Science.gov

Sample records for matter non-standard halos

  1. Cold dark matter halos

    NASA Astrophysics Data System (ADS)

    Dubinski, John Joseph

    The dark halos arising in the Cold Dark Matter (CDM) cosmology are simulated to investigate the relationship between the structure and kinematics of dark halos and galaxies. Realistic cosmological initial conditions and tidal field boundary conditions are used in N-body simulations of the collapse of density peaks to form dark halos. The core radii of dark halos are no greater than the softening radius, rs = 1.4 kpc. The density profiles can be fit with an analytical Hernquist (1990) profile with an effective power law which varies between -1 in the center to -4 at large radii. The rotation curves of dark halos resemble the flat rotation curves of spiral galaxies in the observed range, 1.5 approximately less than r approximately less than 30 kpc. The halos are strongly triaxial and very flat with (c/a) = 0.50 and (b/a) = 0.71. The distribution of ellipticities for dark halos reaches a maximum at epsilon = 0.5 in contrast to the distribution for elliptical galaxies which peaks at epsilon = 0.2 suggesting that ellipticals are much rounder than dark halos. Dark halos are generally flatter than their progenitor density peaks. The final shape and orientation of a dark halo are largely determined by tidal torquing and are sensitive to changes in the strength and orientation of a tidal field. Dark halos are pressure supported objects with negligible rotational support as indicated by the mean dimensionless spin, lamda = 0.042 +/- 0.024. The angular momentum vector tends to align with the true minor axis of dark halos. Elliptical galaxies have a similar behavior implied by the observation of the tendency for alignment of the rotation vector and the apparent minor axis. The origin of this behavior may be traced to the tendency for tidal torques to misalign with the major axis of a density peak. Tidal torques are found to isotropize the velocity ellipsoids of dark halos at large radii, contrary to the expectation of radially anisotropic velocity ellipsoids in cold collapse

  2. Dark Matter Production in Non-Standard Early Universe Cosmologies

    NASA Astrophysics Data System (ADS)

    Rehagen, Thomas Joseph

    Many dark matter candidates, including asymmetric Weakly Interacting Massive Particles (WIMPs) and sterile neutrinos, are produced in the very early Universe, prior to Big Bang Nucleosynthesis (BBN). We show that the relic abundance of asymmetric WIMPs and sterile neutrinos can be very sensitive to the expansion rate of the Universe prior to BBN. In particular, we find that if the production of asymmetric WIMPs occurs during a non-standard cosmological phase, a larger WIMP annihilation cross section is required to produce the present dark matter density than if the WIMPs were produced during a standard, radiation dominated phase. Because of this, the present dark matter annihilation rate could be larger than that of symmetric dark matter produced in the standard cosmology. We also show that if the production of sterile neutrinos occurs during a non-standard cosmological phase, the relic number density of sterile neutrinos could be reduced with respect to the number expected in the standard cosmology, consequently relaxing current bounds on active-sterile neutrino mixing. Finally, we examine whether low reheating temperature cosmologies are allowed by current Cosmic Microwave Background measurements. We find the allowed range of reheating temperatures using monomial and binomial inflationary potentials, and a variety of reheating models. We show that an inflationary model with a φ1 potential and canonical reheating allows the possibility that dark matter could be produced during the reheating epoch, instead of when the Universe is radiation dominated.

  3. Computation of the halo mass function using physical collapse parameters: application to non-standard cosmologies

    SciTech Connect

    Achitouv, I.; Weller, J.; Wagner, C.; Rasera, Y. E-mail: cwagner@MPA-Garching.MPG.DE E-mail: yann.rasera@obspm.fr

    2014-10-01

    In this article we compare the halo mass function predicted by the excursion set theory with a drifting diffusive barrier against the results of N-body simulations for several cosmological models. This includes the standard ΛCDM case for a large range of halo masses, models with different types of primordial non-Gaussianity, and the Ratra-Peebles quintessence model of Dark Energy. We show that in all those cosmological scenarios, the abundance of dark matter halos can be described by a drifting diffusive barrier, where the two parameters describing the barrier have physical content. In the case of the Gaussian ΛCDM, the statistics are precise enough to actually predict those parameters at different redshifts from the initial conditions. Furthermore, we found that the stochasticity in the barrier is non-negligible making the simple deterministic spherical collapse model a bad approximation even at very high halo masses. We also show that using the standard excursion set approach with a barrier inspired by peak patches leads to inconsistent predictions of the halo mass function.

  4. Statistics of substructures in dark matter haloes

    NASA Astrophysics Data System (ADS)

    Contini, E.; De Lucia, G.; Borgani, S.

    2012-03-01

    We study the amount and distribution of dark matter substructures within dark matter haloes, using a large set of high-resolution simulations ranging from group-size to cluster-size haloes, and carried out within a cosmological model consistent with Wilkinson Microwave Anisotropy Probe (WMAP) 7-year data. In particular, we study how the measured properties of subhaloes vary as a function of the parent halo mass, the physical properties of the parent halo and redshift. The fraction of halo mass in substructures increases with increasing mass: it is of the order of 5 per cent for haloes with M200˜ 1013 M⊙ and of the order of 10 per cent for the most massive haloes in our sample, with M200˜ 1015 M⊙. There is, however, a very large halo-to-halo scatter that can be explained only in part by a range of halo physical properties, e.g. concentration. At a given halo mass, less concentrated haloes contain significantly larger fractions of mass in substructures because of the reduced strength of tidal disruption. Most of the substructure mass is located at the outskirts of the parent haloes, in relatively few massive subhaloes. This mass segregation appears to become stronger at increasing redshift, and should reflect into a more significant mass segregation of the galaxy population at different cosmic epochs. When haloes are accreted on to larger structures, their mass is significantly reduced by tidal stripping. Haloes that are more massive at the time of accretion (these should host more luminous galaxies) are brought closer to the centre on shorter time-scales by dynamical friction, and therefore suffer a more significant stripping. The halo merger rate depends strongly on the environment with substructure in more massive haloes suffering more important mergers than their counterparts residing in less massive systems. This should translate into a different morphological mix for haloes of different mass.

  5. Dark matter particles in the galactic halo

    SciTech Connect

    Bernabei, R. Belli, P.; Montecchia, F.; Nozzoli, F.; Cappella, F.; D'Angelo, A.; Incicchitti, A.; Prosperi, D.; Cerulli, R.; Dai, C. J.; He, H. L.; Kuang, H. H.; Ma, J. M.; Sheng, X. D.; Ye, Z. P.

    2009-12-15

    Arguments on the investigation of the DarkMatter particles in the galactic halo are addressed. Recent results obtained by exploiting the annual modulation signature are summarized and the perspectives are discussed.

  6. Dark matter particles in the galactic halo

    NASA Astrophysics Data System (ADS)

    Bernabei, R.; Belli, P.; Montecchia, F.; Nozzoli, F.; Cappella, F.; D'Angelo, A.; Incicchitti, A.; Prosperi, D.; Cerulli, R.; Dai, C. J.; He, H. L.; Kuang, H. H.; Ma, J. M.; Sheng, X. D.; Ye, Z. P.

    2009-12-01

    Arguments on the investigation of the DarkMatter particles in the galactic halo are addressed. Recent results obtained by exploiting the annual modulation signature are summarized and the perspectives are discussed.

  7. On physical scales of dark matter halos

    SciTech Connect

    Zemp, Marcel

    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 the 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.

  8. Halo cold dark matter and microlensing

    SciTech Connect

    Gates, Evalyn; Turner, Michael S.

    1993-12-01

    There is good evidence that most of the baryons in the Universe are dark and some evidence that most of the matter in the Universe is nonbaryonic with cold dark matter (cdm) being a promising possibility. We discuss expectations for the abundance of baryons and cdm in the halo of our galaxy and locally. We show that in plausible cdm models the local density of cdm is at least $10^{-25}\\gcmm3$. We also discuss what one can learn about the the local cdm density from microlensing of stars in the LMC by dark stars in the halo and, based upon a suite of reasonable two-component halo models, conclude that microlensing is not a sensitive probe of the local cdm density.

  9. 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

  10. Asymmetric dark matter annihilation as a test of non-standard cosmologies

    SciTech Connect

    Gelmini, Graciela B.; Huh, Ji-Haeng; Rehagen, Thomas E-mail: jhhuh@physics.ucla.edu

    2013-08-01

    We show that the relic abundance of the minority component of asymmetric dark matter can be very sensitive to the expansion rate of the Universe and the temperature of transition between a non-standard pre-Big Bang Nucleosynthesis cosmological phase and the standard radiation dominated phase, if chemical decoupling happens before this transition. In particular, because the annihilation cross section of asymmetric dark matter is typically larger than that of symmetric dark matter in the standard cosmology, the decrease in relic density of the minority component in non-standard cosmologies with respect to the majority component may be compensated by the increase in annihilation cross section, so that the annihilation rate at present of asymmetric dark matter, contrary to general belief, could be larger than that of symmetric dark matter in the standard cosmology. Thus, if the annihilation cross section of the asymmetric dark matter candidate is known, the annihilation rate at present, if detectable, could be used to test the Universe before Big Bang Nucleosynthesis, an epoch from which we do not yet have any data.

  11. The Shape of Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Olling, Robert Paul

    1995-01-01

    After reviewing our current knowledge of dark matter (DM) in spiral galaxies (Chapter 1), I present a new method of deriving the shape of these dark halos (Chapter 2). Such information, if obtained for a large number of systems, can provide important boundary conditions for theories of the formation of galaxies (Chapter 5). The halo-shape determination method relies on the comparison of model predictions of the thickness of the gas layer with observations of this flaring. Calculating the model gas layer widths from the observed gaseous velocity dispersion and the potential due to the total mass distribution of the galaxy we learn the following: (a) beyond the optical disk the thickness of the gas layer is sensitive to the shape of the DM halo, (b) the thickness of the gas layer is proportional to the ratio of the gaseous velocity dispersion and the rotation speed, (c) the self-gravity of the gas contributes significantly to the vertical force, (d) the derived shape of the DM halo is independent of the dark matter's radial density distribution, and is independent of the mass-to-light ratio of the stellar disk (f). In Chapter 3 I present a new method (usable for inclinations larger than 60^circ) to determine the thickness of the gas layer of spiral galaxies from high resolution H sc I observations. I use VLA H sc I observations of the almost edge-on Scd galaxy NGC 4244 to determine the gaseous velocity dispersion, and the flaring and rotation curves. From the Keplerian decline of the rotation curve beyond the stellar disks it follows that the dark-to-luminous mass ratio is at most two and a half. Combining the model predictions for the radial variation of the thickness of the gas layer with the measured flaring curve I find that the dark matter halo of NGC 4244 is highly flattened. The best fit occurs for a halo with an E8 shape (with a mass one-eight of an E0 halo), while the uncertainty (E5-E9) is dominated by the errors in the gaseous velocity dispersion: a round

  12. 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.

  13. Universal properties of dark matter halos.

    PubMed

    Boyarsky, A; Neronov, A; Ruchayskiy, O; Tkachev, I

    2010-05-14

    We discuss the universal relation between density and size of observed dark matter halos that was recently shown to hold on a wide range of scales, from dwarf galaxies to galaxy clusters. Predictions of cold dark matter (ΛCDM) N-body simulations are consistent with this relation. We demonstrate that this property of ΛCDM can be understood analytically in the secondary infall model. Qualitative understanding given by this model provides a new way to predict which deviations from ΛCDM or large-scale modifications of gravity can affect universal behavior and, therefore, to constrain them observationally. PMID:20866958

  14. 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

  15. Solitonic axion condensates modeling dark matter halos

    SciTech Connect

    Castañeda Valle, David Mielke, Eckehard W.

    2013-09-15

    Instead of fluid type dark matter (DM), axion-like scalar fields with a periodic self-interaction or some truncations of it are analyzed as a model of galaxy halos. It is probed if such cold Bose–Einstein type condensates could provide a viable soliton type interpretation of the DM ‘bullets’ observed by means of gravitational lensing in merging galaxy clusters. We study solitary waves for two self-interacting potentials in the relativistic Klein–Gordon equation, mainly in lower dimensions, and visualize the approximately shape-invariant collisions of two ‘lump’ type solitons. -- Highlights: •An axion model of dark matter is considered. •Collision of axion type solitons are studied in a two dimensional toy model. •Relations to dark matter collisions in galaxy clusters are proposed.

  16. Halos of unified dark matter scalar field

    SciTech Connect

    Bertacca, Daniele; Bartolo, Nicola; Matarrese, Sabino E-mail: nicola.bartolo@pd.infn.it

    2008-05-15

    We investigate the static and spherically symmetric solutions of Einstein's equations for a scalar field with a non-canonical kinetic term, assumed to provide both the dark matter and dark energy components of the Universe. In particular, we give a prescription to obtain solutions (dark halos) whose rotation curve v{sub c}(r) is in good agreement with observational data. We show that there exist suitable scalar field Lagrangians that allow us to describe the cosmological background evolution and the static solutions with a single dark fluid.

  17. Solitonic axion condensates modeling dark matter halos

    NASA Astrophysics Data System (ADS)

    Castañeda Valle, David; Mielke, Eckehard W.

    2013-09-01

    Instead of fluid type dark matter (DM), axion-like scalar fields with a periodic self-interaction or some truncations of it are analyzed as a model of galaxy halos. It is probed if such cold Bose-Einstein type condensates could provide a viable soliton type interpretation of the DM 'bullets' observed by means of gravitational lensing in merging galaxy clusters. We study solitary waves for two self-interacting potentials in the relativistic Klein-Gordon equation, mainly in lower dimensions, and visualize the approximately shape-invariant collisions of two 'lump' type solitons.

  18. The Formation and Evolution of Stripped Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Zhu, Jessica; Tuan, Austin Zong; Lee, Christoph; Primack, Joel R.

    2016-01-01

    We implement a model to describe the density profiles of stripped dark matter halos. Our model generalizes the Navarro-Frenk-White (NFW) distribution to allow for more flexibility in the slope of the outer halo. We find that the density distributions of stripped halos tend to have outer slopes steeper than assumed by the NFW distribution. We also examine the relationship between severity of stripping and halo shape, spin parameter and concentration, and find that highly stripped halos are more spheroidal, have lower spin parameters, and have higher concentrations compared to less stripped halos.

  19. Merger rates of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Neistein, Eyal; Dekel, Avishai

    2008-08-01

    We derive analytic merger rates for dark matter haloes within the framework of the extended Press-Schechter (EPS) formalism. These rates become self-consistent within EPS once we realize that the typical merger in the limit of a small time-step involves more than two progenitors, contrary to the assumption of binary mergers adopted in earlier studies. We present a general method for computing merger rates that span the range of solutions permitted by the EPS conditional mass function, and focus on a specific solution that attempts to match the merger rates in N-body simulations. The corrected EPS merger rates are more accurate than the earlier estimates of Lacey & Cole by ~20 per cent for major mergers and by up to a factor of ~3 for minor mergers of mass ratio 1:104. Based on the revised merger rates, we provide a new algorithm for constructing Monte Carlo EPS merger trees, which could be useful in semi-analytic modelling. We provide analytic expressions and plot numerical results for several quantities that are very useful in studies of galaxy formation. This includes (i) the rate of mergers of a given mass ratio per given final halo, (ii) the fraction of mass added by mergers to a halo and (iii) the rate of mergers per given main progenitor. The creation and destruction rates of haloes serve for a self-consistency check. Our method for computing merger rates can be applied to conditional mass functions beyond EPS, such as those obtained by the ellipsoidal collapse model or extracted from N-body simulations.

