter halo of the Andromeda galaxy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hayashi, Kohei; Chiba, Masashi, E-mail: k.hayasi@astr.tohoku.ac.jp, E-mail: chiba@astr.tohoku.ac.jp

    We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi and Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for itsmore » dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.« less

  19. Length dependence of a halo orthosis on cervical immobilization.

    PubMed

    Triggs, K J; Ballock, R T; Byrne, T; Garfin, S R

    1993-02-01

    This study was designed to observe the length dependence of a well-molded fiberglass body cast attached to a halo on motion restriction in an unstable cadaveric cervical spine. Also, by using this technique, comparison between the immobilization provided by a body cast and that provided by a standard premolded polyethylene halo vest could be made. Extreme cervical instability was created on adult cadavers. A halo ring was applied and then attached to a fiberglass body cast or to a polyethylene halo vest. Sequential lateral cervical radiographs were obtained during maximum flexion as the body cast was shortened from the level of the iliac crests to the level of the xiphoid process. Radiographic motion was also assessed within the polyethylene halo vest. Results revealed minimal motion difference as the fiberglass body cast was sequentially shortened. In contrast, motions within the polyethylene halo vest were variable. These results suggest that cervical immobilization may be relatively independent of support structure length and that immobilization can be maintained by a well-fitting halo vest extending to the level of the xiphoid process.

  20. Optimal linear reconstruction of dark matter from halo catalogues

    DOE PAGES

    Cai, Yan -Chuan; Bernstein, Gary; Sheth, Ravi K.

    2011-04-01

    The dark matter lumps (or "halos") that contain galaxies have locations in the Universe that are to some extent random with respect to the overall matter distributions. We investigate how best to estimate the total matter distribution from the locations of the halos. We derive the weight function w(M) to apply to dark-matter haloes that minimizes the stochasticity between the weighted halo distribution and its underlying mass density field. The optimal w(M) depends on the range of masses of halos being used. While the standard biased-Poisson model of the halo distribution predicts that bias weighting is optimal, the simple factmore » that the mass is comprised of haloes implies that the optimal w(M) will be a mixture of mass-weighting and bias-weighting. In N-body simulations, the Poisson estimator is up to 15× noisier than the optimal. Optimal weighting could make cosmological tests based on the matter power spectrum or cross-correlations much more powerful and/or cost effective.« less

  1. Minimizing the stochasticity of halos in large-scale structure surveys

    NASA Astrophysics Data System (ADS)

    Hamaus, Nico; Seljak, Uroš; Desjacques, Vincent; Smith, Robert E.; Baldauf, Tobias

    2010-08-01

    In recent work (Seljak, Hamaus, and Desjacques 2009) it was found that weighting central halo galaxies by halo mass can significantly suppress their stochasticity relative to the dark matter, well below the Poisson model expectation. This is useful for constraining relations between galaxies and the dark matter, such as the galaxy bias, especially in situations where sampling variance errors can be eliminated. In this paper we extend this study with the goal of finding the optimal mass-dependent halo weighting. We use N-body simulations to perform a general analysis of halo stochasticity and its dependence on halo mass. We investigate the stochasticity matrix, defined as Cij≡⟨(δi-biδm)(δj-bjδm)⟩, where δm is the dark matter overdensity in Fourier space, δi the halo overdensity of the i-th halo mass bin, and bi the corresponding halo bias. In contrast to the Poisson model predictions we detect nonvanishing correlations between different mass bins. We also find the diagonal terms to be sub-Poissonian for the highest-mass halos. The diagonalization of this matrix results in one large and one low eigenvalue, with the remaining eigenvalues close to the Poisson prediction 1/n¯, where n¯ is the mean halo number density. The eigenmode with the lowest eigenvalue contains most of the information and the corresponding eigenvector provides an optimal weighting function to minimize the stochasticity between halos and dark matter. We find this optimal weighting function to match linear mass weighting at high masses, while at the low-mass end the weights approach a constant whose value depends on the low-mass cut in the halo mass function. This weighting further suppresses the stochasticity as compared to the previously explored mass weighting. Finally, we employ the halo model to derive the stochasticity matrix and the scale-dependent bias from an analytical perspective. It is remarkably successful in reproducing our numerical results and predicts that the

  2. Convergence properties of halo merger trees; halo and substructure merger rates across cosmic history

    NASA Astrophysics Data System (ADS)

    Poole, Gregory B.; Mutch, Simon J.; Croton, Darren J.; Wyithe, Stuart

    2017-12-01

    We introduce GBPTREES: an algorithm for constructing merger trees from cosmological simulations, designed to identify and correct for pathological cases introduced by errors or ambiguities in the halo finding process. GBPTREES is built upon a halo matching method utilizing pseudo-radial moments constructed from radially sorted particle ID lists (no other information is required) and a scheme for classifying merger tree pathologies from networks of matches made to-and-from haloes across snapshots ranging forward-and-backward in time. Focusing on SUBFIND catalogues for this work, a sweep of parameters influencing our merger tree construction yields the optimal snapshot cadence and scanning range required for converged results. Pathologies proliferate when snapshots are spaced by ≲0.128 dynamical times; conveniently similar to that needed for convergence of semi-analytical modelling, as established by Benson et al. Total merger counts are converged at the level of ∼5 per cent for friends-of-friends (FoF) haloes of size np ≳ 75 across a factor of 512 in mass resolution, but substructure rates converge more slowly with mass resolution, reaching convergence of ∼10 per cent for np ≳ 100 and particle mass mp ≲ 109 M⊙. We present analytic fits to FoF and substructure merger rates across nearly all observed galactic history (z ≤ 8.5). While we find good agreement with the results presented by Fakhouri et al. for FoF haloes, a slightly flatter dependence on merger ratio and increased major merger rates are found, reducing previously reported discrepancies with extended Press-Schechter estimates. When appropriately defined, substructure merger rates show a similar mass ratio dependence as FoF rates, but with stronger mass and redshift dependencies for their normalization.

  3. Isobar analog states (IAS), double isobar analog states (DIAS), configuration states (CS), and double configuration states (DCS) in halo nuclei. Halo isomers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Izosimov, I. N., E-mail: izosimov@jinr.ru

    2015-10-15

    It has been shown that IAS, DIAS, CS, and DCS can simultaneously have n-n, n-p, and p-p halo components in their wave functions. Differences in halo structure of the excited and ground states can result in the formation of isomers (halo-isomers). Both the Borromean and tango halo types can be observed for n-p configurations of atomic nuclei. The structure of the ground and excited states with different isospin quantum number in halo like nuclei is discussed. B(Mλ) and B(Eλ) for γ-transitions in {sup 6,7,8}Li, {sup 8,9,10}Be, {sup 8,10,11}B, {sup 10,11,12,13,14}C, {sup 13,14,15,16,17}N, {sup 15,16,17,19}O, and {sup 17}F are analyzed. Specialmore » attention is given to nuclei whose ground state does not exhibit halo structure but the excited state may have one.« less

  4. Clouds Dominate the Galactic Halo

    NASA Astrophysics Data System (ADS)

    2003-01-01

    Using the exquisite sensitivity of the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT), astronomer Jay Lockman of the National Radio Astronomy Observatory (NRAO) in Green Bank, W. Va., has produced the best cross-section ever of the Milky Way Galaxy's diffuse halo of hydrogen gas. This image confirms the presence of discrete hydrogen clouds in the halo, and could help astronomers understand the origin and evolution of the rarefied atmosphere that surrounds our Galaxy. Lockman presented his findings at the American Astronomical Society meeting in Seattle, WA. Hydrogen Clouds Graphic Artist's Rendering of the Milky Way (background) with insert showing GBT image of cross-section of neutral atomic Hydrogen Credit: Kirk Woellert/National Science Foundation Patricia Smiley, NRAO. "The first observations with the Green Bank Telescope suggested that the hydrogen in the lower halo, the transition zone between the Milky Way and intergalactic space, is very clumpy," said Lockman. "The latest data confirm these results and show that instead of trailing away smoothly from the Galactic plane, a significant fraction of the hydrogen gas in the halo is concentrated in discrete clouds. There are even some filaments." Beyond the star-filled disk of the Milky Way, there exists an extensive yet diffuse halo of hydrogen gas. For years, astronomers have speculated about the origin and structure of this gas. "Even the existence of neutral hydrogen in the halo has been somewhat of a puzzle," Lockman remarked. "Unlike the Earth's atmosphere, which is hot enough to hold itself up against the force of gravity, the hydrogen in the halo is too cool to support itself against the gravitational pull of the Milky Way." Lockman points out that some additional factor has to be involved to get neutral hydrogen to such large distances from the Galactic plane. "This force could be cosmic rays, a supersonic wind, the blast waves from supernovae, or something we have not thought of

  5. The Mass and Absorption Columns of Galactic Gaseous Halos

    NASA Astrophysics Data System (ADS)

    Qu, Zhijie; Bregman, Joel N.

    2018-03-01

    The galactic gaseous halo is a gas reservoir for the interstellar medium in the galaxy disk, supplying materials for star formation. We developed a gaseous halo model connecting the galaxy disk and the gaseous halo by assuming that the star formation rate on the disk is balanced by the radiative cooling rate of the gaseous halo, including stellar feedback. In addition to a single-temperature gaseous halo in collisional ionization equilibrium, we also consider the photoionization effect and a steady-state cooling model. Photoionization is important for modifying the ion distribution in low-mass galaxies and in the outskirts of massive galaxies due to the low densities. The multiphase cooling model dominates the region within the cooling radius, where t cooling = t Hubble. Our model reproduces most of the observed high ionization state ions for a wide range of galaxy masses (i.e., O VI, O VII, Ne VIII, Mg X, and O VIII). We find that the O VI column density has a narrow range around ≈1014 cm‑2 for halo masses from M ⋆ ≈ 3 × 1010 M ⊙ to 6 × 1012 M ⊙, which is consistent with some but not all observational studies. For galaxies with halo masses ≲3 × 1011 M ⊙, photoionization produces most of the O VI, while for more massive galaxies, the O VI is from the medium that is cooling from higher temperatures. Fitting the Galactic (Milky-Way) O VII and O VIII suggests a gaseous halo model where the metallicity is ≈0.55 Z ⊙ and the gaseous halo has a maximum temperature of ≈1.9 × 106 K. This gaseous halo model does not close the census of baryonic material within R 200.

  6. Constraining the noise-free distribution of halo spin parameters

    NASA Astrophysics Data System (ADS)

    Benson, Andrew J.

    2017-11-01

    Any measurement made using an N-body simulation is subject to noise due to the finite number of particles used to sample the dark matter distribution function, and the lack of structure below the simulation resolution. This noise can be particularly significant when attempting to measure intrinsically small quantities, such as halo spin. In this work, we develop a model to describe the effects of particle noise on halo spin parameters. This model is calibrated using N-body simulations in which the particle noise can be treated as a Poisson process on the underlying dark matter distribution function, and we demonstrate that this calibrated model reproduces measurements of halo spin parameter error distributions previously measured in N-body convergence studies. Utilizing this model, along with previous measurements of the distribution of halo spin parameters in N-body simulations, we place constraints on the noise-free distribution of halo spins. We find that the noise-free median spin is 3 per cent lower than that measured directly from the N-body simulation, corresponding to a shift of approximately 40 times the statistical uncertainty in this measurement arising purely from halo counting statistics. We also show that measurement of the spin of an individual halo to 10 per cent precision requires at least 4 × 104 particles in the halo - for haloes containing 200 particles, the fractional error on spins measured for individual haloes is of order unity. N-body simulations should be viewed as the results of a statistical experiment applied to a model of dark matter structure formation. When viewed in this way, it is clear that determination of any quantity from such a simulation should be made through forward modelling of the effects of particle noise.

  7. The f ( R ) halo mass function in the cosmic web

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Braun-Bates, F. von; Winther, H.A.; Alonso, D.

    An important indicator of modified gravity is the effect of the local environment on halo properties. This paper examines the influence of the local tidal structure on the halo mass function, the halo orientation, spin and the concentration-mass relation. We use the excursion set formalism to produce a halo mass function conditional on large-scale structure. Our simple model agrees well with simulations on large scales at which the density field is linear or weakly non-linear. Beyond this, our principal result is that f ( R ) does affect halo abundances, the halo spin parameter and the concentration-mass relationship in anmore » environment-independent way, whereas we find no appreciable deviation from \\text(ΛCDM) for the mass function with fixed environment density, nor the alignment of the orientation and spin vectors of the halo to the eigenvectors of the local cosmic web. There is a general trend for greater deviation from \\text(ΛCDM) in underdense environments and for high-mass haloes, as expected from chameleon screening.« less

  8. Observation and analysis of halo current in EAST

    NASA Astrophysics Data System (ADS)

    Chen, Da-Long; Shen, Biao; Qian, Jin-Ping; Sun, You-Wen; Liu, Guang-Jun; Shi, Tong-Hui; Zhuang, Hui-Dong; Xiao, Bing-Jia

    2014-06-01

    Plasma in a typically elongated cross-section tokamak (for example, EAST) is inherently unstable against vertical displacement. When plasma loses the vertical position control, it moves downward or upward, leading to disruption, and a large halo current is generated helically in EAST typically in the scrape-off layer. When flowing into the vacuum vessel through in-vessel components, the halo current will give rise to a large J × B force acting on the vessel and the in-vessel components. In EAST VDE experiment, part of the eddy current is measured in halo sensors, due to the large loop voltage. Primary experimental data demonstrate that the halo current first lands on the outer plate and then flows clockwise, and the analysis of the information indicates that the maximum halo current estimated in EAST is about 0.4 times the plasma current and the maximum value of TPF × Ih/IP0 is 0.65, furthermore Ih/Ip0 and TPF × Ih/Ip0 tend to increase with the increase of Ip0. The test of the strong gas injection system shows good success in increasing the radiated power, which may be effective in reducing the halo current.

  9. Statistics of Dark Matter Halos from Gravitational Lensing.

    PubMed

    Jain; Van Waerbeke L

    2000-02-10

    We present a new approach to measure the mass function of dark matter halos and to discriminate models with differing values of Omega through weak gravitational lensing. We measure the distribution of peaks from simulated lensing surveys and show that the lensing signal due to dark matter halos can be detected for a wide range of peak heights. Even when the signal-to-noise ratio is well below the limit for detection of individual halos, projected halo statistics can be constrained for halo masses spanning galactic to cluster halos. The use of peak statistics relies on an analytical model of the noise due to the intrinsic ellipticities of source galaxies. The noise model has been shown to accurately describe simulated data for a variety of input ellipticity distributions. We show that the measured peak distribution has distinct signatures of gravitational lensing, and its non-Gaussian shape can be used to distinguish models with different values of Omega. The use of peak statistics is complementary to the measurement of field statistics, such as the ellipticity correlation function, and is possibly not susceptible to the same systematic errors.

  10. Unmixing the Galactic halo with RR Lyrae tagging

    NASA Astrophysics Data System (ADS)

    Belokurov, V.; Deason, A. J.; Koposov, S. E.; Catelan, M.; Erkal, D.; Drake, A. J.; Evans, N. W.

    2018-06-01

    We show that tagging RR Lyrae stars according to their location in the period-amplitude diagram can be used to shed light on the genesis of the Galactic stellar halo. The mixture of RR Lyrae of ab type, separated into classes along the lines suggested by Oosterhoff, displays a strong and coherent evolution with Galactocentric radius. The change in the RR Lyrae composition appears to coincide with the break in the halo's radial density profile at ˜25 kpc. Using simple models of the stellar halo, we establish that at least three different types of accretion events are necessary to explain the observed RRab behaviour. Given that there exists a correlation between the RRab class fraction and the total stellar content of a dwarf satellite, we hypothesize that the field halo RRab composition is controlled by the mass of the progenitor contributing the bulk of the stellar debris at the given radius. This idea is tested against a suite of cosmological zoom-in simulations of Milky Way-like stellar halo formation. Finally, we study some of the most prominent stellar streams in the Milky Way halo and demonstrate that their RRab class fractions follow the trends established previously.

  11. A Framework for Integrating Environmental and Occupational Health and Primary Care in a Postdisaster Context.

    PubMed

    Kirkland, Katherine; Sherman, Mya; Covert, Hannah; Barlet, Grace; Lichtveld, Maureen

    Integration of environmental and occupational health (EOH) into primary care settings is a critical step to addressing the EOH concerns of a community, particularly in a postdisaster context. Several barriers to EOH integration exist at the physician, patient, and health care system levels. This article presents a framework for improving the health system's capacity to address EOH after the Deepwater Horizon oil spill and illustrates its application in the Environmental and Occupational Health Education and Referral (EOHER) program. This program worked with 11 Federally Qualified Health Center systems in the Gulf Coast region to try to address the EOH concerns of community members and to assist primary care providers to better understand the impact of EOH factors on their patients' health. The framework uses a 3-pronged approach to (1) foster coordination between primary care and EOH facilities through a referral network and peer consultations, (2) increase physician capacity in EOH issues through continuing education and training, and (3) conduct outreach to community members about EOH issues. The EOHER program highlighted the importance of building strong partnerships with community members and other relevant organizations, as well as high organizational capacity and effective leadership to enable EOH integration into primary care settings. Physicians in the EOHER program were constrained in their ability to engage with EOH issues due to competing patient needs and time constraints, indicating the need to improve physicians' ability to assess which patients are at high risk for EOH exposures and to efficiently take environmental and occupational histories. This article highlights the importance of addressing EOH barriers at multiple levels and provides a model that can be applied to promote community health, particularly in the context of future natural or technological disasters.

  12. THE EFFECTS OF ANGULAR MOMENTUM ON HALO PROFILES

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lentz, Erik W; Rosenberg, Leslie J; Quinn, Thomas R, E-mail: lentze@phys.washington.edu, E-mail: ljrosenberg@phys.washington.edu, E-mail: trq@astro.washington.edu

    2016-05-10

    The near universality of DM halo density profiles provided by N -body simulations proved to be robust against changes in total mass density, power spectrum, and some forms of initial velocity dispersion. Here we study the effects of coherently spinning up an isolated DM-only progenitor on halo structure. Halos with spins within several standard deviations of the simulated mean ( λ ≲ 0.20) produce profiles with negligible deviations from the universal form. Only when the spin becomes quite large ( λ ≳ 0.20) do departures become evident. The angular momentum distribution also exhibits a near universal form, which is alsomore » independent of halo spin up to λ ≲ 0.20. A correlation between these epidemic profiles and the presence of a strong bar in the virialized halo is also observed. These bar structures bear resemblance to the radial orbit instability in the rotationless limit.« less

  13. Development of an Automatic Detection Program of Halo CMEs

    NASA Astrophysics Data System (ADS)

    Choi, K.; Park, M. Y.; Kim, J.

    2017-12-01

    The front-side halo CMEs are the major cause for large geomagnetic storms. Halo CMEs can result in damage to satellites, communication, electrical transmission lines and power systems. Thus automated techniques for detecting and analysing Halo CMEs from coronagraph data are of ever increasing importance for space weather monitoring and forecasting. In this study, we developed the algorithm that can automatically detect and do image processing the Halo CMEs in the images from the LASCO C3 coronagraph on board the SOHO spacecraft. With the detection algorithm, we derived the geometric and kinematical parameters of halo CMEs, such as source location, width, actual CME speed and arrival time at 21.5 solar radii.

  14. The massive halos of spiral galaxies

    NASA Technical Reports Server (NTRS)

    Zaritsky, Dennis; White, Simon D. M.

    1994-01-01

    We use a sample of satellite galaxies to demonstrate the existence of extended massive dark halos around spiral galaxies. Isolated spirals with rotation velocities near 250 km/s have a typical halo mass within 200 kpc of 1.5-2.6 x 10(exp 12) solar mass (90% confidence range for H(sub 0) = 75 km/s/Mpc). This result is most easily derived using standard mass estimator techniques, but such techniques do not account for the strong observational selection effects in the sample, nor for the extended mass distributions that the data imply. These complications can be addressed using scale-free models similar to those previously employed to study binary galaxies. When satellite velocities are assumed isotropic, both methods imply massive and extended halos. However, the derived masses depend sensitively on the assumed shape of satellite orbits. Furthermore, both methods ignore the fact that many of the satellites in the sample have orbital periods comparable to the Hubble time. The orbital phases of such satellites cannot be random, and their distribution in radius cannot be freely adjusted; rather these properties reflect ongoing infall onto the outer halos of their primaries. We use detailed dynamical models for halo formation to evaluate these problems, and we devise a maximum likelihood technique for estimating the parameters of such models from the data. The most strongly constrained parameter is the mass within 200-300 kpc, giving the confidence limits quoted above. The eccentricity, e, of satellite orbits is also strongly constrained, 0.50 less than e less than 0.88 at 90% confidence, implying a near-isotropic distribution of satellite velocities. The cosmic density parameter in the vicinity of our isolated halos exceeds 0.13 at 90% confidence, with preferred values exceeding 0.3.

  15. Substructure of fuzzy dark matter haloes

    NASA Astrophysics Data System (ADS)

    Du, Xiaolong; Behrens, Christoph; Niemeyer, Jens C.

    2017-02-01

    We derive the halo mass function (HMF) for fuzzy dark matter (FDM) by solving the excursion set problem explicitly with a mass-dependent barrier function, which has not been done before. We find that compared to the naive approach of the Sheth-Tormen HMF for FDM, our approach has a higher cutoff mass and the cutoff mass changes less strongly with redshifts. Using merger trees constructed with a modified version of the Lacey & Cole formalism that accounts for suppressed small-scale power and the scale-dependent growth of FDM haloes and the semi-analytic GALACTICUS code, we study the statistics of halo substructure including the effects from dynamical friction and tidal stripping. We find that if the dark matter is a mixture of cold dark matter (CDM) and FDM, there will be a suppression on the halo substructure on small scales which may be able to solve the missing satellites problem faced by the pure CDM model. The suppression becomes stronger with increasing FDM fraction or decreasing FDM mass. Thus, it may be used to constrain the FDM model.

  16. Historic halo displays as weather indicator: Criteria and examples

    NASA Astrophysics Data System (ADS)

    Neuhäuser, Dagmar L.; Neuhäuser, Ralph

    2016-04-01

    There are numerous celestial signs reported in historic records, many of them refer to atmospheric ("sub-lunar") phenomena, such as ice halos and aurorae. In an interdisciplinary collaboration between astrophysics and cultural astronomy, we noticed that celestial observations including meteorological phenomena are often misinterpreted, mostly due to missing genuine criteria: especially ice crystal halos were recorded frequently in past centuries for religious reasons, but are mistaken nowadays often for other phenomena like aurorae. Ice halo displays yield clear information on humidity and temperature in certain atmospheric layers, and thereby indicate certain weather patterns. Ancient so-called rain makers used halo observations for weather forecast; e.g., a connection between certain halo displays and rain a few day later is statistically significant. Ice halos exist around sun and moon and are reported for both (they can stay for several days): many near, middle, and far eastern records from day- and night-time include such observations with high frequency. (Partly based on publications on halos by D.L. Neuhäuser & R. Neuhäuser, available at http://www.astro.uni-jena.de/index.php/terra-astronomy.html)

  17. Testing feedback-modified dark matter haloes with galaxy rotation curves: estimation of halo parameters and consistency with ΛCDM scaling relations

    NASA Astrophysics Data System (ADS)

    Katz, Harley; Lelli, Federico; McGaugh, Stacy S.; Di Cintio, Arianna; Brook, Chris B.; Schombert, James M.

    2017-04-01

    Cosmological N-body simulations predict dark matter (DM) haloes with steep central cusps (e.g. NFW). This contradicts observations of gas kinematics in low-mass galaxies that imply the existence of shallow DM cores. Baryonic processes such as adiabatic contraction and gas outflows can, in principle, alter the initial DM density profile, yet their relative contributions to the halo transformation remain uncertain. Recent high-resolution, cosmological hydrodynamic simulations by Di Cintio et al. (DC14) predict that inner density profiles depend systematically on the ratio of stellar-to-DM mass (M*/Mhalo). Using a Markov Chain Monte Carlo approach, we test the NFW and the M*/Mhalo-dependent DC14 halo models against a sample of 147 galaxy rotation curves from the new Spitzer Photometry and Accurate Rotation Curves data set. These galaxies all have extended H I rotation curves from radio interferometry as well as accurate stellar-mass-density profiles from near-infrared photometry. The DC14 halo profile provides markedly better fits to the data compared to the NFW profile. Unlike NFW, the DC14 halo parameters found in our rotation-curve fits naturally fall within two standard deviations of the mass-concentration relation predicted by Λ cold dark matter (ΛCDM) and the stellar mass-halo mass relation inferred from abundance matching with few outliers. Halo profiles modified by baryonic processes are therefore more consistent with expectations from ΛCDM cosmology and provide better fits to galaxy rotation curves across a wide range of galaxy properties than do halo models that neglect baryonic physics. Our results offer a solution to the decade long cusp-core discrepancy.

  18. Globular Cluster Contributions to the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Martell, Sarah; Grebel, Eva; Lai, David

    2010-08-01

    The goal of this project is to confirm chemically that globular clusters are the source of as much as half the population of the Galactic halo. Using moderate-resolution spectroscopy from the SEGUE survey, we have identified a previously unknown population of halo field giants with distinctly strong CN features. CN variations are typically only observed in globular clusters, so these stars are interpreted as immigrants to the halo that originally formed in globular clusters. In one night of Keck/HIRES time, we will obtain high-quality, high- resolution spectra for five such stars, and determine abundances of O, Na, Mg, Al, alpha, iron-peak and neutron-capture elements. With this information we can state clearly whether these unusual CN-strong halo stars carry the full abundance pattern seen in CN-strong globular cluster stars, with depleted C, O, and Mg and enhanced N, Na, and Al. This type of coarse ``chemical tagging'' will allow a clearer division of the Galactic halo into contributions from globular clusters and from dwarf galaxies, and will place constraints on theoretical models of globular cluster formation and evolution.

  19. Galaxy-halo alignments in the Horizon-AGN cosmological hydrodynamical simulation

    NASA Astrophysics Data System (ADS)

    Chisari, N. E.; Koukoufilippas, N.; Jindal, A.; Peirani, S.; Beckmann, R. S.; Codis, S.; Devriendt, J.; Miller, L.; Dubois, Y.; Laigle, C.; Slyz, A.; Pichon, C.

    2017-11-01

    Intrinsic alignments of galaxies are a significant astrophysical systematic affecting cosmological constraints from weak gravitational lensing. Obtaining numerical predictions from hydrodynamical simulations of expected survey volumes is expensive, and a cheaper alternative relies on populating large dark matter-only simulations with accurate models of alignments calibrated on smaller hydrodynamical runs. This requires connecting the shapes and orientations of galaxies to those of dark matter haloes and to the large-scale structure. In this paper, we characterize galaxy-halo alignments in the Horizon-AGN cosmological hydrodynamical simulation. We compare the shapes and orientations of galaxies in the redshift range of 0 < z < 3 to those of their embedding dark matter haloes, and to the matching haloes of a twin dark-matter only run with identical initial conditions. We find that galaxy ellipticities, in general, cannot be predicted directly from halo ellipticities. The mean misalignment angle between the minor axis of a galaxy and its embedding halo is a function of halo mass, with residuals arising from the dependence of alignment on galaxy type, but not on environment. Haloes are much more strongly aligned among themselves than galaxies, and they decrease their alignment towards low redshift. Galaxy alignments compete with this effect, as galaxies tend to increase their alignment with haloes towards low redshift. We discuss the implications of these results for current halo models of intrinsic alignments and suggest several avenues for improvement.

  20. The slight spin of the old stellar halo

    NASA Astrophysics Data System (ADS)

    Deason, Alis J.; Belokurov, Vasily; Koposov, Sergey E.; Gómez, Facundo A.; Grand, Robert J.; Marinacci, Federico; Pakmor, Rüdiger

    2017-09-01

    We combine Gaia data release 1 astrometry with Sloan Digital Sky Survey (SDSS) images taken some ˜10-15 years earlier, to measure proper motions of stars in the halo of our Galaxy. The SDSS-Gaia proper motions have typical statistical errors of 2 mas yr-1 down to r ˜ 20 mag, and are robust to variations with magnitude and colour. Armed with this exquisite set of halo proper motions, we identify RR Lyrae, blue horizontal branch (BHB), and K giant stars in the halo, and measure their net rotation with respect to the Galactic disc. We find evidence for a gently rotating prograde signal (〈Vϕ〉 ˜ 5-25 km s-1) in the halo stars, which shows little variation with Galactocentric radius out to 50 kpc. The average rotation signal for the three populations is 〈Vϕ〉 = 14 ± 2 ± 10 (syst.) km s-1. There is also tentative evidence for a kinematic correlation with metallicity, whereby the metal richer BHB and K giant stars have slightly stronger prograde rotation than the metal poorer stars. Using the Auriga simulation suite, we find that the old (T >10 Gyr) stars in the simulated haloes exhibit mild prograde rotation, with little dependence on radius or metallicity, in general agreement with the observations. The weak halo rotation suggests that the Milky Way has a minor in situ halo component, and has undergone a relatively quiet accretion history.

  1. The Prevalence of the 22 deg Halo in Cirrus Clouds

    NASA Technical Reports Server (NTRS)

    Diedenhoven, vanBastiaan

    2014-01-01

    Halos at 22 deg from the sun attributed to randomly-orientated, pristine hexagonal crystals are frequently observed through ice clouds. These frequent sightings of halos formed by pristine crystals pose an apparent inconsistency with the dominance of distorted, nonpristine ice crystals indicated by in situ and remote sensing data. Furthermore, the 46 deg halo, which is associated with pristine hexagonal crystals as well, is observed far less frequently than the 22 deg halo. Considering that plausible mechanisms that could cause crystal distortion such as aggregation, sublimation, riming and collisions are stochastic processes that likely lead to distributions of crystals with varying distortion levels, here the presence of the 22 deg and 46 deg halo features in phase functions of mixtures of pristine and distorted hexagonal ice crystals is examined. We conclude that the 22 deg halo feature is generally present if the contribution by pristine crystals to the total scattering cross section is greater than only about 10% in the case of compact particles or columns, and greater than about 40% for plates. The 46 deg halo feature is present only if the mean distortion level is low and the contribution of pristine crystals to the total scattering cross section is above about 20%, 50% and 70%, in the case of compact crystals, plates and columns, respectively. These results indicate that frequent sightings of 22 deg halos are not inconsistent with the observed dominance of distorted, non-pristine ice crystals. Furthermore, the low mean distortion levels and large contributions by pristine crystals needed to produce the 461 halo features provide a potential explanation of the common sighting of the 22 deg halo without any detectable 46 deg halo.

  2. Diverse stellar haloes in nearby Milky Way mass disc galaxies

    NASA Astrophysics Data System (ADS)

    Harmsen, Benjamin; Monachesi, Antonela; Bell, Eric F.; de Jong, Roelof S.; Bailin, Jeremy; Radburn-Smith, David J.; Holwerda, Benne W.

    2017-04-01

    We have examined the resolved stellar populations at large galactocentric distances along the minor axis (from 10 kpc up to between 40 and 75 kpc), with limited major axis coverage, of six nearby highly inclined Milky Way (MW) mass disc galaxies using Hubble Space Telescope data from the Galaxy haloes, Outer discs, Substructure, Thick discs, and Star clusters (GHOSTS) survey. We select red giant branch stars to derive stellar halo density profiles. The projected minor axis density profiles can be approximated by power laws with projected slopes of -2 to -3.7 and a diversity of stellar halo masses of 1-6 × 109 M⊙, or 2-14 per cent of the total galaxy stellar masses. The typical intrinsic scatter around a smooth power-law fit is 0.05-0.1 dex owing to substructure. By comparing the minor and major axis profiles, we infer projected axis ratios c/a at ˜25 kpc between 0.4and0.75. The GHOSTS stellar haloes are diverse, lying between the extremes charted out by the (rather atypical) haloes of the MW and M31. We find a strong correlation between the stellar halo metallicities and the stellar halo masses. We compare our results with cosmological models, finding good agreement between our observations and accretion-only models where the stellar haloes are formed by the disruption of dwarf satellites. In particular, the strong observed correlation between stellar halo metallicity and mass is naturally reproduced. Low-resolution hydrodynamical models have unrealistically high stellar halo masses. Current high-resolution hydrodynamical models appear to predict stellar halo masses somewhat higher than observed but with reasonable metallicities, metallicity gradients, and density profiles.

  3. Nucleoid halo expansion indirectly measures DNA damage in single cells.

    PubMed

    Thomas, E A; Thomas, C A

    1989-07-01

    A simple test has been developed that measures how much DNA damage has occurred in a single mammalian cell. The procedure is based on the microscopic examination of "halos" of nucleoids that adhere to coverslips. Nucleoids are produced by flowing salt solutions containing detergents over the attached cells. The nucleoid halos are thought to be a tangle of loops of free DNA that emanate from the remnants of the nucleus. When visualized by staining with ethidium bromide the nucleoid halos first expand, and then contract as the concentration of ethidium increases. Exposure of nucleoids to very low levels of DNA chain-breaking treatments results in the incremental expansion of the halos to a maximum of 15 microns or more. Our assay is based upon quantitating the degree of halo expansion. If intact cells are exposed to DNA-damaging treatments, then allowed increasing periods of post-treatment growth before forming nucleoids, the DNA repair processes result first in expanded and then in contracted halos. By admixing a supercoiled plasma DNA of known length (38 kb) to nucleoids with contracted halos, the fractional halo expansion and the fraction of surviving plasmid supercoils can be measured from the same solution. Use of photodynamic DNA damage showed that the halo expansion was 11.6 times more sensitive than plasmid relaxation. Use of gamma-irradiation showed that the halo expansion was 3.6 times more sensitive than plasmid relaxation. The latter value demonstrates that one break per 137,000 bp results in the expansion of the halos to 63% of their maximal value. We estimate that this method will detect about 5000 breaks per nucleus containing 5 x 10(9) bp.

  4. Halo-independent direct detection analyses without mass assumptions

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Anderson, Adam J.; Fox, Patrick J.; Kahn, Yonatan

    2015-10-01

    Results from direct detection experiments are typically interpreted by employing an assumption about the dark matter velocity distribution, with results presented in the m{sub χ}−σ{sub n} plane. Recently methods which are independent of the DM halo velocity distribution have been developed which present results in the v{sub min}− g-tilde plane, but these in turn require an assumption on the dark matter mass. Here we present an extension of these halo-independent methods for dark matter direct detection which does not require a fiducial choice of the dark matter mass. With a change of variables from v{sub min} to nuclear recoil momentummore » (p{sub R}), the full halo-independent content of an experimental result for any dark matter mass can be condensed into a single plot as a function of a new halo integral variable, which we call h-tilde (p{sub R}). The entire family of conventional halo-independent g-tilde (v{sub min}) plots for all DM masses are directly found from the single h-tilde (p{sub R}) plot through a simple rescaling of axes. By considering results in h-tilde (p{sub R}) space, one can determine if two experiments are inconsistent for all masses and all physically possible halos, or for what range of dark matter masses the results are inconsistent for all halos, without the necessity of multiple g-tilde (v{sub min}) plots for different DM masses. We conduct a sample analysis comparing the CDMS II Si events to the null results from LUX, XENON10, and SuperCDMS using our method and discuss how the results can be strengthened by imposing the physically reasonable requirement of a finite halo escape velocity.« less

  5. Halo-independent direct detection analyses without mass assumptions

    DOE PAGES

    Anderson, Adam J.; Fox, Patrick J.; Kahn, Yonatan; ...

    2015-10-06

    Results from direct detection experiments are typically interpreted by employing an assumption about the dark matter velocity distribution, with results presented in the m χ – σ n plane. Recently methods which are independent of the DM halo velocity distribution have been developed which present results in the v min – g ~ plane, but these in turn require an assumption on the dark matter mass. Here we present an extension of these halo-independent methods for dark matter direct detection which does not require a fiducial choice of the dark matter mass. With a change of variables from v minmore » to nuclear recoil momentum (p R), the full halo-independent content of an experimental result for any dark matter mass can be condensed into a single plot as a function of a new halo integral variable, which we call tilde h(p R). The entire family of conventional halo-independent tilde g ~(v min) plots for all DM masses are directly found from the single tilde h ~(p R) plot through a simple rescaling of axes. By considering results in tildeh ~(p R) space, one can determine if two experiments are inconsistent for all masses and all physically possible halos, or for what range of dark matter masses the results are inconsistent for all halos, without the necessity of multiple tilde g ~(v min) plots for different DM masses. As a result, we conduct a sample analysis comparing the CDMS II Si events to the null results from LUX, XENON10, and SuperCDMS using our method and discuss how the results can be strengthened by imposing the physically reasonable requirement of a finite halo escape velocity.« less

  6. Abort Options for Human Missions to Earth-Moon Halo Orbits

    NASA Technical Reports Server (NTRS)

    Jesick, Mark C.

    2013-01-01

    Abort trajectories are optimized for human halo orbit missions about the translunar libration point (L2), with an emphasis on the use of free return trajectories. Optimal transfers from outbound free returns to L2 halo orbits are numerically optimized in the four-body ephemeris model. Circumlunar free returns are used for direct transfers, and cislunar free returns are used in combination with lunar gravity assists to reduce propulsive requirements. Trends in orbit insertion cost and flight time are documented across the southern L2 halo family as a function of halo orbit position and free return flight time. It is determined that the maximum amplitude southern halo incurs the lowest orbit insertion cost for direct transfers but the maximum cost for lunar gravity assist transfers. The minimum amplitude halo is the most expensive destination for direct transfers but the least expensive for lunar gravity assist transfers. The on-orbit abort costs for three halos are computed as a function of abort time and return time. Finally, an architecture analysis is performed to determine launch and on-orbit vehicle requirements for halo orbit missions.

  7. Dark energy and extended dark matter halos

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.

    2012-03-01

    The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ωm = 0.27. Independently, the local mean density is estimated to be Ωloc = 0.08-0.23 from recent data on galaxy groups at redshifts up to z = 0.01-0.03 (as published by Crook et al. 2007, ApJ, 655, 790 and Makarov & Karachentsev 2011, MNRAS, 412, 2498). If the lower values of Ωloc are reliable, as Makarov & Karachentsev and some other observers prefer, does this mean that the Local Universe of 100-300 Mpc across is an underdensity in the cosmic matter distribution? Or could it nevertheless be representative of the mean cosmic density or even be an overdensity due to the Local Supercluster therein. We focus on dark matter halos of groups of galaxies and check how much dark mass the invisible outer layers of the halos are able to host. The outer layers are usually devoid of bright galaxies and cannot be seen at large distances. The key factor which bounds the size of an isolated halo is the local antigravity produced by the omnipresent background of dark energy. A gravitationally bound halo does not extend beyond the zero-gravity surface where the gravity of matter and the antigravity of dark energy balance, thus defining a natural upper size of a system. We use our theory of local dynamical effects of dark energy to estimate the maximal sizes and masses of the extended dark halos. Using data from three recent catalogs of galaxy groups, we show that the calculated mass bounds conform with the assumption that a significant amount of dark matter is located in the invisible outer parts of the extended halos, sufficient to fill the gap between the observed and expected local matter density. Nearby groups of galaxies and the Virgo cluster have dark halos which seem to extend up to their zero-gravity surfaces. If the extended halo is a common feature of gravitationally bound systems on scales of galaxy groups and clusters, the Local Universe could be typical or even

  8. Dynamical Constraints On The Galaxy-Halo Connection

    NASA Astrophysics Data System (ADS)

    Desmond, Harry

    2017-07-01

    Dark matter halos comprise the bulk of the universe's mass, yet must be probed by the luminous galaxies that form within them. A key goal of modern astrophysics, therefore, is to robustly relate the visible and dark mass, which to first order means relating the properties of galaxies and halos. This may be expected not only to improve our knowledge of galaxy formation, but also to enable high-precision cosmological tests using galaxies and hence maximise the utility of future galaxy surveys. As halos are inaccessible to observations - as galaxies are to N-body simulations - this relation requires an additional modelling step.The aim of this thesis is to develop and evaluate models of the galaxy-halo connection using observations of galaxy dynamics. In particular, I build empirical models based on the technique of halo abundance matching for five key dynamical scaling relations of galaxies - the Tully-Fisher, Faber-Jackson, mass-size and mass discrepancy-acceleration relations, and Fundamental Plane - which relate their baryon distributions and rotation or velocity dispersion profiles. I then develop a statistical scheme based on approximate Bayesian computation to compare the predicted and measured values of a number of summary statistics describing the relations' important features. This not only provides quantitative constraints on the free parameters of the models, but also allows absolute goodness-of-fit measures to be formulated. I find some features to be naturally accounted for by an abundance matching approach and others to impose new constraints on the galaxy-halo connection; the remainder are challenging to account for and may imply galaxy-halo correlations beyond the scope of basic abundance matching.Besides providing concrete statistical tests of specific galaxy formation theories, these results will be of use for guiding the inputs of empirical and semi-analytic galaxy formation models, which require galaxy-halo correlations to be imposed by hand. As

  9. The framework of clinical occupational medicine to provide new insight for workaholism.

    PubMed

    Durand-Moreau, Quentin; LE Deun, Clarisse; Lodde, Brice; Dewitte, Jean-Dominique

    2018-05-17

    There is no single agreed definition of workaholism. Most interventions proposed for people suffering from workaholism target individuals. There is a paucity of descriptions of workplace risk factors. Our study examines case reports of patients suffering from workaholism with a focus on the role of the workplace. We describe case reports from patients of the Occupational Disease Centre in Brest, France between 2013 and 2016. Consultations were conducted within the framework of clinical occupational medicine with a focus on real work situations. Diagnoses of workaholism were made according to Goodman's criteria. The situations of four patients are reported. Three of these suffered from workaholism: a 41-year-old sales representative, a 51-year-old nurse in progressive care and a 30-year-old saleswoman. The last case report concerns the situation of a 41-year-old team leader who was first suspected to have workaholism, but later diagnosed with a bipolar disorder. Bipolar disorders and other addictive behaviours should be assessed. An exclusive variable remuneration and work organization that could induce confusion between the working and personal environment both constitute risk factors. Some patients were ambivalent to their condition and willing to go on working despite ill-health issues. These elements could be integrated into further research on workaholism.

  10. Using the Framework for Health Promotion Action to address staff perceptions of occupational health and safety at a fly-in/fly-out mine in north-west Queensland.

    PubMed

    Devine, Susan G; Muller, Reinhold; Carter, Anthony

    2008-12-01

    An exploratory descriptive study was undertaken to identify staff perceptions of the types and sources of occupational health and safety hazards at a remote fly-in-fly-out minerals extraction and processing plant in northwest Queensland. Ongoing focus groups with all sectors of the operation were conducted concurrently with quantitative research studies from 2001 to 2005. Action research processes were used with management and staff to develop responses to identified issues. Staff identified and generated solutions to the core themes of: health and safety policies and procedures; chemical exposures; hydration and fatigue. The Framework for Health Promotion Action was applied to ensure a comprehensive and holistic response to identified issues. Participatory processes using an action research framework enabled a deep understanding of staff perceptions of occupational health and safety hazards in this setting. The Framework for Health Promotion provided a relevant and useful tool to engage with staff and develop solutions to perceived occupational health and safety issues in the workplace.

  11. Velocity bias in the distribution of dark matter halos

    NASA Astrophysics Data System (ADS)

    Baldauf, Tobias; Desjacques, Vincent; Seljak, Uroš

    2015-12-01

    The standard formalism for the coevolution of halos and dark matter predicts that any initial halo velocity bias rapidly decays to zero. We argue that, when the purpose is to compute statistics like power spectra etc., the coupling in the momentum conservation equation for the biased tracers must be modified. Our new formulation predicts the constancy in time of any statistical halo velocity bias present in the initial conditions, in agreement with peak theory. We test this prediction by studying the evolution of a conserved halo population in N -body simulations. We establish that the initial simulated halo density and velocity statistics show distinct features of the peak model and, thus, deviate from the simple local Lagrangian bias. We demonstrate, for the first time, that the time evolution of their velocity is in tension with the rapid decay expected in the standard approach.

  12. The age of the Milky Way inner halo.

    PubMed

    Kalirai, Jason S

    2012-05-30

    The Milky Way galaxy has several components, such as the bulge, disk and halo. Unravelling the assembly history of these stellar populations is often restricted because of difficulties in measuring accurate ages for low-mass, hydrogen-burning stars. Unlike these progenitors, white dwarf stars, the 'cinders' of stellar evolution, are remarkably simple objects and their fundamental properties can be measured with little ambiguity. Here I report observations of newly formed white dwarf stars in the halo of the Milky Way, and a separate analysis of archival data in the well studied 12.5-billion-year-old globular cluster Messier 4. I measure the mass distribution of the remnant stars and invert the stellar evolution process to develop a mathematical relation that links this final stellar mass to the mass of their immediate progenitors, and therefore to the age of the parent population. By applying this technique to a small sample of four nearby and kinematically confirmed halo white dwarf stars, I calculate the age of local field halo stars to be 11.4 ± 0.7 billion years. The oldest globular clusters formed 13.5 billion years ago. Future observations of newly formed white dwarf stars in the halo could be used to reduce the uncertainty, and to probe relative differences between the formation times of the youngest globular clusters and the inner halo.

  13. ZOMG - III. The effect of halo assembly on the satellite population

    NASA Astrophysics Data System (ADS)

    Garaldi, Enrico; Romano-Díaz, Emilio; Borzyszkowski, Mikolaj; Porciani, Cristiano

    2018-01-01

    We use zoom hydrodynamical simulations to investigate the properties of satellites within galaxy-sized dark-matter haloes with different assembly histories. We consider two classes of haloes at redshift z = 0: 'stalled' haloes that assembled at z > 1 and 'accreting' ones that are still forming nowadays. Previously, we showed that the stalled haloes are embedded within thick filaments of the cosmic web, while the accreting ones lie where multiple thin filaments converge. We find that satellites in the two classes have both similar and different properties. Their mass spectra, radial count profiles, baryonic and stellar content, and the amount of material they shed are indistinguishable. However, the mass fraction locked in satellites is substantially larger for the accreting haloes as they experience more mergers at late times. The largest difference is found in the satellite kinematics. Substructures fall towards the accreting haloes along quasi-radial trajectories whereas an important tangential velocity component is developed, before accretion, while orbiting the filament that surrounds the stalled haloes. Thus, the velocity anisotropy parameter of the satellites (β) is positive for the accreting haloes and negative for the stalled ones. This signature enables us to tentatively categorize the Milky Way halo as stalled based on a recent measurement of β. Half of our haloes contain clusters of satellites with aligned orbital angular momenta corresponding to flattened structures in space. These features are not driven by baryonic physics and are only found in haloes hosting grand-design spiral galaxies, independently of their assembly history.

  14. The globular cluster-dark matter halo connection

    NASA Astrophysics Data System (ADS)

    Boylan-Kolchin, Michael

    2017-12-01

    I present a simple phenomenological model for the observed linear scaling of the stellar mass in old globular clusters (GCs) with z = 0 halo mass in which the stellar mass in GCs scales linearly with progenitor halo mass at z = 6 above a minimum halo mass for GC formation. This model reproduces the observed MGCs-Mhalo relation at z = 0 and results in a prediction for the minimum halo mass at z = 6 required for hosting one GC: Mmin(z = 6) = 1.07 × 109 M⊙. Translated to z = 0, the mean threshold mass is Mhalo(z = 0) ≈ 2 × 1010 M⊙. I explore the observability of GCs in the reionization era and their contribution to cosmic reionization, both of which depend sensitively on the (unknown) ratio of GC birth mass to present-day stellar mass, ξ. Based on current detections of z ≳ 6 objects with M1500<-17, values of ξ > 10 are strongly disfavoured; this, in turn, has potentially important implications for GC formation scenarios. Even for low values of ξ, some observed high-z galaxies may actually be GCs, complicating estimates of reionization-era galaxy ultraviolet luminosity functions and constraints on dark matter models. GCs are likely important reionization sources if 5 ≲ ξ ≲ 10. I also explore predictions for the fraction of accreted versus in situ GCs in the local Universe and for descendants of systems at the halo mass threshold of GC formation (dwarf galaxies). An appealing feature of the model presented here is the ability to make predictions for GC properties based solely on dark matter halo merger trees.

  15. The immitigable nature of assembly bias: the impact of halo definition on assembly bias

    NASA Astrophysics Data System (ADS)

    Villarreal, Antonio S.; Zentner, Andrew R.; Mao, Yao-Yuan; Purcell, Chris W.; van den Bosch, Frank C.; Diemer, Benedikt; Lange, Johannes U.; Wang, Kuan; Campbell, Duncan

    2017-11-01

    Dark matter halo clustering depends not only on halo mass, but also on other properties such as concentration and shape. This phenomenon is known broadly as assembly bias. We explore the dependence of assembly bias on halo definition, parametrized by spherical overdensity parameter, Δ. We summarize the strength of concentration-, shape-, and spin-dependent halo clustering as a function of halo mass and halo definition. Concentration-dependent clustering depends strongly on mass at all Δ. For conventional halo definitions (Δ ∼ 200 - 600 m), concentration-dependent clustering at low mass is driven by a population of haloes that is altered through interactions with neighbouring haloes. Concentration-dependent clustering can be greatly reduced through a mass-dependent halo definition with Δ ∼ 20 - 40 m for haloes with M200 m ≲ 1012 h-1M⊙. Smaller Δ implies larger radii and mitigates assembly bias at low mass by subsuming altered, so-called backsplash haloes into now larger host haloes. At higher masses (M200 m ≳ 1013 h-1M⊙) larger overdensities, Δ ≳ 600 m, are necessary. Shape- and spin-dependent clustering are significant for all halo definitions that we explore and exhibit a relatively weaker mass dependence. Generally, both the strength and the sense of assembly bias depend on halo definition, varying significantly even among common definitions. We identify no halo definition that mitigates all manifestations of assembly bias. A halo definition that mitigates assembly bias based on one halo property (e.g. concentration) must be mass dependent. The halo definitions that best mitigate concentration-dependent halo clustering do not coincide with the expected average splashback radii at fixed halo mass.

  16. Testing approximate predictions of displacements of cosmological dark matter halos

    NASA Astrophysics Data System (ADS)

    Munari, Emiliano; Monaco, Pierluigi; Koda, Jun; Kitaura, Francisco-Shu; Sefusatti, Emiliano; Borgani, Stefano

    2017-07-01

    We present a test to quantify how well some approximate methods, designed to reproduce the mildly non-linear evolution of perturbations, are able to reproduce the clustering of DM halos once the grouping of particles into halos is defined and kept fixed. The following methods have been considered: Lagrangian Perturbation Theory (LPT) up to third order, Truncated LPT, Augmented LPT, MUSCLE and COLA. The test runs as follows: halos are defined by applying a friends-of-friends (FoF) halo finder to the output of an N-body simulation. The approximate methods are then applied to the same initial conditions of the simulation, producing for all particles displacements from their starting position and velocities. The position and velocity of each halo are computed by averaging over the particles that belong to that halo, according to the FoF halo finder. This procedure allows us to perform a well-posed test of how clustering of the matter density and halo density fields are recovered, without asking to the approximate method an accurate reconstruction of halos. We have considered the results at z=0,0.5,1, and we have analysed power spectrum in real and redshift space, object-by-object difference in position and velocity, density Probability Distribution Function (PDF) and its moments, phase difference of Fourier modes. We find that higher LPT orders are generally able to better reproduce the clustering of halos, while little or no improvement is found for the matter density field when going to 2LPT and 3LPT. Augmentation provides some improvement when coupled with 2LPT, while its effect is limited when coupled with 3LPT. Little improvement is brought by MUSCLE with respect to Augmentation. The more expensive particle-mesh code COLA outperforms all LPT methods, and this is true even for mesh sizes as large as the inter-particle distance. This test sets an upper limit on the ability of these methods to reproduce the clustering of halos, for the cases when these objects are

  17. Lithium in halo stars from standard stellar evolution

    NASA Technical Reports Server (NTRS)

    Deliyannis, Constantine P.; Demarque, Pierre; Kawaler, Steven D.

    1990-01-01

    A grid has been constructed of theoretical evolution sequences of models for low-metallicity stars from the premain-sequence to the giant branch phases. The grid is used to study the history of surface Li abundance during standard stellar evolution. The Li-7 observations of halo stars by Spite and Spite (1982) and subsequent observations are synthesized to separate the halo stars by age. The theory of surface Li abundance is illustrated by following the evolution of a reference halo star model from the contracting fully convective premain sequence to the giant branch phase. The theoretical models are compared with observed Li abundances. The results show that the halo star lithium abundances can be explained in the context of standard stellar evolution theory using completely standard assumptions and physics.

  18. Chemical Cartography. I. A Carbonicity Map of the Galactic Halo

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lee, Young Sun; Kim, Young Kwang; Beers, Timothy C.

    We present the first map of carbonicity, [C/Fe], for the halo system of the Milky Way, based on a sample of over 100,000 main-sequence turnoff stars with available spectroscopy from the Sloan Digital Sky Survey. This map, which explores distances up to 15 kpc from the Sun, reveals clear evidence for the dual nature of the Galactic halo, based on the spatial distribution of stellar carbonicity. The metallicity distribution functions of stars in the inner- and outer-halo regions of the carbonicity map reproduce those previously argued to arise from contributions of the inner- and outer-halo populations, with peaks at [Fe/H]more » = −1.5 and −2.2, respectively. From consideration of the absolute carbon abundances for our sample, A (C), we also confirm that the carbon-enhanced metal-poor (CEMP) stars in the outer-halo region exhibit a higher frequency of CEMP-no stars (those with no overabundances of heavy neutron-capture elements) than of CEMP- s stars (those with strong overabundances of elements associated with the s -process), whereas the stars in the inner-halo region exhibit a higher frequency of CEMP- s stars. We argue that the contrast in the behavior of the CEMP-no and CEMP- s fractions in these regions arises from differences in the mass distributions of the mini-halos from which the stars of the inner- and outer-halo populations formed, which gives rise in turn to the observed dichotomy of the Galactic halo.« less

  19. Hierarchical formation of dark matter halos and the free streaming scale

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ishiyama, Tomoaki, E-mail: ishiyama@ccs.tsukuba.ac.jp

    2014-06-10

    The smallest dark matter halos are formed first in the early universe. According to recent studies, the central density cusp is much steeper in these halos than in larger halos and scales as ρ∝r {sup –(1.5-1.3)}. We present the results of very large cosmological N-body simulations of the hierarchical formation and evolution of halos over a wide mass range, beginning from the formation of the smallest halos. We confirmed early studies that the inner density cusps are steeper in halos at the free streaming scale. The cusp slope gradually becomes shallower as the halo mass increases. The slope of halosmore » 50 times more massive than the smallest halo is approximately –1.3. No strong correlation exists between the inner slope and the collapse epoch. The cusp slope of halos above the free streaming scale seems to be reduced primarily due to major merger processes. The concentration, estimated at the present universe, is predicted to be 60-70, consistent with theoretical models and earlier simulations, and ruling out simple power law mass-concentration relations. Microhalos could still exist in the present universe with the same steep density profiles.« less

  20. The Spin and Orientation of Dark Matter Halos Within Cosmic Filaments

    NASA Astrophysics Data System (ADS)

    Zhang, Youcai; Yang, Xiaohu; Faltenbacher, Andreas; Springel, Volker; Lin, Weipeng; Wang, Huiyuan

    2009-11-01

    Clusters, filaments, sheets, and voids are the building blocks of the cosmic web. Forming dark matter halos respond to these different large-scale environments, and this in turn affects the properties of galaxies hosted by the halos. It is therefore important to understand the systematic correlations of halo properties with the morphology of the cosmic web, as this informs both about galaxy formation physics and possible systematics of weak lensing studies. In this study, we present and compare two distinct algorithms for finding cosmic filaments and sheets, a task which is far less well established than the identification of dark matter halos or voids. One method is based on the smoothed dark matter density field and the other uses the halo distributions directly. We apply both techniques to one high-resolution N-body simulation and reconstruct the filamentary/sheet like network of the dark matter density field. We focus on investigating the properties of the dark matter halos inside these structures, in particular, on the directions of their spins and the orientation of their shapes with respect to the directions of the filaments and sheets. We find that both the spin and the major axes of filament halos with masses lsim1013 h -1 M sun are preferentially aligned with the direction of the filaments. The spins and major axes of halos in sheets tend to lie parallel to the sheets. There is an opposite mass dependence of the alignment strength for the spin (negative) and major (positive) axes, i.e. with increasing halo mass the major axis tends to be more strongly aligned with the direction of the filament, whereas the alignment between halo spin and filament becomes weaker with increasing halo mass. The alignment strength as a function of the distance to the most massive node halo indicates that there is a transit large-scale environment impact: from the two-dimensional collapse phase of the filament to the three-dimensional collapse phase of the cluster/node halo at

  1. Unveiling the stellar halo with TGAS

    NASA Astrophysics Data System (ADS)

    Veljanoski, Jovan; Posti, L.; Helmi, A.; Breddels, M. A.