  20. 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.

  1. Matter Radii of Light Halo Nuclei

    NASA Astrophysics Data System (ADS)

    Al-Khalili, J. S.; Tostevin, J. A.

    1996-05-01

    We reexamine the matter radii of diffuse halo nuclei, as deduced from reaction cross section measurements at high energy. Careful consideration is given to the intrinsic few-body structure of these projectiles and the adiabatic nature of the projectile-target interaction. Using 11Li, 11Be, and 8B as examples we show that data require significantly larger matter radii than previously reported. The revised value for 11Li of 3.55 fm is consistent with three-body models with significant 1s-intruder state components, which reproduce experimental 9Li momentum distributions following 11Li breakup, but were hitherto thought to be at variance with cross section data.

  2. Halo-Independent Comparison of Direct Dark Matter Detection Data

    DOE PAGESBeta

    Del Nobile, Eugenio

    2014-01-01

    We review the halo-independent formalism that allows comparing data from different direct dark matter detection experiments without making assumptions on the properties of the dark matter halo. We apply this method to spin-independent WIMP-nuclei interactions, for both isospin-conserving and isospin-violating couplings, and to WIMPs interacting through an anomalous magnetic moment.

  3. HALO-TO-HALO SIMILARITY AND SCATTER IN THE VELOCITY DISTRIBUTION OF DARK MATTER

    SciTech Connect

    Mao, Yao-Yuan; Strigari, Louis E.; Wechsler, Risa H.; Hahn, Oliver; Wu, Hao-Yi

    2013-02-10

    We examine the velocity distribution function (VDF) in dark matter halos from Milky Way to cluster mass scales. We identify an empirical model for the VDF with a wider peak and a steeper tail than a Maxwell-Boltzmann distribution, and discuss physical explanations. We quantify sources of scatter in the VDF of cosmological halos and their implication for direct detection of dark matter. Given modern simulations and observations, we find that the most significant uncertainty in the VDF of the Milky Way arises from the unknown radial position of the solar system relative to the dark matter halo scale radius.

  4. Distribution Function in the Center of the Dark Matter Halo

    NASA Astrophysics Data System (ADS)

    Ma, Ding; He, Ping

    N-body simulations of dark matter halos show that the density profiles of the halos behave as ρ(r) ∝ r-α(r), where the density logarithmic slope α ≃ 1-1.5 in the center and α ≃ 3-4 in the outer parts of the halos. However, some observations are not in agreement with simulations in the very central region of the halos. The simulations also show that the velocity dispersion anisotropy parameter β ≈ 0 in the inner part of the halo and the so-called pseudo-phase-space density ρ/σ3 behaves as a power law in radius r. With these results in mind, we study the distribution function and the pseudo-phase-space density ρ/σ3 of the center of dark matter halos and find that they are closely related.

  5. THE SPHERICALIZATION OF DARK MATTER HALOS BY GALAXY DISKS

    SciTech Connect

    Kazantzidis, Stelios; Abadi, Mario G.; Navarro, Julio F. E-mail: mario@oac.uncor.ed

    2010-09-01

    Cosmological simulations indicate that cold dark matter (CDM) halos should be triaxial. Validating this theoretical prediction is, however, less than straightforward because the assembly of galaxies is expected to modify halo shapes and to render them more axisymmetric. We use a suite of N-body simulations to quantitatively investigate the effect of the growth of a central disk galaxy on the shape of triaxial dark matter halos. In most circumstances, the halo responds to the presence of the disk by becoming more spherical. The net effect depends weakly on the timescale of the disk assembly but noticeably on the orientation of the disk relative to the halo principal axes, and it is maximal when the disk symmetry axis is aligned with the major axis of the halo. The effect depends most sensitively on the overall gravitational importance of the disk. Our results indicate that exponential disks whose contribution peaks at less than {approx}50% of their circular velocity are unable to noticeably modify the shape of the gravitational potential of their surrounding halos. Many dwarf and low surface brightness galaxies are expected to be in this regime, and therefore their detailed kinematics could be used to probe halo triaxiality, one of the basic predictions of the CDM paradigm. We argue that the complex disk kinematics of the dwarf galaxy NGC 2976 might be the reflection of a triaxial halo. Such signatures of halo triaxiality should be common in galaxies where the luminous component is subdominant.

  6. The shapes and alignments of dark matter halos

    SciTech Connect

    Schneider, Michael D.; Frenk, Carlos S.; Cole, Shaun E-mail: c.s.frenk@durham.ac.uk

    2012-05-01

    We present measurements of the triaxial dark matter halo shapes and alignment correlation functions in the Millennium and Millennium-2 dark matter N-body simulations. These two simulations allow us to measure the distributions of halo shapes down to 10% of the virial radius over a halo mass range of 6 × 10{sup 9}–2 × 10{sup 14} h{sup −1}M{sub s}un. We largely confirm previous results on the distributions of halo axis ratios as a function of halo mass, but we find that the median angle between halo major axes at different halo radii can vary by a factor of 2 between the Millennium-1 and 2 simulations because of the different mass resolution. Thus, error in the shape determinations from limited resolution is potentially degenerate with the misalignment of halo inner and outer shapes used to constrain Brightest Cluster Galaxy alignments in previous works. We also present simplifying parameterizations for the 3-D halo-mass alignment correlation functions that are necessary ingredients for triaxial halo models of large-scale structure and models of galaxy intrinsic alignments as contaminants for cosmic shear surveys. We measure strong alignments between halos of all masses and the surrounding dark matter overdensities out to several tens of h{sup −1} Mpc, in agreement with observed shear-galaxy and cluster shape correlations. We use these measurements to forecast the contribution to the weak lensing signal around galaxy clusters from correlated mass along the line-of-sight. For prolate clusters with major axes aligned with the line-of-sight the fraction of the weak lensing signal from mass external to the cluster can be twice that predicted if the excess halo alignment correlation is assumed to be zero.

  7. Optimal linear reconstruction of dark matter from halo catalogues

    SciTech Connect

    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 fact 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.

  8. Optimal linear reconstruction of dark matter from halo catalogues

    DOE PAGESBeta

    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

  9. 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.

  10. Inner caustics of cold dark matter halos

    NASA Astrophysics Data System (ADS)

    Natarajan, Aravind; Sikivie, Pierre

    2006-01-01

    We prove that a flow of cold collisionless particles from all directions in and out of a region necessarily forms a caustic. A corollary is that, in cold dark matter cosmology, galactic halos have inner caustics in addition to the more obvious outer caustics. The outer caustics are fold catastrophes located on topological spheres surrounding the galaxy. To obtain the catastrophe structure of the inner caustics, we simulate the infall of cold collisionless particles in a fixed gravitational potential. The structure of inner caustics depends on the angular momentum distribution of the infalling particles. We confirm a previous result that the inner caustic is a “tricusp ring” when the initial velocity field is dominated by net overall rotation. A tricusp ring is a closed tube whose cross section is a section of an elliptic umbilic catastrophe. However, tidal torque theory predicts that the initial velocity field is irrotational. For irrotational initial velocity fields, we find the inner caustic to have a tentlike structure which we describe in detail in terms of the known catastrophes. We also show how the tent caustic transforms into a tricusp ring when a rotational component is added to the initial velocity field.

  11. Inner caustics of cold dark matter halos

    SciTech Connect

    Natarajan, Aravind; Sikivie, Pierre

    2006-01-15

    We prove that a flow of cold collisionless particles from all directions in and out of a region necessarily forms a caustic. A corollary is that, in cold dark matter cosmology, galactic halos have inner caustics in addition to the more obvious outer caustics. The outer caustics are fold catastrophes located on topological spheres surrounding the galaxy. To obtain the catastrophe structure of the inner caustics, we simulate the infall of cold collisionless particles in a fixed gravitational potential. The structure of inner caustics depends on the angular momentum distribution of the infalling particles. We confirm a previous result that the inner caustic is a 'tricusp ring' when the initial velocity field is dominated by net overall rotation. A tricusp ring is a closed tube whose cross section is a section of an elliptic umbilic catastrophe. However, tidal torque theory predicts that the initial velocity field is irrotational. For irrotational initial velocity fields, we find the inner caustic to have a tentlike structure which we describe in detail in terms of the known catastrophes. We also show how the tent caustic transforms into a tricusp ring when a rotational component is added to the initial velocity field.

  12. 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.

  13. The prolate dark matter halo of the Andromeda galaxy

    SciTech Connect

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

    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 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 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.

  14. Testing gravity using the environmental dependence of dark matter halos.

    PubMed

    Zhao, Gong-Bo; Li, Baojiu; Koyama, Kazuya

    2011-08-12

    In this Letter, we investigate the environmental dependence of dark matter halos in theories which attempt to explain the accelerated expansion of the Universe by modifying general relativity (GR). Using high-resolution N-body simulations in f(R) gravity models which recover GR in dense environments by virtue of the chameleon mechanism, we find a significant difference, which depends on the environment, between the lensing and dynamical masses of dark matter halos. This environmental dependence of the halo properties can be used as a smoking gun to test GR observationally. PMID:21902382

  15. EFFECT OF DARK MATTER HALO SUBSTRUCTURES ON GALAXY ROTATION CURVES

    SciTech Connect

    Roy, Nirupam

    2010-11-01

    In this paper, the effect of halo substructures on galaxy rotation curves is investigated using a simple model of dark matter clustering. A dark matter halo density profile is developed based only on the scale-free nature of clustering that leads to a statistically self-similar distribution of the substructures at the galactic scale. A semi-analytical method is used to derive rotation curves for such a clumpy dark matter density profile. It is found that the halo substructures significantly affect the galaxy velocity field. Based on the fractal geometry of the halo, this self-consistent model predicts a Navarro-Frenk-White-like rotation curve and a scale-free power spectrum of the rotation velocity fluctuations.

  16. SECULAR DAMPING OF STELLAR BARS IN SPINNING DARK MATTER HALOS

    SciTech Connect

    Long, Stacy; Shlosman, Isaac; Heller, Clayton

    2014-03-01

    We demonstrate using numerical simulations of isolated galaxies that growth of stellar bars in spinning dark matter halos is heavily suppressed in the secular phase of evolution. In a representative set of models, we show that for values of the cosmological spin parameter λ ≳ 0.03, bar growth (in strength and size) becomes increasingly quenched. Furthermore, the slowdown of the bar pattern speed weakens considerably with increasing λ until it ceases completely. The terminal structure of the bars is affected as well, including extent and shape of their boxy/peanut bulges. The essence of this effect lies in the modified angular momentum exchange between the disk and the halo facilitated by the bar. For the first time we have demonstrated that a dark matter halo can emit and not purely absorb angular momentum. Although the halo as a whole is not found to emit, the net transfer of angular momentum from the disk to the halo is significantly reduced or completely eliminated. The paradigm shift implies that the accepted view that disks serve as sources of angular momentum and halos serve as sinks must be revised. Halos with λ ≳ 0.03 are expected to form a substantial fraction, based on the lognormal distribution of λ. The dependence of secular bar evolution on halo spin, therefore, implies profound corollaries for the cosmological evolution of galactic disks.

  17. Secular Damping of Stellar Bars in Spinning Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Long, Stacy; Shlosman, Isaac; Heller, Clayton

    2014-03-01

    We demonstrate using numerical simulations of isolated galaxies that growth of stellar bars in spinning dark matter halos is heavily suppressed in the secular phase of evolution. In a representative set of models, we show that for values of the cosmological spin parameter λ >~ 0.03, bar growth (in strength and size) becomes increasingly quenched. Furthermore, the slowdown of the bar pattern speed weakens considerably with increasing λ until it ceases completely. The terminal structure of the bars is affected as well, including extent and shape of their boxy/peanut bulges. The essence of this effect lies in the modified angular momentum exchange between the disk and the halo facilitated by the bar. For the first time we have demonstrated that a dark matter halo can emit and not purely absorb angular momentum. Although the halo as a whole is not found to emit, the net transfer of angular momentum from the disk to the halo is significantly reduced or completely eliminated. The paradigm shift implies that the accepted view that disks serve as sources of angular momentum and halos serve as sinks must be revised. Halos with λ >~ 0.03 are expected to form a substantial fraction, based on the lognormal distribution of λ. The dependence of secular bar evolution on halo spin, therefore, implies profound corollaries for the cosmological evolution of galactic disks.

  18. STATISTICS OF DARK MATTER HALOS FROM THE EXCURSION SET APPROACH

    SciTech Connect

    Lapi, A.; Salucci, P.; Danese, L.

    2013-08-01

    We exploit the excursion set approach in integral formulation to derive novel, accurate analytic approximations of the unconditional and conditional first crossing distributions for random walks with uncorrelated steps and general shapes of the moving barrier; we find the corresponding approximations of the unconditional and conditional halo mass functions for cold dark matter (DM) power spectra to represent very well the outcomes of state-of-the-art cosmological N-body simulations. In addition, we apply these results to derive, and confront with simulations, other quantities of interest in halo statistics, including the rates of halo formation and creation, the average halo growth history, and the halo bias. Finally, we discuss how our approach and main results change when considering random walks with correlated instead of uncorrelated steps, and warm instead of cold DM power spectra.

  19. The outer profile of dark matter haloes: an analytical approach

    NASA Astrophysics Data System (ADS)

    Shi, Xun

    2016-07-01

    A steepening feature in the outer density profiles of dark matter haloes indicating the splashback radius has drawn much attention recently. Possible observational detections have even been made for galaxy clusters. Theoretically, Adhikari et al. have estimated the location of the splashback radius by computing the secondary infall trajectory of a dark matter shell through a growing dark matter halo with an NFW profile. However, since they imposed a shape of the halo profile rather than computing it consistently from the trajectories of the dark matter shells, they could not provide the full shape of the dark matter profile around the splashback radius. We improve on this by extending the self-similar spherical collapse model of Fillmore & Goldreich to a ΛCDM universe. This allows us to compute the dark matter halo profile and the trajectories simultaneously from the mass accretion history. Our results on the splashback location agree qualitatively with Adhikari et al. but with small quantitative differences at large mass accretion rates. We present new fitting formulae for the splashback radius Rsp in various forms, including the ratios of Rsp/R200c and Rsp/R200m. Numerical simulations have made the puzzling discovery that the splashback radius scales well with R200m but not with R200c. We trace the origin of this to be the correlated increase of Ωm and the average halo mass accretion rate with an increasing redshift.