    2018-04-01

    The detailed study of the Galactic stellar halo may hold the key to unlocking the assembly history of the Milky Way. Here, we present a machine learning model for selecting metal poor stars from the TGAS catalogue using 5 dimensional phase-space information, coupled with optical and near-IR photometry. We characterise the degree of substructure in our halo sample in the Solar neighbourhood by measuring the velocity correlation function.

  2. The segregation of baryons and dark matter during halo assembly

    NASA Astrophysics Data System (ADS)

    Liao, Shihong; Gao, Liang; Frenk, Carlos S.; Guo, Qi; Wang, Jie

    2017-09-01

    The standard galaxy formation theory assumes that baryons and dark matter are initially well mixed before becoming segregated due to radiative cooling. We use non-radiative hydrodynamical simulations to explicitly examine this assumption and find that baryons and dark matter can also be segregated due to different characteristics of gas and dark matter during the buildup of the halo. As a result, baryons in many haloes do not originate from the same Lagrangian region as the dark matter. When using the fraction of corresponding dark matter and gas particles in the initial conditions (the 'paired fraction') as a proxy of the dark matter and gas segregation strength of a halo, on average about 25 per cent of the baryonic and dark matter of the final halo are segregated in the initial conditions. This is at odds with the assumption of the standard galaxy formation model. A consequence of this effect is that the baryons and dark matter of the same halo initially experience different tidal torques and thus their angular momentum vectors are often misaligned. The degree of the misalignment is largely preserved during later halo assembly and can be understood with the tidal torque theory. The result challenges the precision of some semi-analytical approaches that utilize dark matter halo merger trees to infer properties of gas associated with dark matter haloes.

  3. Cold dark matter. 1: The formation of dark halos

    NASA Technical Reports Server (NTRS)

    Gelb, James M.; Bertschinger, Edmund

    1994-01-01

    We use numerical simulations of critically closed cold dark matter (CDM) models to study the effects of numerical resolution on observable quantities. We study simulations with up to 256(exp 3) particles using the particle-mesh (PM) method and with up to 144(exp 3) particles using the adaptive particle-particle-mesh (P3M) method. Comparisons of galaxy halo distributions are made among the various simulations. We also compare distributions with observations, and we explore methods for identifying halos, including a new algorithm that finds all particles within closed contours of the smoothed density field surrounding a peak. The simulated halos show more substructure than predicted by the Press-Schechter theory. We are able to rule out all omega = 1 CDM models for linear amplitude sigma(sub 8) greater than or approximately = 0.5 because the simulations produce too many massive halos compared with the observations. The simulations also produce too many low-mass halos. The distribution of halos characterized by their circular velocities for the P3M simulations is in reasonable agreement with the observations for 150 km/s less than or = V(sub circ) less than or = 350 km/s.

  4. Jupiter Ring Halo

    NASA Image and Video Library

    1998-03-26

    A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (km) per picture element (pixel) along the rings; however, because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow peering back toward the Sun; the ring was approximately 2,300,000 kilometers (km) away. The arc on the far right of the image is produced by sunlight scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age. Jupiter's ring system is composed of three parts -- a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, which lies exterior to the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the far left side of the figure. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow. A faint mist of particles can be seen above and below the main rings; this vertically extended, toroidal "halo" is unusual in planetary rings, and is probably caused by electromagnetic forces which can push small grains out of the ring plane. Halo material is present across this entire image, implying that it reaches more than 27,000 km above the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic. In order to accentuate faint features in the image, different brightnesses are shown through color, with the brightest being

  5. Dust-Driven Halos on the Martian South Polar Residual CAP

    NASA Astrophysics Data System (ADS)

    Becerra, P.; Byrne, S.; Brown, A. J.

    2013-12-01

    The CO2 ice South Polar Residual Cap (SPRC) on Mars may be a sensitive indicator of inter-annual planetary climate variability. Imaging by HiRISE [1], and CTX [2] found that many scarps and pits in the 'Swiss cheese terrain' [3] of the SPRC exhibited a bright 'halo' around their edges. These halos appeared during Martian southern summer in Mars Year 28 (MY28, [4]), and have been observed in only one of eight mars years for which observations at high enough resolution exist. We hypothesize that the formation of these features is linked to the late-summer global dust storm of MY28 and report on observations and formation models. We surveyed HiRISE, CTX, and CRISM [5] data to constrain the optical properties and composition of the halos, as well as their time of appearance and location within the SPRC. The halos appeared throughout most of the surface area of the SPRC between Ls 280° and 330° in MY28. The widest portions of the halos occurred adjacent to north-facing walls, and the brightest parts adjacent to sun-facing walls, which points to a connection between insolation and halo appearance. CRISM spectral products rule out the presence of water ice as a factor in the halos' appearance. These data also imply larger CO2 ice grain sizes where the bright halos were seen, which are normally associated with lower, rather than higher, albedos [6]. Thus, we also ruled out CO2 ice grain size differences as the main cause for the halos. The remaining possibility is that the halos appeared due to differences in dust content between the terrain adjacent to the pit walls and the surrounding ice. To investigate this we made a Hapke [7] surface reflectance model in which the CO2 ice grain size, dust volumetric content and dust particle size were free parameters. We used the HiRISE and CRISM bandpass coefficients to simulate HiRISE I/F values and CRISM spectra, and attempted to match the HiRISE RED I/F, HiRISE BG/RED color ratio, and the CRISM 1.43 μm band depths. A self

  6. Dark Matter Halos with VIRUS-P

    NASA Astrophysics Data System (ADS)

    Murphy, Jeremy; Gebhardt, K.

    2010-05-01

    We present new, two-dimensional stellar kinematic data on several of the most massive galaxies in the local universe. These data were taken with the integral field spectrograph, VIRUS-P, and extend to unprecedented radial distances. Once robust stellar kinematics are in hand, we run orbit-based axisymmetric dynamical models in order to constrain the stellar mass-to-light ratio and dark matter halo parameters. We have run a large set of dynamical models on the second rank galaxy in the Virgo cluster, M87, and find clear evidence for a massive dark matter halo. The two-dimensional stellar kinematics for several of our other targets, all first and second rank galaxies, are also presented. Dark matter halos are known to dominate the mass profile of elliptical galaxies somewhere between one to two effective radii, yet due to the low surface brightness at these radial distances, determining stellar dynamics is technologically challenging. To overcome this, constraints on the dark matter halo are often made with planetary nebulae or globular clusters at large radii. However, as results from different groups have returned contradictory results, it remains unclear whether different dynamical tracers always follow the stellar kinematics. Due to VIRUS-P's large field of view and on-sky fiber diameter, we are able to determine stellar kinematics at radial distances that overlap with other dynamical tracers. Understanding what the dynamics of stars, planetary nebula and globular clusters tell us about both the extent of the dark matter halo profile and the formation histories of the largest elliptical galaxies is a primary science driver for this work.

  7. What is the Milky Way outer halo made of?. High resolution spectroscopy of distant red giants

    NASA Astrophysics Data System (ADS)

    Battaglia, G.; North, P.; Jablonka, P.; Shetrone, M.; Minniti, D.; Díaz, M.; Starkenburg, E.; Savoy, M.

    2017-12-01

    In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this work we focus on the outer regions of the Milky Way stellar halo, by determining chemical abundances of halo stars with large present-day Galactocentric distances, >15 kpc. The data-set we acquired consists of high resolution HET/HRS, Magellan/MIKE and VLT/UVES spectra for 28 red giant branch stars covering a wide metallicity range, -3.1 ≲ [Fe/H] ≲-0.6. We show that the ratio of α-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H] ≳-1.5 when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples. Based on ESO program 093.B-0615(A).Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University

  8. Dissipative dark matter halos: The steady state solution

    NASA Astrophysics Data System (ADS)

    Foot, R.

    2018-02-01

    Dissipative dark matter, where dark matter particle properties closely resemble familiar baryonic matter, is considered. Mirror dark matter, which arises from an isomorphic hidden sector, is a specific and theoretically constrained scenario. Other possibilities include models with more generic hidden sectors that contain massless dark photons [unbroken U (1 ) gauge interactions]. Such dark matter not only features dissipative cooling processes but also is assumed to have nontrivial heating sourced by ordinary supernovae (facilitated by the kinetic mixing interaction). The dynamics of dissipative dark matter halos around rotationally supported galaxies, influenced by heating as well as cooling processes, can be modeled by fluid equations. For a sufficiently isolated galaxy with a stable star formation rate, the dissipative dark matter halos are expected to evolve to a steady state configuration which is in hydrostatic equilibrium and where heating and cooling rates locally balance. Here, we take into account the major cooling and heating processes, and numerically solve for the steady state solution under the assumptions of spherical symmetry, negligible dark magnetic fields, and that supernova sourced energy is transported to the halo via dark radiation. For the parameters considered, and assumptions made, we were unable to find a physically realistic solution for the constrained case of mirror dark matter halos. Halo cooling generally exceeds heating at realistic halo mass densities. This problem can be rectified in more generic dissipative dark matter models, and we discuss a specific example in some detail.

  9. Stellar-to-halo mass relation of cluster galaxies

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Niemiec, Anna; Jullo, Eric; Limousin, Marceau

    In the formation of galaxy groups and clusters, the dark matter haloes containing satellite galaxies are expected to be tidally stripped in gravitational interactions with the host. We use galaxy-galaxy weak lensing to measure the average mass of dark matter haloes of satellite galaxies as a function of projected distance to the centre of the host, since stripping is expected to be greater for satellites closer to the centre of the cluster. We further classify the satellites according to their stellar mass: assuming that the stellar component of the galaxy is less disrupted by tidal stripping, stellar mass can bemore » used as a proxy of the infall mass. We study the stellar to halo mass relation of satellites as a function of the cluster-centric distance to measure tidal stripping. We use the shear catalogues of the DES science veri cation archive, the CFHTLenS and the CFHT Stripe 82 surveys, and we select satellites from the redMaPPer catalogue of clusters. For galaxies located in the outskirts of clusters, we nd a stellar to halo mass relation in good agreement with the theoretical expectations from Moster, Naab & White (2013) for central galaxies. In the centre of the cluster, we nd that this relation is shifted to smaller halo mass for a given stellar mass. We interpret this nding as further evidence for tidal stripping of dark matter haloes in high density environments.« less

  10. Stellar-to-halo mass relation of cluster galaxies

    DOE PAGES

    Niemiec, Anna; Jullo, Eric; Limousin, Marceau; ...

    2017-07-04

    In the formation of galaxy groups and clusters, the dark matter haloes containing satellite galaxies are expected to be tidally stripped in gravitational interactions with the host. We use galaxy-galaxy weak lensing to measure the average mass of dark matter haloes of satellite galaxies as a function of projected distance to the centre of the host, since stripping is expected to be greater for satellites closer to the centre of the cluster. We further classify the satellites according to their stellar mass: assuming that the stellar component of the galaxy is less disrupted by tidal stripping, stellar mass can bemore » used as a proxy of the infall mass. We study the stellar to halo mass relation of satellites as a function of the cluster-centric distance to measure tidal stripping. We use the shear catalogues of the DES science veri cation archive, the CFHTLenS and the CFHT Stripe 82 surveys, and we select satellites from the redMaPPer catalogue of clusters. For galaxies located in the outskirts of clusters, we nd a stellar to halo mass relation in good agreement with the theoretical expectations from Moster, Naab & White (2013) for central galaxies. In the centre of the cluster, we nd that this relation is shifted to smaller halo mass for a given stellar mass. We interpret this nding as further evidence for tidal stripping of dark matter haloes in high density environments.« less

  11. The FMOS-COSMOS Survey of Star-forming Galaxies at Z ˜ 1.6. V: Properties of Dark Matter Halos Containing Hα Emitting Galaxies

    NASA Astrophysics Data System (ADS)

    Kashino, Daichi; More, Surhud; Silverman, John D.; Daddi, Emanuele; Renzini, Alvio; Sanders, David B.; Rodighiero, Giulia; Puglisi, Annagrazia; Kajisawa, Masaru; Valentino, Francesco; Kartaltepe, Jeyhan S.; Le Fèvre, Olivier; Nagao, Tohru; Arimoto, Nobuo; Sugiyama, Naoshi

    2017-07-01

    We study the properties of dark matter halos that contain star-forming galaxies at 1.43 ≤ z ≤ 1.74, using the FMOS-COSMOS survey. The sample consists of 516 objects with a detection of the Hα emission line, which represent the star forming population at this epoch, having a stellar mass range of 109.57 ≤ M */M ⊙ ≲ 1011.4 and a star-formation rate range of 15 ≲ SFR/(M ⊙ yr-1) ≲ 600. We measure the projected two-point correlation function while carefully taking into account observational biases, and find a significant clustering amplitude at scales of 0.04-10 h -1 cMpc, with a correlation length {r}0={5.26}-0.62+0.75 {h}-1 {cMpc} and a bias b={2.44}-0.32+0.38. We interpret our clustering measurement using a halo occupation distribution model. The sample galaxies appear to reside in halos with mass {M}{{h}}={4.71}-1.62+1.19× {10}12 {h}-1 {M}⊙ on average, which will likely become present-day halos of mass M h (z = 0) ˜ 2 × 1013 h -1 M ⊙, equivalent to the typical halo mass scale of galaxy groups. We then confirm the decline of the stellar-to-halo mass ratio at M h < 1012 M ⊙, finding M */M h ≈ 5 × 10-3 at M h = 7. 5 × 1011 M ⊙, which is lower by a factor of 2-4 than those measured at higher masses (M h ˜ 1012-13 M ⊙). Finally, we use our results to illustrate the future capabilities of Subaru’s Prime-Focus Spectrograph, a next-generation instrument that will provide strong constraints on the galaxy-formation scenario by obtaining precise measurements of galaxy clustering at z > 1.

  12. Stellar Velocity Dispersion: Linking Quiescent Galaxies to Their Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Zahid, H. Jabran; Sohn, Jubee; Geller, Margaret J.

    2018-06-01

    We analyze the Illustris-1 hydrodynamical cosmological simulation to explore the stellar velocity dispersion of quiescent galaxies as an observational probe of dark matter halo velocity dispersion and mass. Stellar velocity dispersion is proportional to dark matter halo velocity dispersion for both central and satellite galaxies. The dark matter halos of central galaxies are in virial equilibrium and thus the stellar velocity dispersion is also proportional to dark matter halo mass. This proportionality holds even when a line-of-sight aperture dispersion is calculated in analogy to observations. In contrast, at a given stellar velocity dispersion, the dark matter halo mass of satellite galaxies is smaller than virial equilibrium expectations. This deviation from virial equilibrium probably results from tidal stripping of the outer dark matter halo. Stellar velocity dispersion appears insensitive to tidal effects and thus reflects the correlation between stellar velocity dispersion and dark matter halo mass prior to infall. There is a tight relation (≲0.2 dex scatter) between line-of-sight aperture stellar velocity dispersion and dark matter halo mass suggesting that the dark matter halo mass may be estimated from the measured stellar velocity dispersion for both central and satellite galaxies. We evaluate the impact of treating all objects as central galaxies if the relation we derive is applied to a statistical ensemble. A large fraction (≳2/3) of massive quiescent galaxies are central galaxies and systematic uncertainty in the inferred dark matter halo mass is ≲0.1 dex thus simplifying application of the simulation results to currently available observations.

  13. New halo formation mechanism at the KEK compact energy recovery linac

    NASA Astrophysics Data System (ADS)

    Tanaka, Olga; Nakamura, Norio; Shimada, Miho; Miyajima, Tsukasa; Ueda, Akira; Obina, Takashi; Takai, Ryota

    2018-02-01

    The beam halo mitigation is a very important challenge for reliable and safe operation of a high-energy machine. A systematic beam halo study was conducted at the KEK compact energy recovery linac (cERL) since non-negligible beam loss was observed in the recirculation loop during a common operation. We found that the beam loss can be avoided by making use of the collimation system. Beam halo measurements have demonstrated the presence of vertical beam halos at multiple locations in the beam line (except the region near the electron gun). Based on these observations, we made a conjecture that the transverse beam halo is attributed to the longitudinal bunch tail arising at the photocathode. The transfer of particles from the longitudinal space to a transverse halo may have been observed and studied in other machines, considering nonlinear effects as their causes. However, our study demonstrates a new unique halo formation mechanism, in which a transverse beam halo can be generated by a longitudinal bunch tail due to transverse rf kicks from the accelerating (monopole) fields of the radio-frequency cavities. This halo formation occurs when nonrelativistic particles enter the cavities with a transverse offset, even if neither nonlinear optics nor nonlinear beam effects are present. A careful realignment of the injector system will mitigate the present halo. Another possible cure is to reduce the bunch tails by changing the photocathode material from the present GaAs to a multi-alkali that is known to have a shorter longitudinal tail.

  14. Testing approximate predictions of displacements of cosmological dark matter halos

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Munari, Emiliano; Monaco, Pierluigi; Borgani, Stefano

    We present a test to quantify how well some approximate methods, designed to reproduce the mildly non-linear evolution of perturbations, are able to reproduce the clustering of DM halos once the grouping of particles into halos is defined and kept fixed. The following methods have been considered: Lagrangian Perturbation Theory (LPT) up to third order, Truncated LPT, Augmented LPT, MUSCLE and COLA. The test runs as follows: halos are defined by applying a friends-of-friends (FoF) halo finder to the output of an N-body simulation. The approximate methods are then applied to the same initial conditions of the simulation, producing formore » all particles displacements from their starting position and velocities. The position and velocity of each halo are computed by averaging over the particles that belong to that halo, according to the FoF halo finder. This procedure allows us to perform a well-posed test of how clustering of the matter density and halo density fields are recovered, without asking to the approximate method an accurate reconstruction of halos. We have considered the results at z =0,0.5,1, and we have analysed power spectrum in real and redshift space, object-by-object difference in position and velocity, density Probability Distribution Function (PDF) and its moments, phase difference of Fourier modes. We find that higher LPT orders are generally able to better reproduce the clustering of halos, while little or no improvement is found for the matter density field when going to 2LPT and 3LPT. Augmentation provides some improvement when coupled with 2LPT, while its effect is limited when coupled with 3LPT. Little improvement is brought by MUSCLE with respect to Augmentation. The more expensive particle-mesh code COLA outperforms all LPT methods, and this is true even for mesh sizes as large as the inter-particle distance. This test sets an upper limit on the ability of these methods to reproduce the clustering of halos, for the cases when these

  15. Revisiting Scaling Relations for Giant Radio Halos in Galaxy Clusters

    NASA Technical Reports Server (NTRS)

    Cassano, R.; Ettori, S.; Brunetti, G.; Giacintucci, S.; Pratt, G. W.; Venturi, T.; Kale, R.; Dolag, K.; Markevitch, Maxim L.

    2013-01-01

    Many galaxy clusters host megaparsec-scale radio halos, generated by ultrarelativistic electrons in the magnetized intracluster medium. Correlations between the synchrotron power of radio halos and the thermal properties of the hosting clusters were established in the last decade, including the connection between the presence of a halo and cluster mergers. The X-ray luminosity and redshift-limited Extended GMRT Radio Halo Survey provides a rich and unique dataset for statistical studies of the halos. We uniformly analyze the radio and X-ray data for the GMRT cluster sample, and use the new Planck Sunyaev-Zel'dovich (SZ) catalog to revisit the correlations between the power of radio halos and the thermal properties of galaxy clusters. We find that the radio power at 1.4 GHz scales with the cluster X-ray (0.1-2.4 keV) luminosity computed within R(sub 500) as P(sub 1.4) approx. L(2.1+/-0.2) - 500). Our bigger and more homogenous sample confirms that the X-ray luminous (L(sub 500) > 5 × 10(exp 44) erg/s)) clusters branch into two populations-radio halos lie on the correlation, while clusters without radio halos have their radio upper limits well below that correlation. This bimodality remains if we excise cool cores from the X-ray luminosities. We also find that P(sub 1.4) scales with the cluster integrated SZ signal within R(sub 500), measured by Planck, as P(sub 1.4) approx. Y(2.05+/-0.28) - 500), in line with previous findings. However, contrary to previous studies that were limited by incompleteness and small sample size, we find that "SZ-luminous" Y(sub 500) > 6×10(exp -5) Mpc(exp 2) clusters show a bimodal behavior for the presence of radio halos, similar to that in the radio-X-ray diagram. Bimodality of both correlations can be traced to clusters dynamics, with radio halos found exclusively in merging clusters. These results confirm the key role of mergers for the origin of giant radio halos, suggesting that they trigger the relativistic particle acceleration.

  16. Galaxy halo formation in the absence of violent relaxation and a universal density profile of the halo center

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Baushev, A. N., E-mail: baushev@gmail.com; Institut für Physik und Astronomie, Universität Potsdam, D-14476 Potsdam-Golm

    2014-05-01

    While N-body simulations testify to a cuspy profile of the central region of dark matter halos, observations favor a shallow, cored density profile of the central region of at least some spiral galaxies and dwarf spheroidals. We show that a central profile, very close to the observed one, inevitably forms in the center of dark matter halos if we make a supposition about a moderate energy relaxation of the system during the halo formation. If we assume the energy exchange between dark matter particles during the halo collapse is not too intensive, the profile is universal: it depends almost notmore » at all on the properties of the initial perturbation and is very akin, but not identical, to the Einasto profile with a small Einasto index n ∼ 0.5. We estimate the size of the 'central core' of the distribution, i.e., the extent of the very central region with a respectively gentle profile, and show that the cusp formation is unlikely, even if the dark matter is cold. The obtained profile is in good agreement with observational data for at least some types of galaxies but clearly disagrees with N-body simulations.« less

  17. Approximate Bayesian computation in large-scale structure: constraining the galaxy-halo connection

    NASA Astrophysics Data System (ADS)

    Hahn, ChangHoon; Vakili, Mohammadjavad; Walsh, Kilian; Hearin, Andrew P.; Hogg, David W.; Campbell, Duncan

    2017-08-01

    Standard approaches to Bayesian parameter inference in large-scale structure assume a Gaussian functional form (chi-squared form) for the likelihood. This assumption, in detail, cannot be correct. Likelihood free inferences such as approximate Bayesian computation (ABC) relax these restrictions and make inference possible without making any assumptions on the likelihood. Instead ABC relies on a forward generative model of the data and a metric for measuring the distance between the model and data. In this work, we demonstrate that ABC is feasible for LSS parameter inference by using it to constrain parameters of the halo occupation distribution (HOD) model for populating dark matter haloes with galaxies. Using specific implementation of ABC supplemented with population Monte Carlo importance sampling, a generative forward model using HOD and a distance metric based on galaxy number density, two-point correlation function and galaxy group multiplicity function, we constrain the HOD parameters of mock observation generated from selected 'true' HOD parameters. The parameter constraints we obtain from ABC are consistent with the 'true' HOD parameters, demonstrating that ABC can be reliably used for parameter inference in LSS. Furthermore, we compare our ABC constraints to constraints we obtain using a pseudo-likelihood function of Gaussian form with MCMC and find consistent HOD parameter constraints. Ultimately, our results suggest that ABC can and should be applied in parameter inference for LSS analyses.

  18. Co-formation of the disc and the stellar halo

    NASA Astrophysics Data System (ADS)

    Belokurov, V.; Erkal, D.; Evans, N. W.; Koposov, S. E.; Deason, A. J.

    2018-07-01

    Using a large sample of main sequence stars with 7D measurements supplied by Gaia and SDSS, we study the kinematic properties of the local (within ˜10 kpc from the Sun) stellar halo. We demonstrate that the halo's velocity ellipsoid evolves strongly with metallicity. At the low-[Fe/H] end, the orbital anisotropy (the amount of motion in the radial direction compared with the tangential one) is mildly radial, with 0.2 <β< 0.4. For stars with [Fe/H] > -1.7, however, we measure extreme values of β˜ 0.9. Across the metallicity range considered, namely-3 < [Fe/H] < -1, the stellar halo's spin is minimal, at the level of 20< \\bar{v}_{θ }(kms^{-1}) < 30. Using a suite of cosmological zoom-in simulations of halo formation, we deduce that the observed acute anisotropy is inconsistent with the continuous accretion of dwarf satellites. Instead, we argue, the stellar debris in the inner halo was deposited in a major accretion event by a satellite with Mvir > 1010M⊙ around the epoch of the Galactic disc formation, between 8 and 11 Gyr ago. The radical halo anisotropy is the result of the dramatic radialization of the massive progenitor's orbit, amplified by the action of the growing disc.

  19. Improving fast generation of halo catalogues with higher order Lagrangian perturbation theory

    NASA Astrophysics Data System (ADS)

    Munari, Emiliano; Monaco, Pierluigi; Sefusatti, Emiliano; Castorina, Emanuele; Mohammad, Faizan G.; Anselmi, Stefano; Borgani, Stefano

    2017-03-01

    We present the latest version of PINOCCHIO, a code that generates catalogues of dark matter haloes in an approximate but fast way with respect to an N-body simulation. This code version implements a new on-the-fly production of halo catalogue on the past light cone with continuous time sampling, and the computation of particle and halo displacements are extended up to third-order Lagrangian perturbation theory (LPT), in contrast with previous versions that used Zel'dovich approximation. We run PINOCCHIO on the same initial configuration of a reference N-body simulation, so that the comparison extends to the object-by-object level. We consider haloes at redshifts 0 and 1, using different LPT orders either for halo construction or to compute halo final positions. We compare the clustering properties of PINOCCHIO haloes with those from the simulation by computing the power spectrum and two-point correlation function in real and redshift space (monopole and quadrupole), the bispectrum and the phase difference of halo distributions. We find that 2LPT and 3LPT give noticeable improvement. 3LPT provides the best agreement with N-body when it is used to displace haloes, while 2LPT gives better results for constructing haloes. At the highest orders, linear bias is typically recovered at a few per cent level. In Fourier space and using 3LPT for halo displacements, the halo power spectrum is recovered to within 10 per cent up to kmax ∼ 0.5 h Mpc-1. The results presented in this paper have interesting implications for the generation of large ensemble of mock surveys for the scientific exploitation of data from big surveys.

  20. Integrating teamwork, clinician occupational well-being and patient safety - development of a conceptual framework based on a systematic review.

    PubMed

    Welp, Annalena; Manser, Tanja

    2016-07-19

    There is growing evidence that teamwork in hospitals is related to both patient outcomes and clinician occupational well-being. Furthermore, clinician well-being is associated with patient safety. Despite considerable research activity, few studies include all three concepts, and their interrelations have not yet been investigated systematically. To advance our understanding of these potentially complex interrelations we propose an integrative framework taking into account current evidence and research gaps identified in a systematic review. We conducted a literature search in six major databases (Medline, PsycArticles, PsycInfo, Psyndex, ScienceDirect, and Web of Knowledge). Inclusion criteria were: peer reviewed papers published between January 2000 and June 2015 investigating a statistical relationship between at least two of the three concepts; teamwork, patient safety, and clinician occupational well-being in hospital settings, including practicing nurses and physicians. We assessed methodological quality using a standardized rating system and qualitatively appraised and extracted relevant data, such as instruments, analyses and outcomes. The 98 studies included in this review were highly diverse regarding quality, methodology and outcomes. We found support for the existence of independent associations between teamwork, clinician occupational well-being and patient safety. However, we identified several conceptual and methodological limitations. The main barrier to advancing our understanding of the causal relationships between teamwork, clinician well-being and patient safety is the lack of an integrative, theory-based, and methodologically thorough approach investigating the three concepts simultaneously and longitudinally. Based on psychological theory and our findings, we developed an integrative framework that addresses these limitations and proposes mechanisms by which these concepts might be linked. Knowledge about the mechanisms underlying the

  1. The Circumgalactic Medium in Massive Halos

    NASA Astrophysics Data System (ADS)

    Chen, Hsiao-Wen

    This chapter presents a review of the current state of knowledge on the cool (T ˜ 104 K) halo gas content around massive galaxies at z ≈ 0. 2-2. Over the last decade, significant progress has been made in characterizing the cool circumgalactic gas in massive halos of M h ≈ 1012-14 M⊙ at intermediate redshifts using absorption spectroscopy. Systematic studies of halo gas around massive galaxies beyond the nearby universe are made possible by large spectroscopic samples of galaxies and quasars in public archives. In addition to accurate and precise constraints for the incidence of cool gas in massive halos, detailed characterizations of gas kinematics and chemical compositions around massive quiescent galaxies at z ≈ 0. 5 have also been obtained. Combining all available measurements shows that infalling clouds from external sources are likely the primary source of cool gas detected at d 100 d\\gtrsim 100 kpc from massive quiescent galaxies. The origin of the gas closer in is currently less certain, but SNe Ia driven winds appear to contribute significantly to cool gas found at d < 100 kpc. In contrast, cool gas observed at d 200 d\\lesssim 200 kpc from luminous quasars appears to be intimately connected to quasar activities on parsec scales. The observed strong correlation between cool gas covering fraction in quasar host halos and quasar bolometric luminosity remains a puzzle. Combining absorption-line studies with spatially resolved emission measurements of both gas and galaxies is the necessary next step to address remaining questions.

  2. Impact of Neutrinos on Dark Matter Halo Environment

    NASA Astrophysics Data System (ADS)

    Court, Travis; Villaescusa-Navarro, Francisco

    2018-01-01

    The spatial clustering of galaxies is commonly used to infer the shape of the matter power spectrum and therefore to place constraints on the value of the cosmological parameters. In order to extract the maximum information from galaxy surveys it is required to provide accurate theoretical predictions. The first step to model galaxy clustering is to understand the spatial distribution of the structures where they reside: dark matter halos. I will show that the clustering of halos does not depend only on mass, but on other quantities like local matter overdensity. I will point out that halo clustering is also sensitive to the local overdensity of the cosmic neutrino background. I will show that splitting halos according to neutrino overdensity induces a very large scale-dependence bias, an effect that may lead to a new technique to constraint the sum of the neutrino masses.

  3. Summary of the 2014 Beam-Halo Monitoring Workshop

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fisher, Alan

    2015-09-25

    Understanding and controlling beam halo is important for high-intensity hadron accelerators, for high-brightness electron linacs, and for low-emittance light sources. This can only be achieved by developing suitable diagnostics. The main challenge faced by such instrumentation is the high dynamic range needed to observe the halo in the presence of an intense core. In addition, measurements must often be made non-invasively. This talk summarizes the one-day workshop on Beam-Halo Monitoring that was held at SLAC on September 19 last year, immediately following IBIC 2014 in Monterey. Workshop presentations described invasive techniques using wires, screens, or crystal collimators, and non-invasive measurementsmore » with gas or scattered electrons. Talks on optical methods showed the close links between observing halo and astronomical problems like observing the solar corona or directly observing a planet orbiting another star.« less

  4. Search for and analysis of radioactive halos in lunar material

    NASA Technical Reports Server (NTRS)

    Gentry, R. V.

    1976-01-01

    The lunar halo search was conducted because halos in terrestrial minerals serve as pointers to localized radioactivity, and make possible analytical studies on the problems of isotopic dating and mode of crystallization of the host mineral. Ancillary studies were conducted on terrestrial halos and on certain samples of special origin such as tektites and meteorites.

  5. Solar Radiation Measurements Onboard the Research Aircraft HALO

    NASA Astrophysics Data System (ADS)

    Lohse, I.; Bohn, B.; Werner, F.; Ehrlich, A.; Wendisch, M.

    2014-12-01

    Airborne measurements of the separated upward and downward components of solar spectral actinic flux densities for the determination of photolysis frequencies and of upward nadir spectral radiance were performed with the HALO Solar Radiation (HALO-SR) instrument package onboard the High Altitude and Long Range Research Aircraft (HALO). The instrumentation of HALO-SR is characterized and first measurement data from the Next-generation Aircraft Remote-Sensing for Validation Studies (NARVAL) campaigns in 2013 and 2014 are presented. The measured data are analyzed in the context of the retrieved microphysical and optical properties of clouds which were observed underneath the aircraft. Detailed angular sensitivities of the two optical actinic flux receivers were determined in the laboratory. The effects of deviations from the ideal response are investigated using radiative transfer calculations of atmospheric radiance distributions under various atmospheric conditions and different ground albedos. Corresponding correction factors are derived. Example photolysis frequencies are presented, which were sampled in the free troposphere and lower stratosphere over the Atlantic Ocean during the 2013/14 HALO NARVAL campaigns. Dependencies of photolysis frequencies on cloud cover, flight altitude and wavelength range of the photolysis process are investigated. Calculated actinic flux densities in the presence of clouds benefit from the measured spectral radiances. Retrieved cloud optical thicknesses and effective droplet radii are used as model input for the radiative transfer calculations. By comparison with the concurrent measurements of actinic flux densities the retrieval approach is validated. Acknowledgements: Funding by the Deutsche Forschungsgemeinschaft within the priority program HALO (BO 1580/4-1, WE 1900/21-1) is gratefully acknowledged.

  6. Comparison of two laboratory-based systems for evaluation of halos in intraocular lenses

    PubMed Central

    Alexander, Elsinore; Wei, Xin; Lee, Shinwook

    2018-01-01

    Purpose Multifocal intraocular lenses (IOLs) can be associated with unwanted visual phenomena, including halos. Predicting potential for halos is desirable when designing new multifocal IOLs. Halo images from 6 IOL models were compared using the Optikos modulation transfer function bench system and a new high dynamic range (HDR) system. Materials and methods One monofocal, 1 extended depth of focus, and 4 multifocal IOLs were evaluated. An off-the-shelf optical bench was used to simulate a distant (>50 m) car headlight and record images. A custom HDR system was constructed using an imaging photometer to simulate headlight images and to measure quantitative halo luminance data. A metric was developed to characterize halo luminance properties. Clinical relevance was investigated by correlating halo measurements to visual outcomes questionnaire data. Results The Optikos system produced halo images useful for visual comparisons; however, measurements were relative and not quantitative. The HDR halo system provided objective and quantitative measurements used to create a metric from the area under the curve (AUC) of the logarithmic normalized halo profile. This proposed metric differentiated between IOL models, and linear regression analysis found strong correlations between AUC and subjective clinical ratings of halos. Conclusion The HDR system produced quantitative, preclinical metrics that correlated to patients’ subjective perception of halos. PMID:29503526

  7. Bose-Einstein condensate haloes embedded in dark energy

    NASA Astrophysics Data System (ADS)

    Membrado, M.; Pacheco, A. F.

    2018-04-01

    Context. We have studied clusters of self-gravitating collisionless Newtonian bosons in their ground state and in the presence of the cosmological constant to model dark haloes of dwarf spheroidal (dSph) galaxies. Aim. We aim to analyse the influence of the cosmological constant on the structure of these systems. Observational data of Milky Way dSph galaxies allow us to estimate the boson mass. Methods: We obtained the energy of the ground state of the cluster in the Hartree approximation by solving a variational problem in the particle density. We have also developed and applied the virial theorem. Dark halo models were tested in a sample of 19 galaxies. Galaxy radii, 3D deprojected half-light radii, mass enclosed within them, and luminosity-weighted averages of the square of line-of-sight velocity dispersions are used to estimate the particle mass. Results: Cosmological constant repulsive effects are embedded in one parameter ξ. They are appreciable for ξ > 10-5. Bound structures appear for ξ ≤ ξc = 1.65 × 10-4, what imposes a lower bound for cluster masses as a function of the particle mass. In principle, these systems present tunnelling through a potential barrier; however, after estimating their mean lifes, we realize that their existence is not affected by the age of the Universe. When Milky Way dSph galaxies are used to test the model, we obtain 3.5-1.0+1.3 × 10-22 eV for the particle mass and a lower limit of 5.1-2.8+2.2 × 106 M⊙ for bound haloes. Conclusions: Our estimation for the boson mass is in agreement with other recent results which use different methods. From our particle mass estimation, the treated dSph galaxies would present dark halo masses 5-11 ×107 M⊙. With these values, they would not be affected by the cosmological constant (ξ < 10-8). However, dark halo masses smaller than 107 M⊙ (ξ > 10-5) would already feel their effects. Our model that includes dark energy allows us to deal with these dark haloes. Assuming quantities

  8. Formation and Maintenance of Galactic Warps in Triaxial Halos

    NASA Astrophysics Data System (ADS)

    Jeon, M. W.; Kim, S. S.; Ann, H. B.

    2008-10-01

    We investigate the evolution of the self-gravitating disk in a fixed axisymmetric halo with a torus of late cosmic infall that is tilted relative to the initial disk. This is an extension to the study by Shen & Sellwood (2006). We find that the magnitude of the warp is suppressed by a factor of ˜ 2 when the halo is moderately oblate while the magnitude of the warp periodically oscillates when the halo is moderately prolate.

  9. The bulge-halo conspiracy in massive elliptical galaxies: implications for the stellar initial mass function and halo response to baryonic processes

    NASA Astrophysics Data System (ADS)

    Dutton, Aaron A.; Treu, Tommaso

    2014-03-01

    Recent studies have shown that massive elliptical galaxies have total mass density profiles within an effective radius that can be approximated as ρ_tot∝ r^{-γ^', with mean slope <γ'> = 2.08 ± 0.03 and scatter σ _{γ ^' } }=0.16± 0.02. The small scatter of the slope (known as the bulge-halo conspiracy) is not generic in Λ cold dark matter (ΛCDM) based models and therefore contains information about the galaxy formation process. We compute the distribution of γ' for ΛCDM-based models that reproduce the observed correlations between stellar mass, velocity dispersion, and effective radius of early-type galaxies in the Sloan Digital Sky Survey. The models have a range of stellar initial mass functions (IMFs) and dark halo responses to galaxy formation. The observed distribution of γ' is well reproduced by a model with cosmologically motivated but uncontracted dark matter haloes, and a Salpeter-type IMF. Other models are on average ruled out by the data, even though they may happen in individual cases. Models with adiabatic halo contraction (and lighter IMFs) predict too small values of γ'. Models with halo expansion, or mass-follows-light predict too high values of γ'. Our study shows that the non-homologous structure of massive early-type galaxies can be precisely reproduced by ΛCDM models if the IMF is not universal and if mechanisms, such as feedback from active galactic nuclei, or dynamical friction, effectively on average counterbalance the contraction of the halo expected as a result of baryonic cooling.

  10. Universal Dark Halo Scaling Relation for the Dwarf Spheroidal Satellites

    NASA Astrophysics Data System (ADS)

    Hayashi, Kohei; Ishiyama, Tomoaki; Ogiya, Go; Chiba, Masashi; Inoue, Shigeki; Mori, Masao

    2017-07-01

    Motivated by a recently found interesting property of the dark halo surface density within a radius, {r}\\max , giving the maximum circular velocity, {V}\\max , we investigate it for dark halos of the Milky Way’s and Andromeda’s dwarf satellites based on cosmological simulations. We select and analyze the simulated subhalos associated with Milky-Way-sized dark halos and find that the values of their surface densities, {{{Σ }}}{V\\max }, are in good agreement with those for the observed dwarf spheroidal satellites even without employing any fitting procedures. Moreover, all subhalos on the small scales of dwarf satellites are expected to obey the universal relation, irrespective of differences in their orbital evolutions, host halo properties, and observed redshifts. Therefore, we find that the universal scaling relation for dark halos on dwarf galaxy mass scales surely exists and provides us with important clues for understanding fundamental properties of dark halos. We also investigate orbital and dynamical evolutions of subhalos to understand the origin of this universal dark halo relation and find that most subhalos evolve generally along the {r}\\max \\propto {V}\\max sequence, even though these subhalos have undergone different histories of mass assembly and tidal stripping. This sequence, therefore, should be the key feature for understanding the nature of the universality of {{{Σ }}}{V\\max }.

  11. Does the galaxy-halo connection vary with environment?

    NASA Astrophysics Data System (ADS)

    Dragomir, Radu; Rodríguez-Puebla, Aldo; Primack, Joel R.; Lee, Christoph T.

    2018-05-01

    (Sub)halo abundance matching (SHAM) assumes that one (sub) halo property, such as mass Mvir or peak circular velocity Vpeak, determines properties of the galaxy hosted in each (sub) halo such as its luminosity or stellar mass. This assumption implies that the dependence of galaxy luminosity functions (GLFs) and the galaxy stellar mass function (GSMF) on environmental density is determined by the corresponding halo density dependence. In this paper, we test this by determining from a Sloan Digital Sky Survey sample the observed dependence with environmental density of the ugriz GLFs and GSMF for all galaxies, and for central and satellite galaxies separately. We then show that the SHAM predictions are in remarkable agreement with these observations, even when the galaxy population is divided between central and satellite galaxies. However, we show that SHAM fails to reproduce the correct dependence between environmental density and g - r colour for all galaxies and central galaxies, although it better reproduces the colour dependence on environmental density of satellite galaxies.

  12. Dissipative dark matter halos: The steady state solution. II.

    NASA Astrophysics Data System (ADS)

    Foot, R.

    2018-05-01

    Within the mirror dark matter model and dissipative dark matter models in general, halos around galaxies with active star formation (including spirals and gas-rich dwarfs) are dynamical: they expand and contract in response to heating and cooling processes. Ordinary type II supernovae (SNe) can provide the dominant heat source, which is possible if kinetic mixing interaction exists with strength ɛ ˜10-9- 10-10 . Dissipative dark matter halos can be modeled as a fluid governed by Euler's equations. Around sufficiently isolated and unperturbed galaxies the halo can relax to a steady state configuration, where heating and cooling rates locally balance and hydrostatic equilibrium prevails. These steady state conditions can be solved to derive the physical properties, including the halo density and temperature profiles, for model galaxies. Here, we consider idealized spherically symmetric galaxies within the mirror dark particle model, as in our earlier paper [Phys. Rev. D 97, 043012 (2018), 10.1103/PhysRevD.97.043012], but we assume that the local halo heating in the SN vicinity dominates over radiative sources. With this assumption, physically interesting steady state solutions arise which we compute for a representative range of model galaxies. The end result is a rather simple description of the dark matter halo around idealized spherically symmetric systems, characterized in principle by only one parameter, with physical properties that closely resemble the empirical properties of disk galaxies.

  13. Dark-Matter Halos of Tenuous Galaxies

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    A series of recent deep-imaging surveys has revealed dozens of lurking ultra-diffuse galaxies (UDGs) in nearby galaxy clusters. A new study provides key information to help us understand the origins of these faint giants.What are UDGs?There are three main possibilities for how UDGs galaxies with the sizes of giants, but luminosities no brighter than those of dwarfs formed:They are tidal dwarfs, created in galactic collisions when streams of matter were pulled away from the parent galaxies and halos to form dwarfs.They are descended from normal galaxies and were then altered by tidal interactions with the galaxy cluster.They are ancient remnant systems large galaxies whose gas was swept away, putting an early halt to star formation. The gas removal did not, however, affect their large dark matter halos, which permitted them to survive in the cluster environment.The key to differentiating between these options is to obtain mass measurements for the UDGs how large are their dark matter halos? In a recent study led by Michael Beasley (Institute of Astrophysics of the Canary Islands, University of La Laguna), a team of astronomers has determined a clever approach for measuring these galaxies masses: examine their globular clusters.Masses from Globular ClustersVCC 1287s mass measurements put it outside of the usual halo-mass vs. stellar-mass relationships for nearby galaxies: it has a significantly higher halo mass than is normal, given its stellar mass. [Adapted from Beasley et al. 2016]Beasley and collaborators selected one UDG, VCC 1287, from the Virgo galaxy cluster, and they obtained spectra of the globular clusters around it using the OSIRIS spectrograph on the Great Canary Telescope. They then determined VCC 1287s total halo mass in two ways: first by using the dynamics of the globular clusters, and then by relying on a relation between total globular cluster mass and halo mass.The two masses they found are in good agreement with each other; both are around 80

  14. Ionized haloes in planetary nebulae: new discoveries, literature compilation and basic statistical properties

    NASA Astrophysics Data System (ADS)

    Corradi, R. L. M.; Schönberner, D.; Steffen, M.; Perinotto, M.

    2003-04-01

    We present a comprehensive observational study of haloes around planetary nebulae (PNe). Deep Hα+[NII] and/or [OIII] narrow-band images have been obtained for 35 PNe, and faint extended haloes have been newly discovered in the following 10 objects: Cn 1-5, IC 2165, IC 2553, NGC 2792, NGC 2867, NGC 3918, NGC 5979, NGC 6578, PB 4, and possibly IC 1747. New deep images have also been obtained of other known or suspected haloes, including the huge extended emission around NGC 3242 and Sh 2-200. In addition, the literature was searched, and together with the new observations an improved data base containing some 50 PN haloes has been compiled. The halo sample is illustrated in an image atlas contained in this paper, and the original images are made available for use by the scientific community at http://www.ing. iac.es/~rcorradi/HALOES/. The haloes have been classified following the predictions of modern radiation-hydrodynamical simulations that describe the formation and evolution of ionized multiple shells and haloes around PNe. According to the models, the observed haloes have been divided into the following groups: (i) circular or slightly elliptical asymptotic giant branch (AGB) haloes, which contain the signature of the last thermal pulse on the AGB; (ii) highly asymmetrical AGB haloes; (iii) candidate recombination haloes, i.e. limb-brightened extended shells that are expected to be produced by recombination during the late post-AGB evolution, when the luminosity of the central star drops rapidly by a significant factor; (iv) uncertain cases which deserve further study for a reliable classification; (v) non-detections, i.e. PNe in which no halo is found to a level of <~10-3 the peak surface brightness of the inner nebulae. We discuss the properties of the haloes: detection rate, morphology, location of the central stars in the Hertzsprung-Russell diagram, sizes, surface brightness profiles, and kinematical ages. Among the most

  15. The x ray halo of AM Her

    NASA Technical Reports Server (NTRS)

    Catura, Richard C.

    1993-01-01

    The objective of this research was to study the halo surrounding the ROSAT image of the cataclysmic variable AM Her that is formed by scattering of x-rays by interstellar dust grains. AM Her was in a low state of x-ray emission during the 14,400 sec observation and thus an insufficient number of counts were obtained to detect the x-ray halo.

  16. Theoretical relation between halo current-plasma energy displacement/deformation in EAST

    NASA Astrophysics Data System (ADS)

    Khan, Shahab Ud-Din; Khan, Salah Ud-Din; Song, Yuntao; Dalong, Chen

    2018-04-01

    In this paper, theoretical model for calculating halo current has been developed. This work attained novelty as no theoretical calculations for halo current has been reported so far. This is the first time to use theoretical approach. The research started by calculating points for plasma energy in terms of poloidal and toroidal magnetic field orientations. While calculating these points, it was extended to calculate halo current and to developed theoretical model. Two cases were considered for analyzing the plasma energy when flows down/upward to the diverter. Poloidal as well as toroidal movement of plasma energy was investigated and mathematical formulations were designed as well. Two conducting points with respect to (R, Z) were calculated for halo current calculations and derivations. However, at first, halo current was established on the outer plate in clockwise direction. The maximum generation of halo current was estimated to be about 0.4 times of the plasma current. A Matlab program has been developed to calculate halo current and plasma energy calculation points. The main objective of the research was to establish theoretical relation with experimental results so as to precautionary evaluate the plasma behavior in any Tokamak.

  17. THE SEGUE K GIANT SURVEY. III. QUANTIFYING GALACTIC HALO SUBSTRUCTURE

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Janesh, William; Morrison, Heather L.; Ma, Zhibo

    2016-01-10

    We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5–125 kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey’s Sloan Extension for Galactic Understanding and Exploration project. Using a position–velocity clustering estimator (the 4distance) and a model of a smooth stellar halo, we quantify the amount of substructure in the halo, divided by distance and metallicity. Overall, we find that the halo as a whole is highly structured. We also confirm earliermore » work using blue horizontal branch (BHB) stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius, and additionally find that the amount of substructure in the halo increases with increasing metallicity. Comparing to resampled BHB stars, we find that K giants and BHBs have similar amounts of substructure over equivalent ranges of Galactocentric radius. Using a friends-of-friends algorithm to identify members of individual groups, we find that a large fraction (∼33%) of grouped stars are associated with Sgr, and identify stars belonging to other halo star streams: the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. A large fraction of sample K giants (more than 50%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity.« less

  18. A Search for a Near-Infrared Halo Around NGC 4565

    NASA Technical Reports Server (NTRS)

    Uemizu, Kazunori; Bock, James J.; Kawada, Mitsunobu; Lange, Andrew E.; Matsumoto, Toshio; Watabe, Toyoki; Yost, Sarah A.

    1998-01-01

    We present a near-infrared (3.5-5 micron) search for the integrated emission from low-mass stars and/or brown dwarfs in the halo of the nearby edge-on spiral galaxy NGC 4565. The observation was made with a liquid-helium-cooled rocket-borne telescope using a 256 x 256 InSb array with a pixel scale of 17". Images of NGC 4565 were successfully obtained with sensitivity near the natural background limit. Our search reveals no evidence of a faint halo around the galaxy, in contrast with the previous reports of a halo around NGC 5907. The lower limit of the mass-to-light ratio for the halo of NGC 4565 is 260 (2 delta) in solar units at 3.5-5 microns. This implies that hydrogen-burning stars do not contribute significantly to the mass of the dark halo in NGC 4565.

  19. ZOMG - I. How the cosmic web inhibits halo growth and generates assembly bias

    NASA Astrophysics Data System (ADS)

    Borzyszkowski, Mikolaj; Porciani, Cristiano; Romano-Díaz, Emilio; Garaldi, Enrico

    2017-07-01

    The clustering of dark matter haloes with fixed mass depends on their formation history, an effect known as assembly bias. We use zoom N-body simulations to investigate the origin of this phenomenon. For each halo at redshift z = 0, we determine the time in which the physical volume containing its final mass becomes stable. We consider five examples for which this happens at z ˜ 1.5 and two that do not stabilize by z = 0. The zoom simulations show that early-collapsing haloes do not grow in mass at z = 0 while late-forming ones show a net inflow. The reason is that 'accreting' haloes are located at the nodes of a network of thin filaments feeding them. Conversely, each 'stalled' halo lies within a prominent filament that is thicker than the halo size. Infalling material from the surroundings becomes part of the filament while matter within it recedes from the halo. We conclude that assembly bias originates from quenching halo growth due to tidal forces following the formation of non-linear structures in the cosmic web, as previously conjectured in the literature. Also the internal dynamics of the haloes change: the velocity anisotropy profile is biased towards radial (tangential) orbits in accreting (stalled) haloes. Our findings reveal the cause of the yet unexplained dependence of halo clustering on the anisotropy. Finally, we extend the excursion-set theory to account for these effects. A simple criterion based on the ellipticity of the linear tidal field combined with the spherical-collapse model provides excellent predictions for both classes of haloes.

  20. Toward a Combined SAGE II-HALOE Aerosol Climatology: An Evaluation of HALOE Version 19 Stratospheric Aerosol Extinction Coefficient Observations

    NASA Technical Reports Server (NTRS)

    Thomason, L. W.

    2012-01-01

    Herein, the Halogen Occultation Experiment (HALOE) aerosol extinction coefficient data is evaluated in the low aerosol loading period after 1996 as the first necessary step in a process that will eventually allow the production of a combined HALOE/SAGE II (Stratospheric Aerosol and Gas Experiment) aerosol climatology of derived aerosol products including surface area density. Based on these analyses, it is demonstrated that HALOE's 3.46 microns is of good quality above 19 km and suitable for scientific applications above that altitude. However, it is increasingly suspect at lower altitudes and should not be used below 17 km under any circumstances after 1996. The 3.40 microns is biased by about 10% throughout the lower stratosphere due to the failure to clear NO2 but otherwise appears to be a high quality product down to 15 km. The 2.45 and 5.26 micron aerosol extinction coefficient measurements are clearly biased and should not be used for scientific applications after the most intense parts of the Pinatubo period. Many of the issues in the aerosol data appear to be related to either the failure to clear some interfering gas species or doing so poorly. For instance, it is clear that the 3.40micronaerosol extinction coefficient measurements can be improved through the inclusion of an NO2 correction and could, in fact, end up as the highest quality overall HALOE aerosol extinction coefficient measurement. It also appears that the 2.45 and 5.26 micron channels may be improved by updating the Upper Atmosphere Pilot Database which is used as a resource for the removal of gas species otherwise not available from direct HALOE measurements. Finally, a simple model to demonstrate the promise of mixed visible/infrared aerosol extinction coefficient ensembles for the retrieval of bulk aerosol properties demonstrates that a combined HALOE/SAGE II aerosol climatology is feasible and may represent a substantial improvement over independently derived data sets.

  1. DETECTING TRIAXIALITY IN THE GALACTIC DARK MATTER HALO THROUGH STELLAR KINEMATICS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Rojas-Nino, Armando; Valenzuela, Octavio; Pichardo, Barbara

    Assuming the dark matter halo of the Milky Way to be a non-spherical potential (i.e., triaxial, prolate, oblate), we show how the assembling process of the Milky Way halo may have left long-lasting stellar halo kinematic fossils due to the shape of the dark matter halo. In contrast with tidal streams, which are associated with recent satellite accretion events, these stellar kinematic groups will typically show inhomogeneous chemical and stellar population properties. However, they may be dominated by a single accretion event for certain mass assembling histories. If the detection of these peculiar kinematic stellar groups were confirmed, they wouldmore » be the smoking gun for the predicted triaxiality of dark halos in cosmological galaxy formation scenarios.« less

  2. PARALLEL HOP: A SCALABLE HALO FINDER FOR MASSIVE COSMOLOGICAL DATA SETS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Skory, Stephen; Turk, Matthew J.; Norman, Michael L.