  20. The outer profile of dark matter halos: an analytical approach

    NASA Astrophysics Data System (ADS)

    Shi, Xun

    2016-04-01

    A steepening feature in the outer density profiles of dark matter halos indicating the splashback radius has drawn much attention recently. Possible observational detections have even been made for galaxy clusters. Theoretically, Adhikari et al. have estimated the location of the splashback radius by computing the secondary infall trajectory of a dark matter shell through a growing dark matter halo with an NFW profile. However, since they imposed a shape of the halo profile rather than computing it consistently from the trajectories of the dark matter shells, they could not provide the full shape of the dark matter profile around the splashback radius. We improve on this by extending the self-similar spherical collapse model of Fillmore & Goldreich to a ΛCDM universe. This allows us to compute the dark matter halo profile and the trajectories simultaneously from the mass accretion history. Our results on the splashback location agree qualitatively with Adhikari et al. but with small quantitative differences at large mass accretion rates. We present new fitting formulae for the splashback radius Rsp in various forms, including the ratios of Rsp/R200c and Rsp/R200m. Numerical simulations have made the puzzling discovery that the splashback radius scales well with R200m but not with R200c. We trace the origin of this to be the correlated increase of Ωm and the average halo mass accretion rate with an increasing redshift.

  1. 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. PMID:26317711

  2. 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

    2008-11-01

    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. PMID:18987737

  3. 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. PMID:12907809

  4. Flattened halos in a nontopological soliton model of dark matter

    NASA Astrophysics Data System (ADS)

    Mielke, Eckehard W.; Peralta, Humberto H.

    2004-12-01

    Soliton type solutions of a scalar model with a Φ6 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 Black Hole-Dark Matter Halo Connection

    NASA Astrophysics Data System (ADS)

    Sabra, Bassem M.; Saliba, Charbel; Abi Akl, Maya; Chahine, Gilbert

    2015-04-01

    We explore the connection between the central supermassive black holes (SMBH) in galaxies and the dark matter halo through the relation between the masses of the SMBHs and the maximum circular velocities of the host galaxies, as well as the relationship between stellar velocity dispersion of the spheroidal component and the circular velocity. Our assumption here is that the circular velocity is a proxy for the mass of the dark matter halo. We rely on a heterogeneous sample containing galaxies of all types. The only requirement is that the galaxy has a direct measurement of the mass of its SMBH and a direct measurement of its circular velocity and its velocity dispersion. Previous studies have analyzed the connection between the SMBH and dark matter halo through the relationship between the circular velocity and the bulge velocity dispersion, with the assumption that the bulge velocity dispersion stands in for the mass of the SMBH, via the well-established SMBH mass-bulge velocity dispersion relation. Using intermediate relations may be misleading when one is studying them to decipher the active ingredients of galaxy formation and evolution. We believe that our approach will provide a more direct probe of the SMBH and the dark matter halo connection. We find that the correlation between the mass of SMBHs and the circular velocities of the host galaxies is extremely weak, leading us to state the dark matter halo may not play a major role in regulating the black hole growth in the present Universe.

  6. Concentration, ellipsoidal collapse, and the densest dark matter haloes

    NASA Astrophysics Data System (ADS)

    Okoli, Chiamaka; Afshordi, Niayesh

    2016-03-01

    The smallest dark matter haloes are the first objects to form in the hierarchical structure formation of cold dark matter (CDM) cosmology and are expected to be the densest and most fundamental building blocks of CDM structures in our Universe. Nevertheless, the physical characteristics of these haloes have stayed illusive, as they remain well beyond the current resolution of N-body simulations (at redshift zero). However, they dominate the predictions (and uncertainty) in expected dark matter annihilation signal, amongst other astrophysical observables. Using the conservation of total energy and the ellipsoidal collapse framework, we can analytically find the mean and scatter of concentration c and 1D velocity dispersion σ1d for haloes of different virial mass M200. Both c and σ _1d/M_{200}^{1/3} are in good agreement with numerical results within the regime probed by simulations - slowly decreasing functions of mass that approach constant values at large masses. In particular, the predictions for the 1D velocity dispersion of cluster mass haloes are surprisingly robust as the inverse heat capacity of cosmological haloes crosses zero at M200 ˜ 1014 M⊙. However, we find that current extrapolations from simulations to smallest CDM haloes dramatically depend on the assumed profile (e.g. NFW versus Einasto) and fitting function, which is why theoretical considerations, such as the one presented here, can significantly constrain the range of feasible predictions.

  7. 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

  8. Halo-independent tests of dark matter annual modulation signals

    SciTech Connect

    Herrero-Garcia, Juan

    2015-09-02

    New halo-independent lower bounds on the product of the dark matter-nucleon scattering cross section and the local dark matter density that are valid for annual modulations of dark matter direct detection signals are derived. They are obtained by making use of halo-independent bounds based on an expansion of the rate on the Earth’s velocity that were derived in previous works. In combination with astrophysical measurements of the local energy density, an observed annual modulation implies a lower bound on the cross section that is independent of the velocity distribution and that must be fulfilled by any particle physics model. In order to illustrate the power of the bounds we apply them to DAMA/LIBRA data and obtain quite strong results when compared to the standard halo model predictions. We also extend the bounds to the case of multi-target detectors.

  9. Investigating the Origins of Dark Matter Halo Density Profiles

    NASA Astrophysics Data System (ADS)

    Williams, Liliya L. R.; Babul, Arif; Dalcanton, Julianne J.

    2004-03-01

    Although high-resolution N-body simulations make robust empirical predictions of the density distribution within cold dark matter halos, these studies have yielded little physical insight into the origins of the distribution. We therefore attempt to investigate the problem using analytic and semianalytic approaches. Simple analytic considerations suggest that the inner slope of the central cusps in dark matter halos cannot be steeper than α=2 (where ρ~r-α), with α=1.5-1.7 being a more realistic upper limit. Moreover, our analysis suggests that any number of effects, whether real (e.g., angular momentum imparted by tidal torques and secondary perturbations) or artificial (e.g., two-body interactions, the accuracy of the numerical integrator, round-off errors) will result in shallower slopes. We also find that the halos should exhibit a well-defined relationship between rperi/rapo and jθ/jr. We derive this relationship analytically and speculate that it may be ``universal.'' Using a semianalytic scheme based on Ryden & Gunn, we further explore the relationship between the specific angular momentum distribution in a halo and its density profile. For present purposes, we restrict ourselves to halos that form primarily via the nearly smooth accretion of matter, and consider only the specific angular momentum generated by secondary perturbations associated with the cold dark matter spectrum of density fluctuations. Compared to those formed in N-body simulations, our ``semianalytic'' halos are more extended, have flatter rotation curves, and have a higher specific angular momentum, even though we have not yet taken into account the effects of tidal torques. Whether the density profile of numerical halos is indeed the result of loss in angular momentum outside the central region, and whether this loss is a feature of hierarchical merging and major mergers in particular, is under investigation.

  10. The Copernicus Complexio: statistical properties of warm dark matter haloes

    NASA Astrophysics Data System (ADS)

    Bose, Sownak; Hellwing, Wojciech A.; Frenk, Carlos S.; Jenkins, Adrian; Lovell, Mark R.; Helly, John C.; Li, Baojiu

    2016-01-01

    The recent detection of a 3.5 keV X-ray line from the centres of galaxies and clusters by Bulbul et al. and Boyarsky et al. has been interpreted as emission from the decay of 7 keV sterile neutrinos which could make up the (warm) dark matter (WDM). As part of the Copernicus Complexio (COCO) programme, we investigate the properties of dark matter haloes formed in a high-resolution cosmological N-body simulation from initial conditions similar to those expected in a universe in which the dark matter consists of 7 keV sterile neutrinos. This simulation and its cold dark matter (CDM) counterpart have ˜13.4 bn particles, each of mass ˜105 h-1 M⊙, providing detailed information about halo structure and evolution down to dwarf galaxy mass scales. Non-linear structure formation on small scales (M200 ≲ 2 × 109 h-1 M⊙) begins slightly later in COCO-WARM than in COCO-COLD. The halo mass function at the present day in the WDM model begins to drop below its CDM counterpart at a mass ˜2 × 109 h-1 M⊙ and declines very rapidly towards lower masses so that there are five times fewer haloes of mass M200 = 108 h-1 M⊙ in COCO-WARM than in COCO-COLD. Halo concentrations on dwarf galaxy scales are correspondingly smaller in COCO-WARM, and we provide a simple functional form that describes its evolution with redshift. The shapes of haloes are similar in the two cases, but the smallest haloes in COCO-WARM rotate slightly more slowly than their CDM counterparts.

  11. Dark matter annihilation in the first galaxy haloes

    NASA Astrophysics Data System (ADS)

    Schön, S.; Mack, K. J.; Avram, C. A.; Wyithe, J. S. B.; Barberio, E.

    2015-08-01

    We investigate the impact of energy released from self-annihilating dark matter (DM) on heating of gas in the small, high-redshift DM haloes thought to host the first stars. A supersymmetric (SUSY)-neutralino-like particle is implemented as our DM candidate. The PYTHIA code is used to model the final, stable particle distributions produced during the annihilation process. We use an analytic treatment in conjunction with the code MEDEA2 to find the energy transfer and subsequent partition into heating, ionizing and Lyman α photon components. We consider a number of halo density models, DM particle masses and annihilation channels. We find that the injected energy from DM exceeds the binding energy of the gas within a 105-106 M⊙ halo at redshifts above 20, preventing star formation in early haloes in which primordial gas would otherwise cool. Thus we find that DM annihilation could delay the formation of the first galaxies.

  12. The Highly Flattened Dark Matter Halo of NGC 4244

    NASA Astrophysics Data System (ADS)

    Olling, Rob P.

    1996-08-01

    In a previous paper (Olling 1995, AJ, 110,591) a method was developed to determine the shapes of dark matter halos of spiral galaxies from an accurate determination of the rotation curve, the flaring of the gas layer and the velocity dispersion in the HI. Here this method is applied to the almost edge-on Scd galaxy NGC 4244 for which the necessary parameters are determined in the accompanying paper (AJ, 112,457, 1996). The observed flaring of the HI beyond the optical disk puts significant constraints on the shape of the dark matter halo, which are almost independent of the stellar mass-to-light ratio. NGC 4244's dark matter halo is found to be highly flattened with a shortest-to-longest axis ratio of 0.2_-0.1_^+0.3^. If the dark matter is disk-like, the data presented in this paper imply that the vertical velocity dispersion of the dark matter must be 10%-30% larger than the measured tangential dispersion in the H I . Alternatively, the measured flaring curve is consistent with a round halo if the gaseous velocity dispersion ellipsoid is anisotropic. In that case the vertical dispersion of the gas is 50%- 70% of the measured tangential velocity dispersion.

  13. A New Model for Dark Matter Halos Hosting Quasars

    NASA Astrophysics Data System (ADS)

    Cen, Renyue; Safarzadeh, Mohammadtaher

    2015-01-01

    A new model for quasar-hosting dark matter halos, meeting two physical conditions, is put forth. First, significant interactions are taken into consideration to trigger quasar activities. Second, satellites in very massive halos at low redshift are removed from consideration due to their deficiency in cold gas. We analyze the Millennium Simulation to find halos that meet these two conditions and simultaneously match two-point auto-correlation functions of quasars and cross-correlation functions between quasars and galaxies at z = 0.5-3.2. The masses of the quasar hosts found decrease with decreasing redshift, with the mass thresholds being [(2-5) × 1012, (2-5) × 1011, (1-3) × 1011] M ⊙ for median luminosities of ~[1046, 1046, 1045] erg s-1 at z = (3.2, 1.4, 0.53), respectively, an order of magnitude lower than those inferred based on halo occupation distribution modeling. In this model, quasar hosts are primarily massive central halos at z >= 2-3 but increasingly dominated by lower mass satellite halos experiencing major interactions toward lower redshift. However, below z = 1, satellite halos in groups more massive than ~2 × 1013 M ⊙ do not host quasars. Whether for central or satellite halos, imposing the condition of significant interactions substantially boosts the clustering strength compared to the total population with the same mass cut. The inferred lifetimes of quasars at z = 0.5-3.2 of 3-30 Myr are in agreement with observations. Quasars at z ~ 2 would be hosted by halos of mass ~5 × 1011 M ⊙ in this model, compared to ~3 × 1012 M ⊙ previously thought, which would help reconcile with the observed, otherwise puzzling high covering fractions for Lyman limit systems around quasars.

  14. Properties of Galaxy Dark Matter Halos from Weak Lensing

    NASA Astrophysics Data System (ADS)

    Hoekstra, Henk; Yee, H. K. C.; Gladders, Michael D.

    2004-05-01

    We present the results of a study of weak lensing by galaxies based on 45.5 deg2 of RC-band imaging data from the Red-Sequence Cluster Survey (RCS). We define a sample of lenses with 19.5matter halos. We use a simple model in which the ellipticity of the halo is f times the observed ellipticity of the lens. We find a best-fit value of f=0.77+0.18-0.21, which suggests that the dark matter halos are somewhat rounder than the light distribution. The fact that we detect a significant flattening implies that the halos are well aligned with the light distribution. Given the average ellipticity of the lenses, this implies a halo ellipticity of =0.33+0.07-0.09, in fair agreement with results from numerical simulations of cold dark matter. We note that this result is formally a lower limit to the flattening, since the measurements imply a larger flattening if the halos are not aligned with the light distribution. Alternative theories of gravity (without dark matter) predict an isotropic lensing signal, which is excluded with 99.5% confidence. Hence, our results provide strong support for the existence of dark matter. We also study the average mass profile around the lenses, using a maximum likelihood analysis. We consider two models for the halo mass profile: a truncated isothermal sphere (TIS) and a Navarro-Frenk-White (NFW) profile. We adopt observationally motivated scaling relations between the lens luminosity and the velocity dispersion and the extent of the halo. The TIS model yields a best-fit velocity dispersion of σ=136+/-5+/-3 km s-1 (all errors are 68% confidence limits; the first error bar indicates the statistical uncertainty, whereas the second error bar indicates the systematic error) and a truncation radius s=185+30-28h-1 kpc for a galaxy with a fiducial luminosity of LB=1010h-2LB,solar (under the assumption that

  15. Halo-independent methods for inelastic dark matter scattering

    SciTech Connect

    Bozorgnia, Nassim; Schwetz, Thomas; Herrero-Garcia, Juan; Zupan, Jure E-mail: juan.a.herrero@uv.es E-mail: jure.zupan@cern.ch

    2013-07-01

    We present halo-independent methods to analyze the results of dark matter direct detection experiments assuming inelastic scattering. We focus on the annual modulation signal reported by DAMA/LIBRA and present three different halo-independent tests. First, we compare it to the upper limit on the unmodulated rate from XENON100 using (a) the trivial requirement that the amplitude of the annual modulation has to be smaller than the bound on the unmodulated rate, and (b) a bound on the annual modulation amplitude based on an expansion in the Earth's velocity. The third test uses the special predictions of the signal shape for inelastic scattering and allows for an internal consistency check of the data without referring to any astrophysics. We conclude that a strong conflict between DAMA/LIBRA and XENON100 in the framework of spin-independent inelastic scattering can be established independently of the local properties of the dark matter halo.

  16. Particle ejection during mergers of dark matter halos

    SciTech Connect

    Carucci, Isabella P.; Sparre, Martin; Hansen, Steen H.; Joyce, Michael E-mail: sparre@dark-cosmology.dk E-mail: joyce@lpnhe.in2p3.fr

    2014-06-01

    Dark matter halos are built from accretion and merging. During merging some of the dark matter particles may be ejected with velocities higher than the escape velocity. We use both N-body simulations and single-particle smooth-field simulations to demonstrate that rapid changes to the mean field potential are responsible for such ejection, and in particular that dynamical friction plays no significant role in it. Studying a range of minor mergers, we find that typically between 5–15% of the particles from the smaller of the two merging structures are ejected. We also find that the ejected particles originate essentially from the small halo, and more specifically are particles in the small halo which pass later through the region in which the merging occurs.

  17. Systematic uncertainties from halo asphericity in dark matter searches

    SciTech Connect

    Bernal, Nicolás; Forero-Romero, Jaime E.; Garani, Raghuveer; Palomares-Ruiz, Sergio E-mail: je.forero@uniandes.edu.co E-mail: sergio.palomares.ruiz@ific.uv.es

    2014-09-01

    Although commonly assumed to be spherical, dark matter halos are predicted to be non-spherical by N-body simulations and their asphericity has a potential impact on the systematic uncertainties in dark matter searches. The evaluation of these uncertainties is the main aim of this work, where we study the impact of aspherical dark matter density distributions in Milky-Way-like halos on direct and indirect searches. Using data from the large N-body cosmological simulation Bolshoi, we perform a statistical analysis and quantify the systematic uncertainties on the determination of local dark matter density and the so-called J factors for dark matter annihilations and decays from the galactic center. We find that, due to our ignorance about the extent of the non-sphericity of the Milky Way dark matter halo, systematic uncertainties can be as large as 35%, within the 95% most probable region, for a spherically averaged value for the local density of 0.3-0.4 GeV/cm {sup 3}. Similarly, systematic uncertainties on the J factors evaluated around the galactic center can be as large as 10% and 15%, within the 95% most probable region, for dark matter annihilations and decays, respectively.

  18. Generalized halo independent comparison of direct dark matter detection data

    SciTech Connect

    Nobile, Eugenio Del; Gelmini, Graciela; Huh, Ji-Haeng; Gondolo, Paolo E-mail: gelmini@physics.ucla.edu E-mail: jhhuh@physics.ucla.edu

    2013-10-01

    We extend the halo-independent method to compare direct dark matter detection data, so far used only for spin-independent WIMP-nucleon interactions, to any type of interaction. As an example we apply the method to magnetic moment interactions.

  19. The abundance and environment of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Metuki, Ofer; Libeskind, Noam I.; Hoffman, Yehuda

    2016-04-01

    An open question in cosmology and the theory of structure formation is to what extent does environment affect the properties of galaxies and haloes. The present paper aims at shedding light on this problem. The paper focuses on the analysis of a dark matter only simulation and it addresses the issue of how the environment affects the abundance of haloes, which are are assigned four attributes: their virial mass, an ambient density calculated with an aperture that scales with Rvir (ΔM), a fixed-aperture (ΔR) ambient density, and a cosmic web classification (i.e. voids, sheets, filaments, and knots, as defined by the V-web algorithm). ΔM is the mean density around a halo evaluated within a sphere of a radius of 5Rvir, where Rvir is the virial radius. ΔR is the density field Gaussian smoothed with R=4{ {h}^{-1}Mpc}, evaluated at the center of the halo. The main result of the paper is that the difference between haloes in different web elements stems from the difference in their mass functions, and does not depend on their adaptive-aperture ambient density. A dependence on the fixed-aperture ambient density is induced by the cross correlation between the mass of a halo and its fixed-aperture ambient density.

  20. The abundance and environment of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Metuki, Ofer; Libeskind, Noam I.; Hoffman, Yehuda

    2016-07-01

    An open question in cosmology and the theory of structure formation is to what extent does environment affect the properties of galaxies and haloes. The present paper aims at shedding light on this problem. The paper focuses on the analysis of a dark matter only simulation and it addresses the issue of how the environment affects the abundance of haloes, which are assigned four attributes: their virial mass, an ambient density calculated with an aperture that scales with Rvir (ΔM), a fixed-aperture (ΔR) ambient density, and a cosmic web classification (i.e. voids, sheets, filaments, and knots, as defined by the V-web algorithm). ΔM is the mean density around a halo evaluated within a sphere of a radius of 5Rvir, where Rvir is the virial radius. ΔR is the density field Gaussian smoothed with R = 4 h-1 Mpc, evaluated at the centre of the halo. The main result of the paper is that the difference between haloes in different web elements stems from the difference in their mass functions, and does not depend on their adaptive-aperture ambient density. A dependence on the fixed-aperture ambient density is induced by the cross-correlation between the mass of a halo and its fixed-aperture ambient density.

  1. 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.

  2. The abundance and environment of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Metuki, Ofer; Libeskind, Noam I.; Hoffman, Yehuda

    2016-07-01

    An open question in cosmology and the theory of structure formation is to what extent does environment affect the properties of galaxies and haloes. The present paper aims at shedding light on this problem. The paper focuses on the analysis of a dark matter only simulation and it addresses the issue of how the environment affects the abundance of haloes, which are are assigned four attributes: their virial mass, an ambient density calculated with an aperture that scales with $R_{vir}$ ($\\Delta_M$), a fixed-aperture ($\\Delta_R$) ambient density, and a cosmic web classification (i.e. voids, sheets, filaments, and knots, as defined by the V--web algorithm). $\\Delta_M$ is the mean density around a halo evaluated within a sphere of a radius of $5$\\rvir, where \\rvir\\ is the virial radius. $\\Delta_R$ is the density field Gaussian smoothed with $R=4h^{-1}$Mpc, evaluated at the center of the halo. The main result of the paper is that the difference between haloes in different web elements stems from the difference in their mass functions, and does not depend on their adaptive-aperture ambient density. A dependence on the fixed-aperture ambient density is induced by the cross correlation between the mass of a halo and its fixed-aperture ambient density.

  3. Dynamical evolution of primordial dark matter haloes through mergers

    NASA Astrophysics Data System (ADS)

    Ogiya, Go; Nagai, Daisuke; Ishiyama, Tomoaki

    2016-09-01

    Primordial dark matter (DM) haloes are the smallest gravitationally bound DM structures from which the first stars, black holes and galaxies form and grow in the early universe. However, their structures are sensitive to the free streaming scale of DM, which in turn depends on the nature of DM particles. In this work, we test the hypothesis that the slope of the central cusps in primordial DM haloes near the free streaming scale depends on the nature of merging process. By combining and analysing data from a cosmological simulation with the cutoff in the small-scale matter power spectrum as well as a suite of controlled, high-resolution simulations of binary mergers, we find that (1) the primordial DM haloes form preferentially through major mergers in radial orbits; (2) their central DM density profile is more susceptible to a merging process compared to that of galaxy- and cluster-sized DM haloes; (3) consecutive major mergers drive the central density slope to approach the universal form characterized by the Navarro-Frenk-White profile, which is shown to be robust to the impacts of mergers and serves an attractor solution for the density structure of DM haloes. Our work highlights the importance of dynamical processes on the structure formation during the Dark Ages.

  4. Could wormholes form in dark matter galactic halos?

    NASA Astrophysics Data System (ADS)

    Rahaman, Farook; Shit, G. C.; Sen, Banashree; Ray, Saibal

    2016-01-01

    We estimate expression for velocity as a function of the radial coordinate r by using polynomial interpolation based on the experimental data of rotational velocities at distant outer regions of galaxies. The interpolation technique has been used to estimate fifth degree polynomial followed by cubic spline interpolation. This rotational velocity is used to find the geometry of galactic halo regions within the framework of Einstein's general relativity. In this paper we have analyzed features of galactic halo regions based on two possible choices for the dark matter density profile, viz. Navarro, Frenk & White (NFW) type (Navarro et al. in Astrophys. J. 462:563, 1996) and Universal Rotation Curve (URC) (Castignani et al. in Nat. Sci. 4:265, 2012). It is argued that spacetime of the galactic halo possesses some of the characteristics needed to support traversable wormholes.

  5. A Robust Measure of Dark Matter Halo Ellipticities

    NASA Astrophysics Data System (ADS)

    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-like dwarf galaxy with a confidence between 0 and 5σ, depending on the orientation of each halo. With two epochs of observations, TMT will achieve a 5σ discovery of torque and thus asphericity for most such galaxies, thus providing a new and powerful test of the ΛCDM model.

  6. MAGNIFICATION BY GALAXY GROUP DARK MATTER HALOS

    SciTech Connect

    Ford, Jes; Hildebrandt, Hendrik; Van Waerbeke, Ludovic; Leauthaud, Alexie; Tanaka, Masayuki; Capak, Peter; Finoguenov, Alexis; George, Matthew R.; Rhodes, Jason

    2012-08-01

    We report on the detection of gravitational lensing magnification by a population of galaxy groups, at a significance level of 4.9{sigma}. Using X-ray-selected groups in the COSMOS 1.64 deg{sup 2} field, and high-redshift Lyman break galaxies as sources, we measure a lensing-induced angular cross-correlation between the samples. After satisfying consistency checks that demonstrate we have indeed detected a magnification signal, and are not suffering from contamination by physical overlap of samples, we proceed to implement an optimally weighted cross-correlation function to further boost the signal to noise of the measurement. Interpreting this optimally weighted measurement allows us to study properties of the lensing groups. We model the full distribution of group masses using a composite-halo approach, considering both the singular isothermal sphere and Navarro-Frenk-White profiles, and find our best-fit values to be consistent with those recovered using the weak-lensing shear technique. We argue that future weak-lensing studies will need to incorporate magnification along with shear, both to reduce residual systematics and to make full use of all available source information, in an effort to maximize scientific yield of the observations.

  7. Galaxy halos and the nature of dark matter

    NASA Astrophysics Data System (ADS)

    Moore, Ben

    1995-07-01

    One of the few observational facts that we know about dark matter is that within about one tenth of the virial radius, the dark halos of some galaxies have density profiles which fall with the radius as ρ(r)~rn, where n~=0. Any successful dark matter candidate must be able to reproduce these observations. Cold dark matter (CDM) particles interact primarily by gravity and therefore cluster with no preferred scale, hence galaxy halos are predicted to have singular density profiles with approximately isothermal power law slopes on all scales (Filmore & Goldreich 1984, Bertschinger 1985). The theoretical predictions do not take account of the irregular merging and virialisation processes taking place during structure formation. Therefore, we must compare the observations with numerical N-body simulations which are ideally suited for this type of problem and have just begun to probe structure formation on these scales. The highest resolution simulations (Dubinski & Carlberg 1991, Warren et al. 1992, Carlberg 1993, Crone et al. 1994) produce halo density profiles which fall too steeply to match the data (Moore 1994, Flores & Primack 1994). Moreover, Crone et al. (1994) claim that after correcting for force softening the density profiles match the analytic predictions. If these results are confirmed by higher resolution studies then we can reject the hypothesis that the dark matter is a cold, dissipationless particle. However, there is some disagreement between the results of the above authors and the slightly lower resolution studies of Katz & White (1993) and Navarro, Frenk & White (1994).

  8. The evolution of disk galaxies in cold dark matter halos

    NASA Astrophysics Data System (ADS)

    Font, Andreea S.

    2005-11-01

    We use high resolution N-body simulations to investigate the dynamical effects that substructure in Cold Dark Matter (CDM) halos have on galactic disks, with particular emphasis on their secular evolution, heating, tilting and warping. The simulations analyzed here are some of the largest and most realistic simulations of disk heating/warping available in the appropriate cosmological context. Our detailed treatment of the dark matter distinguishes them from previous numerical simulations that have focused on the interaction with a single satellite. Our study shows that substructure halos with masses, densities and orbits expected in the CDM paradigm typically play only a minor dynamical role in the heating of the disk over several Gyrs, and thus do not typically pose a danger to the stability of thin disks. This is largely because the most massive dark satellites, which dominate the secular heating, seldom approach the disk, where tidal effects are strongest. Occasionally, however, massive subhalos couple effectively with the disk, resulting in noticeable tidal effects on the structure of the stellar disk, including: (i) tilting and (ii) the forcing of short-lived, asymmetric warps as a result of tidal impulses that arise during each pericentric passage. I show that this is a viable mechanism for creating asymmetric disk warps such as those observed in the local Universe. Moreover, the fact that a satellite can have recurrent interactions with the disk suggests a natural explanation for the observed frequency of the warps, which would otherwise be very short lived. I conclude that dark matter halo substructure does not preclude virialized CDM halos from being acceptable hosts of thin stellar disks like that of the Milky Way and that the ubiquity of minor stellar warps may be associated with the recurrent tidal influence on the disk of the most massive substructure halos.

  9. Stellar spiral structures in triaxial dark matter haloes

    NASA Astrophysics Data System (ADS)

    Hu, Shaoran; Sijacki, Debora

    2016-09-01

    We employ very high resolution simulations of isolated Milky Way-like galaxies to study the effect of triaxial dark matter haloes on exponential stellar discs. Non-adiabatic halo shape changes can trigger two-armed grand-design spiral structures which extend all the way to the edge of the disc. Their pattern speed coincides with the inner Lindblad resonance indicating that they are kinematic density waves which can persist up to several Gyr. In dynamically cold discs, grand-design spirals are swing amplified and after a few Gyr can lead to the formation of (multi-armed) transient recurrent spirals. Stellar discs misaligned to the principal planes of the host triaxial halo develop characteristic integral shaped warps, but otherwise exhibit very similar spiral structures as aligned discs. For the grand-design spirals in our simulations, their strength dependence with radius is determined by the torque on the disc, suggesting that by studying grand-design spirals without bars it may be possible to set constraints on the tidal field and host dark matter halo shape.

  10. A NEW MODEL FOR DARK MATTER HALOS HOSTING QUASARS

    SciTech Connect

    Cen, Renyue; Safarzadeh, Mohammadtaher

    2015-01-10

    A new model for quasar-hosting dark matter halos, meeting two physical conditions, is put forth. First, significant interactions are taken into consideration to trigger quasar activities. Second, satellites in very massive halos at low redshift are removed from consideration due to their deficiency in cold gas. We analyze the Millennium Simulation to find halos that meet these two conditions and simultaneously match two-point auto-correlation functions of quasars and cross-correlation functions between quasars and galaxies at z = 0.5-3.2. The masses of the quasar hosts found decrease with decreasing redshift, with the mass thresholds being [(2-5) × 10{sup 12}, (2-5) × 10{sup 11}, (1-3) × 10{sup 11}] M {sub ☉} for median luminosities of ∼[10{sup 46}, 10{sup 46}, 10{sup 45}] erg s{sup –1} at z = (3.2, 1.4, 0.53), respectively, an order of magnitude lower than those inferred based on halo occupation distribution modeling. In this model, quasar hosts are primarily massive central halos at z ≥ 2-3 but increasingly dominated by lower mass satellite halos experiencing major interactions toward lower redshift. However, below z = 1, satellite halos in groups more massive than ∼2 × 10{sup 13} M {sub ☉} do not host quasars. Whether for central or satellite halos, imposing the condition of significant interactions substantially boosts the clustering strength compared to the total population with the same mass cut. The inferred lifetimes of quasars at z = 0.5-3.2 of 3-30 Myr are in agreement with observations. Quasars at z ∼ 2 would be hosted by halos of mass ∼5 × 10{sup 11} M {sub ☉} in this model, compared to ∼3 × 10{sup 12} M {sub ☉} previously thought, which would help reconcile with the observed, otherwise puzzling high covering fractions for Lyman limit systems around quasars.