    2010-11-15

    Modern N-body cosmological simulations contain billions (10{sup 9}) of dark matter particles. These simulations require hundreds to thousands of gigabytes of memory and employ hundreds to tens of thousands of processing cores on many compute nodes. In order to study the distribution of dark matter in a cosmological simulation, the dark matter halos must be identified using a halo finder, which establishes the halo membership of every particle in the simulation. The resources required for halo finding are similar to the requirements for the simulation itself. In particular, simulations have become too extensive to use commonly employed halo finders, suchmore » that the computational requirements to identify halos must now be spread across multiple nodes and cores. Here, we present a scalable-parallel halo finding method called Parallel HOP for large-scale cosmological simulation data. Based on the halo finder HOP, it utilizes message passing interface and domain decomposition to distribute the halo finding workload across multiple compute nodes, enabling analysis of much larger data sets than is possible with the strictly serial or previous parallel implementations of HOP. We provide a reference implementation of this method as a part of the toolkit {sup yt}, an analysis toolkit for adaptive mesh refinement data that include complementary analysis modules. Additionally, we discuss a suite of benchmarks that demonstrate that this method scales well up to several hundred tasks and data sets in excess of 2000{sup 3} particles. The Parallel HOP method and our implementation can be readily applied to any kind of N-body simulation data and is therefore widely applicable.« less

  3. Population Health and Occupational Therapy.

    PubMed

    Braveman, Brent

    2016-01-01

    Occupational therapy practitioners play an important role in improving the health of populations through the development of occupational therapy interventions at the population level and through advocacy to address occupational participation and the multiple determinants of health. This article defines and explores population health as a concept and describes the appropriateness of occupational therapy practice in population health. Support of population health practice as evidenced in the official documents of the American Occupational Therapy Association and the relevance of population health for occupational therapy as a profession are reviewed. Recommendations and directions for the future are included related to celebration of the achievements of occupational therapy practitioners in the area of population health, changes to the Occupational Therapy Practice Framework and educational accreditation standards, and the importance of supporting, recognizing, rewarding, and valuing occupational therapy practitioners who assume roles in which direct care is not their primary function. Copyright © 2016 by the American Occupational Therapy Association, Inc.

  4. The X-ray halo of an extremely luminous LSB disk galaxy

    NASA Technical Reports Server (NTRS)

    Weiner, Benjamin J.

    2004-01-01

    We are continuing to refine our upper limit on emission from halo gas in Malin 2. The upper limit is, of course, below the detected flux, but is made more difficult to quantify by the disk and possible AGN sources. We are also exploring spectral and spatial-size constraints to help separate the sources of emission. On the theory side, more recent work on the X-ray halo luminosity from halo gas leftover from galaxy formation has lowered the prediction for disk galaxies (e.g. Toft et al. 2002, MNRAS, 335, 799). While our upper limit is well below the original prediction, refinements in model have moved the theoretical goalposts, so that the observation may be consistent with newer models. A recent theoretical development, which our observations of Malin 2 appear to support, is that a substantial amount of mass can be accreted onto galaxies without being heated at a virial shock. The previous standard theory was that gas accreting into a halo hits a virial shock and is heated to high temperatures, which could produce X-ray halos in massive galaxies. Recent models show that "smooth accretion" of matter bypasses the virial shocking (Murali e t al. 2002, ApJ, 571, 1; Birnboim & Dekel 2003, MNRAS, 345, 349). Additionally, new hydrodynamical simulations of galaxy mergers by UCSC graduate student T. J. Cox show that hot gas halos can be created by gas blown out from the merger, taking up orbital energy of the merging galaxies (Cox et al. 2004, ApJ, 607, L87). If mergers rather than virial shocking are the origin of hot gas halos, the existence of an X-ray halo should depend more on past merger activity than halo mass. Then it makes sense that elliptical galaxies and poor groups with ellipticals, which are probably formed in mergers, have X-ray gas halos; while a giant, quiescent LSB disk galaxy like Malin 2, which has never suffered a major merger, does not have an X-ray halo. While both the observational expectations and theoretical models have changed since we began this

  5. HaloTag Technology: A Versatile Platform for Biomedical Applications

    PubMed Central

    2015-01-01

    Exploration of protein function and interaction is critical for discovering links among genomics, proteomics, and disease state; yet, the immense complexity of proteomics found in biological systems currently limits our investigational capacity. Although affinity and autofluorescent tags are widely employed for protein analysis, these methods have been met with limited success because they lack specificity and require multiple fusion tags and genetic constructs. As an alternative approach, the innovative HaloTag protein fusion platform allows protein function and interaction to be comprehensively analyzed using a single genetic construct with multiple capabilities. This is accomplished using a simplified process, in which a variable HaloTag ligand binds rapidly to the HaloTag protein (usually linked to the protein of interest) with high affinity and specificity. In this review, we examine all current applications of the HaloTag technology platform for biomedical applications, such as the study of protein isolation and purification, protein function, protein–protein and protein–DNA interactions, biological assays, in vitro cellular imaging, and in vivo molecular imaging. In addition, novel uses of the HaloTag platform are briefly discussed along with potential future applications. PMID:25974629

  6. High-resolution disruption halo current measurements using Langmuir probes in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Tinguely, R. A.; Granetz, R. S.; Berg, A.; Kuang, A. Q.; Brunner, D.; LaBombard, B.

    2018-01-01

    Halo currents generated during disruptions on Alcator C-Mod have been measured with Langmuir ‘rail’ probes. These rail probes are embedded in a lower outboard divertor module in a closely-spaced vertical (poloidal) array. The dense array provides detailed resolution of the spatial dependence (~1 cm spacing) of the halo current distribution in the plasma scrape-off region with high time resolution (400 kHz digitization rate). As the plasma limits on the outboard divertor plate, the contact point is clearly discernible in the halo current data (as an inversion of current) and moves vertically down the divertor plate on many disruptions. These data are consistent with filament reconstructions of the plasma boundary, from which the edge safety factor of the disrupting plasma can be calculated. Additionally, the halo current ‘footprint’ on the divertor plate is obtained and related to the halo flux width. The voltage driving halo current and the effective resistance of the plasma region through which the halo current flows to reach the probes are also investigated. Estimations of the sheath resistance and halo region resistivity and temperature are given. This information could prove useful for modeling halo current dynamics.

  7. Halo current diagnostic system of experimental advanced superconducting tokamak

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chen, D. L.; Shen, B.; Sun, Y.

    2015-10-15

    The design, calibration, and installation of disruption halo current sensors for the Experimental Advanced Superconducting Tokamak are described in this article. All the sensors are Rogowski coils that surround conducting structures, and all the signals are analog integrated. Coils with two different cross-section sizes have been fabricated, and their mutual inductances are calibrated. Sensors have been installed to measure halo currents in several different parts of both the upper divertor (tungsten) and lower divertor (graphite) at several toroidal locations. Initial measurements from disruptions show that the halo current diagnostics are working well.

  8. Effect of halo-vest components on stabilizing the injured cervical spine.

    PubMed

    Ivancic, Paul C; Beauchman, Naseem N; Tweardy, Lisa

    2009-01-15

    An in vitro biomechanical study. The objectives were to develop a new biofidelic skull-neck-thorax model capable of quantifying motion patterns of the cervical spine in the presence of a halo-vest; to investigate the effects of vest loosening, superstructure loosening, and removal of the posterior uprights; and to evaluate the ability of the halo-vest to stabilize the neck within physiological motion limits. Previous clinical and biomechanical studies have investigated neck motion with the halo-vest only in the sagittal plane or only at the injured spinal level. No previous studies have quantified three-dimensional intervertebral motion patterns throughout the injured cervical spine stabilized with the halo-vest or studied the effect of halo-vest components on these motions. The halo-vest was applied to the skull-neck-thorax model. Six osteoligamentous whole cervical spine specimens (occiput through T1 vertebra) were used that had sustained multiplanar ligamentous injuries at C3/4 through C7-T1 during a previous protocol. Flexibility tests were performed with normal halo-vest application, loose vest, loose superstructure, and following removal of the posterior uprights. Average total range of motion for each experimental condition was statistically compared (P < 0.05) with the physiologic rotation limit for each spinal level. Cervical spine snaking was observed in both the sagittal and frontal planes. The halo-vest, applied normally, generally limited average spinal motions to within average physiological limits. No significant increases in average spinal motions above physiologic were observed due to loose vest, loose superstructure, or removal of the posterior uprights. However, a trend toward increased motion at C6/7 in lateral bending was observed due to loose superstructure. The halo-vest, applied normally, effectively immobilized the cervical spine. Sagittal or frontal plane snaking of the cervical spine due to the halo-vest may reduce its immobilization

  9. Large-scale assembly bias of dark matter halos

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lazeyras, Titouan; Musso, Marcello; Schmidt, Fabian, E-mail: titouan@mpa-garching.mpg.de, E-mail: mmusso@sas.upenn.edu, E-mail: fabians@mpa-garching.mpg.de

    We present precise measurements of the assembly bias of dark matter halos, i.e. the dependence of halo bias on other properties than the mass, using curved 'separate universe' N-body simulations which effectively incorporate an infinite-wavelength matter overdensity into the background density. This method measures the LIMD (local-in-matter-density) bias parameters b {sub n} in the large-scale limit. We focus on the dependence of the first two Eulerian biases b {sup E} {sup {sub 1}} and b {sup E} {sup {sub 2}} on four halo properties: the concentration, spin, mass accretion rate, and ellipticity. We quantitatively compare our results with previous worksmore » in which assembly bias was measured on fairly small scales. Despite this difference, our findings are in good agreement with previous results. We also look at the joint dependence of bias on two halo properties in addition to the mass. Finally, using the excursion set peaks model, we attempt to shed new insights on how assembly bias arises in this analytical model.« less

  10. Simulating halos and coronas in their atmospheric environment.

    PubMed

    David Gedzelman, Stanley

    2008-12-01

    Models are developed that simulate the light and color of the sky and of circular halos and coronas as a function of atmospheric pressure, cloud height, width, and optical depth, solar zenith angle, aerosol concentration and size, and ozone content. Halos, coronas, and skylight are treated as singly scattered sunbeams that are depleted in their passage through the atmosphere and cloud. Multiple scattering is included only for background cloud light. Halos produced by hexagonal crystal prisms and coronas produced by monodisperse droplets are visible for cloud optical depths in the range 0.0003 halos and coronas can be bright only at smaller cloud optical depths and tend to be faint at their bottoms when produced in high cloud layers but can be bright at the horizon when produced by narrow cloud cells near ground level.

  11. Developing a Model of Occupational Choice.

    ERIC Educational Resources Information Center

    Egner, Joan Roos; And Others

    Review of the literature in counseling, sociology, psychology, and organizational behavior failed to yield a model satisfactory for a comprehensive research framework investigating why people choose different occupations. Rational and irrational occupational decision making models were unsatisfactory in capturing the many dimensions of the…

  12. Strong orientation dependence of surface mass density profiles of dark haloes at large scales

    NASA Astrophysics Data System (ADS)

    Osato, Ken; Nishimichi, Takahiro; Oguri, Masamune; Takada, Masahiro; Okumura, Teppei

    2018-06-01

    We study the dependence of surface mass density profiles, which can be directly measured by weak gravitational lensing, on the orientation of haloes with respect to the line-of-sight direction, using a suite of N-body simulations. We find that, when major axes of haloes are aligned with the line-of-sight direction, surface mass density profiles have higher amplitudes than those averaged over all halo orientations, over all scales from 0.1 to 100 Mpc h-1 we studied. While the orientation dependence at small scales is ascribed to the halo triaxiality, our results indicate even stronger orientation dependence in the so-called two-halo regime, up to 100 Mpc h-1. The orientation dependence for the two-halo term is well approximated by a multiplicative shift of the amplitude and therefore a shift in the halo bias parameter value. The halo bias from the two-halo term can be overestimated or underestimated by up to ˜ 30 per cent depending on the viewing angle, which translates into the bias in estimated halo masses by up to a factor of 2 from halo bias measurements. The orientation dependence at large scales originates from the anisotropic halo-matter correlation function, which has an elliptical shape with the axis ratio of ˜0.55 up to 100 Mpc h-1. We discuss potential impacts of halo orientation bias on other observables such as optically selected cluster samples and a clustering analysis of large-scale structure tracers such as quasars.

  13. A GRAVITATIONAL DOUBLE-SCATTERING MECHANISM FOR GENERATING HIGH-VELOCITY OBJECTS DURING HALO MERGERS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Samsing, Johan; Department of Astrophysical Sciences, Princeton University, Peyton Hall, Princeton, NJ 08544

    2015-02-01

    We present a dynamical model that describes how halo particles can receive a significant energy kick from the merger between their own host halo and a target halo. This could provide a possible explanation for some high-velocity objects, including extended systems like globular clusters (GCs). In the model we especially introduce a double-scattering mechanism, where a halo particle receives a significant part of its total energy kick by first undergoing a gravitational deflection by the target halo and subsequently by its original host halo. This generates an energy kick that is due to the relative velocity between the halos duringmore » the deflections. We derive analytically the total kick energy of the particle, which is composed of energy from the double-scattering mechanism and tidal fields, as a function of its position in its original host halo just before merger. In the case of a 1:10 merger, we find that the presented mechanisms can easily generate particles with a velocity approximately two times the virial velocity of the target halo. This motivates us to suggest that the high velocity of the recently discovered GC HVGC-1 can be explained by a head-on halo merger. Finally, we illustrate the orbital evolution of high-velocity particles outside the virial sphere of the target halo by solving the equation of motion in an expanding universe. We find a sweet spot around a scale factor of 0.3-0.5 for ejecting particles into large orbits, which can easily reach beyond approximately five virial radii.« less

  14. Two Stellar Components in the Halo of the Milky Way

    DTIC Science & Technology

    2007-12-13

    that might be considered, multiple lines of evidence derived from these data clearly confirm that the halo can be resolved into (at least) two primary...of the inner-halo population. Evidence for the dichotomy of the halo The spectroscopy, photometry and astrometry for our large sample of stars were...0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing

  15. A Speeding Binary in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    The recent discovery of a hyper-velocity binary star system in the halo of the Milky Way poses a mystery: how was this system accelerated to its high speed?Accelerating StarsUnlike the uniform motion in the Galactic disk, stars in the Milky Ways halo exhibit a huge diversity of orbits that are usually tilted relative to the disk and have a variety of speeds. One type of halo star, so-called hyper-velocity stars, travel with speeds that can approach the escape velocity of the Galaxy.How do these hyper-velocity stars come about? Assuming they form in the Galactic disk, there are multiple proposed scenarios through which they could be accelerated and injected into the halo, such as:Ejection after a close encounter with the supermassive black hole at the Galactic centerEjection due to a nearby supernova explosionEjection as the result of a dynamical interaction in a dense stellar population.Further observations of hyper-velocity stars are necessary to identify the mechanism responsible for their acceleration.J1211s SurpriseModels of J1211s orbit show it did not originate from the Galactic center (black dot). The solar symbol shows the position of the Sun and the star shows the current position of J1211. The bottom two panels show two depictions(x-y plane and r-z plane) of estimated orbits of J1211 over the past 10 Gyr. [Nmeth et al. 2016]To this end, a team of scientists led by Pter Nmeth (Friedrich Alexander University, Erlangen-Nrnberg) recently studied the candidate halo hyper-velocity star SDSS J121150.27+143716.2. The scientists obtained spectroscopy of J1211 using spectrographs at the Keck Telescope in Hawaii and ESOs Very Large Telescope in Chile. To their surprise, they discovered the signature of a companion in the spectra: J1211 is actually a binary!Nmeth and collaborators found that J1211, located roughly 18,000 light-years away, is moving at a rapid ~570 km/s relative to the galactic rest frame. The binary system consists of a hot (30,600 K) subdwarf and a

  16. Tests and consequences of disk plus halo models of gamma-ray burst sources

    NASA Technical Reports Server (NTRS)

    Smith, I. A.

    1995-01-01

    The gamma-ray burst observations made by the Burst and Transient Source Experiment (BATSE) and by previous experiments are still consistent with a combined Galactic disk (or Galactic spiral arm) plus extended Galactic halo model. Testable predictions and consequences of the disk plus halo model are discussed here; tests performed on the expanded BATSE database in the future will constrain the allowed model parameters and may eventually rule out the disk plus halo model. Using examples, it is shown that if the halo has an appropriate edge, BATSE will never detect an anisotropic signal from the halo of the Andromeda galaxy. A prediction of the disk plus halo model is that the fraction of the bursts observed to be in the 'disk' population rises as the detector sensitivity improves. A careful reexamination of the numbers of bursts in the two populations for the pre-BATSE databases could rule out this class of models. Similarly, it is predicted that different satellites will observe different relative numbers of bursts in the two classes for any model in which there are two different spatial distribiutions of the sources, or for models in which there is one spatial distribution of the sources that is sampled to different depths for the two classes. An important consequence of the disk plus halo model is that for the birthrate of the halo sources to be small compared to the birthrate of the disk sources, it is necessary for the halo sources to release many orders of magnitude more energy over their bursting lifetime than the disk sources. The halo bursts must also be much more luminous than the disk bursts; if this disk-halo model is correct, it is necessary to explain why the disk sources do not produce halo-type bursts.

  17. Jupiter's Ring Halo

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (km) per picture element (pixel) along the rings; however, because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow peering back toward the Sun; the ring was approximately 2,300,000 kilometers (km) away. The arc on the far right of the image is produced by sunlight scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age.

    Jupiter's ring system is composed of three parts -- a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, which lies exterior to the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the far left side of the figure. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow.

    A faint mist of particles can be seen above and below the main rings; this vertically extended, toroidal 'halo' is unusual in planetary rings, and is probably caused by electromagnetic forces which can push small grains out of the ring plane. Halo material is present across this entire image, implying that it reaches more than 27,000 km above the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic. In order to accentuate faint features in the image, different brightnesses are shown through color, with the brightest

  18. Halo histories versus Galaxy properties at z = 0 - I. The quenching of star formation

    NASA Astrophysics Data System (ADS)

    Tinker, Jeremy L.; Wetzel, Andrew R.; Conroy, Charlie; Mao, Yao-Yuan

    2017-12-01

    We test whether halo age and galaxy age are correlated at fixed halo and galaxy mass. The formation histories, and thus ages, of dark matter haloes correlate with their large-scale density ρ, an effect known as assembly bias. We test whether this correlation extends to galaxies by measuring the dependence of galaxy stellar age on ρ. To clarify the comparison between theory and observation, and to remove the strong environmental effects on satellites, we use galaxy group catalogues to identify central galaxies and measure their quenched fraction, fQ, as a function of large-scale environment. Models that match halo age to central galaxy age predict a strong positive correlation between fQ and ρ. However, we show that the amplitude of this effect depends on the definition of halo age: assembly bias is significantly reduced when removing the effects of splashback haloes - those haloes that are central but have passed through a larger halo or experienced strong tidal encounters. Defining age using halo mass at its peak value rather than current mass removes these effects. In Sloan Digital Sky Survey data, at M* ≳ 1010 M⊙ h-2, there is a ∼5 per cent increase in fQ from low-to-high densities, which is in agreement with predictions of dark matter haloes using peak halo mass. At lower stellar mass there is little to no correlation of fQ with ρ. For these galaxies, age matching is inconsistent with the data across the range of halo formation metrics that we tested. This implies that halo formation history has a small but statistically significant impact on quenching of star formation at high masses, while the quenching process in low-mass central galaxies is uncorrelated with halo formation history.

  19. Galaxy formation with BECDM - I. Turbulence and relaxation of idealized haloes

    NASA Astrophysics Data System (ADS)

    Mocz, Philip; Vogelsberger, Mark; Robles, Victor H.; Zavala, Jesús; Boylan-Kolchin, Michael; Fialkov, Anastasia; Hernquist, Lars

    2017-11-01

    We present a theoretical analysis of some unexplored aspects of relaxed Bose-Einstein condensate dark matter (BECDM) haloes. This type of ultralight bosonic scalar field dark matter is a viable alternative to the standard cold dark matter (CDM) paradigm, as it makes the same large-scale predictions as CDM and potentially overcomes CDM's small-scale problems via a galaxy-scale de Broglie wavelength. We simulate BECDM halo formation through mergers, evolved under the Schrödinger-Poisson equations. The formed haloes consist of a soliton core supported against gravitational collapse by the quantum pressure tensor and an asymptotic r-3 NFW-like profile. We find a fundamental relation of the core-to-halo mass with the dimensionless invariant Ξ ≡ |E|/M3/(Gm/ℏ)2 or Mc/M ≃ 2.6Ξ1/3, linking the soliton to global halo properties. For r ≥ 3.5 rc core radii, we find equipartition between potential, classical kinetic and quantum gradient energies. The haloes also exhibit a conspicuous turbulent behaviour driven by the continuous reconnection of vortex lines due to wave interference. We analyse the turbulence 1D velocity power spectrum and find a k-1.1 power law. This suggests that the vorticity in BECDM haloes is homogeneous, similar to thermally-driven counterflow BEC systems from condensed matter physics, in contrast to a k-5/3 Kolmogorov power law seen in mechanically-driven quantum systems. The mode where the power spectrum peaks is approximately the soliton width, implying that the soliton-sized granules carry most of the turbulent energy in BECDM haloes.

  20. Effects of primordial magnetic field on the formation rate of dark matter halos

    NASA Astrophysics Data System (ADS)

    Cheera, Varalakshmi; Nigam, Rahul

    2018-05-01

    We construct and demonstrate a method for computing the formation rate of the dark matter halo in the hierarchical model set up. This method uses the Press-Schecter distribution for the halos and hence applies only to the spherical halos. But this can be generalized to ellipsoidal structures also if one uses the Sheth-Torman distribution. After obtaining the formation rate, we study the effect of primordial magnetic field on the dynamics of these halos. We investigate the effect for different field strengths and conclude that a magnetic field stronger than 10 nG would impact the halos larger than 108 solar masses while a weaker field affects the formation rate of smaller halos.

  1. Velocity Structure and Plasma Properties in Halo CMEs

    NASA Technical Reports Server (NTRS)

    Wagner, William (Technical Monitor); Raymond, John C.

    2003-01-01

    We have identified a set of 23 Halo CMEs through July 2002 and 21 Partial Halo CMEs from the LASCO Halo CME Mail Archive for which Ultraviolet Coronagraph Spectrometer (UVCS) spectra exist. For each event we have collected basic information such as the event speed, whether or not UVCS caught the bright front, lines detected, Doppler shift and associated flare class. We have also obtained excellent observations of some of the spectacular events in November 2003, and we have made theoretical calculations pertaining to CME expansion at the heights observed by UVCS. We first analyzed the halo CMEs on 21 April and 24 August 2002 and the partial halo on 23 July 2002, because the X-class flares associated with these CMEs were extensively observed by RHESSI and other instruments as part of the MAX MILLENIUM campaign. These very fast CMEs showed extremely violent disruption of the pre-CME streamers, little or no cool prominence material, and the unusual (for UVCS heights) hot emission line [Fe XVIII]. Results, including a discussion of the current sheet interpretation for the [Fe XVIII] emission, are published in Raymond et al. and presented at the Fall 2002 AGU meeting and the solar physics summer school in L'Aquila, Italy. We are currently preparing two papers on the Dec. 28, 2000 partial halo event. This event was chosen to take advantage of the SEP event measured by WIND and ACE, and because a Type II radio burst coincides with the time that broad, blue-shifted O VI emission appeared in the UVCS spectra. One paper deals with a new density and velocity diagnostic for very fast CMEs; pumping of O VI lambda 1032 by Ly beta and pumping of O VI lambda 1038 by O VI lambda 1032. The other discusses physics of the shock wave and association with the SEP event. In the coming year we plan to expand the list of Halo and Partial Halo events observed by UVCS through the end of 2003. We will look at those events as a class to search for correlation between UV spectral characteristics

  2. Using self-organizing maps to identify potential halo white dwarfs.

    PubMed

    García-Berro, Enrique; Torres, Santiago; Isern, Jordi

    2003-01-01

    We present the results of an unsupervised classification of the disk and halo white dwarf populations in the solar neighborhood. The classification is done by merging the results of detailed Monte Carlo (MC) simulations, which reproduce very well the characteristics of the white dwarf populations in the solar neighborhood, with a catalogue of real stars. The resulting composite catalogue is analyzed using a competitive learning algorithm. In particular we have used the so-called self-organized map. The MC simulated stars are used as tracers and help in identifying the resulting clusters. The results of such an strategy turn out to be quite satisfactory, suggesting that this approach can provide an useful framework for analyzing large databases of white dwarfs with well determined kinematical, spatial and photometric properties once they become available in the next decade. Moreover, the results are of astrophysical interest as well, since a straightforward interpretation of several recent astronomical observations, like the detected microlensing events in the direction of the Magellanic Clouds, the possible detection of high proper motion white dwarfs in the Hubble Deep Field and the discovery of high velocity white dwarfs in the solar neighborhood, suggests that a fraction of the baryonic dark matter component of our galaxy could be in the form of old and dim halo white dwarfs.

  3. Gaia reveals a metal-rich in-situ component of the local stellar halo

    NASA Astrophysics Data System (ADS)

    Bonaca, Ana; Conroy, Charlie; Wetzel, Andrew; Hopkins, Philip; Keres, Dusan

    2018-01-01

    We use the first Gaia data release, combined with RAVE and APOGEE spectroscopic surveys, to investigate the origin of halo stars within ~3 kpc from the Sun. We identify halo stars kinematically, as moving with a relative speed of at least 220 km/s with respect to the local standard of rest. These stars are in general more metal-poor than the disk, but surprisingly, half of our halo sample is comprised of stars with [Fe/H]>-1. The orbital directions of these metal-rich halo stars are preferentially aligned with the disk rotation, in sharp contrast with the isotropic orbital distribution of the more metal-poor halo stars. We find similar properties in the Latte cosmological zoom-in simulation of a Milky Way-like galaxy from the FIRE project. In Latte, metal-rich halo stars formed primarily inside of the solar circle, while lower-metallicity halo stars preferentially formed at larger distances (extending beyond the virial radius). This suggests that metal-rich halo stars in the Solar neighborhood in fact formed in situ within the Galactic disk rather than having been accreted from satellite systems. These stars, currently on halo-like orbits, therefore have likely undergone substantial radial migration/heating.

  4. Gaia Reveals a Metal-rich, in situ Component of the Local Stellar Halo

    NASA Astrophysics Data System (ADS)

    Bonaca, Ana; Conroy, Charlie; Wetzel, Andrew; Hopkins, Philip F.; Kereš, Dušan

    2017-08-01

    We use the first Gaia data release, combined with the RAVE and APOGEE spectroscopic surveys, to investigate the origin of halo stars within ≲ 3 kpc from the Sun. We identify halo stars kinematically as moving at a relative speed of at least 220 km s-1 with respect to the local standard of rest. These stars are generally less metal-rich than the disk, but surprisingly, half of our halo sample is comprised of stars with [{Fe}/{{H}}]> -1. The orbital directions of these metal-rich halo stars are preferentially aligned with the disk rotation, in sharp contrast with the intrinsically isotropic orbital distribution of the metal-poor halo stars. We find similar properties in the Latte cosmological zoom-in simulation of a Milky Way-like galaxy from the FIRE project. In Latte, metal-rich halo stars formed primarily inside of the solar circle, whereas lower-metallicity halo stars preferentially formed at larger distances (extending beyond the virial radius). This suggests that metal-rich halo stars in the solar neighborhood actually formed in situ within the Galactic disk, rather than having been accreted from satellite systems. These stars, currently on halo-like orbits, therefore have likely undergone substantial radial migration/heating.

  5. Home Economics Related Occupations Training Plans.

    ERIC Educational Resources Information Center

    Kupsinel, P., Ed.

    A framework is provided for teacher use in coordinating related classroom instruction, vocational homemaking student career objectives, and planned training station learning experiences. The details were prepared and revised by students of Home Economics Related Occupations 585 at Indiana State University. Child care occupation plans include those…

  6. Grains in galactic haloes

    NASA Technical Reports Server (NTRS)

    Ferrara, Andrea; Barsella, Bruno; Ferrini, F.; Greenberg, J. Mayo; Aiello, Santi

    1989-01-01

    Researchers considered the effect of extensive forces on dust grains subjected to the light and matter distribution of a spiral galaxy (Greenberg et al. (1987), Ferrini et al. (1987), Barsella et al (1988). Researchers showed that the combined force on a small particle located above the plane of a galactic disk may be either attractive or repulsive depending on a variety of parameters. They found, for example, that graphite grains from 20 nm to 250 nm radius are expelled from a typical galaxy, while silicates and other forms of dielectrics, after initial expulsion, may settle in potential minimum within the halo. They discuss only the statistical behavior of the forces for 17 galaxies whose luminosity and matter distribution in the disk, bulge and halo components are reasonably well known. The preliminary results of the study of the motion of a dust grain for NGC 3198 are given.

  7. The halo boundary of galaxy clusters in the SDSS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Baxter, Eric; Chang, Chihway; Jain, Bhuvnesh

    Analytical models and simulations predict a rapid decline in the halo density profile associated with the transition from the "infalling" regime outside the halo to the "collapsed" regime within the halo. Using data from SDSS, we explore evidence for such a feature in the density profiles of galaxy clusters using several different approaches. We first estimate the steepening of the outer galaxy density profile around clusters, finding evidence for truncation of the halo profile. Next, we measure the galaxy density profile around clusters using two sets of galaxies selected on color. We find evidence of an abrupt change in galaxymore » colors that coincides with the location of the steepening of the density profile. Since galaxies that have completed orbits within the cluster are more likely to be quenched of star formation and thus appear redder, this abrupt change in galaxy color can be associated with the transition from single-stream to multi-stream regimes. We also use a standard model comparison approach to measure evidence for a "splashback"-like feature, but find that this approach is very sensitive to modeling assumptions. Finally, we perform measurements using an independent cluster catalog to test for potential systematic errors associated with cluster selection. We identify several avenues for future work: improved understanding of the small-scale galaxy profile, lensing measurements, identification of proxies for the halo accretion rate, and other tests. As a result, with upcoming data from the DES, KiDS, and HSC surveys, we can expect significant improvements in the study of halo boundaries.« less

  8. The Halo Boundary of Galaxy Clusters in the SDSS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Baxter, Eric; Jain, Bhuvnesh; Sheth, Ravi K.

    Analytical models and simulations predict a rapid decline in the halo density profile associated with the transition from the “infalling” regime outside the halo to the “collapsed” regime within the halo. Using data from SDSS, we explore evidence for such a feature in the density profiles of galaxy clusters using several different approaches. We first estimate the steepening of the outer galaxy density profile around clusters, finding evidence for truncation of the halo profile. Next, we measure the galaxy density profile around clusters using two sets of galaxies selected on color. We find evidence of an abrupt change in galaxymore » colors that coincides with the location of the steepening of the density profile. Since galaxies that have completed orbits within the cluster are more likely to be quenched of star formation and thus appear redder, this abrupt change in galaxy color can be associated with the transition from single-stream to multi-stream regimes. We also use a standard model comparison approach to measure evidence for a “splashback”-like feature, but find that this approach is very sensitive to modeling assumptions. Finally, we perform measurements using an independent cluster catalog to test for potential systematic errors associated with cluster selection. We identify several avenues for future work: improved understanding of the small-scale galaxy profile, lensing measurements, identification of proxies for the halo accretion rate, and other tests. With upcoming data from the DES, KiDS, and HSC surveys, we can expect significant improvements in the study of halo boundaries.« less

  9. The halo boundary of galaxy clusters in the SDSS

    DOE PAGES

    Baxter, Eric; Chang, Chihway; Jain, Bhuvnesh; ...

    2017-05-18

    Analytical models and simulations predict a rapid decline in the halo density profile associated with the transition from the "infalling" regime outside the halo to the "collapsed" regime within the halo. Using data from SDSS, we explore evidence for such a feature in the density profiles of galaxy clusters using several different approaches. We first estimate the steepening of the outer galaxy density profile around clusters, finding evidence for truncation of the halo profile. Next, we measure the galaxy density profile around clusters using two sets of galaxies selected on color. We find evidence of an abrupt change in galaxymore » colors that coincides with the location of the steepening of the density profile. Since galaxies that have completed orbits within the cluster are more likely to be quenched of star formation and thus appear redder, this abrupt change in galaxy color can be associated with the transition from single-stream to multi-stream regimes. We also use a standard model comparison approach to measure evidence for a "splashback"-like feature, but find that this approach is very sensitive to modeling assumptions. Finally, we perform measurements using an independent cluster catalog to test for potential systematic errors associated with cluster selection. We identify several avenues for future work: improved understanding of the small-scale galaxy profile, lensing measurements, identification of proxies for the halo accretion rate, and other tests. As a result, with upcoming data from the DES, KiDS, and HSC surveys, we can expect significant improvements in the study of halo boundaries.« less

  10. The Halo Boundary of Galaxy Clusters in the SDSS

    NASA Astrophysics Data System (ADS)

    Baxter, Eric; Chang, Chihway; Jain, Bhuvnesh; Adhikari, Susmita; Dalal, Neal; Kravtsov, Andrey; More, Surhud; Rozo, Eduardo; Rykoff, Eli; Sheth, Ravi K.

    2017-05-01

    Analytical models and simulations predict a rapid decline in the halo density profile associated with the transition from the “infalling” regime outside the halo to the “collapsed” regime within the halo. Using data from SDSS, we explore evidence for such a feature in the density profiles of galaxy clusters using several different approaches. We first estimate the steepening of the outer galaxy density profile around clusters, finding evidence for truncation of the halo profile. Next, we measure the galaxy density profile around clusters using two sets of galaxies selected on color. We find evidence of an abrupt change in galaxy colors that coincides with the location of the steepening of the density profile. Since galaxies that have completed orbits within the cluster are more likely to be quenched of star formation and thus appear redder, this abrupt change in galaxy color can be associated with the transition from single-stream to multi-stream regimes. We also use a standard model comparison approach to measure evidence for a “splashback”-like feature, but find that this approach is very sensitive to modeling assumptions. Finally, we perform measurements using an independent cluster catalog to test for potential systematic errors associated with cluster selection. We identify several avenues for future work: improved understanding of the small-scale galaxy profile, lensing measurements, identification of proxies for the halo accretion rate, and other tests. With upcoming data from the DES, KiDS, and HSC surveys, we can expect significant improvements in the study of halo boundaries.

  11. Halo-orbit and lunar-swingby missions of the 1990's

    NASA Technical Reports Server (NTRS)

    Farquhar, Robert W.

    1990-01-01

    A significant number of spacecraft are planning to use halo orbits and lunar-swingby trajectories in the next decade. Four spacecraft will be placed into halo orbits around the earth's sunward libration point, while two others will be stationed near the sun-earth L2 libration point in the distant geomagnetic tail. Six spacecraft, including two of the aforementioned halo orbiters, will make use of lunar-swingby maneuvers to fulfill their mission objectives. Thus, a total of ten spacecraft, five from the Soviet Union, two from Japan, two from the United States, and one from the European Space Agency, will employ halo orbits and/or lunar-swingby trajectories in the 1990's. Pertinent facts are presented for each of these missions.

  12. The Angular Momentum of Baryons and Dark Matter Halos Revisited

    NASA Technical Reports Server (NTRS)

    Kimm, Taysun; Devriendt, Julien; Slyz, Adrianne; Pichon, Christophe; Kassin, Susan A.; Dubois, Yohan

    2011-01-01

    Recent theoretical studies have shown that galaxies at high redshift are fed by cold, dense gas filaments, suggesting angular momentum transport by gas differs from that by dark matter. Revisiting this issue using high-resolution cosmological hydrodynamics simulations with adaptive-mesh refinement (AMR), we find that at the time of accretion, gas and dark matter do carry a similar amount of specific angular momentum, but that it is systematically higher than that of the dark matter halo as a whole. At high redshift, freshly accreted gas rapidly streams into the central region of the halo, directly depositing this large amount of angular momentum within a sphere of radius r = 0.1R(sub vir). In contrast, dark matter particles pass through the central region unscathed, and a fraction of them ends up populating the outer regions of the halo (r/R(sub vir) > 0.1), redistributing angular momentum in the process. As a result, large-scale motions of the cosmic web have to be considered as the origin of gas angular momentum rather than its virialised dark matter halo host. This generic result holds for halos of all masses at all redshifts, as radiative cooling ensures that a significant fraction of baryons remain trapped at the centre of the halos. Despite this injection of angular momentum enriched gas, we predict an amount for stellar discs which is in fair agreement with observations at z=0. This arises because the total specific angular momentum of the baryons (gas and stars) remains close to that of dark matter halos. Indeed, our simulations indicate that any differential loss of angular momentum amplitude between the two components is minor even though dark matter halos continuously lose between half and two-thirds of their specific angular momentum modulus as they evolve. In light of our results, a substantial revision of the standard theory of disc formation seems to be required. We propose a new scenario where gas efficiently carries the angular momentum generated

  13. Deep brain transcranial magnetic stimulation using variable "Halo coil" system

    NASA Astrophysics Data System (ADS)

    Meng, Y.; Hadimani, R. L.; Crowther, L. J.; Xu, Z.; Qu, J.; Jiles, D. C.

    2015-05-01

    Transcranial Magnetic Stimulation has the potential to treat various neurological disorders non-invasively and safely. The "Halo coil" configuration can stimulate deeper regions of the brain with lower surface to deep-brain field ratio compared to other coil configurations. The existing "Halo coil" configuration is fixed and is limited in varying the site of stimulation in the brain. We have developed a new system based on the current "Halo coil" design along with a graphical user interface system that enables the larger coil to rotate along the transverse plane. The new system can also enable vertical movement of larger coil. Thus, this adjustable "Halo coil" configuration can stimulate different regions of the brain by adjusting the position and orientation of the larger coil on the head. We have calculated magnetic and electric fields inside a MRI-derived heterogeneous head model for various positions and orientations of the coil. We have also investigated the mechanical and thermal stability of the adjustable "Halo coil" configuration for various positions and orientations of the coil to ensure safe operation of the system.

  14. Taking Halo-Independent Dark Matter Methods Out of the Bin

    DOE PAGES

    Fox, Patrick J.; Kahn, Yonatan; McCullough, Matthew

    2014-10-30

    We develop a new halo-independent strategy for analyzing emerging DM hints, utilizing the method of extended maximum likelihood. This approach does not require the binning of events, making it uniquely suited to the analysis of emerging DM direct detection hints. It determines a preferred envelope, at a given confidence level, for the DM velocity integral which best fits the data using all available information and can be used even in the case of a single anomalous scattering event. All of the halo-independent information from a direct detection result may then be presented in a single plot, allowing simple comparisons betweenmore » multiple experiments. This results in the halo-independent analogue of the usual mass and cross-section plots found in typical direct detection analyses, where limit curves may be compared with best-fit regions in halo-space. The method is straightforward to implement, using already-established techniques, and its utility is demonstrated through the first unbinned halo-independent comparison of the three anomalous events observed in the CDMS-Si detector with recent limits from the LUX experiment.« less

  15. Relation between halo spin and cosmic-web filaments at z ≃ 3

    NASA Astrophysics Data System (ADS)

    González, Roberto E.; Prieto, Joaquin; Padilla, Nelson; Jimenez, Raul

    2017-02-01

    We investigate the spin evolution of dark matter haloes and their dependence on the number of connected filaments from the cosmic web at high redshift (spin-filament relation hereafter). To this purpose, we have simulated 5000 haloes in the mass range 5 × 109 h-1 M⊙ to 5 × 1011 h-1 M⊙ at z = 3 in cosmological N-body simulations. We confirm the relation found by Prieto et al. (2015) where haloes with fewer filaments have larger spin. We also found that this relation is more significant for higher halo masses, and for haloes with a passive (no major mergers) assembly history. Another finding is that haloes with larger spin or with fewer filaments have their filaments more perpendicularly aligned with the spin vector. Our results point to a picture in which the initial spin of haloes is well described by tidal torque theory and then gets subsequently modified in a predictable way because of the topology of the cosmic web, which in turn is given by the currently favoured Lambda cold dark matter (LCDM) model. Our spin-filament relation is a prediction from LCDM that could be tested with observations.

  16. On the halo events observed by Mount Fuji and Mount Kanbala Emulsion Chamber Experiments

    NASA Technical Reports Server (NTRS)

    Ren, J. R.; Kuang, H. H.; Huo, A. X.; Lu, S. L.; Su, S.; Wang, Y. X.; Xue, Y. G.; Wang, C. R.; He, M.; Zhang, N. J.

    1985-01-01

    The intensity of big gamma-ray families associated by halo is obtained from Mt. Fuji experiment (650 g/sq.cm. atmospheric depth) and Mt. Kanbala experiment (515 g/sq.cm.). The results are compared with Monte Carlo calculation based on several assumptions on interaction mechanisms and the primary cosmic ray composition. The results suggest more than 3 times lower proton abundance among primaries than that of 10 to the 12th to 10 to the 13th eV region within the framework of quasi-scaling model of multiple production.

  17. Estimating occupancy dynamics for large-scale monitoring networks: amphibian breeding occupancy across protected areas in the northeast United States

    USGS Publications Warehouse

    Miller, David A.W.; Grant, Evan H. Campbell

    2015-01-01

    Regional monitoring strategies frequently employ a nested sampling design where a finite set of study areas from throughout a region are selected within which intensive sub-sampling occurs. This sampling protocol naturally lends itself to a hierarchical analysis to account for dependence among sub-samples. Implementing such an analysis within a classic likelihood framework is computationally prohibitive with species occurrence data when accounting for detection probabilities. Bayesian methods offer an alternative framework to make this analysis feasible. We demonstrate a general approach for estimating occupancy when data come from a nested sampling design. Using data from a regional monitoring program of wood frogs (Lithobates sylvaticus) and spotted salamanders (Ambystoma maculatum) in vernal pools, we analyzed data using static and dynamic occupancy frameworks. We analyzed observations from 2004-2013collected within 14 protected areas located throughout the northeast United States . We use the data set to estimate trends in occupancy at both the regional and individual protected area level. We show that occupancy at the regional level was relatively stable for both species. Much more variation occurred within individual study areas, with some populations declining and some increasing for both species. We found some evidence for a latitudinal gradient in trends among protected areas. However, support for this pattern is overestimated when the hierarchical nature of the data collection is not controlled for in the analysis. For both species, occupancy appeared to be declining in the most southern areas, while occupancy was stable or increasing in more northern areas. These results shed light on the range-level population status of these pond-breeding amphibians and our approach provides a framework that can be used to examine drivers of change including among-year and among-site variation in occurrence dynamics, while properly accounting for nested structure of

  18. On the galaxy–halo connection in the EAGLE simulation

    DOE PAGES

    Desmond, Harry; Mao, Yao -Yuan; Wechsler, Risa H.; ...

    2017-06-13

    Empirical models of galaxy formation require assumptions about the correlations between galaxy and halo properties. These may be calibrated against observations or inferred from physical models such as hydrodynamical simulations. In this Letter, we use the EAGLE simulation to investigate the correlation of galaxy size with halo properties. We motivate this analysis by noting that the common assumption of angular momentum partition between baryons and dark matter in rotationally supported galaxies overpredicts both the spread in the stellar mass–size relation and the anticorrelation of size and velocity residuals, indicating a problem with the galaxy–halo connection it implies. We find themore » EAGLE galaxy population to perform significantly better on both statistics, and trace this success to the weakness of the correlations of galaxy size with halo mass, concentration and spin at fixed stellar mass. Here by, using these correlations in empirical models will enable fine-grained aspects of galaxy scalings to be matched.« less

  19. On the galaxy–halo connection in the EAGLE simulation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Desmond, Harry; Mao, Yao -Yuan; Wechsler, Risa H.

    Empirical models of galaxy formation require assumptions about the correlations between galaxy and halo properties. These may be calibrated against observations or inferred from physical models such as hydrodynamical simulations. In this Letter, we use the EAGLE simulation to investigate the correlation of galaxy size with halo properties. We motivate this analysis by noting that the common assumption of angular momentum partition between baryons and dark matter in rotationally supported galaxies overpredicts both the spread in the stellar mass–size relation and the anticorrelation of size and velocity residuals, indicating a problem with the galaxy–halo connection it implies. We find themore » EAGLE galaxy population to perform significantly better on both statistics, and trace this success to the weakness of the correlations of galaxy size with halo mass, concentration and spin at fixed stellar mass. Here by, using these correlations in empirical models will enable fine-grained aspects of galaxy scalings to be matched.« less

  20. On the galaxy-halo connection in the EAGLE simulation

    NASA Astrophysics Data System (ADS)

    Desmond, Harry; Mao, Yao-Yuan; Wechsler, Risa H.; Crain, Robert A.; Schaye, Joop

    2017-10-01

    Empirical models of galaxy formation require assumptions about the correlations between galaxy and halo properties. These may be calibrated against observations or inferred from physical models such as hydrodynamical simulations. In this Letter, we use the EAGLE simulation to investigate the correlation of galaxy size with halo properties. We motivate this analysis by noting that the common assumption of angular momentum partition between baryons and dark matter in rotationally supported galaxies overpredicts both the spread in the stellar mass-size relation and the anticorrelation of size and velocity residuals, indicating a problem with the galaxy-halo connection it implies. We find the EAGLE galaxy population to perform significantly better on both statistics, and trace this success to the weakness of the correlations of galaxy size with halo mass, concentration and spin at fixed stellar mass. Using these correlations in empirical models will enable fine-grained aspects of galaxy scalings to be matched.

  1. Wandering Supermassive Black Holes in Milky-Way-mass Halos

    NASA Astrophysics Data System (ADS)

    Tremmel, Michael; Governato, Fabio; Volonteri, Marta; Pontzen, Andrew; Quinn, Thomas R.

    2018-04-01

    We present a self-consistent prediction from a large-scale cosmological simulation for the population of “wandering” supermassive black holes (SMBHs) of mass greater than 106 M ⊙ on long-lived, kpc-scale orbits within Milky Way (MW)-mass galaxies. We extract a sample of MW-mass halos from the ROMULUS25 cosmological simulation, which is uniquely able to capture the orbital evolution of SMBHs during and following galaxy mergers. We predict that such halos, regardless of recent merger history or morphology, host an average of 5.1 ± 3.3 SMBHs, including their central black hole, within 10 kpc from the galactic center and an average of 12.2 ± 8.4 SMBHs total within their virial radius, not counting those in satellite halos. Wandering SMBHs exist within their host galaxies for several Gyr, often accreted by their host halo in the early Universe. We find, with >4σ significance, that wandering SMBHs are preferentially found outside of galactic disks.

  2. Galaxy formation with BECDM - I. Turbulence and relaxation of idealized haloes.

    PubMed

    Mocz, Philip; Vogelsberger, Mark; Robles, Victor H; Zavala, Jesús; Boylan-Kolchin, Michael; Fialkov, Anastasia; Hernquist, Lars

    2017-11-01

    We present a theoretical analysis of some unexplored aspects of relaxed Bose-Einstein condensate dark matter (BECDM) haloes. This type of ultralight bosonic scalar field dark matter is a viable alternative to the standard cold dark matter (CDM) paradigm, as it makes the same large-scale predictions as CDM and potentially overcomes CDM's small-scale problems via a galaxy-scale de Broglie wavelength. We simulate BECDM halo formation through mergers, evolved under the Schrödinger-Poisson equations. The formed haloes consist of a soliton core supported against gravitational collapse by the quantum pressure tensor and an asymptotic r -3 NFW-like profile. We find a fundamental relation of the core-to-halo mass with the dimensionless invariant Ξ ≡ | E |/ M 3 /( Gm/ħ ) 2 or M c / M ≃ 2.6Ξ 1/3 , linking the soliton to global halo properties. For r ≥ 3.5 r c core radii, we find equipartition between potential, classical kinetic and quantum gradient energies. The haloes also exhibit a conspicuous turbulent behaviour driven by the continuous reconnection of vortex lines due to wave interference. We analyse the turbulence 1D velocity power spectrum and find a k -1.1 power law. This suggests that the vorticity in BECDM haloes is homogeneous, similar to thermally-driven counterflow BEC systems from condensed matter physics, in contrast to a k -5/3 Kolmogorov power law seen in mechanically-driven quantum systems. The mode where the power spectrum peaks is approximately the soliton width, implying that the soliton-sized granules carry most of the turbulent energy in BECDM haloes.

  3. Massive Halos in Millennium Gas Simulations: Multivariate Scaling Relations

    NASA Astrophysics Data System (ADS)

    Stanek, R.; Rasia, E.; Evrard, A. E.; Pearce, F.; Gazzola, L.

    2010-06-01

    The joint likelihood of observable cluster signals reflects the astrophysical evolution of the coupled baryonic and dark matter components in massive halos, and its knowledge will enhance cosmological parameter constraints in the coming era of large, multiwavelength cluster surveys. We present a computational study of intrinsic covariance in cluster properties using halo populations derived from Millennium Gas Simulations (MGS). The MGS are re-simulations of the original 500 h -1 Mpc Millennium Simulation performed with gas dynamics under two different physical treatments: shock heating driven by gravity only (GO) and a second treatment with cooling and preheating (PH). We examine relationships among structural properties and observable X-ray and Sunyaev-Zel'dovich (SZ) signals for samples of thousands of halos with M 200 >= 5 × 1013 h -1 M sun and z < 2. While the X-ray scaling behavior of PH model halos at low redshift offers a good match to local clusters, the model exhibits non-standard features testable with larger surveys, including weakly running slopes in hot gas observable-mass relations and ~10% departures from self-similar redshift evolution for 1014 h -1 M sun halos at redshift z ~ 1. We find that the form of the joint likelihood of signal pairs is generally well described by a multivariate, log-normal distribution, especially in the PH case which exhibits less halo substructure than the GO model. At fixed mass and epoch, joint deviations of signal pairs display mainly positive correlations, especially the thermal SZ effect paired with either hot gas fraction (r = 0.88/0.69 for PH/GO at z = 0) or X-ray temperature (r = 0.62/0.83). The levels of variance in X-ray luminosity, temperature, and gas mass fraction are sensitive to the physical treatment, but offsetting shifts in the latter two measures maintain a fixed 12% scatter in the integrated SZ signal under both gas treatments. We discuss halo mass selection by signal pairs, and find a minimum mass

  4. The Peculiar Behavior of Halo Coronal Mass Ejections in Solar Cycle 24

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.; Xie, H.; Akiyama, S.; Makela, P.; Yashiro, S.; Michalek, G.

    2015-01-01

    We report on the remarkable finding that the halo coronal mass ejections (CMEs) in cycle 24 are more abundant than in cycle 23, although the sunspot number in cycle 24 has dropped by approx. 40%. We also find that the distribution of halo-CME source locations is different in cycle 24: the longitude distribution of halos is much flatter with the number of halos originating at a central meridian distance greater than or equal to 60deg twice as large as that in cycle 23. On the other hand, the average speed and associated soft X-ray flare size are the same in both cycles, suggesting that the ambient medium into which the CMEs are ejected is significantly different. We suggest that both the higher abundance and larger central meridian longitudes of halo CMEs can be explained as a consequence of the diminished total pressure in the heliosphere in cycle 24. The reduced total pressure allows CMEs to expand more than usual making them appear as halos.

  5. The Impact of Environment on the Stellar Mass–Halo Mass Relation

    NASA Astrophysics Data System (ADS)

    Golden-Marx, Jesse B.; Miller, Christopher J.

    2018-06-01

    A large variance exists in the amplitude of the stellar mass–halo mass (SMHM) relation for group- and cluster-size halos. Using a sample of 254 clusters, we show that the magnitude gap between the brightest central galaxy (BCG) and its second or fourth brightest neighbor accounts for a significant portion of this variance. We find that at fixed halo mass, galaxy clusters with a larger magnitude gap have a higher BCG stellar mass. This relationship is also observed in semi-analytic representations of low-redshift galaxy clusters in simulations. This SMHM–magnitude gap stratification likely results from BCG growth via hierarchical mergers and may link the assembly of the halo with the growth of the BCG. Using a Bayesian model, we quantify the importance of the magnitude gap in the SMHM relation using a multiplicative stretch factor, which we find to be significantly non-zero. The inclusion of the magnitude gap in the SMHM relation results in a large reduction in the inferred intrinsic scatter in the BCG stellar mass at fixed halo mass. We discuss the ramifications of this result in the context of galaxy formation models of centrals in group- and cluster-size halos.

  6. The Local Group in LCDM - Shapes and masses of dark halos

    NASA Astrophysics Data System (ADS)

    Vera-Ciro, Carlos Andrés

    2013-01-01

    In dit proefschrift bestuderen we de eigenschappen van donkere materie halo's in het LCDM paradigma. Het eerste deel richt zich op de vorm van de massadistributie van dergelijke objecten. We hebben gevonden dat de vorm van ge"isoleerde Melkweg-achtige donkere materie halo's significant afwijkt van bolsymmetrie. De lokale omgeving heeft invloed op de halo's en deze worden daarbij sterk be"invloed door de manier waarop massa aangroeit. We hebben ook de structuur en de baanstructuur van de satellieten van dergelijke halo's in detail onderzocht. In het algemeen zijn deze objecten sferischer dan de halo's zelf. Ze vertonen ook duidelijke afdrukken van getijdenwerking in zowel hun geometrische vorm als in de baanstructuur. Daarna gebruiken we het aantal massieve objecten rond de Melkweg om limieten te zetten op de totale massa van de donkere materie halo van de Melkweg. De eigenschappen van de massaverdeling van de Melkweg worden verder onderzocht in het laatste hoofdstuk. Daar maken we gebruik van de Sagittarius sterstroom om de vorm van de galactische potentiaal beter te bepalen. We komen met een nieuw model dat rekening houdt met de galactische schijf en de invloed van satellietstelsels en die bovendien consistent is met het LCDM paradigma.

  7. The star formation history in the Andromeda halo

    NASA Astrophysics Data System (ADS)

    Brown, Thomas M.

    I present the preliminary results of a program to measure the star formation history in the halo of the Andromeda galaxy. Using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, we obtained the deepest optical images of the sky to date, in a field on the southeast minor axis of Andromeda, 51' (11 kpc) from the nucleus. The resulting color-magnitude diagram (CMD) contains approximately 300,000 stars and extends more than 1.5 mag below the main sequence turnoff, with 50% completeness at V = 30.7 mag. We interpret this CMD using comparisons to ACS observations of five Galactic globular clusters through the same filters, and through χ2-fitting to a finely-spaced grid of calibrated stellar population models. We find evidence for a major (~30%) intermediate-age (6-8 Gyr) metal-rich ([Fe/H])>-0.5) population in the Andromeda halo, along with a significant old metal-poor population akin to that in the Milky Way halo. The large spread in ages suggests that the Andromeda halo formed as a result of a more violent merging history than that in our own Milky Way.