  11. Chandra's Find of Lonely Halo Raises Questions About Dark Matter

    NASA Astrophysics Data System (ADS)

    2004-10-01

    Dark matter continues to confound astronomers, as NASA's Chandra X-ray Observatory demonstrated with the detection of an extensive envelope of dark matter around an isolated elliptical galaxy. This discovery conflicts with optical data that suggest a dearth of dark matter around similar galaxies, and raises questions about how galaxies acquire and keep such dark matter halos. The observed galaxy, known as NGC 4555, is unusual in that it is a fairly large, elliptical galaxy that is not part of a group or cluster of galaxies. In a paper to be published in the November 1, 2004 issue of the Monthly Notices of the Royal Astronomical Society, Ewan O'Sullivan of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA and Trevor Ponman of the University of Birmingham, United Kingdom, use the Chandra data to show that the galaxy is embedded in a cloud of 10-million-degree-Celsius gas. X-ray/Optical Composite of NGC 4555 X-ray/Optical Composite of NGC 4555 This hot gas cloud has a diameter of about 400,000 light years, about twice that of the visible galaxy. An enormous envelope, or halo, of dark matter is needed to confine the hot cloud to the galaxy. The total mass of the dark matter halo is about ten times the combined mass of the stars in the galaxy, and 300 times the mass of the hot gas cloud. A growing body of evidence indicates that dark matter - which interacts with itself and "normal" matter only through gravity - is the dominant form of matter in the universe. According to the popular "cold dark matter" theory, dark matter consists of mysterious particles left over from the dense early universe that were moving slowly when galaxies and galaxy clusters began to form. "The observed properties of NGC 4555 confirm that elliptical galaxies can posses dark matter halos of their own, regardless of their environment," said O'Sullivan. "This raises an important question: what determines whether elliptical galaxies have dark matter halos?" DSS Optical Image of NGC

  12. Probing dark matter halos with strong gravitational lensing

    NASA Astrophysics Data System (ADS)

    Ferreras, Ignacio

    2015-08-01

    Strong gravitational lensing over galaxy scales allows us to explore dark matter halos and their connection with the luminous component. In this talk we present recent work on a sample extracted from the SLACS dataset, where the spectroscopic information from SDSS allows us to study the effect of a non-universal initial mass function on the stellar mass-to-light ratio. In addition, by studying galaxies where the background source probes the central part of the lens, we can derive significant constraints on the properties of the dark matter halo. This is one of the few observational methods that can be used to contrast with the standard concentration-virial mass relationships proposed by numerical simulations.

  13. Dynamics of dark energy in collapsing halo of dark matter

    NASA Astrophysics Data System (ADS)

    Tsizh, M.; Novosyadlyj, B.

    2015-09-01

    We investigate the non-linear evolution of spherical density and velocity perturbations of dark matter and dark energy in the expanding Universe. For this we have used the conservation and Einstein equations to describe the evolution of gravitationally coupled inhomogeneities of dark matter, dark energy and radiation from the linear stage in the early Universe to the non-linear stage at the current epoch. A simple method of numerical integration of the system of non-linear differential equations for evolution of the central part of halo is proposed. The results are presented for the halo of cluster (k=2 Mpc^{-1}) and supercluster scales (k=0.2 Mpc^{-1}) and show that a quintessential scalar field dark energy with a low value of effective speed of sound c_s<0.1 can have a notable impact on the formation of large-scale structures in the expanding Universe.

  14. Dark-matter decays and self-gravitating halos

    SciTech Connect

    Peter, Annika H. G.; Moody, Christopher E.; Kamionkowski, Marc

    2010-05-15

    We consider models in which a dark-matter particle decays to a slightly less massive daughter particle and a noninteracting massless particle. The decay gives the daughter particle a small velocity kick. Self-gravitating dark-matter halos that have a virial velocity smaller than this velocity kick may be disrupted by these particle decays, while those with larger virial velocities will be heated. We use numerical simulations to follow the detailed evolution of the total mass and density profile of self-gravitating systems composed of particles that undergo such velocity kicks as a function of the kick speed (relative to the virial velocity) and the decay time (relative to the dynamical time). We show how these decays will affect the halo mass-concentration relation and mass function. Using measurements of the halo mass-concentration relation and galaxy-cluster mass function to constrain the lifetime-kick-velocity parameter space for decaying dark matter, we find roughly that the observations rule out the combination of kick velocities greater than 100 km s{sup -1} and decay times less than a few times the age of the Universe.

  15. Running of oscillation parameters in matter with flavor-diagonal non-standard interactions of the neutrino

    NASA Astrophysics Data System (ADS)

    Agarwalla, Sanjib Kumar; Kao, Yee; Saha, Debashis; Takeuchi, Tatsu

    2015-11-01

    In this article we unravel the role of matter effect in neutrino oscillation in the presence of lepton-flavor-conserving, non-universal non-standard interactions (NSI's) of the neutrino. Employing the Jacobi method, we derive approximate analytical expressions for the effective mass-squared differences and mixing angles in matter. It is shown that, within the effective mixing matrix, the Standard Model (SM) W -exchange interaction only affects θ 12 and θ 13, while the flavor-diagonal NSI's only affect θ 23. The CP-violating phase δ remains unaffected. Using our simple and compact analytical approximation, we study the impact of the flavor-diagonal NSI's on the neutrino oscillation probabilities for various appearance and disappearance channels. At higher energies and longer baselines, it is found that the impact of the NSI's can be significant in the ν μ → ν μ channel, which can probed in future atmospheric neutrino experiments, if the NSI's are of the order of their current upper bounds. Our analysis also enables us to explore the possible degeneracy between the octant of θ 23 and the sign of the NSI parameter for a given choice of mass hierarchy in a simple manner.

  16. HMcode: Halo-model matter power spectrum computation

    NASA Astrophysics Data System (ADS)

    Mead, Alexander

    2015-08-01

    HMcode computes the halo-model matter power spectrum. It is written in Fortran90 and has been designed to quickly (~0.5s for 200 k-values across 16 redshifts on a single core) produce matter spectra for a wide range of cosmological models. In testing it was shown to match spectra produced by the 'Coyote Emulator' to an accuracy of 5 per cent for k less than 10h Mpc^-1. However, it can also produce spectra well outside of the parameter space of the emulator.

  17. SELF-SIMILAR SOLUTIONS OF TRIAXIAL DARK MATTER HALOS

    SciTech Connect

    Lithwick, Yoram; Dalal, Neal

    2011-06-20

    We investigate the collapse and the internal structure of dark matter halos. We consider halo formation from initially scale-free perturbations, for which gravitational collapse is self-similar. Fillmore and Goldreich and Bertschinger solved the one-dimensional (i.e., spherically symmetric) case. We generalize their results by formulating the three-dimensional self-similar equations. We solve the equations numerically and analyze the similarity solutions in detail, focusing on the internal density profiles of the collapsed halos. By decomposing the total density into subprofiles of particles that collapse coevally, we identify two effects as the main determinants of the internal density structure of halos: adiabatic contraction and the shape of a subprofile shortly after collapse; the latter largely reflects the triaxiality of the subprofile. We develop a simple model that describes the results of our three-dimensional simulations. In a companion paper, we apply this model to more realistic cosmological fluctuations, and thereby explain the origin of the nearly universal (NFW-like) density profiles found in N-body simulations.

  18. The Dark Matter halo of the Milky Way, AD 2013

    SciTech Connect

    Nesti, Fabrizio; Salucci, Paolo E-mail: salucci@sissa.it

    2013-07-01

    We derive the mass model of the Milky Way (MW), crucial for Dark Matter (DM) direct and indirect detection, using recent data and a cored dark matter (DM) halo profile, which is favoured by studies of external galaxies. The method used consists in fitting a spherically symmetric model of the Galaxy with a Burkert DM halo profile to available data: MW terminal velocities in the region inside the solar circle, circular velocity as recently estimated from maser star forming regions at intermediate radii, and velocity dispersions of stellar halo tracers for the outermost Galactic region. The latter are reproduced by integrating the Jeans equation for every modeled mass distribution, and by allowing for different velocity anisotropies for different tracer populations. For comparison we also consider a Navarro-Frenk-White profile. We find that the cored profile is the preferred one, with a shallow central density of ρ{sub H} ∼ 4 × 10{sup 7}M{sub ☉}/kpc{sup 3} and a large core radius R{sub H} ∼ 10 kpc, as observed in external spirals and in agreement with the mass model underlying the Universal Rotation Curve of spirals. We describe also the derived model uncertainties, which are crucially driven by the poorly constrained velocity dispersion anisotropies of halo tracers. The emerging cored DM distribution has implications for the DM annihilation angular profile, which is much less boosted in the Galactic center direction with respect to the case of the standard ΛCDM, NFW profile. Using the derived uncertainties we discuss finally the limitations and prospects to discriminate between cored and cusped DM profile with a possible observed diffuse DM annihilation signal. The present mass model aims to characterize the present-day description of the distribution of matter in our Galaxy, which is needed to frame current crucial issues of Cosmology, Astrophysics and Elementary Particles.

  19. Precision measurement of the local bias of dark matter halos

    NASA Astrophysics Data System (ADS)

    Lazeyras, Titouan; Wagner, Christian; Baldauf, Tobias; 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 & Tormen (1999) and Tinker et al. (2008) halo mass functions matches the measured linear bias parameter only at the level of 10%. The prediction 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 b2(b1) and b3(b1), which work well over a range of redshifts.

  20. Stochastic gravitational wave background from cold dark matter halos

    SciTech Connect

    Carbone, Carmelita; Baccigalupi, Carlo; Matarrese, Sabino

    2006-03-15

    The current knowledge of cosmological structure formation suggests that Cold Dark Matter (CDM) halos possess a nonspherical density profile, implying that cosmic structures can be potential sources of gravitational waves via power transfer from scalar perturbations to tensor metric modes in the nonlinear regime. By means of a previously developed mathematical formalism and a triaxial collapse model, we numerically estimate the stochastic gravitational-wave background generated by CDM halos during the fully nonlinear stage of their evolution. Our results suggest that the energy density associated with this background is comparable to that produced by primordial tensor modes at frequencies {nu}{approx_equal}10{sup -18}-10{sup -17} Hz if the energy scale of inflation is V{sup 1/4}{approx_equal}1-2x10{sup 15} GeV, and that these gravitational waves could give rise to several cosmological effects, including secondary CMB anisotropy and polarization.

  1. Dwarf galaxies in multistate scalar field dark matter halos

    NASA Astrophysics Data System (ADS)

    Martinez-Medina, L. A.; Robles, V. H.; Matos, T.

    2015-01-01

    We analyze the velocity dispersion for eight of the Milky Way dwarf spheroidal satellites in the context of finite temperature scalar field dark matter. In this model the finite temperature allows the scalar field to be in configurations that possess excited states, a feature that has proved to be necessary in order to explain the asymptotic rotational velocities found in low surface brightness (LSB) galaxies. In this work we show that excited states are not only important in large galaxies but also have visible effects in dwarf spheroidals. Additionally, we stress that contrary to previous works where the scalar field dark matter halos are consider to be purely Bose-Einstein condensates, the inclusion of excited states in these halo configurations provides a consistent framework capable of describing LSB and dwarf galaxies of different sizes without arriving to contradictions within the scalar field dark matter model. Using this new framework we find that the addition of excited states accounts very well for the raise in the velocity dispersion in Milky Way dwarf spheroidal galaxies improving the fit compared to the one obtained assuming all the dark matter to be in the form of a Bose-Einstein condensate.

  2. HaloSat: A CubeSat to Map the Distribution of Baryonic Matter in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Miles, Drew M.

    2016-04-01

    Approximately half of predicted baryonic matter in the Milky Way remains unidentified. One possible explanation for the location of this missing matter is in an extended Galactic halo. HaloSat is a CubeSat that aims to constrain the mass and distribution of the halo’s baryonic matter by obtaining an all-sky map of O VII and O VIII emission in the hot gas associated with the halo of the Milky Way. HaloSat offers an improvement in the quality of measurements of oxygen line emission over existing X-ray observatories and an observation plan dedicated to mapping the hot gas in the Galactic halo. In addition to the missing baryon problem, HaloSat will assign a portion of its observations to the solar wind charge exchange (SWCX) in order to calibrate models of SCWX emission. We present here the current status of HaloSat and the progression of instrument development in anticipation of a 2018 launch.

  3. Mapping stellar content to dark matter haloes - II. Halo mass is the main driver of galaxy quenching

    NASA Astrophysics Data System (ADS)

    Zu, Ying; Mandelbaum, Rachel

    2016-04-01

    We develop a simple yet comprehensive method to distinguish the underlying drivers of galaxy quenching, using the clustering and galaxy-galaxy lensing of red and blue galaxies in Sloan Digital Sky Survey. Building on the iHOD framework developed by Zu & Mandelbaum, we consider two quenching scenarios: (1) a `halo' quenching model in which halo mass is the sole driver for turning off star formation in both centrals and satellites; and (2) a `hybrid' quenching model in which the quenched fraction of galaxies depends on their stellar mass, while the satellite quenching has an extra dependence on halo mass. The two best-fitting models describe the red galaxy clustering and lensing equally well, but halo quenching provides significantly better fits to the blue galaxies above 1011 h-2 M⊙. The halo quenching model also correctly predicts the average halo mass of the red and blue centrals, showing excellent agreement with the direct weak lensing measurements of locally brightest galaxies. Models in which quenching is not tied to halo mass, including an age-matching model in which galaxy colour depends on halo age at fixed M*, fail to reproduce the observed halo mass for massive blue centrals. We find similar critical halo masses responsible for the quenching of centrals and satellites (˜1.5 × 1012 h-1 M⊙), hinting at a uniform quenching mechanism for both, e.g. the virial shock heating of infalling gas. The success of the iHOD halo quenching model provides strong evidence that the physical mechanism that quenches star formation in galaxies is tied principally to the masses of their dark matter haloes rather than the properties of their stellar components.

  4. The statistical properties of Λ cold dark matter halo formation

    NASA Astrophysics Data System (ADS)

    Cole, Shaun; Helly, John; Frenk, Carlos S.; Parkinson, Hannah

    2008-01-01

    We present a comparison of the statistical properties of dark matter halo merger trees extracted from the Millennium Simulation with Extended Press-Schechter (EPS) formalism and the related GALFORM Monte Carlo method for generating ensembles of merger trees. The volume, mass resolution and output frequency make the Millennium Simulation a unique resource for the study of the hierarchical growth of structure. We construct the merger trees of present-day friends-of-friends groups and calculate a variety of statistics that quantify the masses of their progenitors as a function of redshift, accretion rates, and the redshift distribution of their most recent major merger. We also look in the forward direction and quantify the present-day mass distribution of haloes into which high-redshift progenitors of a specific mass become incorporated. We find that the EPS formalism and its Monte Carlo extension capture the qualitative behaviour of all these statistics, but as redshift increases they systematically underestimate the masses of the most massive progenitors. This shortcoming is worst for the Monte Carlo algorithm. We present a fitting function to a scaled version of the progenitor mass distribution and show how it can be used to make more accurate predictions of both progenitor and final halo mass distributions.