  8. Pushing down the low-mass halo concentration frontier with the Lomonosov cosmological simulations

    NASA Astrophysics Data System (ADS)

    Pilipenko, Sergey V.; Sánchez-Conde, Miguel A.; Prada, Francisco; Yepes, Gustavo

    2017-12-01

    We introduce the Lomonosov suite of high-resolution N-body cosmological simulations covering a full box of size 32 h-1 Mpc with low-mass resolution particles (2 × 107 h-1 M⊙) and three zoom-in simulations of overdense, underdense and mean density regions at much higher particle resolution (4 × 104 h-1 M⊙). The main purpose of this simulation suite is to extend the concentration-mass relation of dark matter haloes down to masses below those typically available in large cosmological simulations. The three different density regions available at higher resolution provide a better understanding of the effect of the local environment on halo concentration, known to be potentially important for small simulation boxes and small halo masses. Yet, we find the correction to be small in comparison with the scatter of halo concentrations. We conclude that zoom simulations, despite their limited representativity of the volume of the Universe, can be effectively used for the measurement of halo concentrations at least at the halo masses probed by our simulations. In any case, after a precise characterization of this effect, we develop a robust technique to extrapolate the concentration values found in zoom simulations to larger volumes with greater accuracy. Altogether, Lomonosov provides a measure of the concentration-mass relation in the halo mass range 107-1010 h-1 M⊙ with superb halo statistics. This work represents a first important step to measure halo concentrations at intermediate, yet vastly unexplored halo mass scales, down to the smallest ones. All Lomonosov data and files are public for community's use.

  9. ZOMG - II. Does the halo assembly history influence central galaxies and gas accretion?

    NASA Astrophysics Data System (ADS)

    Romano-Díaz, Emilio; Garaldi, Enrico; Borzyszkowski, Mikolaj; Porciani, Cristiano

    2017-08-01

    The growth rate and the internal dynamics of galaxy-sized dark-matter haloes depend on their location within the cosmic web. Haloes that sit at the nodes grow in mass till the present time and are dominated by radial orbits. Conversely, haloes embedded in prominent filaments do not change much in size and are dominated by tangential orbits. Using zoom hydrodynamical simulations including star formation and feedback, we study how gas accretes on to these different classes of objects, which, for simplicity, we dub 'accreting' and 'stalled' haloes. We find that all haloes get a fresh supply of newly accreted gas in their inner regions, although this slowly decreases with time, in particular for the stalled haloes. The inflow of new gas is always higher than (but comparable with) that of recycled material. Overall, the cold-gas fraction increases (decreases) with time for the accreting (stalled) haloes. In all cases, a stellar disc and a bulge form at the centre of the simulated haloes. The total stellar mass is in excellent agreement with expectations based on the abundance-matching technique. Many properties of the central galaxies do not seem to correlate with the large-scale environment in which the haloes reside. However, there are two notable exceptions that characterize stalled haloes with respect to their accreting counterparts: (I) The galaxy disc contains much older stellar populations. (II) Its vertical scaleheight is larger by a factor of 2 or more. This thickening is likely due to the heating of the long-lived discs by mergers and close flybys.

  10. Connecting massive galaxies to dark matter haloes in BOSS - I. Is galaxy colour a stochastic process in high-mass haloes?

    NASA Astrophysics Data System (ADS)

    Saito, Shun; Leauthaud, Alexie; Hearin, Andrew P.; Bundy, Kevin; Zentner, Andrew R.; Behroozi, Peter S.; Reid, Beth A.; Sinha, Manodeep; Coupon, Jean; Tinker, Jeremy L.; White, Martin; Schneider, Donald P.

    2016-08-01

    We use subhalo abundance matching (SHAM) to model the stellar mass function (SMF) and clustering of the Baryon Oscillation Spectroscopic Survey (BOSS) `CMASS' sample at z ˜ 0.5. We introduce a novel method which accounts for the stellar mass incompleteness of CMASS as a function of redshift, and produce CMASS mock catalogues which include selection effects, reproduce the overall SMF, the projected two-point correlation function wp, the CMASS dn/dz, and are made publicly available. We study the effects of assembly bias above collapse mass in the context of `age matching' and show that these effects are markedly different compared to the ones explored by Hearin et al. at lower stellar masses. We construct two models, one in which galaxy colour is stochastic (`AbM' model) as well as a model which contains assembly bias effects (`AgM' model). By confronting the redshift dependent clustering of CMASS with the predictions from our model, we argue that that galaxy colours are not a stochastic process in high-mass haloes. Our results suggest that the colours of galaxies in high-mass haloes are determined by other halo properties besides halo peak velocity and that assembly bias effects play an important role in determining the clustering properties of this sample.

  11. The dust scattering halo of Cygnus X-3

    NASA Astrophysics Data System (ADS)

    Corrales, L. R.; Paerels, F.

    2015-10-01

    Dust grains scatter X-ray light through small angles, producing a diffuse halo image around bright X-ray point sources situated behind a large amount of interstellar material. We present analytic solutions to the integral for the dust scattering intensity, which allow for a Bayesian analysis of the scattering halo around Cygnus X-3. Fitting the optically thin 4-6 keV halo surface brightness profile yields the dust grain size and spatial distribution. We assume a power-law distribution of grain sizes (n ∝ a-p) and fit for p, the grain radius cut-off amax, and dust mass column. We find that a p ≈ 3.5 dust grain size distribution with amax ≈ 0.2 μm fits the halo profile relatively well, whether the dust is distributed uniformly along the line of sight or in clumps. We find that a model consisting of two dust screens, representative of foreground spiral arms, requires the foreground Perseus arm to contain 80 per cent of the total dust mass. The remaining 20 per cent of the dust, which may be associated with the outer spiral arm of the Milky Way, is located within 1 kpc of Cyg X-3. Regardless of which model was used, we found τ_sca ˜ 2 E_keV^{-2}. We examine the energy resolved haloes of Cyg X-3 from 1 to 6 keV and find that there is a sharp drop in scattering halo intensity when E < 2-3 keV, which cannot be explained with multiple scattering effects. We hypothesize that this may be caused by large dust grains or material with unique dielectric properties, causing the scattering cross-section to depart from the Rayleigh-Gans approximation that is used most often in X-ray scattering studies. The foreground Cyg OB2 association, which contains several evolved stars with large extinction values, is a likely culprit for grains of unique size or composition.

  12. Luminosity distance in Swiss-cheese cosmology with randomized voids and galaxy halos

    NASA Astrophysics Data System (ADS)

    Flanagan, Éanna É.; Kumar, Naresh; Wasserman, Ira

    2013-08-01

    We study the fluctuations in luminosity distance due to gravitational lensing produced both by galaxy halos and large-scale voids. Voids are represented via a “Swiss-cheese” model consisting of a ΛCDM Friedmann-Robertson-Walker background from which a number of randomly distributed, spherical regions of comoving radius 35 Mpc are removed. A fraction of the removed mass is then placed on the shells of the spheres, in the form of randomly located halos. The halos are assumed to be nonevolving and are modeled with Navarro-Frenk-White profiles of a fixed mass. The remaining mass is placed in the interior of the spheres, either smoothly distributed or as randomly located halos. We compute the distribution of magnitude shifts using a variant of the method of Holz and Wald [Phys. Rev. D 58, 063501 (1998)], which includes the effect of lensing shear. In the two models we consider, the standard deviation of this distribution is 0.065 and 0.072 magnitudes and the mean is -0.0010 and -0.0013 magnitudes, for voids of radius 35 Mpc and the sources at redshift 1.5, with the voids chosen so that 90% of the mass is on the shell today. The standard deviation due to voids and halos is a factor ˜3 larger than that due to 35 Mpc voids alone with a 1 Mpc shell thickness, which we studied in our previous work. We also study the effect of the existence of evacuated voids, by comparing to a model where all the halos are randomly distributed in the interior of the sphere with none on its surface. This does not significantly change the variance but does significantly change the demagnification tail. To a good approximation, the variance of the distribution depends only on the mean column density of halos (halo mass divided by its projected area), the concentration parameter of the halos, and the fraction of the mass density that is in the form of halos (as opposed to smoothly distributed); it is independent of how the halos are distributed in space. We derive an approximate analytic

  13. An Occupation and Participation Approach to Reading Intervention (OPARI) Part I: Defining Reading as an Occupation

    ERIC Educational Resources Information Center

    Grajo, Lenin C.; Candler, Catherine

    2016-01-01

    This is the first of two papers that explore a role that occupational therapy can play in supporting children with reading challenges. Part I presents the grounding framework for an occupation and participation approach to reading intervention (OPARI) and serves to introduce the clinical application of the approach presented in Part II. In this…

  14. Novel technique for relieving anastomotic tension using halo-vest immobilization after tracheal sleeve resection.

    PubMed

    Imai, Kazuhiro; Minamiya, Yoshihiro; Saito, Hajime; Miyakoshi, Naohisa; Hongo, Michio; Kasukawa, Yuji; Ishikawa, Yoshinori; Motoyama, Satoru; Sato, Yusuke; Shimada, Yoichi; Ogawa, Jun-ichi

    2013-07-01

    We describe a novel technique of using halo-vest-enforced immobilization to relieve anastomotic tension after tracheal sleeve resection. Immediately after the tracheal sleeve resection, four halo titanium pins were inserted in the skulls of the patients to secure the halo-vest. All patients fitted with halo-vests were able to eat and drink and their clinical course was good. Bronchoscopy confirmed the absence of anastomotic leaks and stenoses, and there were no complications associated with the halo-vest. We believe that ensuring neck flexion using a halo-vest after tracheal sleeve resection is an excellent way of relieving anastomotic tension that would predispose the wound to dehiscence.

  15. Halo Coronal Mass Ejections: Comparing Observations and Models

    NASA Technical Reports Server (NTRS)

    Gilbert, Holly; Orlove, Matthew; SaintCyr, O.; Mays, L.; Gopalswamy, N.

    2011-01-01

    Since 1996, the SOHO LASCO coronagraphs have detected "halo" CMEs that appear to be directed toward Earth, but information about the size and speed of these events seen face-on has been limited. From a single vantage point along the Sun-Earth line, the primary limitation has been ambiguity in fitting the cone model (or other forward-modeling techniques, e.g., Thernisian et al., 2006). But in the past few years, the STEREO mission has provided a view of Earth-directed events from the side. These events offer the opportunity to compare measurements (width and speed) of halo CMEs observed by STEREO with models that derive halo CME properties. We report here results of such a comparison on a large sample of LASCO CMEs in the STEREO era.

  16. Particle-in-cell simulation study on halo formation in anisotropic beams

    NASA Astrophysics Data System (ADS)

    Ikegami, Masanori

    2000-11-01

    In a recent paper (M. Ikegami, Nucl. Instr. and Meth. A 435 (1999) 284), we investigated halo formation processes in transversely anisotropic beams based on the particle-core model. The effect of simultaneous excitation of two normal modes of core oscillation, i.e., high- and low-frequency modes, was examined. In the present study, self-consistent particle simulations are performed to confirm the results obtained in the particle-core analysis. In these simulations, it is confirmed that the particle-core analysis can predict the halo extent accurately even in anisotropic situations. Furthermore, we find that the halo intensity is enhanced in some cases where two normal modes of core oscillation are simultaneously excited as expected in the particle-core analysis. This result is of practical importance because pure high-frequency mode oscillation has frequently been assumed in preceding halo studies. The dependence of halo intensity on the 2:1 fixed point locations is also discussed.

  17. The Origin and Survival of Cold Gas in Hot Halos

    NASA Astrophysics Data System (ADS)

    Oh, Siang Peng

    Modern theories of structure formation unequivocally predict that density perturbations seeded in the big bang collapse to produce``halos'' of dark matter filled with hot, virialized gas. The physics of this hot halo gas fundamentally determines the mass-scale of galaxies, and likely plays a critical role in their subsequent evolution. Since this virialized halo gas is typically invisible, however, cosmological simulations have largely overlooked it, understandably focusing on more observable properties of galaxies such as their ISM content and star formation histories. However, as new observational techniques begin to probe the diffuse gas in galaxy halos, they are finding results inconsistent with predictions from cosmological simulations. Though halo gas is fundamental to galaxy formation, it cannot be explained with current models; halo gas thus represents the new frontier in testing and advancing our models of galaxy formation. One particularly surprising development has been the near-ubiquitous finding that galaxy halos are full of tiny, dense clouds of neutral gas. In a recent paper (McCourt et al 2016), we show that these unexpected observations imply that galaxies contain an enormous number of tiny cloudlets, dispersed throughout the halo like the water droplets in a fog. We detail a new hydrodynamical process, which we call ``shattering,'' that explains the tiny characteristic size for these cloudlets. While we can explain many observable properties of this cold gas (such as its broad line-width and tiny volume-filling fraction), we treated the amount of cold gas as a free parameter; this is fundamentally determined by galaxy formation rather than gas dynamics. This proposal extends the work of McCourt et al (2016) by focusing on the origin of the cold gas in galaxy halos. Since cold gas represents the fuel for star formation and feedback in galaxies, this question is crucial for studies of galaxy evolution. We consider two possibilities: 1) that cool CGM

  18. Dark matter haloes determine the masses of supermassive black holes

    NASA Astrophysics Data System (ADS)

    Booth, C. M.; Schaye, Joop

    2010-06-01

    The energy and momentum deposited by the radiation from accretion flows on to the supermassive black holes (BHs) that reside at the centres of virtually all galaxies can halt or even reverse gas inflow, providing a natural mechanism for supermassive BHs to regulate their growth and to couple their properties to those of their host galaxies. However, it remains unclear whether this self-regulation occurs on the scale at which the BH is gravitationally dominant, on that of the stellar bulge, the galaxy or that of the entire dark matter halo. To answer this question, we use self-consistent simulations of the co-evolution of the BH and galaxy populations that reproduce the observed correlations between the masses of the BHs and the properties of their host galaxies. We first confirm unambiguously that the BHs regulate their growth: the amount of energy that the BHs inject into their surroundings remains unchanged when the fraction of the accreted rest mass energy that is injected is varied by four orders of magnitude. The BHs simply adjust their masses so as to inject the same amount of energy. We then use simulations with artificially reduced star formation rates to demonstrate explicitly that BH mass is not set by the stellar mass. Instead, we find that it is determined by the mass of the dark matter halo with a secondary dependence on the halo concentration, of the form that would be expected if the halo binding energy were the fundamental property that controls the mass of the BH. We predict that the BH mass, mBH, scales with halo mass as mBH ~ mαhalo, with α ~ 1.55 +/- 0.05, and that the scatter around the mean relation in part reflects the scatter in the halo concentration-mass relation.

  19. A DISTANT RADIO MINI-HALO IN THE PHOENIX GALAXY CLUSTER

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Van Weeren, R. J.; Andrade-Santos, F.; Forman, W. R.

    We report the discovery of extended radio emission in the Phoenix cluster (SPT-CL J2344-4243, z = 0.596) with the Giant Metrewave Radio Telescope (GMRT) at 610 MHz. The diffuse emission extends over a region of at least 400-500 kpc and surrounds the central radio source of the Brightest Cluster Galaxy, but does not appear to be directly associated with it. We classify the diffuse emission as a radio mini-halo, making it the currently most distant mini-halo known. Radio mini-halos have been explained by synchrotron emitting particles re-accelerated via turbulence, possibly induced by gas sloshing generated from a minor merger event. Chandra observationsmore » show a non-concentric X-ray surface brightness distribution, which is consistent with this sloshing interpretation. The mini-halo has a flux density of 17 ± 5 mJy, resulting in a 1.4 GHz radio power of (10.4 ± 3.5) × 10{sup 24} W Hz{sup –1}. The combined cluster emission, which includes the central compact radio source, is also detected in a shallow GMRT 156 MHz observation and together with the 610 MHz data we compute a spectral index of –0.84 ± 0.12 for the overall cluster radio emission. Given that mini-halos typically have steeper radio spectra than cluster radio galaxies, this spectral index should be taken as an upper limit for the mini-halo.« less

  20. Possible existence of wormholes in the central regions of halos

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Rahaman, Farook, E-mail: rahaman@iucaa.ernet.in; Salucci, P., E-mail: salucci@sissa.it; INFN, Sezione di Trieste, Via Valerio 2, 34127, Trieste

    2014-11-15

    An earlier study (Rahaman, et al., 2014 and Kuhfittig, 2014) has demonstrated the possible existence of wormholes in the outer regions of the galactic halo, based on the Navarro–Frenk–White (NFW) density profile. This paper uses the Universal Rotation Curve (URC) dark matter model to obtain analogous results for the central parts of the halo. This result is an important compliment to the earlier result, thereby confirming the possible existence of wormholes in most of the spiral galaxies. - Highlights: • Earlier we showed possible existence of wormholes in the outer regions of halo. • We obtain here analogous results for themore » central parts of the galactic halo. • Our result is an important compliment to the earlier result. • This confirms possible existence of wormholes in most of the spiral galaxies.« less

  1. Weak Lensing by Large-Scale Structure: A Dark Matter Halo Approach.

    PubMed

    Cooray; Hu; Miralda-Escudé

    2000-05-20

    Weak gravitational lensing observations probe the spectrum and evolution of density fluctuations and the cosmological parameters that govern them, but they are currently limited to small fields and subject to selection biases. We show how the expected signal from large-scale structure arises from the contributions from and correlations between individual halos. We determine the convergence power spectrum as a function of the maximum halo mass and so provide the means to interpret results from surveys that lack high-mass halos either through selection criteria or small fields. Since shot noise from rare massive halos is mainly responsible for the sample variance below 10&arcmin;, our method should aid our ability to extract cosmological information from small fields.

  2. Dynamic occupancy models for explicit colonization processes

    USGS Publications Warehouse

    Broms, Kristin M.; Hooten, Mevin B.; Johnson, Devin S.; Altwegg, Res; Conquest, Loveday

    2016-01-01

    The dynamic, multi-season occupancy model framework has become a popular tool for modeling open populations with occupancies that change over time through local colonizations and extinctions. However, few versions of the model relate these probabilities to the occupancies of neighboring sites or patches. We present a modeling framework that incorporates this information and is capable of describing a wide variety of spatiotemporal colonization and extinction processes. A key feature of the model is that it is based on a simple set of small-scale rules describing how the process evolves. The result is a dynamic process that can account for complicated large-scale features. In our model, a site is more likely to be colonized if more of its neighbors were previously occupied and if it provides more appealing environmental characteristics than its neighboring sites. Additionally, a site without occupied neighbors may also become colonized through the inclusion of a long-distance dispersal process. Although similar model specifications have been developed for epidemiological applications, ours formally accounts for detectability using the well-known occupancy modeling framework. After demonstrating the viability and potential of this new form of dynamic occupancy model in a simulation study, we use it to obtain inference for the ongoing Common Myna (Acridotheres tristis) invasion in South Africa. Our results suggest that the Common Myna continues to enlarge its distribution and its spread via short distance movement, rather than long-distance dispersal. Overall, this new modeling framework provides a powerful tool for managers examining the drivers of colonization including short- vs. long-distance dispersal, habitat quality, and distance from source populations.

  3. Detecting the Disruption of Dark-Matter Halos with Stellar Streams.

    PubMed

    Bovy, Jo

    2016-03-25

    Narrow stellar streams in the Milky Way halo are uniquely sensitive to dark-matter subhalos, but many of these subhalos may be tidally disrupted. I calculate the interaction between stellar and dark-matter streams using analytical and N-body calculations, showing that disrupting objects can be detected as low-concentration subhalos. Through this effect, we can constrain the lumpiness of the halo as well as the orbit and present position of individual dark-matter streams. This will have profound implications for the formation of halos and for direct- and indirect-detection dark-matter searches.

  4. Globular cluster systems - Comparative evolution of Galactic halos

    NASA Astrophysics Data System (ADS)

    Harris, William E.

    Space distributions, metallicity/age distributions, and kinematics are considered for the Milky Way halo system. Comparisons are made with other systems, and time scales for dynamical evolution are considered. It is noted that the globular cluster subsystems of halos resemble each other more closely than their parent galaxies do; this forms a reasonable basis for supposing that they represent a kind of underlying unity in the protogalaxy formation process.

  5. Non-local bias in the halo bispectrum with primordial non-Gaussianity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tellarini, Matteo; Ross, Ashley J.; Wands, David

    2015-07-01

    Primordial non-Gaussianity can lead to a scale-dependent bias in the density of collapsed halos relative to the underlying matter density. The galaxy power spectrum already provides constraints on local-type primordial non-Gaussianity complementary those from the cosmic microwave background (CMB), while the bispectrum contains additional shape information and has the potential to outperform CMB constraints in future. We develop the bias model for the halo density contrast in the presence of local-type primordial non-Gaussianity, deriving a bivariate expansion up to second order in terms of the local linear matter density contrast and the local gravitational potential in Lagrangian coordinates. Nonlinear evolutionmore » of the matter density introduces a non-local tidal term in the halo model. Furthermore, the presence of local-type non-Gaussianity in the Lagrangian frame leads to a novel non-local convective term in the Eulerian frame, that is proportional to the displacement field when going beyond the spherical collapse approximation. We use an extended Press-Schechter approach to evaluate the halo mass function and thus the halo bispectrum. We show that including these non-local terms in the halo bispectra can lead to corrections of up to 25% for some configurations, on large scales or at high redshift.« less

  6. Single cell HaloChip assay on paper for point-of-care diagnosis.

    PubMed

    Ma, Liyuan; Qiao, Yong; Jones, Ross; Singh, Narendra; Su, Ming

    2016-11-01

    This article describes a paper-based low cost single cell HaloChip assay that can be used to assess drug- and radiation-induced DNA damage at point-of-care. Printing ink on paper effectively blocks fluorescence of paper materials, provides high affinity to charged polyelectrolytes, and prevents penetration of water in paper. After exposure to drug or ionizing radiation, cells are patterned on paper to create discrete and ordered single cell arrays, embedded inside an agarose gel, lysed with alkaline solution to allow damaged DNA fragments to diffuse out of nucleus cores, and form diffusing halos in the gel matrix. After staining DNA with a fluorescent dye, characteristic halos formed around cells, and the level of DNA damage can be quantified by determining sizes of halos and nucleus with an image processing program based on MATLAB. With its low fabrication cost and easy operation, this HaloChip on paper platform will be attractive to rapidly and accurately determine DNA damage for point-of-care evaluation of drug efficacy and radiation condition. Graphical Abstract Single cell HaloChip on paper.

  7. Occupation embedded in a real life: interweaving occupational science and occupational therapy. 1993 Eleanor Clarke Slagle Lecture.

    PubMed

    Clark, F

    1993-12-01

    This lecture presents an example of research in the genre of interpretive occupational science and demonstrates how occupational science can inform clinical practice. The innovative qualitative methodology used blended elements of the anthropological tradition of life history ethnography, ethnomethodology, the naturalistic methods used by Mattingly and Schön to study practice, and especially narrative analysis as described by Polkinghorne. The bulk of the paper is presented in the form of a narrative analysis that provides an account of a stroke survivor's personal struggle for recovery, a story that emerged from transcription, coding, and analysis of transcripts from approximately 20 hours of interview time. First, this narrative analysis provides an example of how the occupational science framework can evoke a particular kind of storytelling in which childhood occupation can be related to adult character. Storytelling of this kind is later shown to be therapeutic for the stroke survivor. Next, the narrative illustrates how rehabilitation can be experienced by the survivor as a rite of passage in which a person is moved to disability status and then abandoned. Finally, a picture is given of how occupational story making and occupational storytelling embedded in real life can nurture the human spirit to act and can become the core of clinical practice.

  8. Neutralinos and the Origin of Radio Halos in Clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Colafrancesco, S.; Mele, B.

    2001-11-01

    We assume that the supersymmetric lightest neutralino is a good candidate for the cold dark matter in the galaxy halo and explore the possibility to produce extended diffuse radio emission from high-energy electrons arising from the neutralino annihilation in galaxy clusters whose intracluster medium is filled with a large-scale magnetic field. We show that these electrons fit the population of seed relativistic electrons that is postulated in many models for the origin of cluster radio halos. For a uniform magnetic field of ~1-3 μG the population of seed relativistic electrons from neutralino annihilation can fit the radio halo spectra of two well-studied clusters: Coma and 1E 0657-56. In the case of a magnetic field that is radially decreasing from the cluster center, central values ~8 μG (for Coma) and ~50 μG (for 1E 0657-56) are required to fit the data. The radio halo data strongly favor a centrally peaked dark matter density profile (like a Navarro, Frenk, & White [NFW97] density profile). The shape and the frequency extension of the radio halo spectra are connected with the mass and physical composition of the neutralino. A pure gaugino neutralino with mass Mχ>=80 GeV can reasonably fit the radio halo spectra of both Coma and 1E 0657-56. The model we present here provides a number of extra predictions that make it definitely testable. On the one hand, it agrees quite well with the observations that (1) the radio halo is centered on the cluster dynamical center, usually coincident with the center of its X-ray emission; (2) the radio halo surface brightness is similar to the X-ray one; and (3) the monochromatic radio luminosity at 1.4 GHz correlates strongly with the intracluster (IC) gas temperature. On the other hand, the same model predicts that radio halos should be present in every cluster, which is not presently observed, although the predicted radio halo luminosities can change (decrease) by factors of up to ~102-106, depending on the amplitude and

  9. On the absence of radio haloes in clusters with double relics

    NASA Astrophysics Data System (ADS)

    Bonafede, A.; Cassano, R.; Brüggen, M.; Ogrean, G. A.; Riseley, C. J.; Cuciti, V.; de Gasperin, F.; Golovich, N.; Kale, R.; Venturi, T.; van Weeren, R. J.; Wik, D. R.; Wittman, D.

    2017-09-01

    Pairs of radio relics are believed to form during cluster mergers, and are best observed when the merger occurs in the plane of the sky. Mergers can also produce radio haloes, through complex processes likely linked to turbulent re-acceleration of cosmic ray electrons. However, only some clusters with double relics also show a radio halo. Here, we present a novel method to derive upper limits on the radio halo emission, and analyse archival X-ray Chandra data, as well as galaxy velocity dispersions and lensing data, in order to understand the key parameter that switches on radio halo emission. We place upper limits on the halo power below the P1.4 GHz-M500 correlation for some clusters, confirming that clusters with double relics have different radio properties. Computing X-ray morphological indicators, we find that clusters with double relics are associated with the most disturbed clusters. We also investigate the role of different mass-ratios and time-since-merger. Data do not indicate that the merger mass-ratio has an impact on the presence or absence of radio haloes (the null hypothesis that the clusters belong to the same group cannot be rejected). However, the data suggest that the absence of radio haloes could be associated with early and late mergers, but the sample is too small to perform a statistical test. Our study is limited by the small number of clusters with double relics. Future surveys with LOFAR, ASKAP, MeerKat and SKA will provide larger samples to better address this issue.

  10. Triaxial cosmological haloes and the disc of satellites

    NASA Astrophysics Data System (ADS)

    Bowden, A.; Evans, N. W.; Belokurov, V.

    2013-10-01

    We construct simple triaxial generalizations of Navarro-Frenk-White haloes. The models have elementary gravitational potentials, together with a density that is cusped like 1/r at small radii and falls off like 1/r3 at large radii. The ellipticity varies with radius in a manner that can be tailored to the user's specification. The closed periodic orbits in the planes perpendicular to the short and long axes of the model are well described by epicyclic theory, and can be used as building blocks for long-lived discs. As an application, we carry out the simulations of thin discs of satellites in triaxial dark halo potentials. This is motivated by the recent claims of an extended, thin disc of satellites around the M31 galaxy with a vertical rms scatter of ˜12 kpc and a radial extent of ˜300 kpc. We show that a thin satellite disc can persist over cosmological times if and only if it lies in the planes perpendicular to the long or short axis of a triaxial halo, or in the equatorial or polar planes of a spheroidal halo. In any other orientation, then the disc thickness doubles on ˜5 Gyr time-scales and so must have been born with an implausibly small vertical scaleheight.

  11. The FUSE Survey of 0 VI in the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Sonneborn, George; Savage, B. D.; Wakker, B. P.; Sembach, K. R.; Jenkins, E. B.; Moos, H. W.; Shull, J. M.

    2003-01-01

    This paper summarizes the results of the Far-Ultraviolet Spectroscopic Explorer (FUSE) program to study 0 VI in the Milky Way halo. Spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the velocity range from -100 to 100 km/s reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T approx. 3 x 10(exp 5) K in the Milky Way thick disk/halo. The overall distribution of O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with an average O VI mid-plane density of n(sub 0)(O VI) = 1.7 x 10(exp -2)/cu cm, a scale height of approx. 2.3 kpc, and a approx. 0.25 dex excess of O VI in the northern Galactic polar region. The distribution of O VI over the sky is poorly correlated with other tracers of gas in the halo, including low and intermediate velocity H I, Ha emission from the warm ionized gas at approx. l0(exp 4) K, and hot X-ray emitting gas at approx. l0(exp 6) K . The O VI has an average velocity dispersion, b approx. 60 km/s and standard deviation of 15 km/s. Thermal broadening alone cannot explain the large observed profile widths. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. The preferential venting of hot gas from local bubbles and superbubbles into the northern Galactic polar region may explain the enhancement of O VI in the North.

  12. 40 CFR 721.10063 - Halo substituted hydroxy nitrophenyl amide (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... amide (generic). 721.10063 Section 721.10063 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.10063 Halo substituted hydroxy nitrophenyl amide (generic). (a) Chemical... as halo substituted hydroxy nitrophenyl amide (PMN P-04-792) is subject to reporting under this...

  13. Investigating the Wave Nature of the Outer Envelope of Halo Coronal Mass Ejections

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kwon, Ryun-Young; Vourlidas, Angelos, E-mail: rkwon@gmu.edu

    We investigate the nature of the outer envelope of halo coronal mass ejections (H-CMEs) using multi-viewpoint observations from the Solar Terrestrial Relations Observatory-A , -B , and SOlar and Heliospheric Observatory coronagraphs. The 3D structure and kinematics of the halo envelopes and the driving CMEs are derived separately using a forward modeling method. We analyze three H-CMEs with peak speeds from 1355 to 2157 km s{sup −1}; sufficiently fast to drive shocks in the corona. We find that the angular widths of the halos range from 192° to 252°, while those of the flux ropes range between only 58° andmore » 91°, indicating that the halos are waves propagating away from the CMEs. The halo widths are in agreement with widths of Extreme Ultraviolet (EUV) waves in the low corona further demonstrating the common origin of these structures. To further investigate the wave nature of the halos, we model their 3D kinematic properties with a linear fast magnetosonic wave model. The model is able to reproduce the position of the halo flanks with realistic coronal medium assumptions but fails closer to the CME nose. The CME halo envelope seems to arise from a driven wave (or shock) close to the CME nose, but it is gradually becoming a freely propagating fast magnetosonic wave at the flanks. This interpretation provides a simple unifying picture for CME halos, EUV waves, and the large longitudinal spread of solar energetic particles.« less

  14. The Edges Of Dark Matter Halos: Theory And Observations

    NASA Astrophysics Data System (ADS)

    More, Surhud

    2017-06-01

    I discuss recent theoretical advances which have led us to suggest a physical definition for the boundary of dark matter halos. We propose using the "splashback radius" which corresponds to the apocenter of recently infalling material as a physical boundary for dark matter halos. We also present how the splashback radius can be detected in observations.

  15. Self-similar infall models for cold dark matter haloes

    NASA Astrophysics Data System (ADS)

    Le Delliou, Morgan Patrick

    2002-04-01

    How can we understand the mechanisms for relaxation and the constitution of the density profile in CDM halo formation? Can the old Self-Similar Infall Model (SSIM) be made to contain all the elements essential for this understanding? In this work, we have explored and improved the SSIM, showing it can at once explain large N-body simulations and indirect observations of real haloes alike. With the use of a carefully-crafted simple shell code, we have followed the accretion of secondary infalls in different settings, ranging from a model for mergers to a distribution of angular momentum for the shells, through the modeling of a central black hole. We did not assume self-similar accretion from initial conditions but allowed for it to develop and used coordinates that make it evident. We found self-similar accretion to appear very prominently in CDM halo formation as an intermediate stable (quasi-equilibrium) stage of Large Scale Structure formation. Dark Matter haloes density profiles are shown to be primarily influenced by non-radial motion. The merger paradigm reveals itself through the SSIM to be a secondary but non-trivial factor in those density profiles: it drives the halo profile towards a unique attractor, but the main factor for universality is still the self-similarity. The innermost density cusp flattening observed in some dwarf and Low Surface Brightness galaxies finds a natural and simple explanation in the SSIM embedding a central black hole. Relaxation in cold collisionless collapse is clarified by the SSIM. It is a continuous process involving only the newly-accreted particles for just a few dynamical times. All memory of initial energy is not lost so relaxation is only moderately violent. A sharp cut off, or population inversion, originates in initial conditions and is maintained through relaxation. It characterises moderately violent relaxation in the system's Distribution Function. Finally, the SSIM has shown this relaxation to arise from phase

  16. First Attempts at using Active Halo Control at the LHC

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wagner, Joschka; Bruce, Roderik; Garcia Morales, Hector

    2016-06-01

    The beam halo population is a non-negligible factor for the performance of the LHC collimation system and the machine protection. In particular this could become crucial for aiming at stored beam energies of 700 MJ in the High Luminosity (HL-LHC) project, in order to avoid beam dumps caused by orbit jitter and to ensure safety during a crab cavity failure. Therefore several techniques to safely deplete the halo, i.e. active halo control, are under development. In a first attempt a novel way for safe halo depletion was tested with particle narrow-band excitation employing the LHC Transverse Damper (ADT). At anmore » energy of 450 GeV a bunch selective beam tail scraping without affecting the core distribution was attempted. This paper presents the first measurement results, as well as a simple simulation to model the underlying dynamics.« less

  17. Large-scale gas dynamical processes affecting the origin and evolution of gaseous galactic halos

    NASA Technical Reports Server (NTRS)

    Shapiro, Paul R.

    1991-01-01

    Observations of galactic halo gas are consistent with an interpretation in terms of the galactic fountain model in which supernova heated gas in the galactic disk escapes into the halo, radiatively cools and forms clouds which fall back to the disk. The results of a new study of several large-scale gas dynamical effects which are expected to occur in such a model for the origin and evolution of galactic halo gas will be summarized, including the following: (1) nonequilibrium absorption line and emission spectrum diagnostics for radiatively cooling halo gas in our own galaxy, as well the implications of such absorption line diagnostics for the origin of quasar absorption lines in galactic halo clouds of high redshift galaxies; (2) numerical MHD simulations and analytical analysis of large-scale explosions ad superbubbles in the galactic disk and halo; (3) numerical MHD simulations of halo cloud formation by thermal instability, with and without magnetic field; and (4) the effect of the galactic fountain on the galactic dynamo.

  18. Is the dark halo of the Milky Way prolate?

    NASA Astrophysics Data System (ADS)

    Bowden, A.; Evans, N. W.; Williams, A. A.

    2016-07-01

    We introduce the flattening equation, which relates the shape of the dark halo to the angular velocity dispersions and the density of a tracer population of stars. It assumes spherical alignment of the velocity dispersion tensor, as seen in the data on stellar halo stars in the Milky Way. The angular anisotropy and gradients in the angular velocity dispersions drive the solutions towards prolateness, whilst the gradient in the stellar density is a competing effect favouring oblateness. We provide an efficient numerical algorithm to integrate the flattening equation. Using tests on mock data, we show that there is a strong degeneracy between circular speed and flattening, which can be circumvented with informative priors. Therefore, we advocate the use of the flattening equation to test for oblateness or prolateness, though the precise value of q can only be measured with the addition of the radial Jeans equation. We apply the flattening equation to a sample extracted from the Sloan Digital Sky Survey of ˜15 000 halo stars with full phase space information and errors. We find that between Galactocentric radii of 5 and 10 kpc, the shape of the dark halo is prolate, whilst even mildly oblate models are disfavoured. Strongly oblate models are ruled out. Specifically, for a logarithmic halo model, if the asymptotic circular speed v0 lies between 210 and 250 km s-1, then we find the axis ratio of the equipotentials q satisfies 1.5 ≲ q ≲ 2.

  19. Photoionization in the halo of the Galaxy

    NASA Technical Reports Server (NTRS)

    Bregman, Joel N.; Harrington, J. Patrick

    1986-01-01

    The ionizing radiation field in the halo is calculated and found to be dominated in the 13.6-45 eV range by light from O-B stars that escapes the disk, by planetary nebulae at 45-54 eV, by quasars and the Galactic soft X-ray background at 54-2000 eV, and by the extragalactic X-ray background at higher energies. Photoionization models are calculated with this radiation field incident on halo clouds of constant density for a variety of densities, for normal and depleted abundances, and with variations of the incident spectrum. For species at least triply ionized, such as Si IV, C IV, N V, and O VI, the line ratios are determined by intervening gas with the greatest volume, which is not necessarily the greatest mass component. Column densities from doubly ionized species like Si III should be greater than from triply ionized species. The role of photoionized gas in cosmic ray-supported halos and Galactic fountains is discussed. Observational tests of photoionization models are suggested.

  20. Mergers and Mass Accretion for Infalling Halos Both End Well Outside Cluster Virial Radii

    NASA Astrophysics Data System (ADS)

    Behroozi, Peter S.; Wechsler, Risa H.; Lu, Yu; Hahn, Oliver; Busha, Michael T.; Klypin, Anatoly; Primack, Joel R.

    2014-06-01

    We find that infalling dark matter halos (i.e., the progenitors of satellite halos) begin losing mass well outside the virial radius of their eventual host halos. The peak mass occurs at a range of clustercentric distances, with median and 68th percentile range of 1.8^{+2.3}_{-1.0} \\,R_{vir,host} for progenitors of z = 0 satellites. The peak circular velocity for infalling halos occurs at significantly larger distances (3.7^{+3.3}_{-2.2} \\,R_{vir,host} at z = 0). This difference arises because different physical processes set peak circular velocity (typically, ~1:5 and larger mergers which cause transient circular velocity spikes) and peak mass (typically, smooth accretion) for infalling halos. We find that infalling halos also stop having significant mergers well before they enter the virial radius of their eventual hosts. Mergers larger than a 1:40 ratio in halo mass end for infalling halos at similar clustercentric distances (~1.9 R vir, host) as the end of overall mass accretion. However, mergers larger than 1:3 typically end for infalling halos at more than four virial radial away from their eventual hosts. This limits the ability of mergers to affect quenching and morphology changes in clusters. We also note that the transient spikes which set peak circular velocity may lead to issues with abundance matching on that parameter, including unphysical galaxy stellar mass growth profiles near clusters; we propose a simple observational test to check if a better halo proxy for galaxy stellar mass exists.

  1. Hierarchical Formation of Dark Matter Halos near the Cutoff Scale and Their Impact on Indirect Detections

    NASA Astrophysics Data System (ADS)

    Ishiyama, Tomoaki

    2015-08-01

    The smallest dark matter halos are formed first in the early universe. We present results of very large cosmological N-body simulations of the hierarchical formation and evolution of halos over a wide mass range, beginning from the formation of the smallest halos. In the largest simulation, the motions of 40963 particles in comoving boxes of side lengths 400 pc and 200 pc were followed. The particle masses were 3.4 Χ 10-11 M⊙ and 4.3 Χ 10-12 M⊙, ensuring that halos at the cutoff scale were represented by ˜30,000 and ˜230,000 particles, respectively. We found that the central density cusp is much steeper in these halos than in larger halos (dwarf-galaxy-sized to cluster-sized halos), and scales as ρ ∝ r(-1.5—1.3). The cusp slope gradually becomes shallower as the halo mass increases. The slope of halos 50 times more massive than the smallest halo is approximately -1.3. No strong correlation exists between inner slope and the collapse epoch. The cusp slope of halos above the cutoff scale seems to be reduced primarily due to major merger processes. The concentration, estimated at the present universe, is predicted to be 60—70, consistent with theoretical models and earlier simulations, and ruling out simple power law mass-concentration relations. Such halos could still exist in the present universe with the same steep density profiles. Strongly depending on the subhalo mass function and the adopted concentration model, the steeper inner cusps of halos near the cutoff scale enhance the annihilation luminosity of a Milky Way sized halo between 12 to 67%.

  2. The Initial Conditions and Evolution of Isolated Galaxy Models: Effects of the Hot Gas Halo

    NASA Astrophysics Data System (ADS)

    Hwang, Jeong-Sun; Park, Changbom; Choi, Jun-Hwan

    2013-02-01

    We construct several Milky Way-like galaxy models containing a gas halo (as well as gaseous and stellar disks, a dark matter halo, and a stellar bulge) following either an isothermal or an NFW density profile with varying mass and initial spin. In addition, galactic winds associated with star formation are tested in some of the simulations. We evolve these isolated galaxy models using the GADGET-3 N-body/hydrodynamic simulation code, paying particular attention to the effects of the gaseous halo on the evolution. We find that the evolution of the models is strongly affected by the adopted gas halo component, particularly in the gas dissipation and the star formation activity in the disk. The model without a gas halo shows an increasing star formation rate (SFR) at the beginning of the simulation for some hundreds of millions of years and then a continuously decreasing rate to the end of the run at 3 Gyr. Whereas the SFRs in the models with a gas halo, depending on the density profile and the total mass of the gas halo, emerge to be either relatively flat throughout the simulations or increasing until the middle of the run (over a gigayear) and then decreasing to the end. The models with the more centrally concentrated NFW gas halo show overall higher SFRs than those with the isothermal gas halo of the equal mass. The gas accretion from the halo onto the disk also occurs more in the models with the NFW gas halo, however, this is shown to take place mostly in the inner part of the disk and not to contribute significantly to the star formation unless the gas halo has very high density at the central part. The rotation of a gas halo is found to make SFR lower in the model. The SFRs in the runs including galactic winds are found to be lower than those in the same runs but without winds. We conclude that the effects of a hot gaseous halo on the evolution of galaxies are generally too significant to be simply ignored. We also expect that more hydrodynamical processes in

  3. Global properties of M31's stellar halo from the splash survey. II. Metallicity profile

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gilbert, Karoline M.; Kalirai, Jason S.; Guhathakurta, Puragra

    2014-12-01

    We present the metallicity distribution of red giant branch (RGB) stars in M31's stellar halo, derived from photometric metallicity estimates for over 1500 spectroscopically confirmed RGB halo stars. The stellar sample comes from 38 halo fields observed with the Keck/DEIMOS spectrograph, ranging from 9 to 175 kpc in projected distance from M31's center, and includes 52 confirmed M31 halo stars beyond 100 kpc. While a wide range of metallicities is seen throughout the halo, the metal-rich peak of the metallicity distribution function becomes significantly less prominent with increasing radius. The metallicity profile of M31's stellar halo shows a continuous gradientmore » from 9 to ∼100 kpc, with a magnitude of ∼ – 0.01 dex kpc{sup –1}. The stellar velocity distributions in each field are used to identify stars that are likely associated with tidal debris features. The removal of tidal debris features does not significantly alter the metallicity gradient in M31's halo: a gradient is maintained in fields spanning 10-90 kpc. We analyze the halo metallicity profile, as well as the relative metallicities of stars associated with tidal debris features and the underlying halo population, in the context of current simulations of stellar halo formation. We argue that the large-scale gradient in M31's halo implies M31 accreted at least one relatively massive progenitor in the past, while the field to field variation seen in the metallicity profile indicates that multiple smaller progenitors are likely to have contributed substantially to M31's outer halo.« less

  4. X-ray detection of warm ionized matter in the Galactic halo

    NASA Astrophysics Data System (ADS)

    Nicastro, F.; Senatore, F.; Gupta, A.; Guainazzi, M.; Mathur, S.; Krongold, Y.; Elvis, M.; Piro, L.

    2016-03-01

    We report on a systematic investigation of the cold and mildly ionized gaseous baryonic metal components of our Galaxy, through the analysis of high-resolution Chandra and XMM-Newton spectra of two samples of Galactic and extragalactic sources. The comparison between lines of sight towards sources located in the disc of our Galaxy and extragalactic sources allows us for the first time to clearly distinguish between gaseous metal components in the disc and halo of our Galaxy. We find that a warm ionized metal medium (WIMM) permeates a large volume above and below the Galaxy's disc, perhaps up to the circum-galactic space. This halo WIMM imprints virtually the totality of the O I and O II absorption seen in the spectra of our extragalactic targets, has a temperature of T_{WIMM}^{Halo}=2900 ± 900 K, a density < n_H > _{WIMM}^{Halo} = 0.023 ± 0.009 cm-3 and a metallicity Z_{WIMM}^{Halo} = (0.4 ± 0.1) Z⊙. Consistently with previous works, we also confirm that the disc of the Galaxy contains at least two distinct gaseous metal components, one cold and neutral (the CNMM: cold neutral metal medium) and one warm and mildly ionized, with the same temperature of the halo WIMM, but higher density (< n_H > _{WIMM}^{Disc} = 0.09 ± 0.03 cm-3) and metallicity (Z_{WIMM}^{Disc} = 0.8 ± 0.1 Z⊙). By adopting a simple disc+sphere geometry for the Galaxy, we estimate masses of the CNMM and the total (disc + halo) WIMM of MCNMM ≲ 8 × 108 M⊙ and MWIMM ≃ 8.2 × 109 M⊙.

  5. 77 FR 75672 - Manufacturer of Controlled Substances, Notice of Registration, Halo Pharmaceutical, Inc.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-21

    ..., Notice of Registration, Halo Pharmaceutical, Inc. By Notice dated July 30, 2012, and published in the Federal Register on August 7, 2012, 77 FR 47114, Halo Pharmaceutical, Inc., 30 North Jefferson Road... 21 U.S.C. 823(a), and determined that the registration of Halo Pharmaceutical, Inc., to manufacture...

  6. Fast and accurate mock catalogue generation for low-mass galaxies

    NASA Astrophysics Data System (ADS)

    Koda, Jun; Blake, Chris; Beutler, Florian; Kazin, Eyal; Marin, Felipe

    2016-06-01

    We present an accurate and fast framework for generating mock catalogues including low-mass haloes, based on an implementation of the COmoving Lagrangian Acceleration (COLA) technique. Multiple realisations of mock catalogues are crucial for analyses of large-scale structure, but conventional N-body simulations are too computationally expensive for the production of thousands of realizations. We show that COLA simulations can produce accurate mock catalogues with a moderate computation resource for low- to intermediate-mass galaxies in 1012 M⊙ haloes, both in real and redshift space. COLA simulations have accurate peculiar velocities, without systematic errors in the velocity power spectra for k ≤ 0.15 h Mpc-1, and with only 3-per cent error for k ≤ 0.2 h Mpc-1. We use COLA with 10 time steps and a Halo Occupation Distribution to produce 600 mock galaxy catalogues of the WiggleZ Dark Energy Survey. Our parallelized code for efficient generation of accurate halo catalogues is publicly available at github.com/junkoda/cola_halo.

  7. clustep: Initial conditions for galaxy cluster halo simulations

    NASA Astrophysics Data System (ADS)

    Ruggiero, Rafael

    2017-11-01

    clustep generates a snapshot in GADGET-2 (ascl:0003.001) format containing a galaxy cluster halo in equilibrium; this snapshot can also be read in RAMSES (ascl:1011.007) using the DICE patch. The halo is made of a dark matter component and a gas component, with the latter representing the ICM. Each of these components follows a Dehnen density profile, with gamma=0 or gamma=1. If gamma=1, then the profile corresponds to a Hernquist profile.

  8. Non-Gaussianity and Excursion Set Theory: Halo Bias

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Adshead, Peter; Baxter, Eric J.; Dodelson, Scott

    2012-09-01

    We study the impact of primordial non-Gaussianity generated during inflation on the bias of halos using excursion set theory. We recapture the familiar result that the bias scales asmore » $$k^{-2}$$ on large scales for local type non-Gaussianity but explicitly identify the approximations that go into this conclusion and the corrections to it. We solve the more complicated problem of non-spherical halos, for which the collapse threshold is scale dependent.« less

  9. Galaxy disruption in a halo of dark matter.

    PubMed

    Forbes, Duncan A; Beasley, Michael A; Bekki, Kenji; Brodie, Jean P; Strader, Jay

    2003-08-29

    The relics of disrupted satellite galaxies have been found around the Milky Way and Andromeda, but direct evidence of a satellite galaxy in the early stages of disruption has remained elusive. We have discovered a dwarf satellite galaxy in the process of being torn apart by gravitational tidal forces as it merges with a larger galaxy's dark matter halo. Our results illustrate the morphological transformation of dwarf galaxies by tidal interaction and the continued buildup of galaxy halos.

  10. Protein attributes contribute to halo-stability, bioinformatics approach

    PubMed Central

    2011-01-01

    Halophile proteins can tolerate high salt concentrations. Understanding halophilicity features is the first step toward engineering halostable crops. To this end, we examined protein features contributing to the halo-toleration of halophilic organisms. We compared more than 850 features for halophilic and non-halophilic proteins with various screening, clustering, decision tree, and generalized rule induction models to search for patterns that code for halo-toleration. Up to 251 protein attributes selected by various attribute weighting algorithms as important features contribute to halo-stability; from them 14 attributes selected by 90% of models and the count of hydrogen gained the highest value (1.0) in 70% of attribute weighting models, showing the importance of this attribute in feature selection modeling. The other attributes mostly were the frequencies of di-peptides. No changes were found in the numbers of groups when K-Means and TwoStep clustering modeling were performed on datasets with or without feature selection filtering. Although the depths of induced trees were not high, the accuracies of trees were higher than 94% and the frequency of hydrophobic residues pointed as the most important feature to build trees. The performance evaluation of decision tree models had the same values and the best correctness percentage recorded with the Exhaustive CHAID and CHAID models. We did not find any significant difference in the percent of correctness, performance evaluation, and mean correctness of various decision tree models with or without feature selection. For the first time, we analyzed the performance of different screening, clustering, and decision tree algorithms for discriminating halophilic and non-halophilic proteins and the results showed that amino acid composition can be used to discriminate between halo-tolerant and halo-sensitive proteins. PMID:21592393

  11. Supernova explosions in magnetized, primordial dark matter haloes

    NASA Astrophysics Data System (ADS)

    Seifried, D.; Banerjee, R.; Schleicher, D.

    2014-05-01

    The first supernova explosions are potentially relevant sources for the production of the first large-scale magnetic fields. For this reason, we present a set of high-resolution simulations studying the effect of supernova explosions on magnetized, primordial haloes. We focus on the evolution of an initially small-scale magnetic field formed during the collapse of the halo. We vary the degree of magnetization, the halo mass, and the amount of explosion energy in order to account for expected variations as well as to infer systematical dependences of the results on initial conditions. Our simulations suggest that core collapse supernovae with an explosion energy of 1051 erg and more violent pair instability supernovae with 1053 erg are able to disrupt haloes with masses up to about 106 and 107 M⊙, respectively. The peak of the magnetic field spectra shows a continuous shift towards smaller k-values, i.e. larger length scales, over time reaching values as low as k = 4. On small scales, the magnetic energy decreases at the cost of the energy on large scales resulting in a well-ordered magnetic field with a strength up to ˜10-8 G depending on the initial conditions. The coherence length of the magnetic field inferred from the spectra reaches values up to 250 pc in agreement with those obtained from autocorrelation functions. We find the coherence length to be as large as 50 per cent of the radius of the supernova bubble. Extrapolating this relation to later stages, we suggest that significantly strong magnetic fields with coherence lengths as large as 1.5 kpc could be created. We discuss possible implications of our results on processes like recollapse of the halo, first galaxy formation, and the magnetization of the intergalactic medium.

  12. The Impact of Starbursts on the Gaseous Halos of Galaxies

    NASA Astrophysics Data System (ADS)

    Heckman, Timothy

    2009-07-01

    Perhaps the most important {yet uncertain} aspects of galaxy evolution are the processes by which galaxies accrete gas and by which the resulting star formation and black hole growth affects this accreting gas. It is believed that both the form of the accretion and the nature of the feedback change as a function of the galaxy mass. At low mass the gas comes in cold and the feedback is provided by massive stars. At high mass, the gas comes in hot, and the feedback is from an AGN. The changeover occurs near the mass where the galaxy population transitions from star-forming galaxies to red and dead ones. The population of red and dead galaxies is building with cosmic time, and it is believed that feedback plays an imporant role in this process: shutting down star formation by heating and/or expelling the reservoir of cold halo gas. To investigate these ideas, we propose to use COS far-UV spectra of background QSOs to measure the properties of the halo gas in a sample of galaxies near the transition mass that have undergone starbursts within the past 100 Myr to 1 Gyr. The galactic wind associated with the starburst is predicted to have affected the properties of the gaseous halo. To test this, we will compare the properties of the halos of the post-starburst galaxies to those of a control sample of galaxies matched in mass and QSO impact parameter. Do the halos of the post-starburst galaxies show a higher incidence rate of Ly-Alpha and metal absorption-lines? Are the kinematics of the halo gas more disturbed in the post-starbursts? Has the wind affected the ionization state and/or the metallicity of the halo? These data will provide fresh new insights into the role of feedback from massive stars on the evolution of galaxies, and may also offer clues about the properties of the QSO metal absorption-line systems at high-redshift.

  13. Populating dark matter haloes with galaxies: comparing the 2dFGRS with mock galaxy redshift surveys

    NASA Astrophysics Data System (ADS)

    Yang, Xiaohu; Mo, H. J.; Jing, Y. P.; van den Bosch, Frank C.; Chu, YaoQuan

    2004-06-01

    In two recent papers, we developed a powerful technique to link the distribution of galaxies to that of dark matter haloes by considering halo occupation numbers as a function of galaxy luminosity and type. In this paper we use these distribution functions to populate dark matter haloes in high-resolution N-body simulations of the standard ΛCDM cosmology with Ωm= 0.3, ΩΛ= 0.7 and σ8= 0.9. Stacking simulation boxes of 100 h-1 Mpc and 300 h-1 Mpc with 5123 particles each we construct mock galaxy redshift surveys out to a redshift of z= 0.2 with a numerical resolution that guarantees completeness down to 0.01L*. We use these mock surveys to investigate various clustering statistics. The predicted two-dimensional correlation function ξ(rp, π) reveals clear signatures of redshift space distortions. The projected correlation functions for galaxies with different luminosities and types, derived from ξ(rp, π), match the observations well on scales larger than ~3 h-1 Mpc. On smaller scales, however, the model overpredicts the clustering power by about a factor two. Modelling the `finger-of-God' effect on small scales reveals that the standard ΛCDM model predicts pairwise velocity dispersions (PVD) that are ~400 km s-1 too high at projected pair separations of ~1 h-1 Mpc. A strong velocity bias in massive haloes, with bvel≡σgal/σdm~ 0.6 (where σgal and σdm are the velocity dispersions of galaxies and dark matter particles, respectively) can reduce the predicted PVD to the observed level, but does not help to resolve the overprediction of clustering power on small scales. Consistent results can be obtained within the standard ΛCDM model only when the average mass-to-light ratio of clusters is of the order of 1000 (M/L)solar in the B-band. Alternatively, as we show by a simple approximation, a ΛCDM model with σ8~= 0.75 may also reproduce the observational results. We discuss our results in light of the recent WMAP results and the constraints on σ8 obtained

  14. A similar local immune and oxidative stress phenotype in vitiligo and halo nevus.

    PubMed

    Yang, Yuqi; Li, Shuli; Zhu, Guannan; Zhang, Qian; Wang, Gang; Gao, Tianwen; Li, Chunying; Wang, Lin; Jian, Zhe

    2017-07-01

    Vitiligo and halo nevus are two common T-cell-mediated skin disorders. Although autoimmunity has been suggested to be involved in both diseases, the relationship between vitiligo and halo nevus is not fully understood. The aim of the current study was to investigate whether vitiligo and halo nevus share the same immunological and oxidative stress response. Infiltrations of T cells, and expressions of chemokine receptors (CXCR3, CCR4, CCR5) and cytotoxic markers (Granzyme B, Perforin) in the lesions of vitiligo and halo nevus were examined by immunohistochemistry. Enzyme-linked immunosorbent assay was performed to analyze the expressions of chemokines in the serum samples and cytotoxic markers secreted by CD8 + T cells which were sorted from the peripheral blood mononuclear cells in healthy donors, vitiligo and halo nevus patients. Tissue levels of chemokine receptors and CXCR3 ligands in healthy controls, vitiligo patients and halo nevus patients were determined by qRT-PCR analysis. The percentages of CXCR3 + CD4 + T and CXCR3 + CD8 + T cells from the peripheral blood samples were examined by flow cytometry. Tissue and serum hydrogen peroxide (H 2 O 2 ) concentrations were measured using H 2 O 2 assay kit. Immunohistochemistry revealed a significant T-cell response, with pronounced dermal infiltrates of CD8 + T cells in vitiligo and halo nevus. The inflammatory cytotoxic markers such as Granzyme B and Perforin were also elevated in vitiligo and halo nevus, suggesting inflammatory responses in situ. By qRT-PCR and ELISA assay, we found significantly increased expressions of the chemokine receptor CXCR3 and its ligands, especially the accumulated CXCL10 in the skin lesions of vitiligo and halo nevus. Moreover, the level of H 2 O 2 , a key player involved in regulation of the immune response was significantly upregulated in the skin lesions of vitiligo and halo nevus. In addition, the increased H 2 O 2 concentration correlated positively with CXCL10 level in skin

  15. 77 FR 16264 - Manufacturer of Controlled Substances, Notice of Registration; Halo Pharmaceutical Inc.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-20

    ..., Notice of Registration; Halo Pharmaceutical Inc. By Notice dated December 2, 2011, and published in the Federal Register on December 14, 2011, 76 FR 77850, Halo Pharmaceutical Inc., 30 North Jefferson Road... considered the factors in 21 U.S.C. 823(a) and determined that the registration of Halo Pharmaceutical Inc...

  16. THE DOMINANCE OF METAL-RICH STREAMS IN STELLAR HALOS: A COMPARISON BETWEEN SUBSTRUCTURE IN M31 AND {lambda}CDM MODELS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gilbert, Karoline M.; Font, Andreea S.; Johnston, Kathryn V.

    2009-08-10

    Extensive photometric and spectroscopic surveys of the Andromeda galaxy (M31) have discovered tidal debris features throughout M31's stellar halo. We present stellar kinematics and metallicities in fields with identified substructure from our on-going SPLASH survey of M31 red giant branch stars with the DEIMOS spectrograph on the Keck II 10 m telescope. Radial velocity criteria are used to isolate members of the kinematically cold substructures. The substructures are shown to be metal-rich relative to the rest of the dynamically hot stellar population in the fields in which they are found. We calculate the mean metallicity and average surface brightness ofmore » the various kinematical components in each field, and show that, on average, higher surface brightness features tend to be more metal-rich than lower surface brightness features. Simulations of stellar halo formation via accretion in a cosmological context are used to illustrate that the observed trend can be explained as a natural consequence of the observed dwarf galaxy mass-metallicity relation. A significant spread in metallicity at a given surface brightness is seen in the data; we show that this is due to time effects, namely, the variation in the time since accretion of the tidal streams' progenitor onto the host halo. We show that in this theoretical framework a relationship between the alpha-enhancement and surface brightness of tidal streams is expected, which arises from the varying times of accretion of the progenitor satellites onto the host halo. Thus, measurements of the alpha-enrichment, metallicity, and surface brightness of tidal debris can be used to reconstruct the luminosity and time of accretion onto the host halo of the progenitors of tidal streams.« less

  17. Pneumocranium secondary to halo vest pin penetration through an enlarged frontal sinus.

    PubMed

    Cheong, Min Lee; Chan, Chris Yin Wei; Saw, Lim Beng; Kwan, Mun Keong

    2009-07-01

    We present a case report of a patient with pneumocranium secondary to halo vest pin penetration and a review of literature. The objectives of this study are to report a rare complication of halo vest pin insertion and to discuss methods of prevention of this complication. Halo vest orthosis is a commonly used and well-tolerated upper cervical spinal stabilizing device. Reports of complications related to pin penetration is rare and from our review, there has been no reports of pneumocranium occurring from insertion of pins following standard anatomical landmarks. A 57-year-old male sustained a type 1 traumatic spondylolisthesis of C2/C3 following a motor vehicle accident. During application of the halo vest, penetration of the left anterior pin through the abnormally enlarged frontal sinus occurred. The patient developed headache, vomiting and CSF rhinorrhoea over his left nostril. He was treated with intravenous Ceftriaxone for 1 week. This resulted in resolution of his symptoms as well as the pneumocranium. In conclusion, complications of halo vest pin penetration are rare and need immediate recognition. Despite the use of anatomical landmarks, pin penetration is still possible due to aberrant anatomy. All patients should have a skull X-ray with a radio-opaque marker done prior to placement of the halo vest pins and halo vest pins have to be inserted by experienced personnel to enable early detection of pin penetration.

  18. Shaping knowledge regarding occupation: examining the cultural underpinnings of the evolving concept of occupational identity.

    PubMed

    Rudman, Deborah Laliberte; Dennhardt, Silke

    2008-09-01

    Within occupational therapy and occupational science, knowledge regarding occupation-based concepts is in the process of being developed, disseminated and acted upon internationally. It is critical to reflect on the forces shaping the ways in which this knowledge is being constructed. In this paper, the ways in which cultural assumptions and values have influenced the evolving concept of occupational identity are examined through applying Kluckhohn and Strodtbeck's framework of cultural variations in values to two contemporary conceptualisations of occupational identity. The analysis demonstrates the ways in which values most consistent with Western culture are embedded within and dominate these contemporary conceptualisations of occupational identity, emphasising a future orientation, achievement-based doing, individual choice, and mastery of individuals over nature. This paper points to conceptual boundaries within which occupational identity is currently being shaped and points to alternative possibilities in the hope of prompting dialogue and research that looks at this concept in more diverse ways. Heightened sensitivity to the influence of culture on the shaping of occupation-focussed knowledge will serve to strengthen and enrich the growth of the evolving body of knowledge pertaining to occupation, and foster culturally sensitive research and practice.

  19. Neutron stars and white dwarfs in galactic halos

    NASA Technical Reports Server (NTRS)

    Ryu, Dongsu; Olive, Keith A.; Silk, Joseph

    1989-01-01

    The possibility that galactic halos are composed of stellar remnants such as neutron stars and white dwarfs is discussed. On the basis of a simple model for the evolution of galactic halos, researchers follow the history of halo matter, luminosity, and metal and helium abundances. They assume conventional yields for helium and the heavier elements. By comparing with the observational constraints, which may be considered as fairly conservative, it is found that, for an exponentially decreasing star formation rate (SFR) with e-folding time tau, only values between 6 x 10(8) less than similar to tau less than similar to 2 x 10(9) years are allowed together with a very limited range of masses for the initial mass function (IMF). Star formation is allowed for 2 solar mass less than similar to m less than similar to 8 solar mass if tau = 2 x 10(9) years, and for 4 solar mass less than similar to m less than similar to 6 solar mass if tau = 10(9) years. For tau = 6 x 10(8) years, the lower and upper mass limits merge to similar to 5 solar mass. Researchers conclude that, even though the possibility of neutron stars as halo matter may be ruled out, that of white dwarfs may still be a viable hypothesis, though with very stringent constraints on allowed parameters, that merits further consideration.

  20. ARE HALO-LIKE SOLAR CORONAL MASS EJECTIONS MERELY A MATTER OF GEOMETRIC PROJECTION EFFECTS?

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kwon, Ryun-Young; Zhang, Jie; Vourlidas, Angelos, E-mail: ryunyoung.kwon@gmail.com

    2015-02-01

    We investigated the physical nature of halo coronal mass ejections (CMEs) based on the stereoscopic observations from the two STEREO spacecraft, Ahead and Behind (hereafter A and B), and the SOHO spacecraft. Sixty-two halo CMEs occurred as observed by SOHO LASCO C2 for the three-year period from 2010 to 2012 during which the separation angles between SOHO and STEREO were nearly 90°. In such quadrature configuration, the coronagraphs of STEREO, COR2-A and -B, showed the side view of those halo CMEs seen by C2. It has been widely believed that the halo appearance of a CME is caused by themore » geometric projection effect, i.e., a CME moves along the Sun-observer line. In other words, it would appear as a non-halo CME if viewed from the side. However, to our surprise, we found that 41 out of 62 events (66%) were observed as halo CMEs by all coronagraphs. This result suggests that a halo CME is not just a matter of the propagating direction. In addition, we show that a CME propagating normal to the line of sight can be observed as a halo CME due to the associated fast magnetosonic wave or shock front. We conclude that the apparent width of CMEs, especially halos or partial halos is driven by the existence and the extent of the associated waves or shocks and does not represent an accurate measure of the CME ejecta size. This effect needs to be taken into careful consideration in space weather predictions and modeling efforts.« less

  1. THE DUAL ORIGIN OF STELLAR HALOS. II. CHEMICAL ABUNDANCES AS TRACERS OF FORMATION HISTORY

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zolotov, Adi; Hogg, David W.; Willman, Beth

    2010-09-20

    Fully cosmological, high-resolution N-body+smooth particle hydrodynamic simulations are used to investigate the chemical abundance trends of stars in simulated stellar halos as a function of their origin. These simulations employ a physically motivated supernova feedback recipe, as well as metal enrichment, metal cooling, and metal diffusion. As presented in an earlier paper, the simulated galaxies in this study are surrounded by stellar halos whose inner regions contain both stars accreted from satellite galaxies and stars formed in situ in the central regions of the main galaxies and later displaced by mergers into their inner halos. The abundance patterns ([Fe/H] andmore » [O/Fe]) of halo stars located within 10 kpc of a solar-like observer are analyzed. We find that for galaxies which have not experienced a recent major merger, in situ stars at the high [Fe/H] end of the metallicity distribution function are more [{alpha}/Fe]-rich than accreted stars at similar [Fe/H]. This dichotomy in the [O/Fe] of halo stars at a given [Fe/H] results from the different potential wells within which in situ and accreted halo stars form. These results qualitatively match recent observations of local Milky Way halo stars. It may thus be possible for observers to uncover the relative contribution of different physical processes to the formation of stellar halos by observing such trends in the halo populations of the Milky Way and other local L{sup *} galaxies.« less

  2. Alignments of Dark Matter Halos with Large-scale Tidal Fields: Mass and Redshift Dependence

    NASA Astrophysics Data System (ADS)

    Chen, Sijie; Wang, Huiyuan; Mo, H. J.; Shi, Jingjing

    2016-07-01

    Large-scale tidal fields estimated directly from the distribution of dark matter halos are used to investigate how halo shapes and spin vectors are aligned with the cosmic web. The major, intermediate, and minor axes of halos are aligned with the corresponding tidal axes, and halo spin axes tend to be parallel with the intermediate axes and perpendicular to the major axes of the tidal field. The strengths of these alignments generally increase with halo mass and redshift, but the dependence is only on the peak height, ν \\equiv {δ }{{c}}/σ ({M}{{h}},z). The scaling relations of the alignment strengths with the value of ν indicate that the alignment strengths remain roughly constant when the structures within which the halos reside are still in a quasi-linear regime, but decreases as nonlinear evolution becomes more important. We also calculate the alignments in projection so that our results can be compared directly with observations. Finally, we investigate the alignments of tidal tensors on large scales, and use the results to understand alignments of halo pairs separated at various distances. Our results suggest that the coherent structure of the tidal field is the underlying reason for the alignments of halos and galaxies seen in numerical simulations and in observations.

  3. On the Evolution of Dark Matter Halo Properties Following Major and Minor Mergers

    NASA Astrophysics Data System (ADS)

    Wu, Peter; Zhang, Shawn; Lee, Christoph; Primack, Joel

    2018-01-01

    We conducted an analysis on dark matter halo properties following major and minor mergers to advance our understanding of halo evolution. In this work, we analyzed ~80,000 dark matter halos from the Bolshoi-Planck cosmological simulation and studied halo evolution during relaxation after major mergers. We then applied a Gaussian filter to the property evolutions and characterized peak distributions, frequencies, and variabilities for several halo properties, including centering, spin, shape (prolateness), scale radius, and virial ratio. However, there were also halos that experienced relaxation without the presence of major mergers. We hypothesized that this was due to minor mergers unrecorded by the simulation analysis. By using property peaks to create a novel merger detection algorithm, we attempted to find minor mergers and match them to the unaccounted relaxed halos. Not only did we find evidence that minor mergers were the causes, but we also found similarities between major and minor merger effects, showing the significance of minor mergers for future studies. Through our dark matter merger statistics, we expect our work to ultimately serve as vital parameters towards better understanding galaxy formation and evolution. Most of this work was carried out by high school students working under the auspices of the Science Internship Program (SIP) at UC Santa Cruz.

  4. A Comparative Analysis of Chemical Abundances in Andromeda's Stellar Halo and Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Gilbert, Karoline; Kirby, Evan N.; Escala, Ivanna; Wojno, Jennifer

    2018-06-01

    Stellar halos provide a record of the earliest stages of a galaxy’s formation as well as the mass growth of later epochs. All stages of accretion are represented in the halo: (1) fully phase-mixed stars accreted at early times, (2) stars in distinct tidal streams, and (3) stars in satellite galaxies that will eventually be tidally incorporated into the halo. Chemical abundances encode information about the environment in which a star formed: specifically, the relative abundances of [Fe/H] and [α/Fe] provide an indication of the amount and duration of star formation. While these abundances have been measured for statistically significant samples of halo and dwarf galaxy stars in the Milky Way, they remain largely unknown in Andromeda. We have undertaken a systematic survey to measure [Fe/H] and [α/Fe] in fields throughout the M31 system, including the halo, tidal streams, satellite galaxies, and the disk. I will provide an overview of the survey and its goals and present first results, including the abundance distributions for five M31 dSphs, measurements of [Fe/H] and [α/Fe] of stars in M31's halo, and comparisons to existing measurements of Milky Way dSph and halo stars.

  5. Fractional Yields Inferred from Halo and Thick Disk Stars

    NASA Astrophysics Data System (ADS)

    Caimmi, R.

    2013-12-01

    Linear [Q/H]-[O/H] relations, Q = Na, Mg, Si, Ca, Ti, Cr, Fe, Ni, are inferred from a sample (N=67) of recently studied FGK-type dwarf stars in the solar neighbourhood including different populations (Nissen and Schuster 2010, Ramirez et al. 2012), namely LH (N=24, low-α halo), HH (N=25, high-α halo), KD (N=16, thick disk), and OL (N=2, globular cluster outliers). Regression line slope and intercept estimators and related variance estimators are determined. With regard to the straight line, [Q/H]=a_{Q}[O/H]+b_{Q}, sample stars are displayed along a "main sequence", [Q,O] = [a_{Q},b_{Q},Δ b_{Q}], leaving aside the two OL stars, which, in most cases (e.g. Na), lie outside. The unit slope, a_{Q}=1, implies Q is a primary element synthesised via SNII progenitors in the presence of a universal stellar initial mass function (defined as simple primary element). In this respect, Mg, Si, Ti, show hat a_{Q}=1 within ∓2hatσ_ {hat a_{Q}}; Cr, Fe, Ni, within ∓3hatσ_{hat a_{Q}}; Na, Ca, within ∓ rhatσ_{hat a_{Q}}, r>3. The empirical, differential element abundance distributions are inferred from LH, HH, KD, HA = HH + KD subsamples, where related regression lines represent their theoretical counterparts within the framework of simple MCBR (multistage closed box + reservoir) chemical evolution models. Hence, the fractional yields, hat{p}_{Q}/hat{p}_{O}, are determined and (as an example) a comparison is shown with their theoretical counterparts inferred from SNII progenitor nucleosynthesis under the assumption of a power-law stellar initial mass function. The generalized fractional yields, C_{Q}=Z_{Q}/Z_{O}^{a_{Q}}, are determined regardless of the chemical evolution model. The ratio of outflow to star formation rate is compared for different populations in the framework of simple MCBR models. The opposite situation of element abundance variation entirely due to cosmic scatter is also considered under reasonable assumptions. The related differential element abundance

  6. Sampling scales define occupancy and underlying occupancy-abundance relationships in animals.

    PubMed

    Steenweg, Robin; Hebblewhite, Mark; Whittington, Jesse; Lukacs, Paul; McKelvey, Kevin

    2018-01-01

    Occupancy-abundance (OA) relationships are a foundational ecological phenomenon and field of study, and occupancy models are increasingly used to track population trends and understand ecological interactions. However, these two fields of ecological inquiry remain largely isolated, despite growing appreciation of the importance of integration. For example, using occupancy models to infer trends in abundance is predicated on positive OA relationships. Many occupancy studies collect data that violate geographical closure assumptions due to the choice of sampling scales and application to mobile organisms, which may change how occupancy and abundance are related. Little research, however, has explored how different occupancy sampling designs affect OA relationships. We develop a conceptual framework for understanding how sampling scales affect the definition of occupancy for mobile organisms, which drives OA relationships. We explore how spatial and temporal sampling scales, and the choice of sampling unit (areal vs. point sampling), affect OA relationships. We develop predictions using simulations, and test them using empirical occupancy data from remote cameras on 11 medium-large mammals. Surprisingly, our simulations demonstrate that when using point sampling, OA relationships are unaffected by spatial sampling grain (i.e., cell size). In contrast, when using areal sampling (e.g., species atlas data), OA relationships are affected by spatial grain. Furthermore, OA relationships are also affected by temporal sampling scales, where the curvature of the OA relationship increases with temporal sampling duration. Our empirical results support these predictions, showing that at any given abundance, the spatial grain of point sampling does not affect occupancy estimates, but longer surveys do increase occupancy estimates. For rare species (low occupancy), estimates of occupancy will quickly increase with longer surveys, even while abundance remains constant. Our results

  7. Building occupancy simulation and data assimilation using a graph-based agent-oriented model

    NASA Astrophysics Data System (ADS)

    Rai, Sanish; Hu, Xiaolin

    2018-07-01

    Building occupancy simulation and estimation simulates the dynamics of occupants and estimates their real-time spatial distribution in a building. It requires a simulation model and an algorithm for data assimilation that assimilates real-time sensor data into the simulation model. Existing building occupancy simulation models include agent-based models and graph-based models. The agent-based models suffer high computation cost for simulating large numbers of occupants, and graph-based models overlook the heterogeneity and detailed behaviors of individuals. Recognizing the limitations of existing models, this paper presents a new graph-based agent-oriented model which can efficiently simulate large numbers of occupants in various kinds of building structures. To support real-time occupancy dynamics estimation, a data assimilation framework based on Sequential Monte Carlo Methods is also developed and applied to the graph-based agent-oriented model to assimilate real-time sensor data. Experimental results show the effectiveness of the developed model and the data assimilation framework. The major contributions of this work are to provide an efficient model for building occupancy simulation that can accommodate large numbers of occupants and an effective data assimilation framework that can provide real-time estimations of building occupancy from sensor data.

  8. Soft dipole resonance and halo structure of 11Li

    NASA Astrophysics Data System (ADS)

    Kanungo, Rituparna

    2016-03-01

    The discovery of the nuclear halo in rare isotopes has ushered a new era in nuclear science breaking the boundaries of conventional concepts. The halo properties elucidate new features that till date remain a challenge to decipher from fundamental principles. Our knowledge on the halo is still gradually unfolding and reaching new levels of precision as efforts continue towards new experimental developments. In recent times, low-energy reactions in inverse kinematics have become possible providing a wealth of new structure information. In this presentation we will introduce a new reaction spectroscopy facility, IRIS, with a novel thin windowless solid H2/D2 target for studying transfer and inelastic scattering reactions of rare isotopes with very low yields. It was postulated that the loosely bound halo of two neutrons may lead to a core-halo oscillation resulting in dipole resonance(s) at very low excitation energy, called soft dipole resonance. Despite decades of search for this new phenomenon using various techniques, such as, no firm conclusion was reached. The presentation will discuss new results from IRIS that shows evidence of a soft dipole resonance state and further unveils its isoscalar character. New results of neutron transfer from 11Li will be presented showing resonance state(s) in the neutron unbound 10Li subsystem hence facilitating a description of the wavefunction of 11Li. NSERC, Canada Foundation for Innovation, Nova Scotia Research and Innovation Trust, grant-in-aid program of the Japanese government under Contract No. 23224008, US DOE Contract No. DE-AC52-07NA27344.

  9. Chemical trends in the Galactic halo from APOGEE data

    NASA Astrophysics Data System (ADS)

    Fernández-Alvar, E.; Carigi, L.; Allende Prieto, C.; Hayden, M. R.; Beers, T. C.; Fernández-Trincado, J. G.; Meza, A.; Schultheis, M.; Santiago, B. X.; Queiroz, A. B.; Anders, F.; da Costa, L. N.; Chiappini, C.

    2017-02-01

    The galaxy formation process in the Λ cold dark matter scenario can be constrained from the analysis of stars in the Milky Way's halo system. We examine the variation of chemical abundances in distant halo stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE), as a function of distance from the Galactic Centre (r) and iron abundance ([M/H]), in the range 5 ≲ r ≲ 30 kpc and -2.5 < [M/H] < 0.0. We perform a statistical analysis of the abundance ratios derived by the APOGEE pipeline (ASPCAP) and distances calculated by several approaches. Our analysis reveals signatures of a different chemical enrichment between the inner and outer regions of the halo, with a transition at about 15 kpc. The derived metallicity distribution function exhibits two peaks, at [M/H] ˜ -1.5 and ˜-2.1, consistent with previously reported halo metallicity distributions. We obtain a difference of ˜0.1 dex for α-element-to-iron ratios for stars at r > 15 kpc and [M/H] > -1.1 (larger in the case of O, Mg, and S) with respect to the nearest halo stars. This result confirms previous claims for low-α stars found at larger distances. Chemical differences in elements with other nucleosynthetic origins (Ni, K, Na, and Al) are also detected. C and N do not provide reliable information about the interstellar medium from which stars formed because our sample comprises red giant branch and asymptotic giant branch stars and can experience mixing of material to their surfaces.

  10. Extent of warm haloes around medium-redshift galaxies

    NASA Technical Reports Server (NTRS)

    Burbidge, E. M.; Barlow, T. A.; Cohen, R. D.; Junkkarinen, V. T.; Womble, D. S.

    1989-01-01

    The properties of low-to-medium ionization gaseous haloes around galaxies are briefly reviewed. New observations concerning such haloes are presented. For the galaxy-QSO pair in the field of the radio source 3C303, the higher-redshift QSO has been found to show Mg II absorption at the lower redshift of the faint nearby galaxy. Secondly, new data are presented on one of the galaxies in the environment of the well-known BL Lac object AO 0235 + 164.

  11. Halo density profiles and baryon physics

    NASA Astrophysics Data System (ADS)

    Del Popolo, A.; Li, Xi-Guo

    2017-08-01

    The radial dependence of the pseudo phase-space density, ρ( r)/ σ 3( r) is studied. We find that the pseudo phase-space density for halos consisting both of dark matter and baryons is approximately a power-law only down to 0.1% of the virial radius while it has a non-power law behavior below the quoted scale, with inner profiles changing with mass. Halos consisting just of dark matter, as the one in dark matter only simulations, are characterized by an approximately power-law behavior. The results argue against universality of the pseudo phase-space density, when the baryons effect are included, and as a consequence argue against universality of density profiles constituted by dark matter and baryons as also discussed in [1].

  12. The Structure and Dark Halo Core Properties of Dwarf Spheroidal Galaxies

    NASA Astrophysics Data System (ADS)

    Burkert, A.

    2015-08-01

    The structure and dark matter halo core properties of dwarf spheroidal galaxies (dSphs) are investigated. A double-isothermal (DIS) model of an isothermal, non-self-gravitating stellar system embedded in an isothermal dark halo core provides an excellent fit to the various observed stellar surface density distributions. The stellar core scale length a* is sensitive to the central dark matter density ρ0,d. The maximum stellar radius traces the dark halo core radius {r}c,d. The concentration c* of the stellar system, determined by a King profile fit, depends on the ratio of the stellar-to-dark-matter velocity dispersion {σ }*/{σ }d. Simple empirical relationships are derived that allow us to calculate the dark halo core parameters ρ0,d, {r}c,d, and σd given the observable stellar quantities σ*, a*, and c*. The DIS model is applied to the Milky Way’s dSphs. All dSphs closely follow the same universal dark halo scaling relations {ρ }0,d× {r}c,d={75}-45+85 M⊙ pc-2 that characterize the cores of more massive galaxies over a large range in masses. The dark halo core mass is a strong function of core radius, {M}c,d˜ {r}c,d2. Inside a fixed radius of ˜400 pc the total dark matter mass is, however, roughly constant with {M}d=2.6+/- 1.4× {10}7 M⊙, although outliers are expected. The dark halo core densities of the Galaxy’s dSphs are very high, with {ρ }0,d ≈ 0.2 M⊙ pc-3. dSphs should therefore be tidally undisturbed. Evidence for tidal effects might then provide a serious challenge for the CDM scenario.

  13. Occupational Therapy for School-Aged Children in India

    ERIC Educational Resources Information Center

    Asher, Asha; Jatar, Anuradha; Bijlani, Jyothika

    2015-01-01

    Occupational therapists exploring international opportunities should understand how the profession is practiced globally. This paper describes the framework under which occupational therapy services can be accessed by families of children with disabilities in urban India. Background information about the country, its health care, and occupational…

  14. A ROBUST MEASURE OF DARK MATTER HALO ELLIPTICITIES

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Evslin, Jarah

    2016-08-01

    In simulations of the standard cosmological model (ΛCDM), dark matter halos are aspherical. However, so far the asphericity of an individual galaxy’s halo has never been robustly established. We use the Jeans equations to define a quantity that robustly characterizes a deviation from rotational symmetry. This quantity is essentially the gravitational torque and it roughly provides the ellipticity projected along the line of sight. We show that the Thirty Meter Telescope (TMT), with a single epoch of observations combined with those of the Gaia Space Telescope , can distinguish the ΛCDM value of the torque from zero for each Sculptor-likemore » dwarf galaxy with a confidence between 0 and 5 σ , depending on the orientation of each halo. With two epochs of observations, TMT will achieve a 5 σ discovery of torque and thus asphericity for most such galaxies, thus providing a new and powerful test of the ΛCDM model.« less

  15. Direct photoassociation of halo molecules in ultracold 86 Sr

    NASA Astrophysics Data System (ADS)

    Aman, J. A.; Hill, Joshua; Killian, T. C.

    2017-04-01

    We investigate the creation of 1S0 +1S0 halo molecules in strontium 86 through direct photoassociation in an optical dipole trap. We drive two photon Raman transitions near-resonance with a molecular level of the 1S0 +3P1 interatomic potential as the intermediate state. This provides large Frank-Condon factors and allows us to observe resonances for the creation of halo molecules through higher order Raman processes. The halo molecule is bound by EB 85 kHz at low excitation-laser intensity, but experiments show large AC Stark shifts of the molecular binding energy. These conditions suggest that STIRAP should be very effective for improving molecular conversion efficiency. Further experiments in a 3D lattice will explore molecular lifetimes and collision rates. Travel support provided by Shell Corporation.

  16. Halo-independence with quantified maximum entropy at DAMA/LIBRA

    NASA Astrophysics Data System (ADS)

    Fowlie, Andrew

    2017-10-01

    Using the DAMA/LIBRA anomaly as an example, we formalise the notion of halo-independence in the context of Bayesian statistics and quantified maximum entropy. We consider an infinite set of possible profiles, weighted by an entropic prior and constrained by a likelihood describing noisy measurements of modulated moments by DAMA/LIBRA. Assuming an isotropic dark matter (DM) profile in the galactic rest frame, we find the most plausible DM profiles and predictions for unmodulated signal rates at DAMA/LIBRA. The entropic prior contains an a priori unknown regularisation factor, β, that describes the strength of our conviction that the profile is approximately Maxwellian. By varying β, we smoothly interpolate between a halo-independent and a halo-dependent analysis, thus exploring the impact of prior information about the DM profile.

  17. The impact of feedback and the hot halo on the rates of gas accretion onto galaxies

    NASA Astrophysics Data System (ADS)

    Correa, Camila A.; Schaye, Joop; van de Voort, Freeke; Duffy, Alan R.; Wyithe, J. Stuart B.

    2018-04-01

    We investigate the physics that drives the gas accretion rates onto galaxies at the centers of dark matter haloes using the EAGLE suite of hydrodynamical cosmological simulations. We find that at redshifts z ≤ 2 the accretion rate onto the galaxy increases with halo mass in the halo mass range 1010 - 1011.7 M⊙, flattens between the halo masses 1011.7 - 1012.7 M⊙, and increases again for higher-mass haloes. However, the galaxy gas accretion does not flatten at intermediate halo masses when AGN feedback is switched off. To better understand these trends, we develop a physically motivated semi-analytic model of galaxy gas accretion. We show that the flattening is produced by the rate of gas cooling from the hot halo. The ratio of the cooling radius and the virial radius does not decrease continuously with increasing halo mass as generally thought. While it decreases up to ˜1013 M⊙ haloes, it increases for higher halo masses, causing an upturn in the galaxy gas accretion rate. This may indicate that in high-mass haloes AGN feedback is not sufficiently efficient. When there is no AGN feedback, the density of the hot halo is higher, the ratio of the cooling and virial radii does not decrease as much and the cooling rate is higher. Changes in the efficiency of stellar feedback can also increase or decrease the accretion rates onto galaxies. The trends can plausibly be explained by the re-accretion of gas ejected by progenitor galaxies and by the suppression of black hole growth, and hence AGN feedback, by stellar feedback.

  18. Two-halo term in stacked thermal Sunyaev-Zel'dovich measurements: Implications for self-similarity

    NASA Astrophysics Data System (ADS)

    Hill, J. Colin; Baxter, Eric J.; Lidz, Adam; Greco, Johnny P.; Jain, Bhuvnesh

    2018-04-01

    The relation between the mass and integrated electron pressure of galaxy group and cluster halos can be probed by stacking maps of the thermal Sunyaev-Zel'dovich (tSZ) effect. Perhaps surprisingly, recent observational results have indicated that the scaling relation between integrated pressure and mass follows the prediction of simple, self-similar models down to halo masses as low as 1 012.5 M⊙ . Hydrodynamical simulations that incorporate energetic feedback processes suggest that gas should be depleted from such low-mass halos, thus decreasing their tSZ signal relative to self-similar predictions. Here, we build on the modeling of V. Vikram, A. Lidz, and B. Jain, Mon. Not. R. Astron. Soc. 467, 2315 (2017), 10.1093/mnras/stw3311 to evaluate the bias in the interpretation of stacked tSZ measurements due to the signal from correlated halos (the "two-halo" term), which has generally been neglected in the literature. We fit theoretical models to a measurement of the tSZ-galaxy group cross-correlation function, accounting explicitly for the one- and two-halo contributions. We find moderate evidence of a deviation from self-similarity in the pressure-mass relation, even after marginalizing over conservative miscentering effects. We explore pressure-mass models with a break at 1 014 M⊙, as well as other variants. We discuss and test for sources of uncertainty in our analysis, in particular a possible bias in the halo mass estimates and the coarse resolution of the Planck beam. We compare our findings with earlier analyses by exploring the extent to which halo isolation criteria can reduce the two-halo contribution. Finally, we show that ongoing third-generation cosmic microwave background experiments will explicitly resolve the one-halo term in low-mass groups; our methodology can be applied to these upcoming data sets to obtain a clear answer to the question of self-similarity and an improved understanding of hot gas in low-mass halos.

  19. Occupational Stress: Preventing Suffering, Enhancing Wellbeing.

    PubMed

    Quick, James Campbell; Henderson, Demetria F

    2016-04-29

    Occupational stress is a known health risk for a range of psychological, behavioral, and medical disorders and diseases. Organizations and individuals can mitigate these disorders through preventive stress management and enhanced wellbeing. This article addresses, first, the known health risk evidence related to occupational stress; second, the use of preventive stress management in organizations as the framework for intervention; and third, the emerging domain of enhancing wellbeing, which strengthens the individual. Premature death and disability along with chronic suffering from occupational stress are not inevitable, despite being known outcome risks.

  20. Resolution of vitiligo following excision of halo congenital melanocytic nevus: a rare case report.

    PubMed

    Wang, Kai; Wang, Zhi; Huang, Weiqing

    2016-05-01

    Halo congenital melanocytic nevus (CMN) associated with vitiligo is rare, especially with regard to CMN excision. Only two reports of excision of halo CMN following repigmentation of vitiligo are found in the literature. We present a case of a girl with halo CMN and periorbital vitiligo. The halo CMN was excised and followed by spontaneous improvement of vitiligo. The result suggests excision of the inciting lesion may be a promising way to control vitiligo. © 2015 Wiley Periodicals, Inc.

  1. ELUCID. IV. Galaxy Quenching and its Relation to Halo Mass, Environment, and Assembly Bias

    NASA Astrophysics Data System (ADS)

    Wang, Huiyuan; Mo, H. J.; Chen, Sihan; Yang, Yang; Yang, Xiaohu; Wang, Enci; van den Bosch, Frank C.; Jing, Yipeng; Kang, Xi; Lin, Weipeng; Lim, S. H.; Huang, Shuiyao; Lu, Yi; Li, Shijie; Cui, Weiguang; Zhang, Youcai; Tweed, Dylan; Wei, Chengliang; Li, Guoliang; Shi, Feng

    2018-01-01

    We examine the quenched fraction of central and satellite galaxies as a function of galaxy stellar mass, halo mass, and the matter density of their large-scale environment. Matter densities are inferred from our ELUCID simulation, a constrained simulation of the local universe sampled by SDSS, while halo masses and central/satellite classification are taken from the galaxy group catalog of Yang et al. The quenched fraction for the total population increases systematically with the three quantities. We find that the “environmental quenching efficiency,” which quantifies the quenched fraction as a function of halo mass, is independent of stellar mass. And this independence is the origin of the stellar mass independence of density-based quenching efficiency found in previous studies. Considering centrals and satellites separately, we find that the two populations follow similar correlations of quenching efficiency with halo mass and stellar mass, suggesting that they have experienced similar quenching processes in their host halo. We demonstrate that satellite quenching alone cannot account for the environmental quenching efficiency of the total galaxy population, and that the difference between the two populations found previously arises mainly from the fact that centrals and satellites of the same stellar mass reside, on average, in halos of different mass. After removing these effects of halo mass and stellar mass, there remains a weak, but significant, residual dependence on environmental density, which is eliminated when halo assembly bias is taken into account. Our results therefore indicate that halo mass is the prime environmental parameter that regulates the quenching of both centrals and satellites.

  2. An explosion model for the formation of the radio halo of NGC 891

    NASA Astrophysics Data System (ADS)

    You, Jun-han; Allen, R. J.; Hu, Fu-xing

    1987-06-01

    The explosion model for the formation of the radio halo of NGC 891 proposed here are mainly based on two physical assumptions: a) the relativistic electrons belong to two families, a halo family and a disk family: the disk family originating in supernova events throughout the disk and the halo family, in a violent explosion of the galactic nucleus in the distant past. b) Energy equipartition, that is, the magnetic energy density be proportional to the number density of stars. On these two assumptions, the main observed features of the radio halo of NGC 891 can be satisfactorily explained.

  3. An explosion model for the formation of the radio halo of NGC 891

    NASA Astrophysics Data System (ADS)

    You, Jun-Han; Allen, R. J.; Hu, Fu-Xing

    1986-06-01

    The explosion model for the formation of the radio halo of NGC 891 proposed here is mainly based on two physical assumptions: (1) the relativistic electrons belong to two families, a halo family and a disk family, the disk family originating in supernova events throughout the disk, and the halo family in a violent explosion of the galactic nucleus in the distant past; and (2) energy equipartition, where the magnetic energy density is proportional to the number density of stars. On these two assumptions, the main observed features of the radio halo of NGC 891 can be satisfactorily explained.

  4. The build up of the correlation between halo spin and the large-scale structure

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Kang, Xi

    2018-01-01

    Both simulations and observations have confirmed that the spin of haloes/galaxies is correlated with the large-scale structure (LSS) with a mass dependence such that the spin of low-mass haloes/galaxies tend to be parallel with the LSS, while that of massive haloes/galaxies tend to be perpendicular with the LSS. It is still unclear how this mass dependence is built up over time. We use N-body simulations to trace the evolution of the halo spin-LSS correlation and find that at early times the spin of all halo progenitors is parallel with the LSS. As time goes on, mass collapsing around massive halo is more isotropic, especially the recent mass accretion along the slowest collapsing direction is significant and it brings the halo spin to be perpendicular with the LSS. Adopting the fractional anisotropy (FA) parameter to describe the degree of anisotropy of the large-scale environment, we find that the spin-LSS correlation is a strong function of the environment such that a higher FA (more anisotropic environment) leads to an aligned signal, and a lower anisotropy leads to a misaligned signal. In general, our results show that the spin-LSS correlation is a combined consequence of mass flow and halo growth within the cosmic web. Our predicted environmental dependence between spin and large-scale structure can be further tested using galaxy surveys.

  5. WEAK GALACTIC HALO-DWARF SPHEROIDAL CONNECTION FROM RR LYRAE STARS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fiorentino, Giuliana; Bono, Giuseppe; Monelli, Matteo

    2015-01-01

    We discuss the role that dwarf galaxies may have played in the formation of the Galactic halo (Halo) using RR Lyrae stars (RRL) as tracers of their ancient stellar component. The comparison is performed using two observables (periods, luminosity amplitudes) that are reddening and distance independent. Fundamental mode RRL in 6 dwarf spheroidals (dSphs) and 11 ultra faint dwarf galaxies (∼1300) show a Gaussian period distribution well peaked around a mean period of (Pab) = 0.610 ± 0.001 days (σ = 0.03). The Halo RRL (∼15,000) are characterized by a broader period distribution. The fundamental mode RRL in all the dSphs apart from Sagittariusmore » are completely lacking in High Amplitude Short Period (HASP) variables, defined as those having P ≲ 0.48 days and A{sub V} ≥ 0.75 mag. Such variables are not uncommon in the Halo and among the globular clusters and massive dwarf irregulars. To further interpret this evidence, we considered 18 globulars covering a broad range in metallicity (–2.3 ≲ [Fe/H] ≲ –1.1) and hosting more than 35 RRL each. The metallicity turns out to be the main parameter, since only globulars more metal-rich than [Fe/H] ∼ –1.5 host RRL in the HASP region. This finding suggests that dSphs similar to the surviving ones do not appear to be the major building-blocks of the Halo. Leading physical arguments suggest an extreme upper limit of ∼50% to their contribution. On the other hand, massive dwarfs hosting an old population with a broad metallicity distribution (Large Magellanic Cloud, Sagittarius) may have played a primary role in the formation of the Halo.« less

  6. A Hot Gaseous Galaxy Halo Candidate with Mg X Absorption

    NASA Astrophysics Data System (ADS)

    Qu, Zhijie; Bregman, Joel N.

    2016-12-01

    The hot gas in galaxy halos may account for a significant fraction of missing baryons in galaxies, and some of these gases can be traced by high ionization absorption systems in QSO UV spectra. Using high S/N Hubble Space Telescope/Cosmic Origins Spectrograph spectra, we discovered a high ionization state system at z = 1.1912 in the sightline toward LBQS 1435-0134, and two-component absorption lines are matched for Mg x, Ne viii, Ne VI, O VI, Ne v, O v, Ne IV, O IV, N IV, O III, and H I. Mg x, detected for the first time (5.8σ), is a particularly direct tracer of hot galactic halos, as its peak ion fraction occurs near 106.1 K, about the temperature of a virialized hot galaxy halo of mass ˜ 0.5{M}* . With Mg x and Ne viii, a photoionization model cannot reproduce the observed column densities with path lengths of galaxy halos. For collisional ionization models, one or two-temperature models do not produce acceptable fits, but a three-temperature model or a power-law model can produce the observed results. In the power-law model, {dN}/{dT}={10}4.4+/- 2.2-[Z/X]{T}1.55+/- 0.41 with temperatures in the range of {10}4.39+/- 0.13 {{K}}\\lt T\\lt {10}6.04+/- 0.05 {{K}}, the total hydrogen column density is 8.2× {10}19(0.3 {Z}⊙ /Z) {{cm}}-2 and the positive power-law index indicates most of the mass is at the high temperature end. We suggest that this absorption system is a hot volume-filled galaxy halo rather than interaction layers between the hot halo and cool clouds. The temperature dependence of the column density is likely due to the local mixture of multiple phase gases.

  7. High Angular Momentum Halo Gas: A Feedback and Code-independent Prediction of LCDM

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Stewart, Kyle R.; Maller, Ariyeh H.; Oñorbe, Jose

    We investigate angular momentum acquisition in Milky Way-sized galaxies by comparing five high resolution zoom-in simulations, each implementing identical cosmological initial conditions but utilizing different hydrodynamic codes: Enzo, Art, Ramses, Arepo, and Gizmo-PSPH. Each code implements a distinct set of feedback and star formation prescriptions. We find that while many galaxy and halo properties vary between the different codes (and feedback prescriptions), there is qualitative agreement on the process of angular momentum acquisition in the galaxy’s halo. In all simulations, cold filamentary gas accretion to the halo results in ∼4 times more specific angular momentum in cold halo gas (more » λ {sub cold} ≳ 0.1) than in the dark matter halo. At z > 1, this inflow takes the form of inspiraling cold streams that are co-directional in the halo of the galaxy and are fueled, aligned, and kinematically connected to filamentary gas infall along the cosmic web. Due to the qualitative agreement among disparate simulations, we conclude that the buildup of high angular momentum halo gas and the presence of these inspiraling cold streams are robust predictions of Lambda Cold Dark Matter galaxy formation, though the detailed morphology of these streams is significantly less certain. A growing body of observational evidence suggests that this process is borne out in the real universe.« less

  8. High Angular Momentum Halo Gas: A Feedback and Code-independent Prediction of LCDM

    NASA Astrophysics Data System (ADS)

    Stewart, Kyle R.; Maller, Ariyeh H.; Oñorbe, Jose; Bullock, James S.; Joung, M. Ryan; Devriendt, Julien; Ceverino, Daniel; Kereš, Dušan; Hopkins, Philip F.; Faucher-Giguère, Claude-André

    2017-07-01

    We investigate angular momentum acquisition in Milky Way-sized galaxies by comparing five high resolution zoom-in simulations, each implementing identical cosmological initial conditions but utilizing different hydrodynamic codes: Enzo, Art, Ramses, Arepo, and Gizmo-PSPH. Each code implements a distinct set of feedback and star formation prescriptions. We find that while many galaxy and halo properties vary between the different codes (and feedback prescriptions), there is qualitative agreement on the process of angular momentum acquisition in the galaxy’s halo. In all simulations, cold filamentary gas accretion to the halo results in ˜4 times more specific angular momentum in cold halo gas (λ cold ≳ 0.1) than in the dark matter halo. At z > 1, this inflow takes the form of inspiraling cold streams that are co-directional in the halo of the galaxy and are fueled, aligned, and kinematically connected to filamentary gas infall along the cosmic web. Due to the qualitative agreement among disparate simulations, we conclude that the buildup of high angular momentum halo gas and the presence of these inspiraling cold streams are robust predictions of Lambda Cold Dark Matter galaxy formation, though the detailed morphology of these streams is significantly less certain. A growing body of observational evidence suggests that this process is borne out in the real universe.

  9. Stellar Mass-gap as a Probe of Halo Assembly History and Concentration: Youth Hidden among Old Fossils

    NASA Astrophysics Data System (ADS)

    Deason, A. J.; Conroy, C.; Wetzel, A. R.; Tinker, J. L.

    2013-11-01

    We investigate the use of the halo mass-gap statistic—defined as the logarithmic difference in mass between the host halo and its most massive satellite subhalo—as a probe of halo age and concentration. A cosmological N-body simulation is used to study N ~ 25, 000 group/cluster-sized halos in the mass range 1012.5 < M halo/M ⊙ < 1014.5. In agreement with previous work, we find that halo mass-gap is related to halo formation time and concentration. On average, older and more highly concentrated halos have larger halo mass-gaps, and this trend is stronger than the mass-concentration relation over a similar dynamic range. However, there is a large amount of scatter owing to the transitory nature of the satellite subhalo population, which limits the use of the halo mass-gap statistic on an object-by-object basis. For example, we find that 20% of very large halo mass-gap systems (akin to "fossil groups") are young and have likely experienced a recent merger between a massive satellite subhalo and the central subhalo. We relate halo mass-gap to the observable stellar mass-gap via abundance matching. Using a galaxy group catalog constructed from the Sloan Digital Sky Survey Data Release 7, we find that the star formation and structural properties of galaxies at fixed mass show no trend with stellar mass-gap. This is despite a variation in halo age of ≈2.5 Gyr over ≈1.2 dex in stellar mass-gap. Thus, we find no evidence to suggest that the halo formation history significantly affects galaxy properties.

  10. Prospects for detecting supersymmetric dark matter in the Galactic halo.

    PubMed

    Springel, V; White, S D M; Frenk, C S; Navarro, J F; Jenkins, A; Vogelsberger, M; Wang, J; Ludlow, A; Helmi, A

    2008-11-06

    Dark matter is the dominant form of matter in the Universe, but its nature is unknown. It is plausibly an elementary particle, perhaps the lightest supersymmetric partner of known particle species. In this case, annihilation of dark matter in the halo of the Milky Way should produce gamma-rays at a level that may soon be observable. Previous work has argued that the annihilation signal will be dominated by emission from very small clumps (perhaps smaller even than the Earth), which would be most easily detected where they cluster together in the dark matter haloes of dwarf satellite galaxies. Here we report that such small-scale structure will, in fact, have a negligible impact on dark matter detectability. Rather, the dominant and probably most easily detectable signal will be produced by diffuse dark matter in the main halo of the Milky Way. If the main halo is strongly detected, then small dark matter clumps should also be visible, but may well contain no stars, thereby confirming a key prediction of the cold dark matter model.

  11. Numerical Convergence in the Dark Matter Halos Properties Using Cosmological Simulations

    NASA Astrophysics Data System (ADS)

    Mosquera-Escobar, X. E.; Muñoz-Cuartas, J. C.

    2017-07-01

    Nowadays, the accepted cosmological model is the so called -Cold Dark Matter (CDM). In such model, the universe is considered to be homogeneous and isotropic, composed of diverse components as the dark matter and dark energy, where the latter is the most abundant one. Dark matter plays an important role because it is responsible for the generation of gravitational potential wells, commonly called dark matter halos. At the end, dark matter halos are characterized by a set of parameters (mass, radius, concentration, spin parameter), these parameters provide valuable information for different studies, such as galaxy formation, gravitational lensing, etc. In this work we use the publicly available code Gadget2 to perform cosmological simulations to find to what extent the numerical parameters of the simu- lations, such as gravitational softening, integration time step and force calculation accuracy affect the physical properties of the dark matter halos. We ran a suite of simulations where these parameters were varied in a systematic way in order to explore accurately their impact on the structural parameters of dark matter halos. We show that the variations on the numerical parameters affect the structural pa- rameters of dark matter halos, such as concentration, virial radius, and concentration. We show that these modifications emerged when structures become non- linear (at redshift 2) for the scale of our simulations, such that these variations affected the formation and evolution structure of halos mainly at later cosmic times. As a quantitative result, we propose which would be the most appropriate values for the numerical parameters of the simulations, such that they do not affect the halo properties that are formed. For force calculation accuracy we suggest values smaller or equal to 0.0001, integration time step smaller o equal to 0.005 and for gravitational softening we propose equal to 1/60th of the mean interparticle distance, these values, correspond to the

  12. Halos--a problem for all myopes? A comparison between spectacles, contact lenses, and photorefractive keratectomy.

    PubMed

    Lohmann, C P; Fitzke, F W; O'Brart, D; Muir, M K; Marshall, J

    1993-01-01

    After photorefractive keratectomy (PRK) using excimer lasers (193 nm) many patients report the presence of halos around light sources at night. However, halos are not unique to PRK patients, as they are a common observation in myopic contact lens wearers. We present an objective measurement of the halos using a computerized technique. The patient fixated on a red cross within a white circle in the center of a video monitor which served as the halo source. The screen surrounding the circle was not illuminated. The operator controlled the movement of the white spot and moved the spot toward the halo source until the subject indicated when the cursor was at the outer parameter of the halo. Measurements were made at 30 degree intervals around the halo source and expressed as square degrees. The study found that spectacles, soft contact lenses, and excimer laser surgery were superior to hard contact lenses in terms of the size of the halo. A mean value of 2.51 square degrees was obtained for spectacles wearers compared with 3.18 square degrees for soft contact lenses, 3.14 square degrees for excimer laser patients with 4-millimeter ablation zone, 2.76 square degrees for excimer laser patients with a 5-millimeter ablation zone, and 89.5 square degrees for hard contact lenses. It appears that this device is very useful for measuring the halo size after excimer laser PRK. We concluded that halos were not a problem for our patients after excimer laser photorefractive keratectomy.

  13. Halo Nucleic Molecules: Molecules Formed from at Least One Atom with a Halo Nucleus. Emphasis on 11,11Li_2 Along with Other Exotic Isotopologues.

    NASA Astrophysics Data System (ADS)

    Dattani, Nikesh S.; Welsh, Staszek

    2014-06-01

    Atoms whose nuclei have an exotic number of nucleons can have a `core nucleus' surrounded by a `halo' formed by a nucleon orbiting the core nucleus. For example, due to the two halo neutrons orbiting the core nucleus of 11Li, its nucleus has a cross section that is roughly the same size as that of 208Pb. Halo nucleic atoms have been studied extensively both in theory and in experiments, however halo nucleic molecules have not been studied in either. We first show, using HeH^+, BeH, and MgH as examples, that with measurements of any two isotopologues of a molecule, we can determine crucial properties of a third isotopologue well within spectroscopic accuracy. We then use the extremely precise empirical information available for the low-lying states of 6,6Li_2, 6,7Li_2 and 7,7Li_2 to predict potentials and various properties of the halo nucleic molecule 11,11Li_2, along with isotopologues containing 3Li, 4Li, 5Li, 8Li, 9Li, 10Li, and 12Li. We believe that our predictions of the ro-vibrational energies are reliable for experiments for the first detection of a halo nucleic molecule. R. J. Le Roy, N. S. Dattani, J. A. Coxon, A. J. Ross, P. Crozet, C. Linton, J. Chem. Phys. 131, 204309 (2009). N. S. Dattani, R. J. Le Roy, J. Mol. Spec. 268, 199-210 (2011). M. Semczuk, X. Li, W. Gunton, M. Haw, N. S. Dattani, J. Witz, A. Mills, D. J. Jones, K. W. Madison, Phys. Rev. A 87, 052505 (2013) W. Gunton, M. Semczuk, N. S. Dattani, K. W. Madison, Phys. Rev. A 88, 062510 (2013)

  14. Massive black holes in galactic halos?

    NASA Technical Reports Server (NTRS)

    Lacey, C. G.; Ostriker, J. P.

    1985-01-01

    In the present attempt to resolve the problems posed by the composition of dark halos and the heating of stellar disks, under the assumption that galaxy halos are composed of massive black holes, it is noted that the black holes must have masses of the order of one million solar masses. The heating mechanism proposed yields predictions for the dependence of the velocity dispersion on time, and for the shape of the velocity ellipsoid, which are in good agreement with observations. Attention is given to the constraints set by dynamical friction causing black holes to spiral to the Galactic center, by the possible presence of dark matter in dwarf spheroidal galaxies, and by the accretion of interstellar gas by the black holes that produce luminous objects in the Galaxy.

  15. Halo-independence with quantified maximum entropy at DAMA/LIBRA

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fowlie, Andrew, E-mail: andrew.j.fowlie@googlemail.com

    2017-10-01

    Using the DAMA/LIBRA anomaly as an example, we formalise the notion of halo-independence in the context of Bayesian statistics and quantified maximum entropy. We consider an infinite set of possible profiles, weighted by an entropic prior and constrained by a likelihood describing noisy measurements of modulated moments by DAMA/LIBRA. Assuming an isotropic dark matter (DM) profile in the galactic rest frame, we find the most plausible DM profiles and predictions for unmodulated signal rates at DAMA/LIBRA. The entropic prior contains an a priori unknown regularisation factor, β, that describes the strength of our conviction that the profile is approximately Maxwellian.more » By varying β, we smoothly interpolate between a halo-independent and a halo-dependent analysis, thus exploring the impact of prior information about the DM profile.« less

  16. Synthesis, Properties and Stereochemistry of 2-Halo-1,2λ⁵-oxaphosphetanes.

    PubMed

    Kolodiazhna, Anastasy O; Kolodiazhnyi, Oleg I

    2016-10-17

    Results of research into four-membered 2-halo-1,2λ⁵-oxaphosphetane phosphorus(V)-heterocycles are presented. The preparation of 2-halo-1,2λ⁵-oxaphosphetanes by reaction of P- haloylides with carbonyl compounds is described. The mechanism of asynchronous [2+2]-сycloaddition of ylides to aldehydes was proposed on the base of low-temperature NMR investigations. 2-Halo-1,2λ⁵-oxaphosphetanes were isolated as individual compounds and their structures were confirmed by ¹Н-, 13 C-, 19 F- and 31 Р-NMR spectra. These compounds are convenient reagents for preparing of various organic and organophosphorus compounds hardly available by other methods. Chemical and physical properties of the 2-halo-1,2λ⁵-oxaphosphetanes are reviewed. The 2-chloro-1,2λ⁵-oxaphosphetanes, rearrange with formation of 2-chloroalkyl-phosphonates or convert into trans -phosphorylated alkenes depending on the substituents at the α-carbon atom. Prospective synthetic applications of 2-halo-1,2λ⁵-oxaphosphetanes are analyzed. The 2-halo-1,2λ⁵-oxaphosphetanes may be easily converted to various alkenylphosphonates: allyl- or vinylphosphonates, phosphorus ketenes, thioketenes, ketenimines.