  5. Dissecting the spin distribution of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Antonuccio-Delogu, V.; Dobrotka, A.; Becciani, U.; Cielo, S.; Giocoli, C.; Macciò, A. V.; Romeo-Veloná, A.

    2010-09-01

    The spin probability distribution of dark matter haloes has often been modelled as being very near to a lognormal. Most of the theoretical attempts to explain its origin and evolution invoke some hypotheses concerning the influence of tidal interactions or merging on haloes. Here we apply a very general statistical theorem introduced by Cramér (1936) to study the origin of the deviations from the reference lognormal shape: we find that these deviations originate from correlations between two quantities entering the definition of spin, namely the ratio J/M5/2 (which depends only on mass) and the modulus E of the total (gravitational + kinetic) energy. To reach this conclusion, we have made usage of the results deduced from two high spatial- and mass-resolution simulations. Our simulations cover a relatively small volume and produce a sample of more than 16000 gravitationally bound haloes, each traced by at least 300 particles. We verify that our results are stable to different systematics, by comparing our results with those derived by the GIF2 and by a more recent simulation performed by Macciò et al. We find that the spin probability distribution function shows systematic deviations from a lognormal, at all redshifts z <~ 1. These deviations depend on mass and redshift: at small masses they change little with redshift, and also the best lognormal fits are more stable. The J -M relationship is well described by a power law of exponent α very near to the linear theory prediction (α = 5/3), but systematically lower than this at z <~ 0.3. We argue that the fact that deviations from a lognormal PDF are present only for high-spin haloes could point to a role of large-scale tidal fields in the evolution of the spin PDF.

  6. The galactic halo in mixed dark matter cosmologies

    SciTech Connect

    Anderhalden, D.; Diemand, J.; Schneider, A.; Bertone, G.; Macciò, A.V. E-mail: diemand@physik.uzh.ch E-mail: maccio@mpia.de

    2012-10-01

    A possible solution to the small scale problems of the cold dark matter (CDM) scenario is that the dark matter consists of two components, a cold and a warm one. We perform a set of high resolution simulations of the Milky Way halo varying the mass of the WDM particle (m{sub WDM}) and the cosmic dark matter mass fraction in the WDM component ( f-bar {sub W}). The scaling ansatz introduced in combined analysis of LHC and astroparticle searches postulates that the relative contribution of each dark matter component is the same locally as on average in the Universe (e.g. f{sub W,s}un = f-bar {sub W}). Here we find however, that the normalised local WDM fraction (f{sub W,s}un / f-bar {sub W}) depends strongly on m{sub WDM} for m{sub WDM} < 1 keV. Using the scaling ansatz can therefore introduce significant errors into the interpretation of dark matter searches. To correct this issue a simple formula that fits the local dark matter densities of each component is provided.

  7. Dark matter halos with cores from hierarchical structure formation

    NASA Astrophysics Data System (ADS)

    Strigari, Louis E.; Kaplinghat, Manoj; Bullock, James S.

    2007-03-01

    We show that dark matter emerging from late decays (z≲1000) produces a linear power spectrum identical to that of cold dark matter (CDM) on all observationally relevant scales (≳0.1Mpc), and simultaneously generates observable constant-density cores in small dark matter halos. We refer to this class of models as meta-cold dark matter (mCDM), because it is born with nonrelativistic velocities from the decays of cold thermal relics. The constant-density cores are a result of the low phase-space density of mCDM at birth. Warm dark matter cannot produce similar size phase-space limited cores without saturating the Lyα power spectrum bounds. Dark matter-dominated galaxy rotation curves and stellar velocity dispersion profiles may provide the best means to discriminate between mCDM and CDM. mCDM candidates are motivated by the particle spectrum of supersymmetric and extra dimensional extensions to the standard model of particle physics.

  8. Cold Dark Matter Substructures in Early-type Galaxy Halos

    NASA Astrophysics Data System (ADS)

    Fiacconi, Davide; Madau, Piero; Potter, Doug; Stadel, Joachim

    2016-06-01

    We present initial results from the “Ponos” zoom-in numerical simulations of dark matter substructures in massive ellipticals. Two very highly resolved dark matter halos with M vir = 1.2 × 1013 {M}ȯ and M vir = 6.5 × 1012 {M}ȯ and different (“violent” versus “quiescent”) assembly histories have been simulated down to z = 0 in a ΛCDM cosmology with a total of 921,651,914 and 408,377,544 particles, respectively. Within the virial radius, the total mass fraction in self-bound M sub > 106 {M}ȯ subhalos at the present epoch is 15% for the violent host and 16.5% for the quiescent one. At z = 0.7, these fractions increase to 19% and 33%, respectively, as more recently accreted satellites are less prone to tidal destruction. In projection, the average fraction of surface mass density in substructure at a distance of R/R vir = 0.02 (˜5–10 kpc) from the two halo centers ranges from 0.6% to ≳2%, significantly higher than that measured in simulations of Milky Way-sized halos. The contribution of subhalos with M sub < 109 {M}ȯ to the projected mass fraction is between one-fifth and one-third of the total, with the smallest share found in the quiescent host. We assess the impact of baryonic effects via twin, lower-resolution hydrodynamical simulations that include metallicity-dependent gas cooling, star formation, and a delayed-radiative-cooling scheme for supernova feedback. Baryonic contraction produces a super-isothermal total density profile and increases the number of massive subhalos in the inner regions of the main host. The host density profiles and projected subhalo mass fractions appear to be broadly consistent with observations of gravitational lenses.

  9. Cold Dark Matter Substructures in Early-type Galaxy Halos

    NASA Astrophysics Data System (ADS)

    Fiacconi, Davide; Madau, Piero; Potter, Doug; Stadel, Joachim

    2016-06-01

    We present initial results from the “Ponos” zoom-in numerical simulations of dark matter substructures in massive ellipticals. Two very highly resolved dark matter halos with M vir = 1.2 × 1013 {M}ȯ and M vir = 6.5 × 1012 {M}ȯ and different (“violent” versus “quiescent”) assembly histories have been simulated down to z = 0 in a ΛCDM cosmology with a total of 921,651,914 and 408,377,544 particles, respectively. Within the virial radius, the total mass fraction in self-bound M sub > 106 {M}ȯ subhalos at the present epoch is 15% for the violent host and 16.5% for the quiescent one. At z = 0.7, these fractions increase to 19% and 33%, respectively, as more recently accreted satellites are less prone to tidal destruction. In projection, the average fraction of surface mass density in substructure at a distance of R/R vir = 0.02 (∼5–10 kpc) from the two halo centers ranges from 0.6% to ≳2%, significantly higher than that measured in simulations of Milky Way-sized halos. The contribution of subhalos with M sub < 109 {M}ȯ to the projected mass fraction is between one-fifth and one-third of the total, with the smallest share found in the quiescent host. We assess the impact of baryonic effects via twin, lower-resolution hydrodynamical simulations that include metallicity-dependent gas cooling, star formation, and a delayed-radiative-cooling scheme for supernova feedback. Baryonic contraction produces a super-isothermal total density profile and increases the number of massive subhalos in the inner regions of the main host. The host density profiles and projected subhalo mass fractions appear to be broadly consistent with observations of gravitational lenses.

  10. Cosmological simulations of decaying dark matter: implications for small-scale structure of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Wang, Mei-Yu; Peter, Annika H. G.; Strigari, Louis E.; Zentner, Andrew R.; Arant, Bryan; Garrison-Kimmel, Shea; Rocha, Miguel

    2014-11-01

    We present a set of N-body simulations of a class of models in which an unstable dark matter particle decays into a stable dark matter particle and a non-interacting light particle with decay lifetime comparable to the Hubble time. We study the effects of the recoil kick velocity (Vk) received by the stable dark matter on the structures of dark matter haloes ranging from galaxy-cluster to Milky Way-mass scales. For Milky Way-mass haloes, we use high-resolution, zoom-in simulations to explore the effects of decays on Galactic substructure. In general, haloes with circular velocities comparable to the magnitude of kick velocity are most strongly affected by decays. We show that models with lifetimes Γ-1 ˜ H_0^{-1} and recoil speeds Vk ˜ 20-40 km s-1 can significantly reduce both the abundance of Galactic subhaloes and their internal densities. We find that decaying dark matter models that do not violate current astrophysical constraints can significantly mitigate both the `missing satellites problem' and the more recent `too big to fail problem'. These decaying models predict significant time evolution of haloes, and this implies that at high redshifts decaying models exhibit the similar sequence of structure formation as cold dark matter. Thus, decaying dark matter models are significantly less constrained by high-redshift phenomena than warm dark matter models. We conclude that models of decaying dark matter make predictions that are relevant for the interpretation of small galaxies observations in the Local Group and can be tested as well as by forthcoming large-scale surveys.

  11. The Dynamical Structure of Dark Matter Halos with Universal Properties

    NASA Astrophysics Data System (ADS)

    Van Hese, Emmanuel; Baes, Maarten; Dejonghe, Herwig

    2009-01-01

    N-body simulations have unveiled several apparently universal properties of dark matter halos, including a cusped density profile, a power-law pseudo-phase-space density ρ/σ3 r , and a linear β-γ relation between the density slope and the velocity anisotropy. We present a family of self-consistent phase-space distribution functions (DFs) F(E, L), based on the Dehnen-McLaughlin Jeans models, that incorporate these universal properties very accurately. These DFs, derived using a quadratic programming technique, are analytical, positive, and smooth over the entire phase space and are able to generate four-parameter velocity anisotropy profiles β(r) with arbitrary asymptotic values β0 and β∞. We discuss the orbital structure of six radially anisotropic systems in detail and argue that, apart from its use for generating initial conditions for N-body studies, our dynamical modeling provides a valuable complementary approach to understand the processes involved in the formation of dark matter halos.

  12. Signatures of dark matter halo expansion in galaxy populations

    NASA Astrophysics Data System (ADS)

    Brook, Chris B.; Di Cintio, Arianna

    2015-10-01

    Dark matter cores within galaxy haloes can be formed by energy feedback from star-forming regions: an energy balance suggests that the maximum core formation efficiency arises in galaxies with Mstar ˜ 108.5 M⊙. We show that a model population of galaxies, in which the density profile has been modified by such baryonic feedback, is able to explain the observed galaxy velocity function and Tully-Fisher relations significantly better than a model in which a universal cuspy density profile is assumed. Alternative models, namely warm or self-interacting dark matter, also provide a better match to these observed relations than a universal profile model does, but make different predictions for how halo density profiles vary with mass compared to the baryonic feedback case. We propose that different core formation mechanisms may be distinguished based on the imprint they leave on galaxy populations over a wide range of mass. Within the current observational data we find evidence of the expected signatures of the mass dependence of core formation generated by baryonic feedback.

  13. The Impact of Baryonic Physics on the Structure of Dark Matter Halos: the View from the FIRE Cosmological Simulations

    NASA Astrophysics Data System (ADS)

    Keung Chan, Tsang; Keres, Dusan; Oñorbe, Jose; Hopkins, Philip F.; Muratov, Alexander; Faucher-Giguere, Claude-Andre; Quataert, Eliot

    2016-06-01

    We study the distribution of cold dark matter (CDM) in cosmological simulations from the FIRE (Feedback In Realistic Environments) project, which incorporates explicit stellar feedback in the multi-phase ISM, with energetics from stellar population models. We find that stellar feedback, without ``fine-tuned'' parameters, greatly alleviates small-scale problems in CDM. Feedback causes bursts of star formation and outflows, altering the DM distribution. As a result, the inner slope of the DM halo profile (α) shows a strong mass dependence: profiles are shallow at Mh ∼ 1010-1011 M⊙ and steepen at higher/lower masses. The resulting core sizes and slopes are consistent with observations. Because the star formation efficiency, Ms/Mh is strongly halo mass dependent, a rapid change in α occurs around Mh ∼1010M⊙, (Ms∼106-107M⊙) as sufficient feedback energy becomes available to perturb the DM. Large cores are not established during the period of rapid growth of halos because of ongoing DM mass accumulation. Instead, cores require several bursts of star formation after the rapid buildup has completed. Stellar feedback dramatically reduces circular velocities in the inner kpc of massive dwarfs; this could be sufficient to explain the ``Too Big To Fail'' problem without invoking non-standard DM. Finally, feedback and baryonic contraction in Milky Way-mass halos produce DM profiles slightly shallower than the Navarro-Frenk-White profile, consistent with the normalization of the observed Tully-Fisher relation.

  14. THE COSMIC HISTORY OF THE SPIN OF DARK MATTER HALOS WITHIN THE LARGE-SCALE STRUCTURE

    SciTech Connect

    Trowland, Holly E.; Lewis, Geraint F.; Bland-Hawthorn, Joss

    2013-01-10

    We use N-body simulations to investigate the evolution of the orientation and magnitude of dark matter halo angular momentum within the large-scale structure since z = 3. We look at the evolution of the alignment of halo spins with filaments and with each other, as well as the spin parameter, which is a measure of the magnitude of angular momentum. It was found that the angular momentum vectors of dark matter halos at high redshift have a weak tendency to be orthogonal to filaments and high-mass halos have a stronger orthogonal alignment than low-mass halos. Since z = 1, the spins of low-mass halos have become weakly aligned parallel to filaments, whereas high-mass halos kept their orthogonal alignment. This recent parallel alignment of low-mass halos casts doubt on tidal torque theory as the sole mechanism for the buildup of angular momentum. We see evidence for bulk flows and the broadening of filaments over time in the alignments of halo spin and velocities. We find a significant alignment of the spin of neighboring dark matter halos only at very small separations, r < 0.3 Mpc h {sup -1}, which is driven by substructure. A correlation of the spin parameter with halo mass is confirmed at high redshift.

  15. CALET's sensitivity to Dark Matter annihilation in the galactic halo

    NASA Astrophysics Data System (ADS)

    Motz, H.; Asaoka, Y.; Torii, S.; Bhattacharyya, S.

    2015-12-01

    CALET (Calorimetric Electron Telescope), installed on the ISS in August 2015, directly measures the electron+positron cosmic rays flux up to 20 TeV. With its proton rejection capability of 1 : 105 and an aperture of 1200 cm2· sr, it will provide good statistics even well above one TeV, while also featuring an energy resolution of 2%, which allows it to detect fine structures in the spectrum. Such structures may originate from Dark Matter annihilation or decay, making indirect Dark Matter search one of CALET's main science objectives among others such as identification of signatures from nearby supernova remnants, study of the heavy nuclei spectra and gamma astronomy. The latest results from AMS-02 on positron fraction and total electron+positron flux can be fitted with a parametrization including a single pulsar as an extra power law source with exponential cut-off, which emits an equal amount of electrons and positrons. This single pulsar scenario for the positron excess is extrapolated into the TeV region and the expected CALET data for this case are simulated. Based on this prediction for CALET data, the sensitivity of CALET to Dark Matter annihilation in the galactic halo has been calculated. It is shown that CALET could significantly improve the limits compared to current data, especially for those Dark Matter candidates that feature a large fraction of annihilation directly into e+ + e-, such as the LKP (Lightest Kaluza-Klein particle).