  17. Measuring the Dust Grains and Distance to X Persei Via Its X-ray Halo

    NASA Astrophysics Data System (ADS)

    Smith, Randall

    2006-09-01

    We propose to observe the X-ray halo of the high mass X-ray binary pulsar X Per to measure interstellar dust grains along the line of sight (LOS) and to determine the distance to X Per. The X-ray halo is formed by scattering from grains along the LOS, which for X Per appear to be concentrated in one molecular cloud. Unlike many other X-ray halo observations, this low-absorption high-latitude sightline is well-characterized from absorption spectroscopy done with HST, Copernicus, and FUSE. This halo observation will measure the distance to the cloud and the dust size distribution in it. We will also be able to determine the distance to X Per by measuring the time delayed pulses in the X-ray halo.

  18. Evaluation of beam halo from beam-gas scattering at the KEK Accelerator Test Facility

    NASA Astrophysics Data System (ADS)

    Yang, R.; Naito, T.; Bai, S.; Aryshev, A.; Kubo, K.; Okugi, T.; Terunuma, N.; Zhou, D.; Faus-Golfe, A.; Kubytskyi, V.; Liu, S.; Wallon, S.; Bambade, P.

    2018-05-01

    In circular colliders, as well as in damping rings and synchrotron radiation light sources, beam halo is one of the critical issues limiting the performance as well as potentially causing component damage and activation. It is imperative to clearly understand the mechanisms that lead to halo formation and to test the available theoretical models. Elastic beam-gas scattering can drive particles to large oscillation amplitudes and be a potential source of beam halo. In this paper, numerical estimation and Monte Carlo simulations of this process at the ATF of KEK are presented. Experimental measurements of beam halo in the ATF2 beam line using a diamond sensor detector are also described, which clearly demonstrate the influence of the beam-gas scattering process on the transverse halo distribution.

  19. Testing the Caustic Ring Dark Matter Halo Model Against Observations in the Milky Way

    NASA Astrophysics Data System (ADS)

    Dumas, Julie; Newberg, Heidi Jo; Niedzielski, Bethany; Susser, Adam; Thompson, Jeffery M.; Weiss, Jake; Lewis, Kim M.

    2016-06-01

    One prediction of axion dark matter models is they can form Bose-Einstein condensates and rigid caustic rings as a halo collapses in the non-linear regime. In this thesis, we undertake the first study of a caustic ring model for the Milky Way halo (Duffy & Sikivie 2008), paying particular attention to observational consequences. We first present the formalism for calculating the gravitational acceleration of a caustic ring halo. The caustic ring dark matter theory reproduces a roughly logarithmic halo, with large perturbations near the rings. We show that this halo can reasonably match the known Galactic rotation curve. We are not able to confirm or rule out an association between the positions of the caustic rings and oscillations in the observed rotation curve, due to insufficient rotation curve data. We explore the effects of dark matter caustic rings on dwarf galaxy tidal disruption with N-body simulations. Simulations of the Sagittarius (Sgr) dwarf galaxy in a caustic ring halo potential, with disk and bulge parameters that are tuned to match the Galactic rotation curve, match observations of the Sgr trailing tidal tails as far as 90 kpc from the Galactic center. Like the Navarro-Frenk-White (NFW) halo, they are, however, unable to match the leading tidal tail. None of the caustic, NFW, or triaxial logarithmic halos are able to simultaneously match observations of the leading and trailing arms of the Sagittarius stream. We further show that simulations of dwarf galaxies that move through caustic rings are qualitatively similar to those moving in a logarithmic halo. This research was funded by NSF grant AST 10-09670, the NASA-NY Space Grant, and the American Fellowship from AAUW.

  20. The Newly-Discovered Outer Halo Globular Cluster System of M31

    NASA Astrophysics Data System (ADS)

    Mackey, D.; Huxor, A.; Ferguson, A.

    2012-08-01

    In this contribution we describe the discovery of a large number of globular clusters in the outer halo of M31 from the Pan-Andromeda Archaeological Survey (PAndAS). New globular clusters have also been found in the outskirts of M33, and NGC 147 and 185. Many of the remote M31 clusters are observed to preferentially project onto tidal debris streams in the stellar halo, suggesting that much of the outer M31 globular cluster system has been assembled via the accretion of satellite galaxies. We briefly discuss the global properties of the M31 halo globular cluster system.

  1. Real- and redshift-space halo clustering in f(R) cosmologies

    NASA Astrophysics Data System (ADS)

    Arnalte-Mur, Pablo; Hellwing, Wojciech A.; Norberg, Peder

    2017-05-01

    We present two-point correlation function statistics of the mass and the haloes in the chameleon f(R) modified gravity scenario using a series of large-volume N-body simulations. Three distinct variations of f(R) are considered (F4, F5 and F6) and compared to a fiducial Λ cold dark matter (ΛCDM) model in the redshift range z ∈ [0, 1]. We find that the matter clustering is indistinguishable for all models except for F4, which shows a significantly steeper slope. The ratio of the redshift- to real-space correlation function at scales >20 h-1 Mpc agrees with the linear General Relativity (GR) Kaiser formula for the viable f(R) models considered. We consider three halo populations characterized by spatial abundances comparable to that of luminous red galaxies and galaxy clusters. The redshift-space halo correlation functions of F4 and F5 deviate significantly from ΛCDM at intermediate and high redshift, as the f(R) halo bias is smaller than or equal to that of the ΛCDM case. Finally, we introduce a new model-independent clustering statistic to distinguish f(R) from GR: the relative halo clustering ratio - R. The sampling required to adequately reduce the scatter in R will be available with the advent of the next-generation galaxy redshift surveys. This will foster a prospective avenue to obtain largely model-independent cosmological constraints on this class of modified gravity models.

  2. STELLAR MASS-GAP AS A PROBE OF HALO ASSEMBLY HISTORY AND CONCENTRATION: YOUTH HIDDEN AMONG OLD FOSSILS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Deason, A. J.; Conroy, C.; Wetzel, A. R.

    We investigate the use of the halo mass-gap statistic—defined as the logarithmic difference in mass between the host halo and its most massive satellite subhalo—as a probe of halo age and concentration. A cosmological N-body simulation is used to study N ∼ 25, 000 group/cluster-sized halos in the mass range 10{sup 12.5} < M{sub halo}/M{sub ☉} < 10{sup 14.5}. In agreement with previous work, we find that halo mass-gap is related to halo formation time and concentration. On average, older and more highly concentrated halos have larger halo mass-gaps, and this trend is stronger than the mass-concentration relation over amore » similar dynamic range. However, there is a large amount of scatter owing to the transitory nature of the satellite subhalo population, which limits the use of the halo mass-gap statistic on an object-by-object basis. For example, we find that 20% of very large halo mass-gap systems (akin to {sup f}ossil groups{sup )} are young and have likely experienced a recent merger between a massive satellite subhalo and the central subhalo. We relate halo mass-gap to the observable stellar mass-gap via abundance matching. Using a galaxy group catalog constructed from the Sloan Digital Sky Survey Data Release 7, we find that the star formation and structural properties of galaxies at fixed mass show no trend with stellar mass-gap. This is despite a variation in halo age of ≈2.5 Gyr over ≈1.2 dex in stellar mass-gap. Thus, we find no evidence to suggest that the halo formation history significantly affects galaxy properties.« less

  3. Ecology of dark matter haloes - II. Effects of interactions on the alignment of halo pairs

    NASA Astrophysics Data System (ADS)

    L'Huillier, Benjamin; Park, Changbom; Kim, Juhan

    2017-04-01

    We use the Horizon Run 4 cosmological N-body simulation to study the effects of distant and close interactions on the alignments of the shapes, spins and orbits of targets haloes with their neighbours, and their dependence on the local density environment and neighbour separation. Interacting targets have a significantly lower spin and higher sphericity and oblateness than all targets. Interacting pairs initially have antiparallel spins, but the spins develop parallel alignment as time goes on. Neighbours tend to evolve in the plane of rotation of the target, and in the direction of the major axis of prolate haloes. Moreover, interactions are preferentially radial, while pairs with non-radial orbits are preferentially prograde. The alignment signals are stronger at high mass and for close separations, and independent of the large-scale density. Positive alignment signals are found at redshifts up to 4, and increase with decreasing redshifts. Moreover, the orbits tend to become prograde at low redshift, while no alignment is found at high redshift (z = 4).

  4. Genetically modified haloes: towards controlled experiments in ΛCDM galaxy formation

    NASA Astrophysics Data System (ADS)

    Roth, Nina; Pontzen, Andrew; Peiris, Hiranya V.

    2016-01-01

    We propose a method to generate `genetically modified' (GM) initial conditions for high-resolution simulations of galaxy formation in a cosmological context. Building on the Hoffman-Ribak algorithm, we start from a reference simulation with fully random initial conditions, then make controlled changes to specific properties of a single halo (such as its mass and merger history). The algorithm demonstrably makes minimal changes to other properties of the halo and its environment, allowing us to isolate the impact of a given modification. As a significant improvement over previous work, we are able to calculate the abundance of the resulting objects relative to the reference simulation. Our approach can be applied to a wide range of cosmic structures and epochs; here we study two problems as a proof of concept. First, we investigate the change in density profile and concentration as the collapse times of three individual haloes are varied at fixed final mass, showing good agreement with previous statistical studies using large simulation suites. Secondly, we modify the z = 0 mass of haloes to show that our theoretical abundance calculations correctly recover the halo mass function. The results demonstrate that the technique is robust, opening the way to controlled experiments in galaxy formation using hydrodynamic zoom simulations.

  5. Neck motion due to the halo-vest in prone and supine positions.

    PubMed

    Ivancic, Paul C; Telles, Connor J

    2010-05-01

    An in vitro biomechanical study of the effectiveness of halo-vest fixation. The objective was to evaluate motion of the injured cervical spine with normal halo-vest application and vest loose in the prone and supine positions. Snaking motion of the neck is defined as rotation in opposing directions throughout the cervical spine. Previous clinical studies have suggested snaking neck motion due to the halo-vest may lead to inadequate healing or nonunion. The halo-vest was applied to a Human Model of the Neck, which consisted of a cervical spine specimen mounted to the torso of an anthropometric test dummy and carrying a surrogate head. The model was transitioned from prone, to upright, to supine with the halo-vest applied normally and with the vest loose. Average peak spinal motions were computed in the prone and supine positions and contrasted with the physiologic rotation range, obtained from the intact flexibility test, and statistically compared (P < 0.05) between normal halo-vest application and vest loose. Snaking motion of the neck was observed in the prone and supine positions, consisting of extension at head/C1 and C1/2 and flexion at the inferior spinal levels. The intervertebral rotation peaks generally exceeded the physiologic range throughout the cervical spine due to the loose vest in the prone position. Significant increases in the extension peaks at head/C1 (16.9 degrees vs. 5.7 degrees) and flexion peaks at C4/5 (6.9 degrees vs. 3.6 degrees) and C7-T1 (5.2 degrees vs. 0.7 degrees) were observed in the prone position due to the loose vest, as compared to normal halo-vest application. Axial neck separation was consistently observed in the prone and supine positions. The present results, which document snaking motion of the cervical spine due to the halo-vest, indicate that an inadequately fitting or loose vest may significantly diminish its immobilization capacity leading to delayed healing or nonunion.

  6. Promoting Translational Research Among Movement Science, Occupational Science, and Occupational Therapy.

    PubMed

    Sainburg, Robert L; Liew, Sook-Lei; Frey, Scott H; Clark, Florence

    2017-01-01

    Integration of research in the fields of neural control of movement and biomechanics (collectively referred to as movement science) with the field of human occupation directly benefits both areas of study. Specifically, incorporating many of the quantitative scientific methods and analyses employed in movement science can help accelerate the development of rehabilitation-relevant research in occupational therapy (OT) and occupational science (OS). Reciprocally, OT and OS, which focus on the performance of everyday activities (occupations) to promote health and well-being, provide theoretical frameworks to guide research on the performance of actions in the context of social, psychological, and environmental factors. Given both fields' mutual interest in the study of movement as it relates to health and disease, the authors posit that combining OS and OT theories and principles with the theories and methods in movement science may lead to new, impactful, and clinically relevant knowledge. The first step is to ensure that individuals with OS or OT backgrounds are academically prepared to pursue advanced study in movement science. In this article, the authors propose 2 strategies to address this need.

  7. Detection of Hot Halo Gets Theory Out of Hot Water

    NASA Astrophysics Data System (ADS)

    2006-02-01

    Scientists using NASA's Chandra X-ray Observatory have detected an extensive halo of hot gas around a quiescent spiral galaxy. This discovery is evidence that galaxies like our Milky Way are still accumulating matter from the gradual inflow of intergalactic gas. "What we are likely witnessing here is the ongoing galaxy formation process," said Kristian Pedersen of the University of Copenhagen, Denmark, and lead author of a report on the discovery. Chandra observations show that the hot halo extends more than 60,000 light years on either side of the disk of the galaxy known as NGC 5746. The detection of such a large halo alleviates a long-standing problem for the theory of galaxy formation. Spiral galaxies are thought to form from enormous clouds of intergalactic gas that collapse to form giant, spinning disks of stars and gas. Chandra X-ray Image of NGC 5746 Chandra X-ray Image of NGC 5746 One prediction of this theory is that large spiral galaxies should be immersed in halos of hot gas left over from the galaxy formation process. Hot gas has been detected around spiral galaxies in which vigorous star formation is ejecting matter from the galaxy, but until now hot halos due to infall of intergalactic matter have not been detected. "Our observations solve the mystery of the missing hot halos around spiral galaxies," said Pedersen. "The halos exist, but are so faint that an extremely sensitive telescope such as Chandra is needed to detect them." DSS Optical Image of NGC 5746 DSS Optical Image of NGC 5746 NGC 5746 is a massive spiral galaxy about a 100 million light years from Earth. Its disk of stars and gas is viewed almost edge-on. The galaxy shows no signs of unusual star formation, or energetic activity from its nuclear region, making it unlikely that the hot halo is produced by gas flowing out of the galaxy. "We targeted NGC 5746 because we thought its distance and orientation would give us the best chance to detect a hot halo caused by the infall of

  8. A Comprehensive Analysis of Uncertainties Affecting the Stellar Mass-Halo Mass Relation for 0

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Behroozi, Peter S.; Conroy, Charlie; Wechsler, Risa H.

    2010-06-07

    We conduct a comprehensive analysis of the relationship between central galaxies and their host dark matter halos, as characterized by the stellar mass - halo mass (SM-HM) relation, with rigorous consideration of uncertainties. Our analysis focuses on results from the abundance matching technique, which assumes that every dark matter halo or subhalo above a specific mass threshold hosts one galaxy. We provide a robust estimate of the SM-HM relation for 0 < z < 1 and discuss the quantitative effects of uncertainties in observed galaxy stellar mass functions (GSMFs) (including stellar mass estimates and counting uncertainties), halo mass functions (includingmore » cosmology and uncertainties from substructure), and the abundance matching technique used to link galaxies to halos (including scatter in this connection). Our analysis results in a robust estimate of the SM-HM relation and its evolution from z=0 to z=4. The shape and evolution are well constrained for z < 1. The largest uncertainties at these redshifts are due to stellar mass estimates (0.25 dex uncertainty in normalization); however, failure to account for scatter in stellar masses at fixed halo mass can lead to errors of similar magnitude in the SM-HM relation for central galaxies in massive halos. We also investigate the SM-HM relation to z = 4, although the shape of the relation at higher redshifts remains fairly unconstrained when uncertainties are taken into account. We find that the integrated star formation at a given halo mass peaks at 10-20% of available baryons for all redshifts from 0 to 4. This peak occurs at a halo mass of 7 x 10{sup 11} M{sub {circle_dot}} at z = 0 and this mass increases by a factor of 5 to z = 4. At lower and higher masses, star formation is substantially less efficient, with stellar mass scaling as M{sub *} {approx} M{sub h}{sup 2.3} at low masses and M{sub *} {approx} M{sub h}{sup 0.29} at high masses. The typical stellar mass for halos with mass less than 10{sup 12} M

  9. Investigation of the halo-artifact in 68Ga-PSMA-11-PET/MRI.

    PubMed

    Heußer, Thorsten; Mann, Philipp; Rank, Christopher M; Schäfer, Martin; Dimitrakopoulou-Strauss, Antonia; Schlemmer, Heinz-Peter; Hadaschik, Boris A; Kopka, Klaus; Bachert, Peter; Kachelrieß, Marc; Freitag, Martin T

    2017-01-01

    Combined positron emission tomography (PET) and magnetic resonance imaging (MRI) targeting the prostate-specific membrane antigen (PSMA) with a 68Ga-labelled PSMA-analog (68Ga-PSMA-11) is discussed as a promising diagnostic method for patients with suspicion or history of prostate cancer. One potential drawback of this method are severe photopenic (halo-) artifacts surrounding the bladder and the kidneys in the scatter-corrected PET images, which have been reported to occur frequently in clinical practice. The goal of this work was to investigate the occurrence and impact of these artifacts and, secondly, to evaluate variants of the standard scatter correction method with regard to halo-artifact suppression. Experiments using a dedicated pelvis phantom were conducted to investigate whether the halo-artifact is modality-, tracer-, and/or concentration-dependent. Furthermore, 31 patients with history of prostate cancer were selected from an ongoing 68Ga-PSMA-11-PET/MRI study. For each patient, PET raw data were reconstructed employing six different variants of PET scatter correction: absolute scatter scaling, relative scatter scaling, and relative scatter scaling combined with prompt gamma correction, each of which was combined with a maximum scatter fraction (MaxSF) of MaxSF = 75% or MaxSF = 40%. Evaluation of the reconstructed images with regard to halo-artifact suppression was performed both quantitatively using statistical analysis and qualitatively by two independent readers. The phantom experiments did not reveal any modality-dependency (PET/MRI vs. PET/CT) or tracer-dependency (68Ga vs. 18F-FDG). Patient- and phantom-based data indicated that halo-artifacts derive from high organ-to-background activity ratios (OBR) between bladder/kidneys and surrounding soft tissue, with a positive correlation between OBR and halo size. Comparing different variants of scatter correction, reducing the maximum scatter fraction from the default value MaxSF = 75% to MaxSF = 40

  10. Investigation of the halo-artifact in 68Ga-PSMA-11-PET/MRI

    PubMed Central

    Rank, Christopher M.; Schäfer, Martin; Dimitrakopoulou-Strauss, Antonia; Schlemmer, Heinz-Peter; Hadaschik, Boris A.; Kopka, Klaus; Bachert, Peter; Kachelrieß, Marc

    2017-01-01

    Objectives Combined positron emission tomography (PET) and magnetic resonance imaging (MRI) targeting the prostate-specific membrane antigen (PSMA) with a 68Ga-labelled PSMA-analog (68Ga-PSMA-11) is discussed as a promising diagnostic method for patients with suspicion or history of prostate cancer. One potential drawback of this method are severe photopenic (halo-) artifacts surrounding the bladder and the kidneys in the scatter-corrected PET images, which have been reported to occur frequently in clinical practice. The goal of this work was to investigate the occurrence and impact of these artifacts and, secondly, to evaluate variants of the standard scatter correction method with regard to halo-artifact suppression. Methods Experiments using a dedicated pelvis phantom were conducted to investigate whether the halo-artifact is modality-, tracer-, and/or concentration-dependent. Furthermore, 31 patients with history of prostate cancer were selected from an ongoing 68Ga-PSMA-11-PET/MRI study. For each patient, PET raw data were reconstructed employing six different variants of PET scatter correction: absolute scatter scaling, relative scatter scaling, and relative scatter scaling combined with prompt gamma correction, each of which was combined with a maximum scatter fraction (MaxSF) of MaxSF = 75% or MaxSF = 40%. Evaluation of the reconstructed images with regard to halo-artifact suppression was performed both quantitatively using statistical analysis and qualitatively by two independent readers. Results The phantom experiments did not reveal any modality-dependency (PET/MRI vs. PET/CT) or tracer-dependency (68Ga vs. 18F-FDG). Patient- and phantom-based data indicated that halo-artifacts derive from high organ-to-background activity ratios (OBR) between bladder/kidneys and surrounding soft tissue, with a positive correlation between OBR and halo size. Comparing different variants of scatter correction, reducing the maximum scatter fraction from the default value

  11. Scale dependence of halo bispectrum from non-Gaussian initial conditions in cosmological N-body simulations

    NASA Astrophysics Data System (ADS)

    Nishimichi, Takahiro; Taruya, Atsushi; Koyama, Kazuya; Sabiu, Cristiano

    2010-07-01

    We study the halo bispectrum from non-Gaussian initial conditions. Based on a set of large N-body simulations starting from initial density fields with local type non-Gaussianity, we find that the halo bispectrum exhibits a strong dependence on the shape and scale of Fourier space triangles near squeezed configurations at large scales. The amplitude of the halo bispectrum roughly scales as fNL2. The resultant scaling on the triangular shape is consistent with that predicted by Jeong & Komatsu based on perturbation theory. We systematically investigate this dependence with varying redshifts and halo mass thresholds. It is shown that the fNL dependence of the halo bispectrum is stronger for more massive haloes at higher redshifts. This feature can be a useful discriminator of inflation scenarios in future deep and wide galaxy redshift surveys.

  12. The Dark Matter Halo Profile Of NGC 2976 Via Stellar Kinematics

    NASA Astrophysics Data System (ADS)

    Adams, Joshua J.; Gebhardt, K.; Hill, G. J.; van den Bosch, R. C. E.; Blanc, G. A.

    2011-01-01

    The observations of kinematics in low surface brightness (LSB) and dwarf late type galaxies have stubbornly resisted giving clear evidence for the cuspy Navarro-Frenk-White (NFW) dark matter (DM) halo profiles that simulations with ΛCDM inputs predict. Instead, most LSBs and late type dwarfs suggest cored DM halos or the observations are not yet constraining enough to rule out cusps. One viable theory to explain cored DM halos relies on the gravitational perturbation of a growing baryonic disk that is then rapidly removed causing the halo to expand to a cored equilibrium. Weakly self-interacting dark matter has also been invoked to explain cored DM halos. This problem may loom large over small galaxy formation and growth. However, different measurements can be taken to further test the apparent problem. Most previous data have relied on HI or Hα as kinematic tracers. A small number of works have studied the problem with longslit stellar kinematics. Ideally, the advantages of 2D spectroscopic coverage and a collisionless kinematic tracer would be combined. So far, NGC 2976 has made one of the cleanest cases for a cored DM halo via integral field spectroscopy in Hα. We here report on observations of NGC 2976 with the large field-of-view fiber-fed Visible Integral field Replicable Unit Spectrograph Prototype (VIRUS-P) at R=3200 to concurrently measure the gaseous and stellar kinematics and probe the DM halo. We find that the gas and stellar kinematics disagree both in the magnitude of their second velocity moments and their detailed profiles. We unexpectedly find emission features in one of NGC 2976's two large star-forming regions which may be indicative of carbon-rich Wolf-Rayet stars. A putative bar further complicates the use of gaseous tracers. We solve the Jeans equations with stellar kinematics to reevaluate the DM profile in this exemplar galaxy of the core-cusp problem.

  13. New detections of embedded clusters in the Galactic halo

    NASA Astrophysics Data System (ADS)

    Camargo, D.; Bica, E.; Bonatto, C.

    2016-09-01

    Context. Until recently it was thought that high Galactic latitude clouds were a non-star-forming ensemble. However, in a previous study we reported the discovery of two embedded clusters (ECs) far away from the Galactic plane (~ 5 kpc). In our recent star cluster catalogue we provided additional high and intermediate latitude cluster candidates. Aims: This work aims to clarify whether our previous detection of star clusters far away from the disc represents just an episodic event or whether star cluster formation is currently a systematic phenomenon in the Galactic halo. We analyse the nature of four clusters found in our recent catalogue and report the discovery of three new ECs each with an unusually high latitude and distance from the Galactic disc midplane. Methods: The analysis is based on 2MASS and WISE colour-magnitude diagrams (CMDs), and stellar radial density profiles (RDPs). The CMDs are built by applying a field-star decontamination procedure, which uncovers the cluster's intrinsic CMD morphology. Results: All of these clusters are younger than 5 Myr. The high-latitude ECs C 932, C 934, and C 939 appear to be related to a cloud complex about 5 kpc below the Galactic disc, under the Local arm. The other clusters are above the disc, C 1074 and C 1100 with a vertical distance of ~3 kpc, C 1099 with ~ 2 kpc, and C 1101 with ~1.8 kpc. Conclusions: According to the derived parameters ECs located below and above the disc occur, which gives evidence of widespread star cluster formation throughout the Galactic halo. This study therefore represents a paradigm shift, by demonstrating that a sterile halo must now be understood as a host for ongoing star formation. The origin and fate of these ECs remain open. There are two possibilities for their origin, Galactic fountains or infall. The discovery of ECs far from the disc suggests that the Galactic halo is more actively forming stars than previously thought. Furthermore, since most ECs do not survive the infant

  14. The Mass and Absorption Columns of Galactic Gaseous Halos

    NASA Astrophysics Data System (ADS)

    Qu, Zhijie; Bregman, Joel N.

    2018-01-01

    The gaseous halo surrounding the galaxy is a reservoir for the gas on the galaxy disk, supplying materials for the star formation. We developed a gaseous halo model connecting the galactic disk and the gaseous halo by assuming the star formation rate is equal to the radiative cooling rate. Besides the single-phase collisional gaseous halo, we also consider the photoionization effect and a time-independent cooling model that assumes the mass cooling rate is constant over all temperatures. The photoionization dominates the low mass galaxy and the outskirts of the massive galaxy due to the low-temperature or low-density nature. The multi-phase cooling model dominates the denser region within the cooling radius, where the efficient radiative cooling must be included. Applying these two improvements, our model can reproduce the most of observed high ionization state ions (i.e., O VI, O VII, Ne VIII and Mg X). Our models show that the O VI column density is almost a constant of around 10^14 cm^-2 over a wide stellar mass from M_\\star ~10^8 M_Sun to 10^11 M_Sun, which is constant with current observations. This model also implies the O VI is photoionized for the galaxy with a halo mass <~ 3 * 10^11 M_Sun, while for more massive galaxies, the O VI is from the cooling-down medium from higher temperature materials (collisional ionized). As higher ionization states, Mg X and Ne VIII are also consistent with observations with the column density of 10^13.5 - 10^14.0 cm^-2, however, the absorber-galaxy pair sample is few to constrain the connection with the galaxy. Based on our calculation, such a gaseous halo cannot close the census of baryonic materials in the galaxy, which shows the same tendency as the baryonic fraction function of the EAGLE simulation. Finally, our model predicts plateaus of the Ne VIII and the Mg X column densities above the sub-L^* galaxy, and the possibly detectable O VII and O VIII column densities for low-mass galaxies, which help to determine the

  15. The Sagittarius Stream: Probing the Outer Halo Potential

    NASA Astrophysics Data System (ADS)

    Fardal, Mark; HSTPROMO

    2018-01-01

    The Sagittarius Stream should be the premier probe of the outer Milky Way halo potential. Instead it has generated a series of puzzles that have frustrated modelers and prevented us from measuring the halo forces. The latest such puzzle is the factor of two difference between leading and trailing apocenter distances, seen most clearly in a recent sample of RR Lyraes from PS1. Using a set of dynamical models, we explain how to match this feature. The key element are that the debris at apocenter should dynamically young, originating from the last two pericentric passages only. We also explain the important roles played by the mass profile of the halo, dynamical friction, and departures from sphericity. The models show that the separate components already visible in the PS1 data should separate clearly once velocities are obtained, and the youngest component should probe the potential even beyond the observed distances of >~ 100 kpc. We explain what observations would be useful to eliminate remaining degeneracies in the models and fulfill the promise of the stream for understanding the Milky Way.

  16. Spatial occupancy models for large data sets

    USGS Publications Warehouse

    Johnson, Devin S.; Conn, Paul B.; Hooten, Mevin B.; Ray, Justina C.; Pond, Bruce A.

    2013-01-01

    Since its development, occupancy modeling has become a popular and useful tool for ecologists wishing to learn about the dynamics of species occurrence over time and space. Such models require presence–absence data to be collected at spatially indexed survey units. However, only recently have researchers recognized the need to correct for spatially induced overdisperison by explicitly accounting for spatial autocorrelation in occupancy probability. Previous efforts to incorporate such autocorrelation have largely focused on logit-normal formulations for occupancy, with spatial autocorrelation induced by a random effect within a hierarchical modeling framework. Although useful, computational time generally limits such an approach to relatively small data sets, and there are often problems with algorithm instability, yielding unsatisfactory results. Further, recent research has revealed a hidden form of multicollinearity in such applications, which may lead to parameter bias if not explicitly addressed. Combining several techniques, we present a unifying hierarchical spatial occupancy model specification that is particularly effective over large spatial extents. This approach employs a probit mixture framework for occupancy and can easily accommodate a reduced-dimensional spatial process to resolve issues with multicollinearity and spatial confounding while improving algorithm convergence. Using open-source software, we demonstrate this new model specification using a case study involving occupancy of caribou (Rangifer tarandus) over a set of 1080 survey units spanning a large contiguous region (108 000 km2) in northern Ontario, Canada. Overall, the combination of a more efficient specification and open-source software allows for a facile and stable implementation of spatial occupancy models for large data sets.

  17. Examining the effect of galaxy evolution on the stellar-halo mass relation in the EAGLE simulation

    NASA Astrophysics Data System (ADS)

    Kulier, Andrea; Padilla, Nelson; Schaye, Joop; Crain, Robert; Schaller, Matthieu; Bower, Richard; Theuns, Tom; Paillas, Enrique

    2018-01-01

    The EAGLE hydrodynamical simulation was used in Matthee et al. 2016 to examine the scatter in the stellar mass-halo mass relation of central galaxies, finding that the stellar mass (M*) correlates well with the maximum circular velocity (Vmax) of the host halo, but with a substantial scatter that does not correlate significantly with other host halo properties. Here we further examine the scatter in the stellar mass-halo mass relation of central galaxies in EAGLE, its correlation with other properties, and its origin. We find that at fixed Vmax, galaxies with lower concentration have younger stellar populations, as expected from the relationship between concentration and halo assembly time. However, at fixed Vmax and halo concentration, galaxies with larger M* have younger stellar ages, so that combining the two effects, galaxies with younger stellar ages at fixed halo mass have higher stellar masses. The host halos of galaxies with larger M* at fixed Vmax and concentration also contain more gas than those with smaller stellar masses at z = 0.1, i.e. the baryon fraction of the halos is larger. There is an even stronger correlation between the scatter in M* at z = 0.1 and the scatter in the baryon fraction of the galaxy's progenitors at z ~ 1, such that the latter sets ~50% of the scatter in M* at z = 0.1. We conclude that most of the scatter between Vmax and M* at z = 0.1 is set at earlier redshifts by the scatter in the baryon fraction of halos, which in turn is primarily the result of differences in feedback strength within halos.

  18. Weak-Lensing Determination of the Mass in Galaxy Halos

    NASA Astrophysics Data System (ADS)

    Smith, D. R.; Bernstein, G. M.; Fischer, P.; Jarvis, M.

    2001-04-01

    We detect the weak gravitational lensing distortion of 450,000 background galaxies (20halo in absolute physical units (modulo H0), and to investigate the dependence of halo mass upon galaxy luminosity. This is also the first galaxy-galaxy lensing study for which the calibration errors due to uncertainty in the background galaxy redshift distribution and the seeing correction are negligible. Within a projected radius of 200 h-1 kpc, the shear profile is consistent with an isothermal profile with circular velocity vc=164+/-20 km s-1 for an L* galaxy, consistent with the typical circular velocity for the disks of spirals at this luminosity. This halo mass normalization, combined with the halo profile derived by Fischer and coworkers from a galaxy-galaxy lensing analysis of the Sloan Digital Sky Survey, places a lower limit of (2.7+/-0.6)×1012 h-1 Msolar on the mass of an L* galaxy halo, in good agreement with the satellite galaxy studies of Zaritsky et al. Given the known luminosity function of LCRS galaxies, and assuming that M~Lβ for galaxies, we determine that the mass within 260 h-1 kpc of normal galaxies contributes Ω=0.16+/-0.03 to the density of the universe (for β=1) or Ω=0.24+/-0.06 for β=0.5. These lensing data suggest that 0.6<β<2.4 (95% confidence level), only marginally in agreement with the usual β~0.5 Faber-Jackson or Tully-Fisher scaling. This is the most complete direct inventory of the matter content of the universe to date.

  19. Cleaning and disinfecting environmental surfaces in health care: Toward an integrated framework for infection and occupational illness prevention.

    PubMed

    Quinn, Margaret M; Henneberger, Paul K; Braun, Barbara; Delclos, George L; Fagan, Kathleen; Huang, Vanthida; Knaack, Jennifer L S; Kusek, Linda; Lee, Soo-Jeong; Le Moual, Nicole; Maher, Kathryn A E; McCrone, Susan H; Mitchell, Amber Hogan; Pechter, Elise; Rosenman, Kenneth; Sehulster, Lynne; Stephens, Alicia C; Wilburn, Susan; Zock, Jan-Paul

    2015-05-01

    The Cleaning and Disinfecting in Healthcare Working Group of the National Institute for Occupational Safety and Health, National Occupational Research Agenda, is a collaboration of infection prevention and occupational health researchers and practitioners with the objective of providing a more integrated approach to effective environmental surface cleaning and disinfection (C&D) while protecting the respiratory health of health care personnel. The Working Group, comprised of >40 members from 4 countries, reviewed current knowledge and identified knowledge gaps and future needs for research and practice. An integrated framework was developed to guide more comprehensive efforts to minimize harmful C&D exposures without reducing the effectiveness of infection prevention. Gaps in basic knowledge and practice that are barriers to an integrated approach were grouped in 2 broad areas related to the need for improved understanding of the (1) effectiveness of environmental surface C&D to reduce the incidence of infectious diseases and colonization in health care workers and patients and (2) adverse health impacts of C&D on health care workers and patients. Specific needs identified within each area relate to basic knowledge, improved selection and use of products and practices, effective hazard communication and training, and safer alternatives. A more integrated approach can support multidisciplinary teams with the capacity to maximize effective and safe C&D in health care. Copyright © 2015 Association for Professionals in Infection Control and Epidemiology, Inc. All rights reserved.

  20. The MassiveBlack-II simulation: The evolution of haloes and galaxies to z ~ 0

    DOE PAGES

    Khandai, Nishikanta; Di Matteo, Tiziana; Croft, Rupert; ...

    2015-04-24

    We investigate the properties and clustering of halos, galaxies and blackholes to z = 0 in the high resolution hydrodynamical simulation MassiveBlack-II (MBII). MBII evolves a ΛCDM cosmology in a cubical comoving volume V box = (100Mpc/h)³. It is the highest resolution simulation of this size which includes a self-consistent model for star formation, black hole accretion and associated feedback. We provide a simulation browser web application which enables interactive search and tagging of the halos, subhalos and their properties and publicly release our galaxy catalogs to the scientific community. Our analysis of the halo mass function in MBII revealsmore » that baryons have strong effects with changes in the halo abundance of 20–35% below the knee of the mass function (M halo 10 13.2 M ⊙ h at z = 0) when compared to dark-matter-only simulations. We provide a fitting function for the halo MF out to redshift z = 11 and discuss its limitations.« less

  1. Ice crystal characterization in cirrus clouds: a sun-tracking camera system and automated detection algorithm for halo displays

    NASA Astrophysics Data System (ADS)

    Forster, Linda; Seefeldner, Meinhard; Wiegner, Matthias; Mayer, Bernhard

    2017-07-01

    Halo displays in the sky contain valuable information about ice crystal shape and orientation: e.g., the 22° halo is produced by randomly oriented hexagonal prisms while parhelia (sundogs) indicate oriented plates. HaloCam, a novel sun-tracking camera system for the automated observation of halo displays is presented. An initial visual evaluation of the frequency of halo displays for the ACCEPT (Analysis of the Composition of Clouds with Extended Polarization Techniques) field campaign from October to mid-November 2014 showed that sundogs were observed more often than 22° halos. Thus, the majority of halo displays was produced by oriented ice crystals. During the campaign about 27 % of the cirrus clouds produced 22° halos, sundogs or upper tangent arcs. To evaluate the HaloCam observations collected from regular measurements in Munich between January 2014 and June 2016, an automated detection algorithm for 22° halos was developed, which can be extended to other halo types as well. This algorithm detected 22° halos about 2 % of the time for this dataset. The frequency of cirrus clouds during this time period was estimated by co-located ceilometer measurements using temperature thresholds of the cloud base. About 25 % of the detected cirrus clouds occurred together with a 22° halo, which implies that these clouds contained a certain fraction of smooth, hexagonal ice crystals. HaloCam observations complemented by radiative transfer simulations and measurements of aerosol and cirrus cloud optical thickness (AOT and COT) provide a possibility to retrieve more detailed information about ice crystal roughness. This paper demonstrates the feasibility of a completely automated method to collect and evaluate a long-term database of halo observations and shows the potential to characterize ice crystal properties.

  2. The Dearth of Mental Health Research in Occupational Therapy.

    ERIC Educational Resources Information Center

    Gibson, Diane

    1984-01-01

    Reasons for the lack of research in occupational therapy include small numbers of doctoral level occupational therapists, the psychobehavioral/biochemical dichotomy, the lack of a theoretical framework, the level of research instruction, the impact of a predominantly female profession, and the attitudes of institutions. (SK)

  3. Probing stochastic inter-galactic magnetic fields using blazar-induced gamma ray halo morphology

    NASA Astrophysics Data System (ADS)

    Duplessis, Francis; Vachaspati, Tanmay

    2017-05-01

    Inter-galactic magnetic fields can imprint their structure on the morphology of blazar-induced gamma ray halos. We show that the halo morphology arises through the interplay of the source's jet and a two-dimensional surface dictated by the magnetic field. Through extensive numerical simulations, we generate mock halos created by stochastic magnetic fields with and without helicity, and study the dependence of the halo features on the properties of the magnetic field. We propose a sharper version of the Q-statistics and demonstrate its sensitivity to the magnetic field strength, the coherence scale, and the handedness of the helicity. We also identify and explain a new feature of the Q-statistics that can further enhance its power.

  4. Halo Histories vs. Galaxy Properties at z=0, III: The Properties of Star-Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Tinker, Jeremy L.; Hahn, ChangHoon; Mao, Yao-Yuan; Wetzel, Andrew R.

    2018-05-01

    We measure how the properties of star-forming central galaxies correlate with large-scale environment, δ, measured on 10 h-1Mpc scales. We use galaxy group catalogs to isolate a robust sample of central galaxies with high purity and completeness. The galaxy properties we investigate are star formation rate (SFR), exponential disk scale length Rexp, and Sersic index of the galaxy light profile, nS. We find that, at all stellar masses, there is an inverse correlation between SFR and δ, meaning that above-average star forming centrals live in underdense regions. For nS and Rexp, there is no correlation with δ at M_\\ast ≲ 10^{10.5} M⊙, but at higher masses there are positive correlations; a weak correlation with Rexp and a strong correlation with nS. These data are evidence of assembly bias within the star-forming population. The results for SFR are consistent with a model in which SFR correlates with present-day halo accretion rate, \\dot{M}_h. In this model, galaxies are assigned to halos using the abundance matching ansatz, which maps galaxy stellar mass onto halo mass. At fixed halo mass, SFR is then assigned to galaxies using the same approach, but \\dot{M}_h is used to map onto SFR. The best-fit model requires some scatter in the \\dot{M}_h-SFR relation. The Rexp and nS measurements are consistent with a model in which both of these quantities are correlated with the spin parameter of the halo, λ. Halo spin does not correlate with δ at low halo masses, but for higher mass halos, high-spin halos live in higher density environments at fixed Mh. Put together with the earlier installments of this series, these data demonstrate that quenching processes have limited correlation with halo formation history, but the growth of active galaxies, as well as other detailed galaxies properties, are influenced by the details of halo assembly.

  5. Distant Galactic Halo Substructures Observed by the Palomar Transient Factory

    NASA Astrophysics Data System (ADS)

    Sesar, Branimir

    2013-01-01

    Characterization of Galactic halo substructures is important as their kinematic and chemical properties help constrain the properties of the Galactic dark matter halo, the formation history of the Milky Way, and the galaxy formation process in general. The best practical choice for finding distant halo substructures are pulsating RR Lyrae stars, due to their intrinsic brightness (M_V = 0.6 mag) and distinct light curves. I will present kinematic and chemical properties of two distant halo substructures that were traced using RR Lyrae stars observed by the Palomar Transient Factory. One of these substructures, located at 90 kpc from the Sun in the Cancer constellation, consists of two groups of RR Lyrae stars moving away from the Galaxy at ~80 and ~20 km/s, respectively. The second substructure is located at ~65 kpc from the Sun in the Hercules constellation. The kinematics of RR Lyrae stars tracing this substructure suggest a presence of 2 or 3 stellar streams extending in the similar direction on the sky. Due to their spatial extent, both of these substructures are clearly disrupted and would be very difficult to detect using tradiitonal techniques such as the color-magnitude diagram filtering.

  6. Baryonic impact on the dark matter orbital properties of Milky Way-sized haloes

    NASA Astrophysics Data System (ADS)

    Zhu, Qirong; Hernquist, Lars; Marinacci, Federico; Springel, Volker; Li, Yuexing

    2017-04-01

    We study the orbital properties of dark matter haloes by combining a spectral method and cosmological simulations of Milky Way-sized Galaxies. We compare the dynamics and orbits of individual dark matter particles from both hydrodynamic and N-body simulations, and find that the fraction of box, tube and resonant orbits of the dark matter halo decreases significantly due to the effects of baryons. In particular, the central region of the dark matter halo in the hydrodynamic simulation is dominated by regular, short-axis tube orbits, in contrast to the chaotic, box and thin orbits dominant in the N-body run. This leads to a more spherical dark matter halo in the hydrodynamic run compared to a prolate one as commonly seen in the N-body simulations. Furthermore, by using a kernel-based density estimator, we compare the coarse-grained phase-space densities of dark matter haloes in both simulations and find that it is lower by ˜0.5 dex in the hydrodynamic run due to changes in the angular momentum distribution, which indicates that the baryonic process that affects the dark matter is irreversible. Our results imply that baryons play an important role in determining the shape, kinematics and phase-space density of dark matter haloes in galaxies.

  7. Hierarchical Galaxy Growth and Scatter in the Stellar Mass-Halo Mass Relation

    NASA Astrophysics Data System (ADS)

    Gu, Meng; Conroy, Charlie; Behroozi, Peter

    2016-12-01

    The relation between galaxies and dark matter halos reflects the combined effects of many distinct physical processes. Observations indicate that the z = 0 stellar mass-halo mass (SMHM) relation has remarkably small scatter in stellar mass at fixed halo mass (≲0.2 dex), with little dependence on halo mass. We investigate the origins of this scatter by combining N-body simulations with observational constraints on the SMHM relation. We find that at the group and cluster scale ({M}{vir}\\gt {10}14 {M}⊙ ) the scatter due purely to hierarchical assembly is ≈ 0.16 dex, which is comparable to recent direct observational estimates. At lower masses, mass buildup since z≈ 2 is driven largely by in situ growth. We include a model for the in situ buildup of stellar mass and find that an intrinsic scatter in this growth channel of 0.2 dex produces a relation between scatter and halo mass that is consistent with observations from {10}12 {M}⊙ \\lt {M}{vir}\\lt {10}14.75 {M}⊙ . The approximately constant scatter across a wide range of halo masses at z = 0 thus appears to be a coincidence, as it is determined largely by in situ growth at low masses and by hierarchical assembly at high masses. These results indicate that the scatter in the SMHM relation can provide unique insight into the regularity of the galaxy formation process.

  8. Null Environmental Effects of the Cosmic Web on Dark Matter Halo Properties

    NASA Astrophysics Data System (ADS)

    Goh, Tze; Primack, Joel; Aragon-Calvo, Miguel; Hellinger, Doug; Rodriguez-Puebla, Aldo; Lee, Christoph; Eckleholm, Elliot; Johnston, Kathryn

    2018-01-01

    We study the effects of the cosmic web environment (filaments, voids and walls) and environmental density on key properties of dark matter halos at redshift z = 0 using the Bolshoi-Planck ΛCDM. The z=0 Bolshoi-Planck simulation is analysed into filaments, voids and walls using the SpineWeb method, as well as VIDE method, both of which use Voronoi tessellation and the watershed transform. The key halo properties that we study are the mass accretion rate, spin parameter, concentration, prolateness, scale factor of the last major merger, and scale factor when the halo had half of its z=0 mass. For all these properties, we find that there is no discernible difference between the halo properties in filaments, walls or voids when compared at the same environmental density. As a result, we conclude that environmental density is the core attribute that affects these properties. This conclusion is in line with recent findings that properties of galaxies in redshift surveys are independent of their cosmic web environment at the same environmental density. We also find that the local web environment of the Milky Way and the Andromeda galaxy near the centre of a cosmic wall does not appear to have any effect on the key properties of these galaxies' dark matter halos, although we find that it is rather rare to have such massive halos near the centre of a relatively small cosmic wall.

  9. STRUCTURAL PROPERTIES OF NON-SPHERICAL DARK HALOS IN MILKY WAY AND ANDROMEDA DWARF SPHEROIDAL GALAXIES

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hayashi, Kohei; Chiba, Masashi, E-mail: kohei.hayashi@ipmu.jp, E-mail: chiba@astr.tohoku.ac.jp

    We investigate the non-spherical density structure of dark halos of the dwarf spheroidal (dSph) galaxies in the Milky Way and Andromeda galaxies based on revised axisymmetric mass models from our previous work. The models we adopt here fully take into account velocity anisotropy of tracer stars confined within a flattened dark halo. Applying our models to the available kinematic data of the 12 bright dSphs, we find that these galaxies associate with, in general, elongated dark halos, even considering the effect of this velocity anisotropy of stars. We also find that the best-fit parameters, especially for the shapes of darkmore » halos and velocity anisotropy, are susceptible to both the availability of velocity data in the outer regions and the effect of the lack of sample stars in each spatial bin. Thus, to obtain more realistic limits on dark halo structures, we require photometric and kinematic data over much larger areas in the dSphs than previously explored. The results obtained from the currently available data suggest that the shapes of dark halos in the dSphs are more elongated than those of ΛCDM subhalos. This mismatch needs to be solved by theory including baryon components and the associated feedback to dark halos as well as by further observational limits in larger areas of dSphs. It is also found that more diffuse dark halos may have undergone consecutive star formation history, thereby implying that dark-halo structure plays an important role in star formation activity.« less

  10. Earth-mass haloes and the emergence of NFW density profiles

    NASA Astrophysics Data System (ADS)

    Angulo, Raul E.; Hahn, Oliver; Ludlow, Aaron D.; Bonoli, Silvia

    2017-11-01

    We simulate neutralino dark matter (χDM) haloes from their initial collapse, at ˜ earth mass, up to a few percent solar. Our results confirm that the density profiles of the first haloes are described by a ˜r-1.5 power law. As haloes grow in mass, their density profiles evolve significantly. In the central regions, they become shallower and reach on average ˜r-1, the asymptotic form of an NFW profile. Using non-cosmological controlled simulations, we observe that temporal variations in the gravitational potential caused by major mergers lead to a shallowing of the inner profile. This transformation is more significant for shallower initial profiles and for a higher number of merging systems. Depending on the merger details, the resulting profiles can be shallower or steeper than NFW in their inner regions. Interestingly, mergers have a much weaker effect when the profile is given by a broken power law with an inner slope of -1 (such as NFW or Hernquist profiles). This offers an explanation for the emergence of NFW-like profiles: after their initial collapse, r-1.5 χDM haloes suffer copious major mergers, which progressively shallows the profile. Once an NFW-like profile is established, subsequent merging does not change the profile anymore. This suggests that halo profiles are not universal but rather a combination of (1) the physics of the formation of the microhaloes and (2) their early merger history - both set by the properties of the dark matter particle - as well as (3) the resilience of NFW-like profiles to perturbations.

  11. Ghostly Halos in Dwarf Galaxies: a probe of star formation in the Early Universe

    NASA Astrophysics Data System (ADS)

    Kang, Hoyoung; Ricotti, Massimo

    2016-01-01

    We carry out numerical simulations to characterize the size, stellar mass, and stellar mass surface density of extended stellar halos in dwarf galaxies as a function of dark matter halo mass. We expect that for galaxies smaller than a critical value, these ghostly halos will not exist because the smaller galactic subunits that build it up, do not form any stars. The detection of ghostly halos around isolated dwarf galaxies is a sensitive test of the efficiency of star formation in the first galaxies and of whether ultra-faint dwarf satellites of the Milky Way are fossils of the first galaxies.

  12. Oxygen abundances in halo giants. I - Giants in the very metal-poor globular clusters M92 and M15 and the metal-poor halo field

    NASA Astrophysics Data System (ADS)

    Sneden, Christopher; Kraft, Robert P.; Prosser, Charles F.; Langer, G. E.

    1991-12-01

    Oxygen, iron, vanadium, and scandium abundances are derived for very metal-poor giants in the globular clusters M92 and M15, and giants of comparable metallicity in the local halo field. The forbidden O I line dublet (6300, 6363) and nearby metallic lines in spectra are analyzed using line analysis and spectral synthesis codes. The Fe/H abundance for M92 is estimated at -2.25 +/-0.02 based on nine giants with a range of 500 K in effective temperature. No evidence for star-to-star variations in the Fe/H abundance was found. O-rich and O-poor stars appear intermixed in the H-R diagram. O - N nuclear synthesis and mixing to the surface are proposed as the best explanation for the low-oxygen giants. The nitrogen abundances obtained earlier for nine of the ten halo field giants in this sample are incompatible with the very large nitrogen abundances expected of the O/Fe abundance of about + 1.2 in halo field subdwarfs, as found by Abia and Rebolo (1989), and not more than 0.6 in halo giants, as found in this and other studies.

  13. On the life and death of satellite haloes

    NASA Astrophysics Data System (ADS)

    Taffoni, Giuliano; Mayer, Lucio; Colpi, Monica; Governato, Fabio

    2003-05-01

    We study the evolution of dark matter satellites orbiting inside more massive haloes using semi-analytical tools coupled with high-resolution N-body simulations. We select initial satellite sizes, masses, orbital energies, and eccentricities as predicted by hierarchical models of structure formation. Both the satellite (of initial mass Ms,0) and the main halo (of mass Mh) are described by a Navarro, Frenk & White density profile with various concentrations. We explore the interplay between dynamic friction and tidal mass loss/evaporation in determining the final fate of the satellite. We provide a user-friendly expression for the dynamic friction time-scale τdf,live and for the disruption time for a live (i.e. mass-losing) satellite. This can be easily implemented into existing semi-analytical models of galaxy formation improving considerably the way they describe the evolution of satellites. Massive satellites (Ms,0 > 0.1Mh) starting from typical cosmological orbits sink rapidly (irrespective of the initial circularity) toward the centre of the main halo where they merge after a time τdf,rig, as if they were rigid. Satellites of intermediate mass (0.01Mh < Ms,0 < 0.1Mh) suffer severe tidal mass losses as dynamic friction reduces their pericentre distance. In this case, mass loss increases substantially their decay time with respect to a rigid satellite. The final fate depends on the concentration of the satellite, cs, relative to that of the main halo, ch. Only in the unlikely case where cs/ch<~ 1 are satellites disrupted. In this mass range, τdf,live gives a measure of the merging time. Among the satellites whose orbits decay significantly, those that survive must have been moving preferentially on more circular orbits since the beginning as dynamical friction does not induce circularization. Lighter satellites (Ms,0 < 0.01Mh) do not suffer significant orbital decay and tidal mass loss stabilizes the orbit even further. Their orbits should map those at the

  14. Moving-mesh cosmology: characteristics of galaxies and haloes

    NASA Astrophysics Data System (ADS)

    Kereš, Dušan; Vogelsberger, Mark; Sijacki, Debora; Springel, Volker; Hernquist, Lars

    2012-09-01

    We discuss cosmological hydrodynamic simulations of galaxy formation performed with the new moving-mesh code AREPO, which promises higher accuracy compared with the traditional smoothed particle hydrodynamics (SPH) technique that has been widely employed for this problem. In this exploratory study, we deliberately limit the complexity of the physical processes followed by the code for ease of comparison with previous calculations, and include only cooling of gas with a primordial composition, heating by a spatially uniform ultraviolet background, and a simple subresolution model for regulating star formation in the dense interstellar medium. We use an identical set of physics in corresponding simulations carried out with the well-tested SPH code GADGET, adopting also the same high-resolution gravity solver. We are thus able to compare both simulation sets on an object-by-object basis, allowing us to cleanly isolate the impact of different hydrodynamical methods on galaxy and halo properties. In accompanying papers, Vogelsberger et al. and Sijacki et al., we focus on an analysis of the global baryonic statistics predicted by the simulation codes, and complementary idealized simulations that highlight the differences between the hydrodynamical schemes. Here we investigate their influence on the baryonic properties of simulated galaxies and their surrounding haloes. We find that AREPO leads to significantly higher star formation rates for galaxies in massive haloes and to more extended gaseous discs in galaxies, which also feature a thinner and smoother morphology than their GADGET counterparts. Consequently, galaxies formed in AREPO have larger sizes and higher specific angular momentum than their SPH correspondents. Interestingly, the more efficient cooling flows in AREPO yield higher densities and lower entropies in halo centres compared to GADGET, whereas the opposite trend is found in halo outskirts. The cooling differences leading to higher star formation rates

  15. The impact of feedback and the hot halo on the rates of gas accretion on to galaxies

    NASA Astrophysics Data System (ADS)

    Correa, Camila A.; Schaye, Joop; van de Voort, Freeke; Duffy, Alan R.; Wyithe, J. Stuart B.

    2018-07-01

    We investigate the physics that drives the gas accretion rates on to galaxies at the centres of dark matter haloes using the EAGLE suite of hydrodynamical cosmological simulations. We find that at redshifts z ≤ 2, the accretion rate on to the galaxy increases with halo mass in the halo mass range 1010-1011.7 M⊙, flattens between the halo masses 1011.7 and 1012.7 M⊙, and increases again for higher mass haloes. However, the galaxy gas accretion does not flatten at intermediate halo masses when active galactic nucleus (AGN) feedback is switched off. To better understand these trends, we develop a physically motivated semi-analytic model of galaxy gas accretion. We show that the flattening is produced by the rate of gas cooling from the hot halo. The ratio of the cooling radius and the virial radius does not decrease continuously with increasing halo mass as generally thought. While it decreases up to ˜1013 M⊙ haloes, it increases for higher halo masses, causing an upturn in the galaxy gas accretion rate. This may indicate that in high-mass haloes, AGN feedback is not sufficiently efficient. When there is no AGN feedback, the density of the hot halo is higher, the ratio of the cooling and virial radii does not decrease as much, and the cooling rate is higher. Changes in the efficiency of stellar feedback can also increase or decrease the accretion rates on to galaxies. The trends can plausibly be explained by the re-accretion of gas ejected by progenitor galaxies and by the suppression of black hole growth, and hence AGN feedback, by stellar feedback.