  16. Galaxy mass models: MOND versus dark matter haloes

    NASA Astrophysics Data System (ADS)

    Randriamampandry, Toky H.; Carignan, Claude

    2014-04-01

    Mass models of 15 nearby dwarf and spiral galaxies are presented. The galaxies are selected to be homogeneous in terms of the method used to determine their distances, the sampling of their rotation curves (RCs) and the mass-to-light ratio (M/L) of their stellar contributions, which will minimize the uncertainties on the mass model results. Those RCs are modelled using the MOdified Newtonian Dynamics (MOND) prescription and the observationally motivated pseudo-isothermal (ISO) dark matter (DM) halo density distribution. For the MOND models with fixed M/L, better fits are obtained when the constant a0 is allowed to vary, giving a mean value of (1.13 ± 0.50) × 10-8 cm s-2, compared to the standard value of 1.21 × 10-8 cm s-2. Even with a0 as a free parameter, MOND provides acceptable fits (reduced χ 2_r < 2) for only 60 per cent (9/15) of the sample. The data suggest that galaxies with higher central surface brightnesses tend to favour higher values of the constant a0. This poses a serious challenge to MOND since a0 should be a universal constant. For the DM models, our results confirm that the DM halo surface density of ISO models is nearly constant at ρ0 RC ˜ 120 M⊙ pc-2. This means that if the M/L is determined by stellar population models, ISO DM models are left with only one free parameter, the DM halo central surface density.

  17. 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. PMID:27058067

  18. Possible evidence of thermodynamic equilibrium in dark matter halos

    SciTech Connect

    Davidson, Joshua; Sarker, Sanjoy K.; Stern, Allen E-mail: ssarker@ua.edu

    2014-06-10

    After deducing the density profiles and gravitational potential functions of eight galaxies from the rotation velocity data from THINGS, we find that the density decreases exponentially with the potential in substantial regions of the halos. This behavior is in agreement with that of a single-component isothermal Boltzmann gas, and it suggests that an effective description in terms of a Boltzmann gas is possible for dark matter in these regions. This could be an indication that dark matter self-interactions are sufficient in strength and number to lead to thermal equilibrium in these regions. We write down the dynamics and boundary conditions for a Boltzmann gas description and examine some of its qualitative and quantitative consequences. Solutions to the dynamical system are determined by three dimensionfull parameters, and they provide reasonable fits to the rotational velocity data in the regions where the Boltzmann-like behavior was found. Unlike in the usual approach to curve fitting, we do not assume a specific form for the dark matter density profile, and we do not require a detailed knowledge of the baryonic content of the galaxy.

  19. Properties of dark matter haloes and their correlations: the lesson from principal component analysis

    NASA Astrophysics Data System (ADS)

    Skibba, Ramin A.; Macciò, Andrea V.

    2011-09-01

    We study the correlations between the structural parameters of dark matter haloes using principal component analysis. We consider a set of eight parameters, six of which are commonly used to characterize dark matter halo properties: mass, concentration, spin, shape, overdensity and the angle (ΦL) between the major axis and the angular momentum vector. Two additional parameters (xoff and ρrms) are used to describe the degree of 'relaxedness' of the halo. We find that we can account for much of the variance of these properties with halo mass and concentration, on the one hand, and halo relaxedness on the other. None the less, three principal components are usually required to account for most of the variance. We argue that halo mass is not as dominant as expected, which is a challenge for halo occupation models and semi-analytic models that assume that mass determines other halo (and galaxy) properties. In addition, we find that the angle ΦL is not significantly correlated with other halo parameters, which may present a difficulty for models in which galaxy discs are oriented in haloes in a particular way. Finally, at fixed mass, we find that a halo's environment (quantified by the large-scale overdensity) is relatively unimportant.

  20. Three-point galaxy-galaxy lensing as a probe of dark matter halo shapes

    SciTech Connect

    Adhikari, Susmita; Chue, Chun Yin Ricky; Dalal, Neal E-mail: chue2@illinois.edu

    2015-01-01

    We propose a method to measure the ellipticities of dark matter halos using the lens-shear-shear 3-point correlation function. This method is immune to effects of galaxy-halo misalignments that can potentially limit 2-point galaxy-galaxy lensing measurements of halo anisotropy. Using a simple model for the projected mass distributions of dark matter halos, we construct an ellipticity estimator that sums over all possible triangular configurations of the 3-point function. By applying our estimator to halos from N-body simulations, we find that systematic errors in the recovered ellipticity will be at the ∼< 5% fractional level. We estimate that future imaging surveys like LSST will have sufficient statistics to detect halo ellipticities using 3-point lensing.

  1. The impact of baryonic physics on the structure of dark matter haloes: the view from the FIRE cosmological simulations

    NASA Astrophysics Data System (ADS)

    Chan, T. K.; Kereš, D.; Oñorbe, J.; Hopkins, P. F.; Muratov, A. L.; Faucher-Giguère, C.-A.; Quataert, E.

    2015-12-01

    We study the distribution of cold dark matter (CDM) in cosmological simulations from the FIRE (Feedback In Realistic Environments) project, for M* ˜ 104-11 M⊙ galaxies in Mh ˜ 109-12 M⊙ haloes. FIRE incorporates explicit stellar feedback in the multiphase interstellar medium, with energetics from stellar population models. We find that stellar feedback, without `fine-tuned' parameters, greatly alleviates small-scale problems in CDM. Feedback causes bursts of star formation and outflows, altering the DM distribution. As a result, the inner slope of the DM halo profile (α) shows a strong mass dependence: profiles are shallow at Mh ˜ 1010-1011 M⊙ and steepen at higher/lower masses. The resulting core sizes and slopes are consistent with observations. This is broadly consistent with previous work using simpler feedback schemes, but we find steeper mass dependence of α, and relatively late growth of cores. Because the star formation efficiency M*/Mh is strongly halo mass dependent, a rapid change in α occurs around Mh ˜ 1010 M⊙ (M* ˜ 106-107 M⊙), as sufficient feedback energy becomes available to perturb the DM. Large cores are not established during the period of rapid growth of haloes because of ongoing DM mass accumulation. Instead, cores require several bursts of star formation after the rapid build-up has completed. Stellar feedback dramatically reduces circular velocities in the inner kpc of massive dwarfs; this could be sufficient to explain the `Too Big To Fail' problem without invoking non-standard DM. Finally, feedback and baryonic contraction in Milky Way-mass haloes produce DM profiles slightly shallower than the Navarro-Frenk-White profile, consistent with the normalization of the observed Tully-Fisher relation.

  2. 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. PMID:25933304

  3. A two-parameter matching scheme for massive galaxies and dark matter haloes

    NASA Astrophysics Data System (ADS)

    Kulier, Andrea; Ostriker, Jeremiah P.

    2015-10-01

    Halo abundance matching has been used to construct a one-parameter mapping between galaxies and dark matter haloes by assuming that halo mass and galaxy luminosity (or stellar mass) are monotonically related. While this approach has been reasonably successful, it is known that galaxies must be described by at least two parameters, as can be seen from the two-parameter Fundamental Plane on which massive early-type galaxies lie. In this paper, we derive a connection between initial dark matter density perturbations in the early Universe and present-day virialized dark matter haloes by assuming simple spherical collapse combined with conservation of mass and energy. We find that z = 0 halo concentration, or alternatively the inner slope of the halo density profile α, is monotonically and positively correlated with the collapse redshift of the halo. This is qualitatively similar to the findings of some previous works based on numerical simulations, with which we compare our results. We then describe how the halo mass and concentration (or inner slope α) can be used as two halo parameters in combination with two parameters of early-type galaxies to create an improved abundance matching scheme. In a forthcoming paper, we will show an application of this scheme to galaxies on the Fundamental Plane.

  4. ASSEMBLY BIAS AND THE DYNAMICAL STRUCTURE OF DARK MATTER HALOS

    SciTech Connect

    Faltenbacher, Andreas; White, Simon D. M.

    2010-01-01

    Based on the Millennium Simulation we examine assembly bias for the halo properties: shape, triaxiality, concentration, spin, shape of the velocity ellipsoid, and velocity anisotropy. For consistency, we determine all these properties using the same set of particles, namely all gravitationally self-bound particles belonging to the most massive substructure of a given friends-of-friends halo. We confirm that near-spherical and high-spin halos show enhanced clustering. The opposite is true for strongly aspherical and low-spin halos. Further, below the typical collapse mass, M{sub *}, more concentrated halos show stronger clustering, whereas less concentrated halos are less clustered which is reversed for masses above M{sub *}. Going beyond earlier work we show that: (1) oblate halos are more strongly clustered than prolate ones; (2) the dependence of clustering on the shape of the velocity ellipsoid coincides with that of the real-space shape, although the signal is stronger; (3) halos with weak velocity anisotropy are more clustered, whereas radially anisotropic halos are more weakly clustered; (4) for all highly clustered subsets we find systematically less radially biased velocity anisotropy profiles. These findings indicate that the velocity structure of halos is tightly correlated with environment.

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

    SciTech Connect

    Chae, Kyu-Hyun; Kravtsov, Andrey V.; Frieman, Joshua A.; Bernardi, Mariangela E-mail: andrey@oddjob.uchicago.edu E-mail: bernardm@physics.upenn.edu

    2012-11-01

    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. The 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∼halos of nearby elliptical and lenticular galaxies can, in principle, be promising targets for γ-ray emission from dark matter annihilation.

  6. MultiDark simulations: the story of dark matter halo concentrations and density profiles

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Predicting structural properties of dark matter haloes is one of the fundamental goals of modern cosmology. We use the suite of MultiDark cosmological simulations to study the evolution of dark matter halo density profiles, concentrations, and velocity anisotropies. We find that in order to understand the structure of dark matter haloes and to make 1-2 per cent accurate predictions for density profiles, one needs to realize that halo concentration is more complex than the ratio of the virial radius to the core radius in the Navarro-Frenk-White (NFW) profile. For massive haloes, the average density profile is far from the NFW shape and the concentration is defined by both the core radius and the shape parameter α in the Einasto approximation. We show that haloes progress through three stages of evolution. They start as rare density peaks and experience fast and nearly radial infall that brings mass closer to the centre, producing a highly concentrated halo. Here, the halo concentration increases with increasing halo mass and the concentration is defined by the α parameter with a nearly constant core radius. Later haloes slide into the plateau regime where the accretion becomes less radial, but frequent mergers still affect even the central region. At this stage, the concentration does not depend on halo mass. Once the rate of accretion and merging slows down, haloes move into the domain of declining concentration-mass relation because new accretion piles up mass close to the virial radius while the core radius is staying constant. Accurate analytical fits are provided.

  7. Clustering in the phase space of dark matter haloes - II. Stable clustering and dark matter annihilation

    NASA Astrophysics Data System (ADS)

    Zavala, Jesús; Afshordi, Niayesh

    2014-06-01

    We present a model for the structure of the particle phase space average density (P2SAD) in galactic haloes, introduced recently as a novel measure of the clustering of dark matter. Our model is based on the stable clustering hypothesis in phase space, the spherical collapse model, and tidal disruption of substructures, which is calibrated against the Aquarius simulations. Using this model, we can predict the behaviour of P2SAD in the numerically unresolved regime, down to the decoupling mass limit of generic weakly interacting massive particle models. This prediction can be used to estimate signals sensitive to the small-scale structure of dark matter. For example, the dark matter annihilation rate can be estimated for arbitrary velocity-dependent cross-sections in a convenient way using a limit of P2SAD to zero separation in physical space. We illustrate our method by computing the global and local subhalo annihilation boost to that of the smooth dark matter distribution in a Milky Way-sized halo. Two cases are considered, one where the cross-section is velocity independent and one that approximates Sommerfeld-enhanced models. We find that the global boost is ˜10-30, which is at the low end of current estimates (weakening expectations of large extragalactic signals), while the boost at the solar radius is below the percent level. We make our code to compute P2SAD publicly available, which can be used to estimate various observables that probe the nanostructure of dark matter haloes.

  8. The response of dark matter haloes to elliptical galaxy formation: a new test for quenching scenarios

    NASA Astrophysics Data System (ADS)

    Dutton, Aaron A.; Macciò, Andrea V.; Stinson, Gregory S.; Gutcke, Thales A.; Penzo, Camilla; Buck, Tobias

    2015-11-01

    We use cosmological hydrodynamical zoom-in simulations with the smoothed particle hydrodynamics code GASOLINE of four haloes of mass M200 ˜ 1013 M⊙ to study the response of the dark matter to elliptical galaxy formation. Our simulations include metallicity-dependent gas cooling, star formation and feedback from massive stars and supernovae, but not active galactic nuclei (AGN). At z = 2 the progenitor galaxies have stellar-to-halo mass ratios consistent with halo abundance matching, assuming a Salpeter initial mass function. However, by z = 0 the standard runs suffer from the well-known overcooling problem, overpredicting the stellar masses by a factor of ≳ 4. To mimic a suppressive halo quenching scenario, in our forced quenching (FQ) simulations, cooling and star formation are switched off at z = 2. The resulting z = 0 galaxies have stellar masses, sizes and circular velocities close to what is observed. Relative to the control simulations, the dark matter haloes in the FQ simulations have contracted, with central dark matter density slopes d log ρ/d log r ˜ -1.5, showing that dry merging alone is unable to fully reverse the contraction that occurs at z > 2. Simulations in the literature with AGN feedback, however, have found expansion or no net change in the dark matter halo. Thus, the response of the dark matter halo to galaxy formation may provide a new test to distinguish between ejective and suppressive quenching mechanisms.

  9. Estimating the dark matter halo mass of our Milky Way using dynamical tracers

    NASA Astrophysics Data System (ADS)

    Wang, Wenting; Han, Jiaxin; Cooper, Andrew P.; Cole, Shaun; Frenk, Carlos; Lowing, Ben

    2015-10-01

    The mass of the dark matter halo of the Milky Way can be estimated by fitting analytical models to the phase-space distribution of dynamical tracers. We test this approach using realistic mock stellar haloes constructed from the Aquarius N-body simulations of dark matter haloes in the Λ cold dark matter cosmology. We extend the standard treatment to include a Navarro-Frenk-White potential and use a maximum likelihood method to recover the parameters describing the simulated haloes from the positions and velocities of their mock halo stars. We find that the estimate of halo mass is highly correlated with the estimate of halo concentration. The best-fitting halo masses within the virial radius, R200, are biased, ranging from a 40 per cent underestimate to a 5 per cent overestimate in the best case (when the tangential velocities of the tracers are included). There are several sources of bias. Deviations from dynamical equilibrium can potentially cause significant bias; deviations from spherical symmetry are relatively less important. Fits to stars at different galactocentric radii can give different mass estimates. By contrast, the model gives good constraints on the mass within the half-mass radius of tracers even when restricted to tracers within 60 kpc. The recovered velocity anisotropies of tracers, β, are biased systematically, but this does not affect other parameters if tangential velocity data are used as constraints.