  16. Revealing modified gravity signals in matter and halo hierarchical clustering

    NASA Astrophysics Data System (ADS)

    Hellwing, Wojciech A.; Koyama, Kazuya; Bose, Benjamin; Zhao, Gong-Bo

    2017-07-01

    We use a set of N-body simulations employing a modified gravity (MG) model with Vainshtein screening to study matter and halo hierarchical clustering. As test-case scenarios we consider two normal branch Dvali-Gabadadze-Porrati (nDGP) gravity models with mild and strong growth rate enhancement. We study higher-order correlation functions ξn(R ) up to n =9 and associated reduced cumulants Sn(R )≡ξn(R )/σ (R )2n -2. We find that the matter probability distribution functions are strongly affected by the fifth force on scales up to 50 h-1 Mpc , and the deviations from general relativity (GR) are maximized at z =0 . For reduced cumulants Sn, we find that at small scales R ≤6 h-1 Mpc the MG is characterized by lower values, with the deviation growing from 7% in the reduced skewness up to even 40% in S5. To study the halo clustering we use a simple abundance matching and divide haloes into thee fixed number density samples. The halo two-point functions are weakly affected, with a relative boost of the order of a few percent appearing only at the smallest pair separations (r ≤5 h-1 Mpc ). In contrast, we find a strong MG signal in Sn(R )'s, which are enhanced compared to GR. The strong model exhibits a >3 σ level signal at various scales for all halo samples and in all cumulants. In this context, we find that the reduced kurtosis to be an especially promising cosmological probe of MG. Even the mild nDGP model leaves a 3 σ imprint at small scales R ≤3 h-1 Mpc , while the stronger model deviates from a GR signature at nearly all scales with a significance of >5 σ . Since the signal is persistent in all halo samples and over a range of scales, we advocate that the reduced kurtosis estimated from galaxy catalogs can potentially constitute a strong MG-model discriminatory as well as GR self-consistency test.

  17. One dark matter mystery: halos in the cosmic web

    NASA Astrophysics Data System (ADS)

    Gaite, Jose

    2015-01-01

    The current cold dark matter cosmological model explains the large scale cosmic web structure but is challenged by the observation of a relatively smooth distribution of matter in galactic clusters. We consider various aspects of modeling the dark matter around galaxies as distributed in smooth halos and, especially, the smoothness of the dark matter halos seen in N-body cosmological simulations. We conclude that the problems of the cold dark matter cosmology on small scales are more serious than normally admitted.

  18. Occupational Stress: Preventing Suffering, Enhancing Wellbeing †

    PubMed Central

    Quick, James Campbell; Henderson, Demetria F.

    2016-01-01

    Occupational stress is a known health risk for a range of psychological, behavioral, and medical disorders and diseases. Organizations and individuals can mitigate these disorders through preventive stress management and enhanced wellbeing. This article addresses, first, the known health risk evidence related to occupational stress; second, the use of preventive stress management in organizations as the framework for intervention; and third, the emerging domain of enhancing wellbeing, which strengthens the individual. Premature death and disability along with chronic suffering from occupational stress are not inevitable, despite being known outcome risks. PMID:27136575

  19. The outskirts of spiral galaxies: touching stellar halos at z˜0 and z˜1

    NASA Astrophysics Data System (ADS)

    Bakos, J.; Trujillo, I.

    Taking advantage of ultra-deep imaging of SDSS Stripe82 and the Hubble Ultra Deep Field by HST, we explore the properties of stellar halos at two relevant epochs of cosmic history. At z˜0 we find that the radial surface brightness profiles of disks have a smooth continuation into the stellar halo that starts to affect the surface brightness profiles at mu r'˜28 {mag arcsec-2}, and at a radial distance of gtrsim 4-10 inner scale-lengths. The light contribution of the stellar halo to the total galaxy light varies from ˜1% to ˜5%, but in case of ongoing mergers, the halo light fraction can be as high as ˜10%. The integrated (g'-r') color of the stellar halo of our galaxies range from ˜0.4 to ˜1.2. By confronting these colors with model predictions, these halos can be attributed to moderately aged and metal-poor populations, however the extreme red colors (˜1) cannot be explained by populations of conventional IMFs. Very red halo colors can be attributed to stellar populations dominated by very low mass stars of low to intermediate metallicity produced by bottom-heavy IMFs. At z˜1 stellar halos appear to be ˜2 magnitudes brighter than their local counterparts, meanwhile they exhibit bluer colors ((g'-r')≲0.3 mag), as well. The stellar populations corresponding to these colors are compatible with having ages ≲1 Gyr. This latter observation strongly suggests the possibility that these halos were formed between z˜1 and z˜2. This result matches very well the theoretical predictions that locate most of the formation of the stellar halos at those early epochs. A pure passive evolutionary scenario, where the stellar populations of our high-z haloes simply fade to match the stellar halo properties found in the local universe, is consistent with our data.

  20. The Linear Bias in the Zeldovich Approximation and a Relation between the Number Density and the Linear Bias of Dark Halos

    NASA Astrophysics Data System (ADS)

    Fan, Zuhui

    2000-01-01

    The linear bias of the dark halos from a model under the Zeldovich approximation is derived and compared with the fitting formula of simulation results. While qualitatively similar to the Press-Schechter formula, this model gives a better description for the linear bias around the turnaround point. This advantage, however, may be compromised by the large uncertainty of the actual behavior of the linear bias near the turnaround point. For a broad class of structure formation models in the cold dark matter framework, a general relation exists between the number density and the linear bias of dark halos. This relation can be readily tested by numerical simulations. Thus, instead of laboriously checking these models one by one, numerical simulation studies can falsify a whole category of models. The general validity of this relation is important in identifying key physical processes responsible for the large-scale structure formation in the universe.

  1. Conceptual frameworks of individual work performance: a systematic review.

    PubMed

    Koopmans, Linda; Bernaards, Claire M; Hildebrandt, Vincent H; Schaufeli, Wilmar B; de Vet Henrica, C W; van der Beek, Allard J

    2011-08-01

    Individual work performance is differently conceptualized and operationalized in different disciplines. The aim of the current review was twofold: (1) identifying conceptual frameworks of individual work performance and (2) integrating these to reach a heuristic conceptual framework. A systematic review was conducted in medical, psychological, and management databases. Studies were selected independently by two researchers and included when they presented a conceptual framework of individual work performance. A total of 17 generic frameworks (applying across occupations) and 18 job-specific frameworks (applying to specific occupations) were identified. Dimensions frequently used to describe individual work performance were task performance, contextual performance, counterproductive work behavior, and adaptive performance. On the basis of the literature, a heuristic conceptual framework of individual work performance was proposed. This framework can serve as a theoretical basis for future research and practice.

  2. Probing stochastic inter-galactic magnetic fields using blazar-induced gamma ray halo morphology

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Duplessis, Francis; Vachaspati, Tanmay, E-mail: fdupless@asu.edu, E-mail: tvachasp@asu.edu

    Inter-galactic magnetic fields can imprint their structure on the morphology of blazar-induced gamma ray halos. We show that the halo morphology arises through the interplay of the source's jet and a two-dimensional surface dictated by the magnetic field. Through extensive numerical simulations, we generate mock halos created by stochastic magnetic fields with and without helicity, and study the dependence of the halo features on the properties of the magnetic field. We propose a sharper version of the Q-statistics and demonstrate its sensitivity to the magnetic field strength, the coherence scale, and the handedness of the helicity. We also identify andmore » explain a new feature of the Q-statistics that can further enhance its power.« less

  3. Galactic googly: the rotation-metallicity bias in the inner stellar halo of the Milky Way

    NASA Astrophysics Data System (ADS)

    Kafle, Prajwal R.; Sharma, Sanjib; Robotham, Aaron S. G.; Pradhan, Raj K.; Guglielmo, Magda; Davies, Luke J. M.; Driver, Simon P.

    2017-09-01

    The first and second moments of stellar velocities encode important information about the formation history of the Galactic halo. However, due to the lack of tangential motion and inaccurate distances of the halo stars, the velocity moments in the Galactic halo have largely remained 'known unknowns'. Fortunately, our off-centric position within the Galaxy allows us to estimate these moments in the galactocentric frame using the observed radial velocities of the stars alone. We use these velocities coupled with the hierarchical Bayesian scheme, which allows easy marginalization over the missing data (the proper motion, and uncertainty-free distance and line-of-sight velocity), to measure the velocity dispersions, orbital anisotropy (β) and streaming motion (vrot) of the halo main-sequence turn-off (MSTO) and K-giant (KG) stars in the inner stellar halo (r ≲ 15 kpc). We study the metallicity bias in kinematics of the halo stars and observe that the comparatively metal-rich ([Fe/H] > -1.4) and the metal-poor ([Fe/H] ≤ -1.4) MSTO samples show a clear systematic difference in vrot ˜ 20-40 km s - 1, depending on how restrictive the spatial cuts to cull the disc contamination are. The bias is also detected in KG samples but with less certainty. Both MSTO and KG populations suggest that the inner stellar halo of the Galaxy is radially biased I.e. σr > σθ or σϕ and β ≃ 0.5. The apparent metallicity contrariety in the rotation velocity among the halo sub-populations supports the co-existence of multiple populations in the galactic halo that may have formed through distinct formation scenarios, I.e. in situ versus accretion.

  4. Flattened halos in a nontopological soliton model of dark matter

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Mielke, Eckehard W.; Peralta, Humberto H.

    2004-12-15

    Soliton type solutions of a scalar model with a {phi}{sup 6} self-interaction are analyzed for their density profiles as toy model of dark matter halos. We construct exact solutions with nontrivial ellipticity due to angular momentum and propose a 'nonlinear superposition' of round and flattened halos in order to improve the scaling relations and the correspondence of the predicted rotation curves to the empirical Burkert fit.

  5. The contribution of occupation to health inequality

    PubMed Central

    Ravesteijn, Bastian; van Kippersluis, Hans; van Doorslaer, Eddy

    2014-01-01

    Health is distributed unequally by occupation. Workers on a lower rung of the occupational ladder report worse health, have a higher probability of disability and die earlier than workers higher up the occupational hierarchy. Using a theoretical framework that unveils some of the potential mechanisms underlying these disparities, three core insights emerge: (i) there is selection into occupation on the basis of initial wealth, education, and health, (ii) there will be behavioural responses to adverse working conditions, which can have compensating or reinforcing effects on health, and (iii) workplace conditions increase health inequalities if workers with initially low socioeconomic status choose harmful occupations and don’t offset detrimental health effects. We provide empirical illustrations of these insights using data for the Netherlands and assess the evidence available in the economics literature. PMID:24899789

  6. What makes the family of barred disc galaxies so rich: damping stellar bars in spinning haloes

    NASA Astrophysics Data System (ADS)

    Collier, Angela; Shlosman, Isaac; Heller, Clayton

    2018-05-01

    We model and analyse the secular evolution of stellar bars in spinning dark matter (DM) haloes with the cosmological spin λ ˜ 0-0.09. Using high-resolution stellar and DM numerical simulations, we focus on angular momentum exchange between stellar discs and DM haloes of various axisymmetric shapes - spherical, oblate, and prolate. We find that stellar bars experience a diverse evolution that is guided by the ability of parent haloes to absorb angular momentum, J, lost by the disc through the action of gravitational torques, resonant and non-resonant. We confirm that dynamical bar instability is accelerated via resonant J-transfer to the halo. Our main findings relate to the long-term secular evolution of disc-halo systems: with an increasing λ, bars experience less growth and basically dissolve after they pass through vertical buckling instability. Specifically, with increasing λ, (1) the vertical buckling instability in stellar bars colludes with inability of the inner halo to absorb J - this emerges as the main factor weakening or destroying bars in spinning haloes; (2) bars lose progressively less J, and their pattern speeds level off; (3) bars are smaller, and for λ ≳ 0.06 cease their growth completely following buckling; (4) bars in λ > 0.03 haloes have ratio of corotation-to-bar radii, RCR/Rb > 2, and represent so-called slow bars without offset dust lanes. We provide a quantitative analysis of J-transfer in disc-halo systems, and explain the reasons for absence of growth in fast spinning haloes and its observational corollaries. We conclude that stellar bar evolution is substantially more complex than anticipated, and bars are not as resilient as has been considered so far.

  7. Structure and Population of the Andromeda Stellar Halo from a Subaru/Suprime-Cam Survey

    NASA Astrophysics Data System (ADS)

    Tanaka, Mikito; Chiba, Masashi; Komiyama, Yutaka; Guhathakurta, Puragra; Kalirai, Jason S.; Iye, Masanori

    2010-01-01

    We present a photometric survey of the stellar halo of the nearest giant spiral galaxy, Andromeda (M31), using Suprime-Cam on the Subaru Telescope. A detailed analysis of VI color-magnitude diagrams of the resolved stellar population is used to measure properties such as line-of-sight distance, surface brightness, metallicity, and age. These are used to isolate and characterize different components of the M31 halo: (1) the giant southern stream (GSS); (2) several other substructures; and (3) the smooth halo. First, the GSS is characterized by a broad red giant branch (RGB) and a metal-rich/intermediate-age red clump (RC). The I magnitude of the well-defined tip of the RGB suggests that the distance to the observed GSS field is (m - M)0 = 24.73 ± 0.11 (883 ± 45 kpc) at a projected radius of R ~ 30 kpc from M31's center. The GSS shows a high metallicity peaked at [Fe/H]gsim-0.5 with a mean (median) of -0.7 (-0.6), estimated via comparison with theoretical isochrones. Combined with the luminosity of the RC, we estimate the mean age of its stellar population to be ~8 Gyr. The mass of its progenitor galaxy is likely in the range of 107-109 M sun. Second, we study M31's halo substructure along the northwest/southeast minor axis out to R ~ 100 kpc and the southwest major-axis region at R ~ 60 kpc. We confirm two substructures in the southeast halo reported by Ibata et al. and discover two overdense substructures in the northwest halo. We investigate the properties of these four substructures as well as other structures including the western shelf and find that differences in stellar populations among these systems, thereby suggesting each has a different origin. Our statistical analysis implies that the M31 halo as a whole may contain at least 16 substructures, each with a different origin, so its outer halo has experienced at least this many accretion events involving dwarf satellites with mass 107-109 M sun since a redshift of z ~ 1. Third, we investigate the

  8. A general explanation on the correlation of dark matter halo spin with the large-scale environment

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Kang, Xi

    2017-06-01

    Both simulations and observations have found that the spin of halo/galaxy is correlated with the large-scale environment, and particularly the spin of halo flips in filament. A consistent picture of halo spin evolution in different environments is still lacked. Using N-body simulation, we find that halo spin with its environment evolves continuously from sheet to cluster, and the flip of halo spin happens both in filament and nodes. The flip in filament can be explained by halo formation time and migrating time when its environment changes from sheet to filament. For low-mass haloes, they form first in sheets and migrate into filaments later, so their mass and spin growth inside filament are lower, and the original spin is still parallel to filament. For high-mass haloes, they migrate into filaments first, and most of their mass and spin growth are obtained in filaments, so the resulted spin is perpendicular to filament. Our results well explain the overall evolution of cosmic web in the cold dark matter model and can be tested using high-redshift data. The scenario can also be tested against alternative models of dark matter, such as warm/hot dark matter, where the structure formation will proceed in a different way.

  9. Revised Model of the Steady-state Solar Wind Halo Electron Velocity Distribution Function

    NASA Astrophysics Data System (ADS)

    Yoon, Peter H.; Kim, Sunjung; Choe, G. S.; moon, Y.-J.

    2016-08-01

    A recent study discussed the steady-state model for solar wind electrons during quiet time conditions. The electrons emanating from the Sun are treated in a composite three-population model—the low-energy Maxwellian core with an energy range of tens of eV, the intermediate ˜102-103 eV energy-range (“halo”) electrons, and the high ˜103-105 eV energy-range (“super-halo”) electrons. In the model, the intermediate energy halo electrons are assumed to be in resonance with transverse EM fluctuations in the whistler frequency range (˜102 Hz), while the high-energy super-halo electrons are presumed to be in steady-state wave-particle resonance with higher-frequency electrostatic fluctuations in the Langmuir frequency range (˜105 Hz). A comparison with STEREO and WIND spacecraft data was also made. However, ignoring the influence of Langmuir fluctuations on the halo population turns out to be an unjustifiable assumption. The present paper rectifies the previous approach by including both Langmuir and whistler fluctuations in the construction of the steady-state velocity distribution function for the halo population, and demonstrates that the role of whistler-range fluctuation is minimal unless the fluctuation intensity is arbitrarily raised. This implies that the Langmuir-range fluctuations, known as the quasi thermal noise, are important for both halo and super-halo electron velocity distribution.

  10. Building the Galactic halo from globular clusters: evidence from chemically unusual red giants

    NASA Astrophysics Data System (ADS)

    Martell, S. L.; Smolinski, J. P.; Beers, T. C.; Grebel, E. K.

    2011-10-01

    We present a spectroscopic search for halo field stars that originally formed in globular clusters. Using moderate-resolution SDSS-III/SEGUE-2 spectra of 561 red giants with typical halo metallicities (-1.8 ≤ [Fe/H] ≤ -1.0), we identify 16 stars, 3% of the sample, with CN and CH bandstrength behavior indicating depleted carbon and enhanced nitrogen abundances relative to the rest of the data set. Since globular clusters are the only environment known in which stars form with this pattern of atypical light-element abundances, we claim that these stars are second-generation globular cluster stars that have been lost to the halo field via normal cluster mass-loss processes. Extrapolating from theoretical models of two-generation globular cluster formation, this result suggests that globular clusters contributed significant numbers of stars to the construction of the Galactic halo: we calculate that a minimum of 17% of the present-day mass of the stellar halo was originally formed in globular clusters. The ratio of CN-strong to CN-normal stars drops with Galactocentric distance, suggesting that the inner-halo population may be the primary repository of these stars. Full Tables 1 and 3 are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/534/A136

  11. Angular momentum properties of haloes and their baryon content in the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Zjupa, Jolanta; Springel, Volker

    2017-04-01

    The angular momentum properties of virialized dark matter haloes have been measured with good statistics in collisionless N-body simulations, but an equally accurate analysis of the baryonic spin is still missing. We employ the Illustris simulation suite, one of the first simulations of galaxy formation with full hydrodynamics that produces a realistic galaxy population in a sizeable volume, to quantify the baryonic spin properties for more than ˜320 000 haloes. We first compare the systematic differences between different spin parameter and halo definitions, and the impact of sample selection criteria on the derived properties. We confirm that dark-matter-only haloes exhibit a close to self-similar spin distribution in mass and redshift of lognormal form. However, the physics of galaxy formation radically changes the baryonic spin distribution. While the dark matter component remains largely unaffected, strong trends with mass and redshift appear for the spin of diffuse gas and the formed stellar component. With time, the baryons staying bound to the halo develop a misalignment of their spin vector with respect to dark matter, and increase their specific angular momentum by a factor of ˜1.3 in the non-radiative case and ˜1.8 in the full physics setup at z = 0. We show that this enhancement in baryonic spin can be explained by the combined effect of specific angular momentum transfer from dark matter on to gas during mergers and from feedback expelling low specific angular momentum gas from the halo. Our results challenge certain models for spin evolution and underline the significant changes induced by baryonic physics in the structure of haloes.

  12. Chemical Compositions of Kinematically Selected Outer Halo Stars

    NASA Astrophysics Data System (ADS)

    Zhang, Lan; Ishigaki, Miho; Aoki, Wako; Zhao, Gang; Chiba, Masashi

    2009-12-01

    Chemical abundances of 26 metal-poor dwarfs and giants are determined from high-resolution and high signal-to-noise ratio spectra obtained with the Subaru/High Dispersion Spectrograph. The sample is selected so that most of the objects have outer-halo kinematics. Self-consistent atmospheric parameters were determined by an iterative procedure based on spectroscopic analysis. Abundances of 13 elements, including α-elements (Mg, Si, Ca, Ti), odd-Z light elements (Na, Sc), iron-peak elements (Cr, Mn, Fe, Ni, Zn), and neutron-capture elements (Y, Ba), are determined by two independent data reduction and local thermodynamic equillibrium analysis procedures, confirming the consistency of the stellar parameters and abundances results. We find a decreasing trend of [α/Fe] with increasing [Fe/H] for the range of -3.5< [Fe/H] <-1, as found by Stephens & Boesgaard. [Zn/Fe] values of most objects in our sample are slightly lower than the bulk of halo stars previously studied. These results are discussed as possible chemical properties of the outer halo in the Galaxy. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  13. Evidence of lensing of the cosmic microwave background by dark matter halos.

    PubMed

    Madhavacheril, Mathew; Sehgal, Neelima; Allison, Rupert; Battaglia, Nick; Bond, J Richard; Calabrese, Erminia; Caligiuri, Jerod; Coughlin, Kevin; Crichton, Devin; Datta, Rahul; Devlin, Mark J; Dunkley, Joanna; Dünner, Rolando; Fogarty, Kevin; Grace, Emily; Hajian, Amir; Hasselfield, Matthew; Hill, J Colin; Hilton, Matt; Hincks, Adam D; Hlozek, Renée; Hughes, John P; Kosowsky, Arthur; Louis, Thibaut; Lungu, Marius; McMahon, Jeff; Moodley, Kavilan; Munson, Charles; Naess, Sigurd; Nati, Federico; Newburgh, Laura; Niemack, Michael D; Page, Lyman A; Partridge, Bruce; Schmitt, Benjamin; Sherwin, Blake D; Sievers, Jon; Spergel, David N; Staggs, Suzanne T; Thornton, Robert; Van Engelen, Alexander; Ward, Jonathan T; Wollack, Edward J

    2015-04-17

    We present evidence of the gravitational lensing of the cosmic microwave background by 10(13) solar mass dark matter halos. Lensing convergence maps from the Atacama Cosmology Telescope Polarimeter (ACTPol) are stacked at the positions of around 12 000 optically selected CMASS galaxies from the SDSS-III/BOSS survey. The mean lensing signal is consistent with simulated dark matter halo profiles and is favored over a null signal at 3.2σ significance. This result demonstrates the potential of microwave background lensing to probe the dark matter distribution in galaxy group and galaxy cluster halos.

  14. Occupational health management: an audit tool.

    PubMed

    Shelmerdine, L; Williams, N

    2003-03-01

    Organizations must manage occupational health risks in the workplace and the UK Health & Safety Executive (HSE) has published guidance on successful health and safety management. This paper describes a method of using the published guidance to audit the management of occupational health and safety, first at an organizational level and, secondly, to audit an occupational health service provider's role in the management of health risks. The paper outlines the legal framework in the UK for health risk management and describes the development and use of a tool for qualitative auditing of the efficiency, effectiveness and reliability of occupational health service provision within an organization. The audit tool is presented as a question set and the paper concludes with discussion of the strengths and weaknesses of using this tool, and recommendations on its use.

  15. Biomechanics of halo-vest and dens screw fixation for type II odontoid fracture.

    PubMed

    Ivancic, Paul C; Beauchman, Naseem N; Mo, Fred; Lawrence, Brandon D

    2009-03-01

    An in vitro biomechanical study of halo-vest and odontoid screw fixation of Type II dens fracture. The objective were to determine upper cervical spine instability due to simulated dens fracture and investigate stability provided by the halo-vest and odontoid screw, applied individually and combined. Previous studies have evaluated posterior fixation techniques for stabilizing dens fracture. No previous biomechanical study has investigated the halo-vest and odontoid screw for stabilizing dens fracture. A biofidelic skull-neck-thorax model was used with 5 osteoligamentous whole cervical spine specimens. Three-dimensional flexibility tests were performed on the specimens while intact, following simulated dens fracture, and following application of the halo-vest alone, odontoid screw alone, and halo-vest and screw combined. Average total neutral zone and total ranges of motion at C0/1 and C1/2 were computed for each experimental condition and statistically compared with physiologic motion limits, obtained from the intact flexibility test. Significance was set at P < 0.05 with a trend toward significance at P < 0.1. Type II dens fracture caused trends toward increased sagittal neutral zone and lateral bending range of motion at C1/2. Spinal motions with the dens screw alone could not be differentiated from physiologic limits. Significant reductions in motion were observed at C0/1 and C1/2 in flexion-extension and axial rotation due to the halo-vest, applied individually or combined with the dens screw. At C1/2, the halo-vest combined with the dens screw generally allowed the smallest average percentages of intact motion: 3% in axial rotation, 17% in flexion-extension, and 18% in lateral bending. The present reduction in C1/2 motion observed, due to the halo-vest and dens screw combined is similar to previously reported immobilization provided by the polyaxial screw/rod system and transarticular screw fixation combined with wiring. The present biomechanical data may be

  16. The sagittarius tidal stream and the shape of the galactic stellar halo

    NASA Astrophysics Data System (ADS)

    Newby, Matthew T.

    The stellar halo that surrounds our Galaxy contains clues to understanding galaxy formation, cosmology, stellar evolution, and the nature of dark matter. Gravitationally disrupted dwarf galaxies form tidal streams, which roughly trace orbits through the Galactic halo. The Sagittarius (Sgr) dwarf tidal debris is the most dominant of these streams, and its properties place important constraints on the distribution of mass (including dark matter) in the Galaxy. Stars not associated with substructures form the "smooth" component of the stellar halo, the origin of which is still under investigation. Characterizing halo substructures such as the Sgr stream and the smooth halo provides valuable information on the formation history and evolution of our galaxy, and places constraints on cosmological models. This thesis is primarily concerned with characterizing the 3-dimensional stellar densities of the Sgr tidal debris system and the smooth stellar halo, using data from the Sloan Digital Sky Survey (SDSS). F turnoff stars are used to infer distances, as they are relatively bright, numerous, and distributed about a single intrinsic brightness (magnitude). The inherent spread in brightnesses of these stars is overcome through the use of the recently-developed technique of statistical photometric parallax, in which the bulk properties of a stellar population are used to create a probability distribution for a given star's distance. This was used to build a spatial density model for the smooth stellar halo and tidal streams. The free parameters in this model are then fit to SDSS data with a maximum likelihood technique, and the parameters are optimized by advanced computational methods. Several computing platforms are used in this study, including the RPI SUR Bluegene and the Milkyway home volunteer computing project. Fits to the Sgr stream in 18 SDSS data stripes were performed, and a continuous density profile is found for the major Sgr stream. The stellar halo is found to

  17. The two-component giant radio halo in the galaxy cluster Abell 2142

    NASA Astrophysics Data System (ADS)

    Venturi, T.; Rossetti, M.; Brunetti, G.; Farnsworth, D.; Gastaldello, F.; Giacintucci, S.; Lal, D. V.; Rudnick, L.; Shimwell, T. W.; Eckert, D.; Molendi, S.; Owers, M.

    2017-07-01

    Aims: We report on a spectral study at radio frequencies of the giant radio halo in A 2142 (z = 0.0909), which we performed to explore its nature and origin. The optical and X-ray properties of the cluster suggest that A 2142 is not a major merger and the presence of a giant radio halo is somewhat surprising. Methods: We performed deep radio observations of A 2142 with the Giant Metrewave Radio Telescope (GMRT) at 608 MHz, 322 MHz, and 234 MHz and with the Very Large Array (VLA) in the 1-2 GHz band. We obtained high-quality images at all frequencies in a wide range of resolutions, from the galaxy scale, I.e. 5'', up to 60'' to image the diffuse cluster-scale emission. The radio halo is well detected at all frequencies and extends out to the most distant cold front in A 2142, about 1 Mpc away from the cluster centre. We studied the spectral index in two regions: the central part of the halo, where the X-ray emission peaks and the two brightest dominant galaxies are located; and a second region, known as the ridge (in the direction of the most distant south-eastern cold front), selected to follow the bright part of the halo and X-ray emission. We complemented our deep observations with a preliminary LOw Frequency ARray (LOFAR) image at 118 MHz and with the re-analysis of archival VLA data at 1.4 GHz. Results: The two components of the radio halo show different observational properties. The central brightest part has higher surface brightess and a spectrum whose steepness is similar to those of the known radio halos, I.e. α1.78 GHz118 MHz = 1.33 ± 0.08 . The ridge, which fades into the larger scale emission, is broader in size and has considerably lower surface brightess and a moderately steeper spectrum, I.e. α1.78 GHz118 MHz 1.5. We propose that the brightest part of the radio halo is powered by the central sloshing in A 2142, in a process similar to what has been suggested for mini-halos, or by secondary electrons generated by hadronic collisions in the ICM. On

  18. Spectroscopic decomposition of the galaxy and halo of the cD galaxy NGC 3311

    NASA Astrophysics Data System (ADS)

    Johnston, Evelyn J.; Merrifield, Michael; Aragón-Salamanca, Alfonso

    2018-05-01

    Information on the star-formation histories of cD galaxies and their extended stellar haloes lie in their spectra. Therefore, to determine whether these structures evolved together or through a two-phase formation, we need to spectroscopically separate the light from each component. We present a pilot study to use BUDDI to fit and extract the spectra of the cD galaxy NGC 3311 and its halo in an Integral Field Spectroscopy datacube, and carry out a simple stellar populations analysis to study their star-formation histories. Using MUSE data, we were able to isolate the light of the galaxy and its halo throughout the datacube, giving spectra representing purely the light from each of these structures. The stellar populations analysis of the two components indicates that, in this case, the bulk of the stars in both the halo and the central galaxy are very old, but the halo is more metal poor and less α-enriched than the galaxy. This result is consistent with the halo forming through the accretion of much smaller satellite galaxies with more extended star formation. It is noteworthy that the apparent gradients in age and metallicity indicators across the galaxy are entirely consistent with the radially-varying contributions of galaxy and halo components, which individually display no gradients. The success of this study is promising for its application to a larger sample of cD galaxies that are currently being observed by IFU surveys.

  19. Localized massive halo properties in BAHAMAS and MACSIS simulations: scalings, log-normality, and covariance

    NASA Astrophysics Data System (ADS)

    Farahi, Arya; Evrard, August E.; McCarthy, Ian; Barnes, David J.; Kay, Scott T.

    2018-05-01

    Using tens of thousands of halos realized in the BAHAMAS and MACSIS simulations produced with a consistent astrophysics treatment that includes AGN feedback, we validate a multi-property statistical model for the stellar and hot gas mass behavior in halos hosting groups and clusters of galaxies. The large sample size allows us to extract fine-scale mass-property relations (MPRs) by performing local linear regression (LLR) on individual halo stellar mass (Mstar) and hot gas mass (Mgas) as a function of total halo mass (Mhalo). We find that: 1) both the local slope and variance of the MPRs run with mass (primarily) and redshift (secondarily); 2) the conditional likelihood, p(Mstar, Mgas| Mhalo, z) is accurately described by a multivariate, log-normal distribution, and; 3) the covariance of Mstar and Mgas at fixed Mhalo is generally negative, reflecting a partially closed baryon box model for high mass halos. We validate the analytical population model of Evrard et al. (2014), finding sub-percent accuracy in the log-mean halo mass selected at fixed property, ⟨ln Mhalo|Mgas⟩ or ⟨ln Mhalo|Mstar⟩, when scale-dependent MPR parameters are employed. This work highlights the potential importance of allowing for running in the slope and scatter of MPRs when modeling cluster counts for cosmological studies. We tabulate LLR fit parameters as a function of halo mass at z = 0, 0.5 and 1 for two popular mass conventions.

  20. A core-halo pattern of entropy creation in gravitational collapse

    NASA Astrophysics Data System (ADS)

    Wren, Andrew J.

    2018-03-01

    This paper presents a kinetic theory model of gravitational collapse due to a small perturbation. Solving the relevant equations yields a pattern of entropy destruction in a spherical core around the perturbation, and entropy creation in a surrounding halo. This indicates collisional "de-relaxation" in the core, and collisional relaxation in the halo. Core-halo patterns are ubiquitous in the astrophysics of gravitational collapse, and are found here without any of the prior assumptions of such a pattern usually made in analytical models. Motivated by this analysis, the paper outlines a possible scheme for identifying structure formation in a set of observations or a simulation. This scheme involves a choice of coarse-graining scale appropriate to the structure under consideration, and might aid exploration of hierarchical structure formation, supplementing the usual density-based methods for highlighting astrophysical and cosmological structure at various scales.

  1. An extended Zel'dovich model for the halo mass function

    NASA Astrophysics Data System (ADS)

    Lim, Seunghwan; Lee, Jounghun

    2013-01-01

    A new way to construct a fitting formula for the halo mass function is presented. Our formula is expressed as a solution to the modified Jedamzik matrix equation that automatically satisfies the normalization constraint. The characteristic parameters expressed in terms of the linear shear eigenvalues are empirically determined by fitting the analytic formula to the numerical results from the high-resolution N-body simulation and found to be independent of scale, redshift and background cosmology. Our fitting formula with the best-fit parameters is shown to work excellently in the wide mass-range at various redshifts: The ratio of the analytic formula to the N-body results departs from unity by up to 10% and 5% over 1011 <= M/(h-1Msolar) <= 5 × 1015 at z = 0,0.5 and 1 for the FoF-halo and SO-halo cases, respectively.

  2. A core-halo pattern of entropy creation in gravitational collapse

    NASA Astrophysics Data System (ADS)

    Wren, Andrew J.

    2018-07-01

    This paper presents a kinetic theory model of gravitational collapse due to a small perturbation. Solving the relevant equations yields a pattern of entropy destruction in a spherical core around the perturbation, and entropy creation in a surrounding halo. This indicates collisional `de-relaxation' in the core, and collisional relaxation in the halo. Core-halo patterns are ubiquitous in the astrophysics of gravitational collapse and are found here without any of the prior assumptions of such a pattern usually made in analytical models. Motivated by this analysis, the paper outlines a possible scheme for identifying structure formation in a set of observations or a simulation. This scheme involves a choice of coarse-graining scale appropriate to the structure under consideration, and might aid exploration of hierarchical structure formation, supplementing the usual density-based methods for highlighting astrophysical and cosmological structure at various scales.

  3. Faraday rotation in the M87 radio/X-ray halo

    NASA Technical Reports Server (NTRS)

    Dennison, B.

    1980-01-01

    Comparison of polarization maps at various wavelengths demonstrates the existence of a large Faraday rotation uniform over the radio core of M87. Much of this rotation must be external to the core, lest it appear completely depolarized when the rotation is about 90 degrees. The Faraday rotation is shown to occur primarily in the surrounding radio/X-ray halo. Using the electron density inferred from X-ray observations, the magnetic field in the halo is found to be 2.5 microgauss. The deduced magnetic field strength permits an evaluation of the importance of Compton scattering of 3 K background photons by relativistic electrons in the radio halo. The emergent Compton-scattered spectrum is calculated, and its contribution to the observed X-ray flux is small, probably about a percent or so, while the rest is due to thermal bremsstrahlung.

  4. Uncovering the hidden iceberg structure of the Galactic halo

    NASA Astrophysics Data System (ADS)

    Moss, Vanessa A.; Di Teodoro, Enrico M.; McClure-Griffiths, Naomi M.; Lockman, Felix; Pisano, D. J.; Price, Daniel; Rees, Glen

    2018-01-01

    How the Milky Way gets its gas and keeps its measured star formation rate going are both long-standing mysteries in Galactic studies, with important implications for galaxy evolution across the Universe. I will present our recent discovery of two populations of neutral hydrogen (HI) in the halo of the Milky Way: 1) a narrow line-width dense population typical of the majority of bright high velocity cloud (HVC) components, and 2) a fainter, broad line-width diffuse population that aligns well with the population found in very sensitive pointings such as in Lockman et al. (2002). From our existing data, we concluded that the diffuse population likely outweighs the dense HI by a factor of 3. This discovery of diffuse HI, which appears to be prevalent throughout the halo, takes us closer to solving the Galactic mystery of accretion and reveals a gaseous neutral halo hidden from the view of most large-scale surveys. We are currently carrying out deep Parkes observations to investigate these results further, in order to truly uncover the nature of the diffuse HI and determine whether our 3:1 ratio (based on the limited existing data) is consistent with what is seen when Parkes and the 140 ft Green Bank telescope are employed at comparable sensitivity. With these data, through a combination of both known and new sightline measurements, we aim to reveal the structure of the Galactic halo in more detail than ever before.

  5. Halogen occultation experiment (HALOE) optical witness-plate program

    NASA Technical Reports Server (NTRS)

    Harvey, Gale A.; Raper, James L.

    1989-01-01

    An optical witness plate program was implemented to monitor buildup of molecular contamination in the clean room during the assembly and testing of the Halogen Occulation Experiment (HALOE) instrument. Travel plates to monitor molecular contamination when the instrument is not in the clean room are also measured. The instrument technique is high-resolution transmission spectroscopy in the 3 micron spectral region using a Fourier transform spectrometer. Witness specimens of low index of refraction, infrared transmitting material are used for contaminant monitoring and for spectral signature analysis. Spectral signatures of possible molecular contamination are presented. No condensible volatile material contamination of HALOE optical witness specimens have yet been found.

  6. Indications and complications of crown halo vest placement: A review.

    PubMed

    Lee, Dennis; Adeoye, Adeola L; Dahdaleh, Nader S

    2017-06-01

    Crown halo vest placement remains an option for the treatment of a variety of upper and subaxial cervical spinal fractures. While the device remains a useful non-operative option for the treatment of these injuries, it has been associated with a variety of complications. This manuscript represents an up to date narrative review of the indications, complications, and complication avoidance for the placement of crown halo vests. Copyright © 2017 Elsevier Ltd. All rights reserved.

  7. Signatures of compact halos of sterile-neutrino dark matter

    NASA Astrophysics Data System (ADS)

    Kühnel, Florian; Ohlsson, Tommy

    2017-11-01

    We investigate compact halos of sterile-neutrino dark matter and examine observable signatures with respect to neutrino and photon emission. Primarily, we consider two cases: primordial black-hole halos and ultracompact minihalos. In both cases, we find that there exists a broad range of possible parameter choices such that detection in the near future with x-ray and gamma-ray telescopes might be well possible. In fact, for energies above 10 TeV, the neutrino telescope IceCube would be a splendid detection machine for such macroscopic dark-matter candidates.

  8. The Profile of the Galactic Halo from Pan-STARRS1 3π RR Lyrae

    NASA Astrophysics Data System (ADS)

    Hernitschek, Nina; Cohen, Judith G.; Rix, Hans-Walter; Sesar, Branimir; Martin, Nicolas F.; Magnier, Eugene; Wainscoat, Richard; Kaiser, Nick; Tonry, John L.; Kudritzki, Rolf-Peter; Hodapp, Klaus; Chambers, Ken; Flewelling, Heather; Burgett, William

    2018-05-01

    We characterize the spatial density of the Pan-STARRS1 (PS1) sample of Rrab stars to study the properties of the old Galactic stellar halo. This sample, containing 44,403 sources, spans galactocentric radii of 0.55 kpc ≤ R gc ≤ 141 kpc with a distance precision of 3% and thus is able to trace the halo out to larger distances than most previous studies. After excising stars that are attributed to dense regions such as stellar streams, the Galactic disk and bulge, and halo globular clusters, the sample contains ∼11,000 sources within 20 kpc ≤ R gc ≤ 131 kpc. We then apply forward modeling using Galactic halo profile models with a sample selection function. Specifically, we use ellipsoidal stellar density models ρ(l, b, R gc) with a constant and a radius-dependent halo flattening q(R gc). Assuming constant flattening q, the distribution of the sources is reasonably well fit by a single power law with n={4.40}-0.04+0.05 and q={0.918}-0.014+0.016 and comparably well fit by an Einasto profile with n={9.53}-0.28+0.27, an effective radius r eff = 1.07 ± 0.10 kpc, and a halo flattening of q = 0.923 ± 0.007. If we allow for a radius-dependent flattening q(R gc), we find evidence for a distinct flattening of q ∼ 0.8 of the inner halo at ∼25 kpc. Additionally, we find that the south Galactic hemisphere is more flattened than the north Galactic hemisphere. The results of our work are largely consistent with many earlier results (e.g., Watkins et al.; Iorio et al.). We find that the stellar halo, as traced in RR Lyrae stars, exhibits a substantial number of further significant over- and underdensities, even after masking all known overdensities.

  9. The connection between the host halo and the satellite galaxies of the Milky Way

    DOE PAGES

    Lu, Yu; Benson, Andrew; Mao, Yao -Yuan; ...

    2016-10-11

    Many properties of the Milky Way's (MW) dark matter halo, including its mass-assembly history, concentration, and subhalo population, remain poorly constrained. We explore the connection between these properties of the MW and its satellite galaxy population, especially the implication of the presence of the Magellanic Clouds for the properties of the MW halo. Using a suite of high-resolution N-body simulations of MW-mass halos with a fixed finalmore » $${M}_{\\mathrm{vir}}\\sim {10}^{12.1}\\,{M}_{\\odot }$$, we find that the presence of Magellanic Cloud-like satellites strongly correlates with the assembly history, concentration, and subhalo population of the host halo, such that MW-mass systems with Magellanic Clouds have lower concentration, more rapid recent accretion, and more massive subhalos than typical halos of the same mass. Using a flexible semi-analytic galaxy formation model that is tuned to reproduce the stellar mass function of the classical dwarf galaxies of the MW with Markov-Chain Monte-Carlo, we show that adopting host halos with different mass-assembly histories and concentrations can lead to different best-fit models for galaxy-formation physics, especially for the strength of feedback. These biases arise because the presence of the Magellanic Clouds boosts the overall population of high-mass subhalos, thus requiring a different stellar-mass-to-halo-mass ratio to match the data. These biases also lead to significant differences in the mass–metallicity relation, the kinematics of low-mass satellites, the number counts of small satellites associated with the Magellanic Clouds, and the stellar mass of MW itself. Finally, observations of these galaxy properties can thus provide useful constraints on the properties of the MW halo.« less

  10. Cosmic stellar relics in the Galactic halo

    NASA Astrophysics Data System (ADS)

    Salvadori, Stefania; Schneider, Raffaella; Ferrara, Andrea

    2007-10-01

    We study the stellar population history and chemical evolution of the Milky Way (MW) in a hierarchical Λ cold dark matter model for structure formation. Using a Monte Carlo method based on the semi-analytical extended Press & Schechter formalism, we develop a new code GALAXY MERGER TREE AND EVOLUTION (GAMETE) to reconstruct the merger tree of the Galaxy and follow the evolution of gas and stars along the hierarchical tree. Our approach allows us to compare the observational properties of the MW with model results, exploring different properties of primordial stars, such as their initial mass function and the critical metallicity for low-mass star formation, Zcr. In particular, by matching our predictions to the metallicity distribution function (MDF) of metal-poor stars in the Galactic halo we find that: (i) a strong supernova (SN) feedback is required to reproduce the observed properties of the MW; (ii) stars with [Fe/H] < -2.5 form in haloes accreting Galactic medium (GM) enriched by earlier SN explosions; (iii) the fiducial model (Zcr = 10-4Zsolar, mPopIII = 200 Msolar) provides an overall good fit to the MDF, but cannot account for the two hyper-metal-poor (HMP) stars with [Fe/H] < -5 the latter can be accommodated if Zcr <= 10-6 Zsolar but such model overpopulates the `metallicity desert', that is, the range -5.3 < [Fe/H] < -4 in which no stars have been detected; (iv) the current non-detection of metal-free stars robustly constrains either Zcr > 0 or the masses of the first stars mPopIII > 0.9 Msolar (v) the statistical impact of truly second-generation stars, that is, stars forming out of gas polluted only by metal-free stars, is negligible in current samples; and (vi) independent of Zcr, 60 per cent of metals in the GM are ejected through winds by haloes with masses M < 6 × 109 Msolar, thus showing that low-mass haloes are the dominant population contributing to cosmic metal enrichment. We discuss the limitations of our study and comparison with previous

  11. The clustering of QSOs and the dark matter halos that host them

    NASA Astrophysics Data System (ADS)

    Zhao, Dong-Yao; Yan, Chang-Shuo; Lu, Youjun

    2013-10-01

    The spatial clustering of QSOs is an important measurable quantity which can be used to infer the properties of dark matter halos that host them. We construct a simple QSO model to explain the linear bias of QSOs measured by recent observations and explore the properties of dark matter halos that host a QSO. We assume that major mergers of dark matter halos can lead to the triggering of QSO phenomena, and the evolution of luminosity for a QSO generally shows two accretion phases, i.e., initially having a constant Eddington ratio due to the self-regulation of the accretion process when supply is sufficient, and then declining in rate with time as a power law due to either diminished supply or long term disk evolution. Using a Markov Chain Monte Carlo method, the model parameters are constrained by fitting the observationally determined QSO luminosity functions (LFs) in the hard X-ray and in the optical band simultaneously. Adopting the model parameters that best fit the QSO LFs, the linear bias of QSOs can be predicted and then compared with the observational measurements by accounting for various selection effects in different QSO surveys. We find that the latest measurements of the linear bias of QSOs from both the SDSS and BOSS QSO surveys can be well reproduced. The typical mass of SDSS QSOs at redshift 1.5 < z < 4.5 is ~ (3 - 6) × 1012 h-1 Msolar and the typical mass of BOSS QSOs at z ~ 2.4 is ~ 2 × 1012 h-1 Msolar. For relatively faint QSOs, the mass distribution of their host dark matter halos is wider than that of bright QSOs because faint QSOs can be hosted in both big halos and smaller halos, but bright QSOs are only hosted in big halos, which is part of the reason for the predicted weak dependence of the linear biases on the QSO luminosity.

  12. Star formation onset in baryonic disks: The role of a triaxial halo

    NASA Astrophysics Data System (ADS)

    Mazzei, P.; Curir, A.

    2001-06-01

    We investigate the effects of the onset of star formation on the growth of bar instability using a smooth particle hydrodynamics code implemented to account for chemo-photometric evolution from UV to near-IR wavelengths. We analyze the role of a non axisymmetric dark matter halo on the bar triggering and the feedback due to the ongoing star formation rate in the disk. We find that the dark matter halo plays a very important role in the evolution of the luminous matter. The star formation rate (SFR) depends indeed both on its mass, which leads the total gravitational field, and on its dynamical state. Stronger initial bursts of star formation are triggered in the more massive unrelaxed haloes than in the relaxed ones, which are also the more concentrated at the beginning. We point out further that the dark matter concentration is different in haloes with a different initial triaxiality ratio, suggesting a dependence of the SFR also on the halo geometry. By mapping the predicted B surface brightness of the new stars formed, we find that a luminous bar along the whole disk develops only in the first stages of such an instability, then later, new stars are born in the inner regions and the bar is reduced to the central 3-4 kpc. After 1.7 Gyr the young stellar component shows stronger bars in the presence of the relaxed haloes with a lower initial triaxiality ratio; strong bars still appear in the old star isodensity contours of the same systems, at variance with our results when star formation is switched off. The formation of new stars causes indeed a lower dynamical coupling between dark matter and baryonic particles, which lengthens the life-time of the bar. Colours and metallicity gradients of new stars allow us to understand deeply the observational consequences of initial geometry and dynamical state of the halo on the star formation process.

  13. Occupation and its relationship with health and wellbeing: the threshold concept for occupational therapy.

    PubMed

    Fortune, Tracy; Kennedy-Jones, Mary

    2014-10-01

    We introduce the educational framework of 'threshold concepts' and discuss its utility in understanding the fundamental difficulties learners have in understanding ways of thinking and practising as occupational therapists. We propose that the relationship between occupation and health is a threshold concept for occupational therapy because of students' trouble in achieving lasting conceptual change in relation to their understanding of it. The authors present and discuss key ideas drawn from educational writings on threshold concepts, review the emerging literature on threshold concepts in occupational therapy, and pose a series of questions in order to prompt consideration of the pedagogical issues requiring action by academic and fieldwork educators. Threshold concepts in occupational therapy have been considered in a primarily cross-disciplinary sense, that is, the understandings that occupational therapy learners grapple with are relevant to learners in other disciplines. In contrast, we present a more narrowly defined conception that emphasises the 'bounded-ness' of the concept to the discipline. A threshold concept that captures the essential nature of occupational therapy is likely to be (highly) troublesome in terms of a learner's acquisition of it. Rather than simplifying these learning 'jewels' educators are encouraged to sit with the discomfort that they and the learner may experience as the learner struggles to grasp them. Moreover, they should reshape their curricula to provoke such struggles if transformative learning is to be the outcome. © 2014 Occupational Therapy Australia.

  14. Towards Accurate Modelling of Galaxy Clustering on Small Scales: Testing the Standard ΛCDM + Halo Model

    NASA Astrophysics Data System (ADS)

    Sinha, Manodeep; Berlind, Andreas A.; McBride, Cameron K.; Scoccimarro, Roman; Piscionere, Jennifer A.; Wibking, Benjamin D.

    2018-04-01

    Interpreting the small-scale clustering of galaxies with halo models can elucidate the connection between galaxies and dark matter halos. Unfortunately, the modelling is typically not sufficiently accurate for ruling out models statistically. It is thus difficult to use the information encoded in small scales to test cosmological models or probe subtle features of the galaxy-halo connection. In this paper, we attempt to push halo modelling into the "accurate" regime with a fully numerical mock-based methodology and careful treatment of statistical and systematic errors. With our forward-modelling approach, we can incorporate clustering statistics beyond the traditional two-point statistics. We use this modelling methodology to test the standard ΛCDM + halo model against the clustering of SDSS DR7 galaxies. Specifically, we use the projected correlation function, group multiplicity function and galaxy number density as constraints. We find that while the model fits each statistic separately, it struggles to fit them simultaneously. Adding group statistics leads to a more stringent test of the model and significantly tighter constraints on model parameters. We explore the impact of varying the adopted halo definition and cosmological model and find that changing the cosmology makes a significant difference. The most successful model we tried (Planck cosmology with Mvir halos) matches the clustering of low luminosity galaxies, but exhibits a 2.3σ tension with the clustering of luminous galaxies, thus providing evidence that the "standard" halo model needs to be extended. This work opens the door to adding interesting freedom to the halo model and including additional clustering statistics as constraints.

  15. A new smooth-k space filter approach to calculate halo abundances

    NASA Astrophysics Data System (ADS)

    Leo, Matteo; Baugh, Carlton M.; Li, Baojiu; Pascoli, Silvia

    2018-04-01

    We propose a new filter, a smooth-k space filter, to use in the Press-Schechter approach to model the dark matter halo mass function which overcomes shortcomings of other filters. We test this against the mass function measured in N-body simulations. We find that the commonly used sharp-k filter fails to reproduce the behaviour of the halo mass function at low masses measured from simulations of models with a sharp truncation in the linear power spectrum. We show that the predictions with our new filter agree with the simulation results over a wider range of halo masses for both damped and undamped power spectra than is the case with the sharp-k and real-space top-hat filters.

  16. The host dark matter haloes of [O II] emitters at 0.5 < z < 1.5

    NASA Astrophysics Data System (ADS)

    Gonzalez-Perez, V.; Comparat, J.; Norberg, P.; Baugh, C. M.; Contreras, S.; Lacey, C.; McCullagh, N.; Orsi, A.; Helly, J.; Humphries, J.

    2018-03-01

    Emission line galaxies (ELGs) are used in several ongoing and upcoming surveys (SDSS-IV/eBOSS, DESI) as tracers of the dark matter distribution. Using a new galaxy formation model, we explore the characteristics of [O II] emitters, which dominate optical ELG selections at z ≃ 1. Model [O II] emitters at 0.5 < z < 1.5 are selected to mimic the DEEP2, VVDS, eBOSS and DESI surveys. The luminosity functions of model [O II] emitters are in reasonable agreement with observations. The selected [O II] emitters are hosted by haloes with Mhalo ≥ 1010.3h-1M⊙, with ˜90 per cent of them being central star-forming galaxies. The predicted mean halo occupation distributions of [O II] emitters have a shape typical of that inferred for star-forming galaxies, with the contribution from central galaxies, < N > _{[O II] cen}, being far from the canonical step function. The < N > _{[O II] cen}} can be described as the sum of an asymmetric Gaussian for discs and a step function for spheroids, which plateau below unity. The model [O II] emitters have a clustering bias close to unity, which is below the expectations for eBOSS and DESI ELGs. At z ˜ 1, a comparison with observed g-band-selected galaxy, which is expected to be dominated by [O II] emitters, indicates that our model produces too few [O II] emitters that are satellite galaxies. This suggests the need to revise our modelling of hot gas stripping in satellite galaxies.

  17. Educational Mismatches and Earnings: Extensions of Occupational Mobility Theory and Evidence of Human Capital Depreciation

    ERIC Educational Resources Information Center

    Rubb, Stephen

    2006-01-01

    Using a human capital theory framework, this study examines the impact of educational mismatches on earnings and occupational mobility. Occupational mobility theory suggests that overeducated workers observe greater upward occupational mobility and undereducated workers observe lower upward occupational mobility. By extension, this leads to…

  18. Morphology of blazar-induced gamma ray halos due to a helical intergalactic magnetic field

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Long, Andrew J.; Vachaspati, Tanmay, E-mail: andrewjlong@asu.edu, E-mail: tvachasp@asu.edu

    We study the characteristic size and shape of idealized blazar-induced cascade halos in the 1–100,GeV energy range assuming various non-helical and helical configurations for the intergalactic magnetic field (IGMF). While the magnetic field creates an extended halo, the helicity provides the halo with a twist. Under simplifying assumptions, we assess the parameter regimes for which it is possible to measure the size and shape of the halo from a single source and then to deduce properties of the IGMF. We find that blazar halo measurements with an experiment similar to Fermi-LAT are best suited to probe a helical magnetic fieldmore » with strength and coherence length today in the ranges 10{sup −17} ∼< B{sub 0} / Gauss ∼< 10{sup −13} and 10 Mpc ∼< λ ∼< 10 Gpc where H ∼ B{sub 0}{sup 2} / λ is the magnetic helicity density. Stronger magnetic fields or smaller coherence scales can still potentially be investigated, but the connection between the halo morphology and the magnetic field properties is more involved. Weaker magnetic fields or longer coherence scales require high photon statistics or superior angular resolution.« less

  19. Maximising Occupancy. Accommodation Management Module. Operational Management Programme.

    ERIC Educational Resources Information Center

    Holland, Julia

    This module on maximizing occupancy is intended to cover the basic framework for analysis of occupancy in accommodations and for identification of ways to improve it on both a long-term and day-to-day basis. The material is presented in a self-instructional format in seven sections. At the beginning of each section is a statement of the objectives…

  20. Hierarchical phase space structure of dark matter haloes: Tidal debris, caustics, and dark matter annihilation

    NASA Astrophysics Data System (ADS)

    Afshordi, Niayesh; Mohayaee, Roya; Bertschinger, Edmund

    2009-04-01

    Most of the mass content of dark matter haloes is expected to be in the form of tidal debris. The density of debris is not constant, but rather can grow due to formation of caustics at the apocenters and pericenters of the orbit, or decay as a result of phase mixing. In the phase space, the debris assemble in a hierarchy that is truncated by the primordial temperature of dark matter. Understanding this phase structure can be of significant importance for the interpretation of many astrophysical observations and, in particular, dark matter detection experiments. With this purpose in mind, we develop a general theoretical framework to describe the hierarchical structure of the phase space of cold dark matter haloes. We do not make any assumption of spherical symmetry and/or smooth and continuous accretion. Instead, working with correlation functions in the action-angle space, we can fully account for the hierarchical structure (predicting a two-point correlation function ∝ΔJ-1.6 in the action space), as well as the primordial discreteness of the phase space. As an application, we estimate the boost to the dark matter annihilation signal due to the structure of the phase space within virial radius: the boost due to the hierarchical tidal debris is of order unity, whereas the primordial discreteness of the phase structure can boost the total annihilation signal by up to an order of magnitude. The latter is dominated by the regions beyond 20% of the virial radius, and is largest for the recently formed haloes with the least degree of phase mixing. Nevertheless, as we argue in a companion paper, the boost due to small gravitationally-bound substructure can dominate this effect at low redshifts.

  1. Scaling Laws for Dark Matter Halos in Late-type and Dwarf Spheroidal Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John; Freeman, K. C.

    2016-02-01

    Dark matter (DM) halos of Sc-Im and dwarf spheroidal (dSph) galaxies satisfy scaling laws: halos in lower-luminosity galaxies have smaller core radii, higher central densities, and smaller velocity dispersions. These results are based on maximum-disk rotation curve decompositions for giant galaxies and Jeans equation analysis for dwarfs. (1) We show that spiral, Im, and Sph galaxies with absolute magnitudes MV > -18 form a sequence of decreasing baryon-to-DM surface density with decreasing luminosity. We suggest that this is a sequence of decreasing baryon retention versus supernova-driven losses or decreasing baryon capture after cosmological reionization. (2) The structural differences between S+Im and Sph galaxies are small. Both are affected mostly by the physics that controls baryon depletion. (3) There is a linear correlation between the maximum rotation velocities of baryonic disks and the outer circular velocities Vcirc of test particles in their DM halos. Baryons become unimportant at Vcirc = 42 ± 4 km s-1. Smaller galaxies are dim or dark. (4) We find that, absent baryon “depletion” and with all baryons converted into stars, dSph galaxies would be brighter by ˜4.6 mag and dIm galaxies would be brighter by ˜3.5 mag. Both have DM halos that are massive enough to help to solve the “too big to fail” problem with DM galaxy formation. (5) We suggest that there exist many galaxies that are too dark to be discovered by current techniques, as required by cold DM theory. (6) Central surface densities of DM halos are constant from MB ˜ -5 to -22. This implies a Faber-Jackson law with halo mass M ∝ (halo dispersion)4.

  2. SCALING LAWS FOR DARK MATTER HALOS IN LATE-TYPE AND DWARF SPHEROIDAL GALAXIES

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kormendy, John; Freeman, K. C., E-mail: kormendy@astro.as.utexas.edu, E-mail: kenneth.freeman@anu.edu.au

    2016-02-01

    Dark matter (DM) halos of Sc–Im and dwarf spheroidal (dSph) galaxies satisfy scaling laws: halos in lower-luminosity galaxies have smaller core radii, higher central densities, and smaller velocity dispersions. These results are based on maximum-disk rotation curve decompositions for giant galaxies and Jeans equation analysis for dwarfs. (1) We show that spiral, Im, and Sph galaxies with absolute magnitudes M{sub V} > −18 form a sequence of decreasing baryon-to-DM surface density with decreasing luminosity. We suggest that this is a sequence of decreasing baryon retention versus supernova-driven losses or decreasing baryon capture after cosmological reionization. (2) The structural differences betweenmore » S+Im and Sph galaxies are small. Both are affected mostly by the physics that controls baryon depletion. (3) There is a linear correlation between the maximum rotation velocities of baryonic disks and the outer circular velocities V{sub circ} of test particles in their DM halos. Baryons become unimportant at V{sub circ} = 42 ± 4 km s{sup −1}. Smaller galaxies are dim or dark. (4) We find that, absent baryon “depletion” and with all baryons converted into stars, dSph galaxies would be brighter by ∼4.6 mag and dIm galaxies would be brighter by ∼3.5 mag. Both have DM halos that are massive enough to help to solve the “too big to fail” problem with DM galaxy formation. (5) We suggest that there exist many galaxies that are too dark to be discovered by current techniques, as required by cold DM theory. (6) Central surface densities of DM halos are constant from M{sub B} ∼ −5 to −22. This implies a Faber–Jackson law with halo mass M ∝ (halo dispersion){sup 4}.« less

  3. REVISED MODEL OF THE STEADY-STATE SOLAR WIND HALO ELECTRON VELOCITY DISTRIBUTION FUNCTION

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yoon, Peter H.; Kim, Sunjung; Choe, G. S.

    2016-08-01

    A recent study discussed the steady-state model for solar wind electrons during quiet time conditions. The electrons emanating from the Sun are treated in a composite three-population model—the low-energy Maxwellian core with an energy range of tens of eV, the intermediate ∼10{sup 2}–10{sup 3} eV energy-range (“halo”) electrons, and the high ∼10{sup 3}–10{sup 5} eV energy-range (“super-halo”) electrons. In the model, the intermediate energy halo electrons are assumed to be in resonance with transverse EM fluctuations in the whistler frequency range (∼10{sup 2} Hz), while the high-energy super-halo electrons are presumed to be in steady-state wave–particle resonance with higher-frequency electrostaticmore » fluctuations in the Langmuir frequency range (∼10{sup 5} Hz). A comparison with STEREO and WIND spacecraft data was also made. However, ignoring the influence of Langmuir fluctuations on the halo population turns out to be an unjustifiable assumption. The present paper rectifies the previous approach by including both Langmuir and whistler fluctuations in the construction of the steady-state velocity distribution function for the halo population, and demonstrates that the role of whistler-range fluctuation is minimal unless the fluctuation intensity is arbitrarily raised. This implies that the Langmuir-range fluctuations, known as the quasi thermal noise, are important for both halo and super-halo electron velocity distribution.« less

  4. The dependence of halo mass on galaxy size at fixed stellar mass using weak lensing

    NASA Astrophysics Data System (ADS)

    Charlton, Paul J. L.; Hudson, Michael J.; Balogh, Michael L.; Khatri, Sumeet

    2017-12-01

    Stellar mass has been shown to correlate with halo mass, with non-negligible scatter. The stellar mass-size and luminosity-size relationships of galaxies also show significant scatter in galaxy size at fixed stellar mass. It is possible that, at fixed stellar mass and galaxy colour, the halo mass is correlated with galaxy size. Galaxy-galaxy lensing allows us to measure the mean masses of dark matter haloes for stacked samples of galaxies. We extend the analysis of the galaxies in the CFHTLenS catalogue by fitting single Sérsic surface brightness profiles to the lens galaxies in order to recover half-light radius values, allowing us to determine halo masses for lenses according to their size. Comparing our halo masses and sizes to baselines for that stellar mass yields a differential measurement of the halo mass-galaxy size relationship at fixed stellar mass, defined as Mh(M_{*}) ∝ r_{eff}^{η }(M_{*}). We find that, on average, our lens galaxies have an η = 0.42 ± 0.12, i.e. larger galaxies live in more massive dark matter haloes. The η is strongest for high-mass luminous red galaxies. Investigation of this relationship in hydrodynamical simulations suggests that, at a fixed M*, satellite galaxies have a larger η and greater scatter in the Mh and reff relationship compared to central galaxies.

  5. Models for determining the geometrical properties of halo coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Zhao, X.; Liu, Y.

    2005-12-01

    To this day, the prediction of space weather effects near the Earth suffer from a fundamental problem: the necessary condition for determining whether or not and when a part of the huge interplanetary counterpart (ICME) of frontside halo coronal mass ejections (CMEs) is able to hit the Earth and generate goemagnetic storms, i.e., the real angular width, the propagation direction and speed of the CMEs, cannot be measured directly because of the unfavorable geometry. To inverse these geometrical and kinematical properties we have recently developed a few geometrical models, such as the cone model, the ice cream cone model, and the spherical cone model. The inversing solution of the cone model for the 12 may 1997 halo CME has been used as an input to the ENLIL model (a 3D MHD solar wind code) and successfully predicted the ICME near the Earth (Zhao, Plukett & Liu, 2002; Odstrcil, Riley & Zhao, 2004). After briefly describing the geometrical models this presentation will discuss: 1. What kind of halo CMEs can be inversed? 2. How to select the geometrical models given a specific halo CME? 3. Whether or not the inversing solution is unique?

  6. The upper bound on the lowest mass halo

    NASA Astrophysics Data System (ADS)

    Jethwa, P.; Erkal, D.; Belokurov, V.

    2018-01-01

    We explore the connection between galaxies and dark matter haloes in the Milky Way (MW) and quantify the implications on properties of the dark matter particle and the phenomenology of low-mass galaxy formation. This is done through a probabilistic comparison of the luminosity function of MW dwarf satellite galaxies to models based on two suites of zoom-in simulations. One suite is dark-matter-only, while the other includes a disc component, therefore we can quantify the effect of the MW's baryonic disc on our results. We apply numerous stellar-mass-halo-mass (SMHM) relations allowing for multiple complexities: scatter, a characteristic break scale, and subhaloes which host no galaxy. In contrast to previous works, we push the model/data comparison to the faintest dwarfs by modelling observational incompleteness, allowing us to draw three new conclusions. First, we constrain the SMHM relation for 102 < M*/ M⊙ < 108 galaxies, allowing us to bound the peak halo mass of the faintest MW satellite to Mvir > 2.4 × 108 M⊙ (1σ). Secondly, by translating to a warm dark matter (WDM) cosmology, we bound the thermal relic mass mWDM > 2.9 keV at 95 per cent confidence, on a par with recent constraints from the Lyman-α forest. Lastly, we find that the observed number of ultra-faint MW dwarfs is in tension with the theoretical prediction that reionization prevents galaxy formation in almost all 108 M⊙ haloes. This can be tested with the next generation of deep imaging surveys. To this end, we predict the likely number of detectable satellite galaxies in the Subaru/Hyper Suprime-Cam survey and the Large Synoptic Survey Telescope. Confronting these predictions with future observations will be amongst our strongest tests of WDM and the effect reionization on low-mass systems.

  7. Implementation of a 3D halo neutral model in the TRANSP code and application to projected NSTX-U plasmas

    NASA Astrophysics Data System (ADS)

    Medley, S. S.; Liu, D.; Gorelenkova, M. V.; Heidbrink, W. W.; Stagner, L.

    2016-02-01

    A 3D halo neutral code developed at the Princeton Plasma Physics Laboratory and implemented for analysis using the TRANSP code is applied to projected National Spherical Torus eXperiment-Upgrade (NSTX-U plasmas). The legacy TRANSP code did not handle halo neutrals properly since they were distributed over the plasma volume rather than remaining in the vicinity of the neutral beam footprint as is actually the case. The 3D halo neutral code uses a ‘beam-in-a-box’ model that encompasses both injected beam neutrals and resulting halo neutrals. Upon deposition by charge exchange, a subset of the full, one-half and one-third beam energy components produce first generation halo neutrals that are tracked through successive generations until an ionization event occurs or the descendant halos exit the box. The 3D halo neutral model and neutral particle analyzer (NPA) simulator in the TRANSP code have been benchmarked with the Fast-Ion D-Alpha simulation (FIDAsim) code, which provides Monte Carlo simulations of beam neutral injection, attenuation, halo generation, halo spatial diffusion, and photoemission processes. When using the same atomic physics database, TRANSP and FIDAsim simulations achieve excellent agreement on the spatial profile and magnitude of beam and halo neutral densities and the NPA energy spectrum. The simulations show that the halo neutral density can be comparable to the beam neutral density. These halo neutrals can double the NPA flux, but they have minor effects on the NPA energy spectrum shape. The TRANSP and FIDAsim simulations also suggest that the magnitudes of beam and halo neutral densities are relatively sensitive to the choice of the atomic physics databases.

  8. Implementation of a 3D halo neutral model in the TRANSP code and application to projected NSTX-U plasmas

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Medley, S. S.; Liu, D.; Gorelenkova, M. V.

    2016-01-12

    A 3D halo neutral code developed at the Princeton Plasma Physics Laboratory and implemented for analysis using the TRANSP code is applied to projected National Spherical Torus eXperiment-Upgrade (NSTX-U plasmas). The legacy TRANSP code did not handle halo neutrals properly since they were distributed over the plasma volume rather than remaining in the vicinity of the neutral beam footprint as is actually the case. The 3D halo neutral code uses a 'beam-in-a-box' model that encompasses both injected beam neutrals and resulting halo neutrals. Upon deposition by charge exchange, a subset of the full, one-half and one-third beam energy components producemore » first generation halo neutrals that are tracked through successive generations until an ionization event occurs or the descendant halos exit the box. The 3D halo neutral model and neutral particle analyzer (NPA) simulator in the TRANSP code have been benchmarked with the Fast-Ion D-Alpha simulation (FIDAsim) code, which provides Monte Carlo simulations of beam neutral injection, attenuation, halo generation, halo spatial diffusion, and photoemission processes. When using the same atomic physics database, TRANSP and FIDAsim simulations achieve excellent agreement on the spatial profile and magnitude of beam and halo neutral densities and the NPA energy spectrum. The simulations show that the halo neutral density can be comparable to the beam neutral density. These halo neutrals can double the NPA flux, but they have minor effects on the NPA energy spectrum shape. The TRANSP and FIDAsim simulations also suggest that the magnitudes of beam and halo neutral densities are relatively sensitive to the choice of the atomic physics databases.« less

  9. What is occupational therapy’s role in addressing sleep problems among older adults?

    PubMed Central

    Leland, Natalie E.; Marcione, Nicole; Niemiec, Stacey L. Schepens; Don Fogelberg, Kaivalya Kelkar

    2014-01-01

    Sleep problems, prevalent among older adults, are associated with poor outcomes and high healthcare costs. In 2008, rest and sleep became its own area of occupation in the AOTA Occupational Therapy Practice Framework. This scoping review examined a broad context of sleep research in order to highlight efficacious interventions for older adults that fall within the occupational therapy scope of practice and present an agenda for research and practice. Four sleep intervention areas clearly aligned with the Practice Framework, including cognitive behavioral therapy for insomnia, physical activity, and multi-component interventions. Occupational therapy is primed to address sleep problems by targeting the context and environment, performance patterns, and limited engagement in evening activities that may contribute to poor sleep. Occupational therapy researchers and clinicians need to work collaboratively to establish the evidence-base for occupation-centered sleep interventions in order to improve the health and quality of life of the older adult. PMID:24844879

  10. Reduction of halo pin site morbidity with a new pin care regimen.

    PubMed

    Kazi, Hussain Anthony; de Matas, Marcus; Pillay, Robin

    2013-06-01

    A retrospective analysis of halo device associated morbidity over a 4-year period. To assess the impact of a new pin care regimen on halo pin site related morbidity. Halo orthosis treatment still has a role in cervical spine pathology, despite increasing possibilities of open surgical treatment. Published figures for pin site infection range from 12% to 22% with pin loosening from 7% to 50%. We assessed the outcome of a new pin care regimen on morbidity associated with halo spinal orthoses, using a retrospective cohort study from 2001 to 2004. In the last two years, our pin care regimen was changed. This involved pin site care using chlorhexidene & regular torque checking as part of a standard protocol. Previously, povidone iodine was used as skin preparation in theatre, followed by regular sterile saline cleansing when pin sites became encrusted with blood. There were 37 patients in the series, the median age was 49 (range, 22-83) and 20 patients were male. The overall infection rate prior to the new pin care protocol was 30% (n=6) and after the introduction, it dropped to 5.9% (n=1). This difference was statistically significant (p<0.05). Pin loosening occurred in one patient in the group prior to the formal pin care protocol (3%) and none thereafter. Reduced morbidity from halo use can be achieved with a modified pin cleansing and tightening regimen.

  11. Life in the Outer Limits: Insight into Hierarchical Merging from the Outermost Structure of the Andromeda Stellar Halo

    NASA Astrophysics Data System (ADS)

    Beaton, Rachael; Majewski, S. R.; Patterson, R. J.; Guhathakurta, P.; Gilbert, K.; Kalirai, J. S.; Tollerud, E. J.; SPLASH Team

    2014-01-01

    Owing to their large dynamical timescales, the stellar haloes of Milky Way (MW) sized galaxies represent ideal environments to test modern theories of galaxy formation in the Lambda-CDM paradigm. Only in stellar haloes can the remnants of hierarchical accretion be preserved over long timescales as in-tact dwarf satellites or as tidal debris and can be easily distinguished from the underlying smooth structure. Stellar haloes, however, remain some of the most difficult galactic structures to constrain due to their large angular extent and extremely low surface brightness. Thus, the basic properties of stellar haloes -- the overall stellar distribution, substructure fraction, global kinematics and detailed stellar content -- remained relatively unconstrained. In this thesis, we present several projects designed to understand the current structure and the the formation of the Andromeda (M31) stellar halo, the only stellar halo -- besides our own -- that is within reach of current ground based facilities on the large scale required to constrain the basic properties of stellar haloes. First, we describe a seven season imaging campaign comprising the backbone of the Spectroscopic and Photometric Landscape of the Andromeda Stellar Halo (SPLASH) program. This survey is unique in its application of the Washington + DDO51 filter system to select individual M31 RGB stars without spectroscopic follow up. Second, we use the SPLASH photometric survey to identify sample of halo stars at projected radii of 120 kpc, for which we have obtained spectroscopic follow-up. Third, we add this large radius sample to the existing spectroscopic results from SPLASH, and use this unique sample to explore the stellar kinematics of the halo at large radii with full azimuthal coverage. Lastly, we preview on-going work to constrain the formation of the Andromeda stellar halo, using both in-tact satellites and resolved M31 halo members as tracers of its accretion history.

  12. 10 AU scale halo structure around DG Tauri

    NASA Technical Reports Server (NTRS)

    Chen, Wen P.; Howell, R. R.; Simon, M.; Benson, J. A.

    1992-01-01

    Lunar occultation observations of the active T Tauri star DG Tau show that in the infrared K band it has a core-halo structure: 20-25 percent of the flux comes from a region 10 AU in extent and the rest from an unresolved core smaller than an AU. These results are consistent with those reported by Leinert et al. from a separate observation. The results obtained here and those of Leinert et al., measuring the intensity distribution projected along directions spanning roughly 40 deg, indicate that the resolved structure is not highly elongated. The extended emission is interpreted as star light scattered by optically thin dust located in a halo surrounding the star.

  13. Framework for Considering Productive Aging and Work.

    PubMed

    Schulte, Paul A; Grosch, James; Scholl, Juliann C; Tamers, Sara L

    2018-05-01

    The U.S. population is experiencing a demographic transition resulting in an aging workforce. The objective of this article is to elucidate and expand an approach to keep that workforce safe, healthy, and productive. This article elucidates the framework for the National Center for Productive Aging at Work of the National Institute for Occupational Safety and Health. Subject matter experts used a snowball method to review published literature to substantiate elements in the framework. Evidence-based literature supports a productive aging framework for the workforce involving the following elements: 1) life span perspective; 2) comprehensive and integrated approaches to occupational safety and health; 3) emphasis on positive outcomes for both workers and organizations; and 4) supportive work culture for multigenerational issues. The productive aging framework provides a foundational and comprehensive approach for addressing the aging workforce.

  14. Towards accurate modelling of galaxy clustering on small scales: testing the standard ΛCDM + halo model

    NASA Astrophysics Data System (ADS)

    Sinha, Manodeep; Berlind, Andreas A.; McBride, Cameron K.; Scoccimarro, Roman; Piscionere, Jennifer A.; Wibking, Benjamin D.

    2018-07-01

    Interpreting the small-scale clustering of galaxies with halo models can elucidate the connection between galaxies and dark matter haloes. Unfortunately, the modelling is typically not sufficiently accurate for ruling out models statistically. It is thus difficult to use the information encoded in small scales to test cosmological models or probe subtle features of the galaxy-halo connection. In this paper, we attempt to push halo modelling into the `accurate' regime with a fully numerical mock-based methodology and careful treatment of statistical and systematic errors. With our forward-modelling approach, we can incorporate clustering statistics beyond the traditional two-point statistics. We use this modelling methodology to test the standard Λ cold dark matter (ΛCDM) + halo model against the clustering of Sloan Digital Sky Survey (SDSS) seventh data release (DR7) galaxies. Specifically, we use the projected correlation function, group multiplicity function, and galaxy number density as constraints. We find that while the model fits each statistic separately, it struggles to fit them simultaneously. Adding group statistics leads to a more stringent test of the model and significantly tighter constraints on model parameters. We explore the impact of varying the adopted halo definition and cosmological model and find that changing the cosmology makes a significant difference. The most successful model we tried (Planck cosmology with Mvir haloes) matches the clustering of low-luminosity galaxies, but exhibits a 2.3σ tension with the clustering of luminous galaxies, thus providing evidence that the `standard' halo model needs to be extended. This work opens the door to adding interesting freedom to the halo model and including additional clustering statistics as constraints.

  15. A New Determination of the Luminosity Function of the Galactic Halo.

    NASA Astrophysics Data System (ADS)

    Dawson, Peter Charles

    The luminosity function of the galactic halo is determined by subtracting from the observed numbers of proper motion stars in the LHS Catalogue the expected numbers of main-sequence, degenerate, and giant stars of the disk population. Selection effects are accounted for by Monte Carlo simulations based upon realistic colour-luminosity relations and kinematic models. The catalogue is shown to be highly complete, and a calibration of the magnitude estimates therein is presented. It is found that, locally, the ratio of disk to halo material is close to 950, and that the mass density in main sequence and subgiant halo stars with 3 < M(,v) < 14 is about 2 x 10('-5) M(,o) pc('-3). With due allowance for white dwarfs and binaries, and taking into account the possibility of a moderate rate of halo rotation, it is argued that the total density does not much exceed 5 x 10('-5) M(,o) pc('-3), in which case the total mass interior to the sun is of the order of 5 x 10('8) M(,o) for a density distribution which projects to a de Vaucouleurs r(' 1/4) law. It is demonstrated that if the Wielen luminosity function is a faithful representation of the stellar distribution in the solar neighbourhood, then the observed numbers of large proper motion stars are inconsistent with the presence of an intermediate popula- tion at the level, and with the kinematics advocated recently by Gilmore and Reid. The initial mass function (IMF) of the halo is considered, and weak evidence is presented that its slope is at least not shallower than that of the disk population IMF. A crude estimate of the halo's age, based on a comparison of the main sequence turnoff in the reduced proper motion diagram with theoretical models is obtained; a tentative lower limit is 15 Gyr with a best estimate of between 15 and 18 Gyr. Finally, the luminosity function obtained here is compared with those determined in other investigations.

  16. Benchmark of 3D halo neutral simulation in TRANSP and FIDASIM and application to projected neutral-beam-heated NSTX-U plasmas

    NASA Astrophysics Data System (ADS)

    Liu, D.; Medley, S. S.; Gorelenkova, M. V.; Heidbrink, W. W.; Stagner, L.

    2014-10-01

    A cloud of halo neutrals is created in the vicinity of beam footprint during the neutral beam injection and the halo neutral density can be comparable with beam neutral density. Proper modeling of halo neutrals is critical to correctly interpret neutral particle analyzers (NPA) and fast ion D-alpha (FIDA) signals since these signals strongly depend on local beam and halo neutral density. A 3D halo neutral model has been recently developed and implemented inside TRANSP code. The 3D halo neutral code uses a ``beam-in-a-box'' model that encompasses both injected beam neutrals and resulting halo neutrals. Upon deposition by charge exchange, a subset of the full, one-half and one-third beam energy components produce thermal halo neutrals that are tracked through successive halo neutral generations until an ionization event occurs or a descendant halo exits the box. A benchmark between 3D halo neural model in TRANSP and in FIDA/NPA synthetic diagnostic code FIDASIM is carried out. Detailed comparison of halo neutral density profiles from two codes will be shown. The NPA and FIDA simulations with and without 3D halos are applied to projections of plasma performance for the National Spherical Tours eXperiment-Upgrade (NSTX-U) and the effects of halo neutral density on NPA and FIDA signal amplitude and profile will be presented. Work supported by US DOE.

  17. VizieR Online Data Catalog: The SEGUE K giant survey. III. Galactic halo (Janesh+, 2016)

    NASA Astrophysics Data System (ADS)

    Janesh, W.; Morrison, H. L.; Ma, Z.; Rockosi, C.; Starkenburg, E.; Xue, X. X.; Rix, H.-W.; Harding, P.; Beers, T. C.; Johnson, J.; Lee, Y. S.; Schneider, D. P.

    2016-03-01

    We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5-125kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey's Sloan Extension for Galactic Understanding and Exploration (SEGUE) project. Using a position-velocity clustering estimator (the 4distance) and a model of a smooth stellar halo, we quantify the amount of substructure in the halo, divided by distance and metallicity. Overall, we find that the halo as a whole is highly structured. We also confirm earlier work using blue horizontal branch (BHB) stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius, and additionally find that the amount of substructure in the halo increases with increasing metallicity. Comparing to resampled BHB stars, we find that K giants and BHBs have similar amounts of substructure over equivalent ranges of Galactocentric radius. Using a friends-of-friends algorithm to identify members of individual groups, we find that a large fraction (~33%) of grouped stars are associated with Sgr, and identify stars belonging to other halo star streams: the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. A large fraction of sample K giants (more than 50%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity. (2 data files).

  18. An accurate halo model for fitting non-linear cosmological power spectra and baryonic feedback models

    NASA Astrophysics Data System (ADS)

    Mead, A. J.; Peacock, J. A.; Heymans, C.; Joudaki, S.; Heavens, A. F.

    2015-12-01

    We present an optimized variant of the halo model, designed to produce accurate matter power spectra well into the non-linear regime for a wide range of cosmological models. To do this, we introduce physically motivated free parameters into the halo-model formalism and fit these to data from high-resolution N-body simulations. For a variety of Λ cold dark matter (ΛCDM) and wCDM models, the halo-model power is accurate to ≃ 5 per cent for k ≤ 10h Mpc-1 and z ≤ 2. An advantage of our new halo model is that it can be adapted to account for the effects of baryonic feedback on the power spectrum. We demonstrate this by fitting the halo model to power spectra from the OWLS (OverWhelmingly Large Simulations) hydrodynamical simulation suite via parameters that govern halo internal structure. We are able to fit all feedback models investigated at the 5 per cent level using only two free parameters, and we place limits on the range of these halo parameters for feedback models investigated by the OWLS simulations. Accurate predictions to high k are vital for weak-lensing surveys, and these halo parameters could be considered nuisance parameters to marginalize over in future analyses to mitigate uncertainty regarding the details of feedback. Finally, we investigate how lensing observables predicted by our model compare to those from simulations and from HALOFIT for a range of k-cuts and feedback models and quantify the angular scales at which these effects become important. Code to calculate power spectra from the model presented in this paper can be found at https://github.com/alexander-mead/hmcode.

  19. Modelling giant radio halos. Doctoral Thesis Award Lecture 2012

    NASA Astrophysics Data System (ADS)

    Donnert, J. M. F.

    2013-06-01

    We review models for giant radio halos in clusters of galaxies, with a focus on numerical and theoretical work. After summarising the most important observations of these objects, we present an introduction to the theoretical aspects of hadronic models. We compare these models with observations using simulations and find severe problems for hadronic models. We give a short introduction to reacceleration models and show results from the first simulation of CRe reacceleration in cluster mergers. We find that in-line with previous theoretical work, reacceleration models are able to elegantly explain main observables of giant radio halos.

  20. Techniques for the measurement of disruption halo currents in the National Spherical Torus Experiment.

    PubMed

    Gerhardt, S P; Fredrickson, E; Guttadora, L; Kaita, R; Kugel, H; Menard, J; Takahashi, H

    2011-10-01

    This paper describes techniques for measuring halo currents, and their associated toroidal peaking, in the National Spherical Torus Experiments [M. Ono et al., Nucl. Fusion 40, 557 (2000)]. The measurements are based on three techniques: (1) measurement of the toroidal field created by the poloidal halo current, either with segmented Rogowski coils or discrete toroidal field sensors, (2) the direct measurement of halo currents into specially instrument tiles, and (3) small Rogowski coils placed on the mechanical supports of in-vessel components. For the segmented Rogowski coils and discrete toroidal field detectors, it is shown that the toroidal peaking factor inferred from the data is significantly less than the peaking factor of the underlying halo current distribution, and a simple model is developed to relate the two. For the array of discrete toroidal field detectors and small Rogowski sensors, the compensation steps that are used to isolate the halo current signal are described. The electrical and mechanical design of compact under-tile resistive shunts and mini-Rogowski coils is described. Example data from the various systems are shown.

  1. Using tidal streams to investigate the rotation of the Milky Way's dark matter halo

    NASA Astrophysics Data System (ADS)

    Valluri, Monica; Snyder, Sarah Jean; Price-Whelan, Adrian M.

    2017-06-01

    The dark matter halos surrounding Milky Way-like galaxies that are formed in cosmological simulations are triaxial. These simulated triaxial halos are expected to be slowly rotating with log-normal distribution of pattern speeds centered on ~0.148h km/s/kpc (Bailin & Steinmetz 2004, ApJ., 616, 27). Stellar streams arising from a satellite experiencing tidal disruption inside such a slowly rotating triaxial halo are expected to be subject to additional forces (e.g. Coriolis forces) that affect the structure of the tidal streams. Using the Python Galaxy dynamics package Gala (Price-Whelan, http://gala.adrian.pw) we have generated simulations of tidal streams in a range of triaxial potentials to explore how the structure of Milky Way's tidal streams, especially the structure of stream bifurcations and the stream orbital plane, are altered by a slow figure rotation of the triaxial dark matter halo. We investigate what can be inferred about halo rotation from current and future data including upcoming data from Gaia. This work is supported by NASA-ATP award NNX15AK79G to the University of Michigan.

  2. Double gate graphene nanoribbon field effect transistor with single halo pocket in channel region

    NASA Astrophysics Data System (ADS)

    Naderi, Ali

    2016-01-01

    A new structure for graphene nanoribbon field-effect transistors (GNRFETs) is proposed and investigated using quantum simulation with a nonequilibrium Green's function (NEGF) method. Tunneling leakage current and ambipolar conduction are known effects for MOSFET-like GNRFETs. To minimize these issues a novel structure with a simple change of the GNRFETs by using single halo pocket in the intrinsic channel region, "Single Halo GNRFET (SH-GNRFET)", is proposed. An appropriate halo pocket at source side of channel is used to modify potential distribution of the gate region and weaken band to band tunneling (BTBT). In devices with materials like Si in channel region, doping type of halo and source/drain regions are different. But, here, due to the smaller bandgap of graphene, the mentioned doping types should be the same to reduce BTBT. Simulations have shown that in comparison with conventional GNRFET (C-GNRFET), an SH-GNRFET with appropriately halo doping results in a larger ON current (Ion), smaller OFF current (Ioff), a larger ON-OFF current ratio (Ion/Ioff), superior ambipolar characteristics, a reduced power-delay product and lower delay time.

  3. Techniques for the measurement of disruption halo currents in the National Spherical Torus Experiment

    DOE PAGES

    Gerhardt, S. P.; Fredrickson, E.; Guttadora, L.; ...

    2011-10-06

    This paper describes techniques for measuring halo currents, and their associated toroidal peaking, in the National Spherical Torus Experiments. The measurements are based on three techniques: (i) measurement of the toroidal field created by the poloidal halo current, either with segmented Rogowski coils or discrete toroidal field sensors, (ii) the direct measurement of halo currents into specially instrument tiles, and (iii) small Rogowski coils placed on the mechanical supports of in-vessel components. For the segmented Rogowski coils and discrete toroidal field detectors, it is shown that the toroidal peaking factor inferred from the data is significantly less than the peakingmore » factor of the underlying halo current distribution, and a simple model is developed to relate the two. For the array of discrete toroidal field detectors and small Rogowski sensors, the compensation steps that are used to isolate the halo current signal are described. The electrical and mechanical design of compact under-tile resistive shunts and mini-Rogowski coils is described. Example data from the various systems is shown.« less

  4. A COMPREHENSIVE ANALYSIS OF UNCERTAINTIES AFFECTING THE STELLAR MASS-HALO MASS RELATION FOR 0 < z < 4

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Behroozi, Peter S.; Wechsler, Risa H.; Conroy, Charlie

    2010-07-01

    We conduct a comprehensive analysis of the relationship between central galaxies and their host dark matter halos, as characterized by the stellar mass-halo mass (SM-HM) relation, with rigorous consideration of uncertainties. Our analysis focuses on results from the abundance matching technique, which assumes that every dark matter halo or subhalo above a specific mass threshold hosts one galaxy. We provide a robust estimate of the SM-HM relation for 0 < z < 1 and discuss the quantitative effects of uncertainties in observed galaxy stellar mass functions (including stellar mass estimates and counting uncertainties), halo mass functions (including cosmology and uncertaintiesmore » from substructure), and the abundance matching technique used to link galaxies to halos (including scatter in this connection). Our analysis results in a robust estimate of the SM-HM relation and its evolution from z = 0 to z = 4. The shape and the evolution are well constrained for z < 1. The largest uncertainties at these redshifts are due to stellar mass estimates (0.25 dex uncertainty in normalization); however, failure to account for scatter in stellar masses at fixed halo mass can lead to errors of similar magnitude in the SM-HM relation for central galaxies in massive halos. We also investigate the SM-HM relation to z = 4, although the shape of the relation at higher redshifts remains fairly unconstrained when uncertainties are taken into account. We find that the integrated star formation at a given halo mass peaks at 10%-20% of available baryons for all redshifts from 0 to 4. This peak occurs at a halo mass of 7 x 10{sup 11} M{sub sun} at z = 0 and this mass increases by a factor of 5 to z = 4. At lower and higher masses, star formation is substantially less efficient, with stellar mass scaling as M{sub *} {approx} M {sup 2.3}{sub h} at low masses and M{sub *} {approx} M {sup 0.29}{sub h} at high masses. The typical stellar mass for halos with mass less than 10{sup 12} M{sub sun

  5. Distribution and Characteristics of Boulder Halos at High Latitudes on Mars: Ground Ice and Surface Processes Drive Surface Reworking

    NASA Astrophysics Data System (ADS)

    Levy, J. S.; Fassett, C. I.; Rader, L. X.; King, I. R.; Chaffey, P. M.; Wagoner, C. M.; Hanlon, A. E.; Watters, J. L.; Kreslavsky, M. A.; Holt, J. W.; Russell, A. T.; Dyar, M. D.

    2018-02-01

    Boulder halos are circular arrangements of clasts present at Martian middle to high latitudes. Boulder halos are thought to result from impacts into a boulder-poor surficial unit that is rich in ground ice and/or sediments and that is underlain by a competent substrate. In this model, boulders are excavated by impacts and remain at the surface as the crater degrades. To determine the distribution of boulder halos and to evaluate mechanisms for their formation, we searched for boulder halos over 4,188 High Resolution Imaging Science Experiment images located between 50-80° north and 50-80° south latitude. We evaluate geological and climatological parameters at halo sites. Boulder halos are about three times more common in the northern hemisphere than in the southern hemisphere (19% versus 6% of images) and have size-frequency distributions suggesting recent Amazonian formation (tens to hundreds of millions of years). In the north, boulder halo sites are characterized by abundant shallow subsurface ice and high thermal inertia. Spatial patterns of halo distribution indicate that excavation of boulders from beneath nonboulder-bearing substrates is necessary for the formation of boulder halos, but that alone is not sufficient. Rather, surface processes either promote boulder halo preservation in the north or destroy boulder halos in the south. Notably, boulder halos predate the most recent period of near-surface ice emplacement on Mars and persist at the surface atop mobile regolith. The lifetime of observed boulders at the Martian surface is greater than the lifetime of the craters that excavated them. Finally, larger minimum boulder halo sizes in the north indicate thicker icy soil layers on average throughout climate variations driven by spin/orbit changes during the last tens to hundreds of millions of years.

  6. Chameleon halo modeling in f(R) gravity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li Yin; Department of Physics, University of Chicago, Chicago Illinois 60637; Hu, Wayne

    2011-10-15

    We model the chameleon effect on cosmological statistics for the modified gravity f(R) model of cosmic acceleration. The chameleon effect, required to make the model compatible with local tests of gravity, reduces force enhancement as a function of the depth of the gravitational potential wells of collapsed structure and so is readily incorporated into a halo model by including parameters for the chameleon mass threshold and rapidity of transition. We show that the abundance of halos around the chameleon mass threshold is enhanced by both the merging from below and the lack of merging to larger masses. This property alsomore » controls the power spectrum in the nonlinear regime and we provide a description of the transition to the linear regime that is valid for a wide range of f(R) models.« less

  7. FASTPM: a new scheme for fast simulations of dark matter and haloes

    NASA Astrophysics Data System (ADS)

    Feng, Yu; Chu, Man-Yat; Seljak, Uroš; McDonald, Patrick

    2016-12-01

    We introduce FASTPM, a highly scalable approximated particle mesh (PM) N-body solver, which implements the PM scheme enforcing correct linear displacement (1LPT) evolution via modified kick and drift factors. Employing a two-dimensional domain decomposing scheme, FASTPM scales extremely well with a very large number of CPUs. In contrast to Comoving-Lagrangian (COLA) approach, we do not require to split the force or track separately the 2LPT solution, reducing the code complexity and memory requirements. We compare FASTPM with different number of steps (Ns) and force resolution factor (B) against three benchmarks: halo mass function from friends-of-friends halo finder; halo and dark matter power spectrum; and cross-correlation coefficient (or stochasticity), relative to a high-resolution TREEPM simulation. We show that the modified time stepping scheme reduces the halo stochasticity when compared to COLA with the same number of steps and force resolution. While increasing Ns and B improves the transfer function and cross-correlation coefficient, for many applications FASTPM achieves sufficient accuracy at low Ns and B. For example, Ns = 10 and B = 2 simulation provides a substantial saving (a factor of 10) of computing time relative to Ns = 40, B = 3 simulation, yet the halo benchmarks are very similar at z = 0. We find that for abundance matched haloes the stochasticity remains low even for Ns = 5. FASTPM compares well against less expensive schemes, being only 7 (4) times more expensive than 2LPT initial condition generator for Ns = 10 (Ns = 5). Some of the applications where FASTPM can be useful are generating a large number of mocks, producing non-linear statistics where one varies a large number of nuisance or cosmological parameters, or serving as part of an initial conditions solver.

  8. Halo Profiles and the Concentration–Mass Relation for a ΛCDM Universe

    NASA Astrophysics Data System (ADS)

    Child, Hillary L.; Habib, Salman; Heitmann, Katrin; Frontiere, Nicholas; Finkel, Hal; Pope, Adrian; Morozov, Vitali

    2018-05-01

    Profiles of dark matter-dominated halos at the group and cluster scales play an important role in modern cosmology. Using results from two very large cosmological N-body simulations, which increase the available volume at their mass resolution by roughly two orders of magnitude, we robustly determine the halo concentration–mass (c‑M) relation over a wide range of masses, employing multiple methods of concentration measurement. We characterize individual halo profiles, as well as stacked profiles, relevant for galaxy–galaxy lensing and next-generation cluster surveys; the redshift range covered is 0 ≤ z ≤ 4, with a minimum halo mass of M 200c ∼ 2 × 1011 M ⊙. Despite the complexity of a proper description of a halo (environmental effects, merger history, nonsphericity, relaxation state), when the mass is scaled by the nonlinear mass scale M ⋆(z), we find that a simple non-power-law form for the c–M/M ⋆ relation provides an excellent description of our simulation results across eight decades in M/M ⋆ and for 0 ≤ z ≤ 4. Over the mass range covered, the c–M relation has two asymptotic forms: an approximate power law below a mass threshold M/M ⋆ ∼ 500–1000, transitioning to a constant value, c 0 ∼ 3 at higher masses. The relaxed halo fraction decreases with mass, transitioning to a constant value of ∼0.5 above the same mass threshold. We compare Navarro–Frenk–White (NFW) and Einasto fits to stacked profiles in narrow mass bins at different redshifts; as expected, the Einasto profile provides a better description of the simulation results. At cluster scales at low redshift, however, both NFW and Einasto profiles are in very good agreement with the simulation results, consistent with recent weak lensing observations.

  9. What to expect from dynamical modelling of galactic haloes - II. The spherical Jeans equation

    NASA Astrophysics Data System (ADS)

    Wang, Wenting; Han, Jiaxin; Cole, Shaun; More, Surhud; Frenk, Carlos; Schaller, Matthieu

    2018-06-01

    The spherical Jeans equation (SJE) is widely used in dynamical modelling of the Milky Way (MW) halo potential. We use haloes and galaxies from the cosmological Millennium-II simulation and hydrodynamical APOSTLE (A Project of Simulations of The Local Environment) simulations to investigate the performance of the SJE in recovering the underlying mass profiles of MW mass haloes. The best-fitting halo mass and concentration parameters scatter by 25 per cent and 40 per cent around their input values, respectively, when dark matter particles are used as tracers. This scatter becomes as large as a factor of 3 when using star particles instead. This is significantly larger than the estimated statistical uncertainty associated with the use of the SJE. The existence of correlated phase-space structures that violate the steady-state assumption of the SJE as well as non-spherical geometries is the principal source of the scatter. Binary haloes show larger scatter because they are more aspherical in shape and have a more perturbed dynamical state. Our results confirm that the number of independent phase-space structures sets an intrinsic limiting precision on dynamical inferences based on the steady-state assumption. Modelling with a radius-independent velocity anisotropy, or using tracers within a limited outer radius, result in significantly larger scatter, but the ensemble-averaged measurement over the whole halo sample is approximately unbiased.

  10. Evolution and statistics of non-sphericity of dark matter halos from cosmological N-body simulation

    NASA Astrophysics Data System (ADS)

    Suto, Daichi; Kitayama, Tetsu; Nishimichi, Takahiro; Sasaki, Shin; Suto, Yasushi

    2016-12-01

    We revisit the non-sphericity of cluster-mass-scale halos from cosmological N-body simulation on the basis of triaxial modeling. In order to understand the difference between the simulation results and the conventional ellipsoidal collapse model (EC), we first consider the evolution of individual simulated halos. The major difference between EC and the simulation becomes appreciable after the turnaround epoch. Moreover, it is sensitive to the individual evolution history of each halo. Despite such strong dependence on individual halos, the resulting non-sphericity of halos exhibits weak but robust mass dependence in a statistical fashion; massive halos are more spherical up to the turnaround, but gradually become less spherical by z = 0. This is clearly inconsistent with the EC prediction: massive halos are usually more spherical. In addition, at z = 0, inner regions of the simulated halos are less spherical than outer regions; that is, the density distribution inside the halos is highly inhomogeneous and therefore not self-similar (concentric ellipsoids with the same axis ratio and orientation). This is also inconsistent with the homogeneous density distribution that is commonly assumed in EC. Since most of previous fitting formulae for the probability distribution function (PDF) of the axis ratio of triaxial ellipsoids have been constructed under the self-similarity assumption, they are not accurate. Indeed, we compute the PDF of the projected axis ratio a1/a2 directly from the simulation data without the self-similarity assumption, and find that it is very sensitive to the assumption. The latter needs to be carefully taken into account in direct comparison with observations, and therefore we provide an empirical fitting formula for the PDF of a1/a2. Our preliminary analysis suggests that the derived PDF of a1/a2 roughly agrees with the current weak-lensing observations. More importantly, the present results will be useful for future exploration of the non

  11. Precision measurement of the local bias of dark matter halos

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lazeyras, Titouan; Wagner, Christian; Schmidt, Fabian

    2016-02-01

    We present accurate measurements of the linear, quadratic, and cubic local bias of dark matter halos, using curved 'separate universe' N-body simulations which effectively incorporate an infinite-wavelength overdensity. This can be seen as an exact implementation of the peak-background split argument. We compare the results with the linear and quadratic bias measured from the halo-matter power spectrum and bispectrum, and find good agreement. On the other hand, the standard peak-background split applied to the Sheth and Tormen (1999) and Tinker et al. (2008) halo mass functions matches the measured linear bias parameter only at the level of 10%. The predictionmore » from the excursion set-peaks approach performs much better, which can be attributed to the stochastic moving barrier employed in the excursion set-peaks prediction. We also provide convenient fitting formulas for the nonlinear bias parameters b{sub 2}(b{sub 1}) and b{sub 3}(b{sub 1}), which work well over a range of redshifts.« less

  12. Current halo structures in high-current plasma experiments: θ-pinch

    NASA Astrophysics Data System (ADS)

    Matveev, Yu. V.

    2007-03-01

    Experimental data elucidating mechanisms for halo formation in θ-pinch discharges are presented and discussed. The experiments were performed with different gases (H2, D2, He, and Ar) in a theta-pinch device with a porcelain vacuum chamber and an excitation coil 15 cm in diameter and 30 cm in length. The stored energy, the current in the excitation coil, and the current half-period were W = 10 kJ, I = 400 kA, and T/2 = 14 μs, respectively. It is found that the plasma rings (halos) surrounding the pinch core arise as a result of coaxial pinch stratification due to both the excitation of closed currents (inductons) inside the pinch and the radial convergence of the plasma current sheaths produced after the explosion of T-layers formed near the wall in the initial stage of the discharge. It is concluded that halo structures observed in pinches, tokamaks, and other high-current devices used in controlled fusion research have the same nature.

  13. Distribution and Kinematics of O VI in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Savage, B. D.; Sembach, K. R.; Wakker, B. P.; Richter, P.; Meade, M.; Jenkins, E. B.; Shull, J. M.; Moos, H. W.; Sonneborn, G.

    2003-05-01

    Far-Ultraviolet Spectroscopic Explorer (FUSE) spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI λλ1031.93, 1037.62 absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the velocity range from -100 to 100 km s-1 reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T~3×105 K in the Milky Way thick disk/halo. The integrated column density, log[N(O VI) cm-2], ranges from 13.85 to 14.78 with an average value of 14.38 and a standard deviation of 0.18. Large irregularities in the gas distribution are found to be similar over angular scales extending from <1° to 180°, implying a considerable amount of small- and large-scale structure in the absorbing gas. The overall distribution of O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with an average O VI midplane density of n0(O VI)=1.7×10-8 cm-3, a scale height of ~2.3 kpc, and a ~0.25 dex excess of O VI in the northern Galactic polar region. The distribution of O VI over the sky is poorly correlated with other tracers of gas in the halo, including low- and intermediate-velocity H I, Hα emission from the warm ionized gas at ~104 K, and hot X-ray-emitting gas at ~106 K. The O VI has an average velocity dispersion, b~60 km s-1, and standard deviation of 15 km s-1. Thermal broadening alone cannot explain the large observed profile widths. The average O VI absorption velocities toward high-latitude objects (|b|>45deg) range from -46 to 82 km s-1, with a high-latitude sample average of 0 km s-1 and a standard deviation of 21 km s-1. High positive velocity O VI absorbing wings extending from ~100 to ~250 km s-1 observed along 21 lines of sight may be tracing the flow of O VI into the halo

  14. [Application of Halo-vest head ring in replantation of total scalp avulsion].

    PubMed

    Jian, Lin; Lizhi, Wu; Yuhua, Guo; Tianhao, Zhang; Shilin, Gu; Cheng, Wang; Zhongyi, Chen; Haixiao, Chen

    2015-11-01

    To investigate the clinical effect of Halo-vest head ring in the treatment of replantation of total scalp avulsion. We treated 11 cases of total scalp avulsion with the anastomosis of arteriovenous vessels and Halo-vest head ring from December 2006 to February 2015. One patient's replanted scalp got necrosis because of serious contusion which was healed without hair growth after free skin graft and dressing. All the scalp flaps in the other 10 patients survived. After 3-96 months follow-up, the wound completely healed, the scalp and hair grew well with satisfactory appearance. The use of Halo-vest head ring for replantation of total scalp avulsion can effectively improve the survival rate and survival area.

  15. Cool carbon stars in the halo and in dwarf galaxies: Hα, colours, and variability

    NASA Astrophysics Data System (ADS)

    Mauron, N.; Gigoyan, K. S.; Berlioz-Arthaud, P.; Klotz, A.

    2014-02-01

    The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Hα in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars. Based on observations made with the NTT and 3.6 m telescope at the European Southern Observatory (La Silla, Chile; programs 084.D-0302 and 070.D-0203), with the TAROT telescopes at La Silla and at Observatoire de la Côte d'Azur (France), and on the exploitation of the Catalina Sky Survey and the LINEAR variability databases.Appendix A is available in electronic form at http://www.aanda.org

  16. GBT CHANG-ES: Enhancing Radio Halos in Edge-on Galaxies Through Short-Spacing Corrections

    NASA Astrophysics Data System (ADS)

    Trent Braun, Timothy; Kepley, Amanda; Rand, Richard J.; Mason, Brian Scott; CHANG-ES

    2018-01-01

    We present L- and C-band continuum Stokes I data from the Green Bank Telescope (GBT) of 35 edge-on spiral galaxies that are part of the Continuum Halos in Nearby Galaxies, an EVLA Survey (CHANG-ES). CHANG-ES is an Expanded Very Large Array (EVLA) large program to measure radio continuum emission from the halos of 35 edge-on spiral galaxies in order to address a wide variety of science goals, including constraining the structure of magnetic fields, understanding the origins of radio halos, and probing both cosmic ray transport and cosmic ray driven winds. These goals can be reached by studying radio halo scale heights, spectral index variations with height, and the distribution of intensity and position angle of polarized emission. In particular, we are interested in modeling non-thermal presssure gradients in the gaseous halos of nearby galaxies to predict how they contribute to the decrease in the rotation of extraplanar gas with increasing height off of the galactic midplanes (lagging halos). Ultimately, the study of lagging halos will help us probe the efficacy of gas cycling between the disk and the halo in nearby galaxies. Crucial to this and the rest of the CHANG-ES analysis is the combination of the VLA data (B,C,D configurations in L-band and C,D configurations in C-band) with the GBT data in order to fill in the missing short-spacings in the u-v plane, which increases our sensitivity to large-scale emission and allows us to recover the total flux density. We present preliminary results from two methods of combining single-dish and interferometic data, namely the use of GBT data cubes as a model for the CASA task tclean and combining the Fourier transforms of the images as weighted sums in the u-v plane (feathering). Lastly, we detail our new data reduction pipeline for our wideband GBT continuum data, with an emphasis on the application of a least-squares basket-weaving technique used to remove striping image artifacts that notoriously plague single

  17. 78 FR 51210 - Manufacturer of Controlled Substances; Notice of Application; Halo Pharmaceutical, Inc.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-20

    ... DEPARTMENT OF JUSTICE Drug Enforcement Administration Manufacturer of Controlled Substances; Notice of Application; Halo Pharmaceutical, Inc. Pursuant to Sec. 1301.33(a), Title 21 of the Code of Federal Regulations (CFR), this is notice that on July 8, 2013, Halo Pharmaceutical, Inc., 30 North...

  18. 77 FR 47114 - Manufacturer of Controlled Substances; Notice of Application; Halo Pharmaceutical Inc.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-08-07

    ... DEPARTMENT OF JUSTICE Drug Enforcement Administration Manufacturer of Controlled Substances; Notice of Application; Halo Pharmaceutical Inc. Pursuant to Sec. 1301.33(a), Title 21 of the Code of Federal Regulations (CFR), this is notice that on July 6, 2012, Halo Pharmaceutical Inc., 30 North...

  19. Unified halo-independent formalism from convex hulls for direct dark matter searches

    NASA Astrophysics Data System (ADS)

    Gelmini, Graciela B.; Huh, Ji-Haeng; Witte, Samuel J.

    2017-12-01

    Using the Fenchel-Eggleston theorem for convex hulls (an extension of the Caratheodory theorem), we prove that any likelihood can be maximized by either a dark matter 1- speed distribution F(v) in Earth's frame or 2- Galactic velocity distribution fgal(vec u), consisting of a sum of delta functions. The former case applies only to time-averaged rate measurements and the maximum number of delta functions is (Script N‑1), where Script N is the total number of data entries. The second case applies to any harmonic expansion coefficient of the time-dependent rate and the maximum number of terms is Script N. Using time-averaged rates, the aforementioned form of F(v) results in a piecewise constant unmodulated halo function tilde eta0BF(vmin) (which is an integral of the speed distribution) with at most (Script N-1) downward steps. The authors had previously proven this result for likelihoods comprised of at least one extended likelihood, and found the best-fit halo function to be unique. This uniqueness, however, cannot be guaranteed in the more general analysis applied to arbitrary likelihoods. Thus we introduce a method for determining whether there exists a unique best-fit halo function, and provide a procedure for constructing either a pointwise confidence band, if the best-fit halo function is unique, or a degeneracy band, if it is not. Using measurements of modulation amplitudes, the aforementioned form of fgal(vec u), which is a sum of Galactic streams, yields a periodic time-dependent halo function tilde etaBF(vmin, t) which at any fixed time is a piecewise constant function of vmin with at most Script N downward steps. In this case, we explain how to construct pointwise confidence and degeneracy bands from the time-averaged halo function. Finally, we show that requiring an isotropic Galactic velocity distribution leads to a Galactic speed distribution F(u) that is once again a sum of delta functions, and produces a time-dependent tilde etaBF(vmin, t) function

  20. A qualitative review of existing national and international occupational safety and health policies relating to occupational sedentary behaviour.

    PubMed

    Coenen, Pieter; Gilson, Nicholas; Healy, Genevieve N; Dunstan, David W; Straker, Leon M

    2017-04-01

    Prolonged sedentary time is now recognised as an emergent ergonomics issue. We aimed to review current occupational safety and health policies relevant to occupational sedentary behaviour. An electronic search for documents was conducted on websites of ergonomics and occupational safety and health organisations from 10 countries and six international/pan-European agencies. Additionally, 43 informants (nine countries) were contacted and an international conference workshop held. 119 documents (e.g. legislation, guidelines, codes of practice) were identified. Using a qualitative synthesis, it was observed that many jurisdictions had legal frameworks establishing a duty of care for employers, designers/manufacturers/suppliers and employees. While no occupational authority policies focusing specifically on sedentary behaviour were found, relevant aspects of existing policies were identified. We highlight implications for ergonomics research and practice and recommend the development of policy to specifically address occupational sedentary behaviour and support workplace initiatives to assess and control the risks of this emergent hazard. Copyright © 2016 Elsevier Ltd. All rights reserved.