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

    SciTech Connect

    Ishiyama, Tomoaki

    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 halos 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.

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

    SciTech Connect

    Rojas-Nino, Armando; Valenzuela, Octavio; Pichardo, Barbara; Aguilar, Luis A. E-mail: barbara@astro.unam.mx

    2012-10-01

    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 would be the smoking gun for the predicted triaxiality of dark halos in cosmological galaxy formation scenarios.

  12. The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Ishiyama, Tomoaki; Rieder, Steven; Makino, Junichiro; Portegies Zwart, Simon; Groen, Derek; Nitadori, Keigo; de Laat, Cees; McMillan, Stephen; Hiraki, Kei; Harfst, Stefan

    2013-04-01

    We present the results of the "Cosmogrid" cosmological N-body simulation suites based on the concordance LCDM model. The Cosmogrid simulation was performed in a 30 Mpc box with 20483 particles. The mass of each particle is 1.28 × 105 M ⊙, which is sufficient to resolve ultra-faint dwarfs. We found that the halo mass function shows good agreement with the Sheth & Tormen fitting function down to ~107 M ⊙. We have analyzed the spherically averaged density profiles of the three most massive halos which are of galaxy group size and contain at least 170 million particles. The slopes of these density profiles become shallower than -1 at the innermost radius. We also find a clear correlation of halo concentration with mass. The mass dependence of the concentration parameter cannot be expressed by a single power law, however a simple model based on the Press-Schechter theory proposed by Navarro et al. gives reasonable agreement with this dependence. The spin parameter does not show a correlation with the halo mass. The probability distribution functions for both concentration and spin are well fitted by the log-normal distribution for halos with the masses larger than ~108 M ⊙. The subhalo abundance depends on the halo mass. Galaxy-sized halos have 50% more subhalos than ~1011 M ⊙ halos have.

  13. How does gas cool in dark matter haloes?

    NASA Astrophysics Data System (ADS)

    Viola, M.; Monaco, P.; Borgani, S.; Murante, G.; Tornatore, L.

    2008-01-01

    In order to study the process of cooling in dark matter haloes and assess how well simple models can represent it, we run a set of radiative smoothed particle hydrodynamics (SPH) simulations of isolated haloes, with gas sitting initially in hydrostatic equilibrium within Navarro-Frenk-White potential wells. Simulations include radiative cooling and a scheme to convert high-density cold gas particles into collisionless stars, neglecting any astrophysical source of energy feedback. After having assessed the numerical stability of the simulations, we compare the resulting evolution of the cooled mass with the predictions of the classical cooling model of White & Frenk and of the cooling model proposed in the MORGANA code of galaxy formation. We find that the classical model predicts fractions of cooled mass which, after about 2 central cooling times, are about one order of magnitude smaller than those found in simulations. Although this difference decreases with time, after 8 central cooling times, when simulations are stopped, the difference still amounts to a factor of 2-3. We ascribe this difference to the lack of validity of the assumption that a mass shell takes one cooling time, as computed on the initial conditions, to cool to very low temperature. Indeed, we find from simulations that cooling SPH particles take most time in travelling, at roughly constant temperature and increasing density, from their initial position to a central cooling region, where they quickly cool down to ~104 K. We show that in this case the total cooling time is shorter than that computed on the initial conditions, as a consequence of the stronger radiative losses associated to the higher density experienced by these particles. As a consequence the mass cooling flow is stronger than that predicted by the classical model. The MORGANA model, which computes the cooling rate as an integral over the contribution of cooling shells and does not make assumptions on the time needed by shells to

  14. THE SPIN AND ORIENTATION OF DARK MATTER HALOS WITHIN COSMIC FILAMENTS

    SciTech Connect

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

    2009-11-20

    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 approx<10{sup 13} h {sup -1} M{sub 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

  15. The role of galaxy formation in the structure and dynamics of dark matter halos

    NASA Astrophysics Data System (ADS)

    Tonini, Chiara

    2009-02-01

    The structure and dynamics of dark matter halos, as predicted by the hierarchical clustering scenario, are at odds with the properties inferred from the observations at galactic scales. My Thesis addresses this problem by taking an evolutionary approach. I analysed in detail the many and different observational evidences of a discrepancy the predicted halo equilibrium state and the one inferred from the measurable properties of disk galaxies, as well as of the scaling relations existing between the angular momentum, geometry and mass distribution of the luminous and dark components, and realized that they all seem to point towards the same conclusion: the baryons hosted inside the halo, by collapsing and assembling to form the galaxy, perturb the halo equilibrium structure and made it evolve into new configurations. From the theoretical point of view, the behaviour of dark matter halos as collisionless systems of particles makes their equilibrium structure and mass distribution extremely sensitive to perturbations of their inner dynamics. The galaxy formation occurring inside the halos is a tremendous event, and the dynamical coupling between the baryons and the dark matter during the protogalaxy collapse represents a perturbation of the halo dynamical structure large enough to trigger a halo evolution, according to the relative mass and angular momentum of the two components. My conclusion is that the structure and dynamics of dark matter halos, as well as the origin of the connection between the halo and galaxy properties, are to be understood in in terms of a joint evolution of the baryonic and dark components, originating at the epoch of the collapse and formation of the galaxy.

  16. Study of the nature of dark matter in halos of dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Karmakar, Pradip; Chattopadhyay, Tanuka; Chattopadhyay, Asis Kumar

    2015-08-01

    The kinematics of dwarf galaxies are strongly influenced by dark matter down to small galactocentric radii. So they are good candidates to investigate the nature of Dark Matter. In the present work we have carried out mass modeling of a number of recently observed dwarf galaxies Swaters et al. in Astron. Astrophys. 493:871, 2009. We have used a Navarro-Frenk-White (NFW) halo, Freeman disc along with a gaseous disc for modeling the observed rotation curves of those dwarf galaxies. For comparison we also used a Burkert halo, Freeman disc and gaseous disc. For both the scenario we have performed Kolmogorov-Smirnov (KS) test between the observed and predicted rotational velocity profiles. The tests are rejected for NFW halo almost in 50 per cent cases but they are accepted almost for all cases for Burkert halo, preferring a Burkert halo model generally for dwarf galaxies. The above results reveal a constant density core of dark matter (DM) in the halos of dwarf galaxies compared to a cuspy nature of NFW halo and a possible challenge to -CDM scenario for the nature of dark matter in most of the dwarf galaxies.

  17. THE GROWTH OF GALAXY STELLAR MASS WITHIN DARK MATTER HALOS

    SciTech Connect

    Zehavi, Idit; Patiri, Santiago; Zheng Zheng

    2012-02-20

    We study the evolution of stellar mass in galaxies as a function of host halo mass, using the 'MPA' and 'Durham' semi-analytic models, implemented on the Millennium Run simulation. For both models, the stellar mass of the central galaxies increases rapidly with halo mass at the low-mass end and more slowly in halos of larger masses at the three redshifts probed (z {approx} 0, 1, 2). About 45% of the stellar mass in central galaxies in present-day halos less massive than {approx}10{sup 12} h{sup -1} M{sub Sun} is already in place at z {approx} 1, and this fraction increases to {approx}65% for more massive halos. The baryon conversion efficiency into stars has a peaked distribution with halo mass, and the peak location shifts toward lower mass from z {approx} 1 to z {approx} 0. The stellar mass in low-mass halos grows mostly by star formation since z {approx} 1, while in high-mass halos most of the stellar mass is assembled by mergers, reminiscent of 'downsizing'. We compare our findings to empirical results from the Sloan Digital Sky Survey and DEEP2 surveys utilizing galaxy clustering measurements to study galaxy evolution. The theoretical predictions are in qualitative agreement with these phenomenological results, but there are large discrepancies. The most significant one concerns the number of stars already in place in the progenitor galaxies at z {approx} 1, which is about a factor of two larger in both semi-analytic models. We demonstrate that methods studying galaxy evolution from the galaxy-halo connection are powerful in constraining theoretical models and can guide future efforts of modeling galaxy evolution. Conversely, semi-analytic models serve an important role in improving such methods.

  18. Physical Properties and Evolution of Gravitationally Bound Halo Structures in Cosmological Dark Matter Simulations

    NASA Astrophysics Data System (ADS)

    Lin, David; Rocha, Miguel E.; Primack, Joel R.

    2015-01-01

    Dark matter halos existing around visible galaxies are important for studies of galaxy formation and evolution. Since dark matter does not interact with light and cannot be observed directly, studies of dark matter halos are advanced by computer simulations. Normally, halos are defined by their virialized regions; however, regions that are non-virialized can still be gravitationally bound, like the collision-bound Milky Way and Andromeda galaxies. Our project is the first comprehensive characterization of gravitationally bound halo structures, their properties, and their evolution. This study found the bound regions surrounding every dark matter halo from a 100 Mpc cube of the Bolshoi Simulation at redshifts 0, 1, and 2. We optimized computation by removing subhalos, implementing a search radius, and parallelizing code across 160 supercomputer cores. Then, we created a mass function, circular velocity function, and correlation function to describe these regions. The evolution of these properties was consistent with predictions from a ΛCDM universe model. We characterized the sizes and shapes of these bound regions across different mass intervals and redshifts. Most bound regions are elongated, although they become more spheroidal with time. The results enable astronomers to predict how dark matter halos behave in non-virialized regions of space and deepen our understanding of galaxy formation.

  19. Behavior of luminous matter in the head-on encounter of two ultralight BEC dark matter halos

    NASA Astrophysics Data System (ADS)

    Guzmán, F. S.; González, J. A.; Cruz-Pérez, J. P.

    2016-05-01

    Within the context of ultralight Bose-Einstein condensate (BEC) dark matter, we analyze the head-on encounters of two structures. These structures are made of a BEC component, which is a ground-state equilibrium solution of the Gross-Pitaevskii-Poisson (GPP) system, together with a component of luminous matter. The evolution of the condensate dark matter is carried out by solving the time-dependent GPP equations, whereas the luminous matter is modeled with particles interacting gravitationally on top of the BEC dark matter halos. We track the evolution of frontal encounters for various values of the collision velocity and analyze the high-velocity regime showing solitonic behavior of the BEC halos and that of slow velocities producing a single final structure. We measure the relative velocity of the dark matter with respect to the luminous matter after the encounters in the solitonic case and track the evolution of luminous matter in the case of merger.

  20. The mass-concentration-redshift relation of cold and warm dark matter haloes

    NASA Astrophysics Data System (ADS)

    Ludlow, Aaron D.; Bose, Sownak; Angulo, Raúl E.; Wang, Lan; Hellwing, Wojciech A.; Navarro, Julio F.; Cole, Shaun; Frenk, Carlos S.

    2016-08-01

    We use a suite of cosmological simulations to study the mass-concentration-redshift relation, c(M, z), of dark matter haloes. Our simulations include standard Λ-cold dark matter (CDM) models, and additional runs with truncated power spectra, consistent with a thermal warm dark matter (WDM) scenario. We find that the mass profiles of CDM and WDM haloes are self-similar and well approximated by the Einasto profile. The c(M, z) relation of CDM haloes is monotonic: concentrations decrease with increasing virial mass at fixed redshift, and decrease with increasing redshift at fixed mass. The mass accretion histories (MAHs) of CDM haloes are also scale-free, and can be used to infer concentrations directly. These results do not apply to WDM haloes: their MAHs are not scale-free because of the characteristic scale imposed by the power spectrum suppression. Further, the WDM c(M, z) relation is non-monotonic: concentrations peak at a mass scale dictated by the truncation scale, and decrease at higher and lower masses. We show that the assembly history of a halo can still be used to infer its concentration, provided that the total mass of its progenitors is considered (the `collapsed mass history'; CMH), rather than just that of its main ancestor. This exploits the scale-free nature of CMHs to derive a simple scaling that reproduces the mass-concentration-redshift relation of both CDM and WDM haloes over a vast range of halo masses and redshifts. Our model therefore provides a robust account of the mass, redshift, cosmology and power spectrum dependence of dark matter halo concentrations.

  1. The Mass-Concentration-Redshift Relation of Cold and Warm Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Ludlow, Aaron D.; Bose, Sownak; Angulo, Raúl E.; Wang, Lan; Hellwing, Wojciech A.; Navarro, Julio F.; Cole, Shaun; Frenk, Carlos S.

    2016-05-01

    We use a suite of cosmological simulations to study the mass-concentration-redshift relation, c(M, z), of dark matter halos. Our simulations include standard Λ-cold dark matter (CDM) models, and additional runs with truncated power spectra, consistent with a thermal warm dark matter (WDM) scenario. We find that the mass profiles of CDM and WDM halos are self-similar and well approximated by the Einasto profile. The c(M, z) relation of CDM halos is monotonic: concentrations decrease with increasing virial mass at fixed redshift, and decrease with increasing redshift at fixed mass. The mass accretion histories (MAHs) of CDM halos are also scale-free, and can be used to infer concentrations directly. These results do not apply to WDM halos: their MAHs are not scale-free because of the characteristic scale imposed by the power-spectrum suppression. Further, the WDM c(M, z) relation is non-monotonic: concentrations peak at a mass scale dictated by the truncation scale, and decrease at higher and lower masses. We show that the assembly history of a halo can still be used to infer its concentration, provided that the total mass of its progenitors is considered (the "collapsed mass history"; CMH), rather than just that of its main ancestor. This exploits the scale-free nature of CMHs to derive a simple scaling that reproduces the mass-concentration-redshift relation of both CDM and WDM halos over a vast range of halo masses and redshifts. Our model therefore provides a robust account of the mass, redshift, cosmology and power spectrum dependence of dark matter halo concentrations.

  2. Evidence for a Triaxial Milky Way Dark Matter Halo from the Sagittarius Stellar Tidal Stream

    NASA Astrophysics Data System (ADS)

    Law, David R.; Majewski, S. R.; Johnston, K. V.

    2010-01-01

    Observations of the lengthy tidal streams produced by the destruction of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) are capable of providing strong constraints on the shape of the Galactic gravitational potential. However, previous work, based on modeling different stream properties in axisymmetric Galactic models has yielded conflicting results: while the angular precession of the Sgr leading arm is most consistent with a spherical or slightly oblate halo, the radial velocities of stars in this arm are only reproduced by prolate halo models. We demonstrate that this apparent paradox can be resolved by instead adopting a triaxial potential. Our new Galactic halo model, which simultaneously fits all well-established phase space constraints from the Sgr stream, provides the first conclusive evidence for, and tentative measurement of, triaxiality in an individual dark matter halo. In this model, the minor axis of the dark halo is approximately coincident with the Galactic X axis connecting the Sun and the Galactic Center.

  3. 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.

  4. Statistics of dark matter halos in the excursion set peak framework

    SciTech Connect

    Lapi, A.; Danese, L. E-mail: danese@sissa.it

    2014-07-01

    We derive approximated, yet very accurate analytical expressions for the abundance and clustering properties of dark matter halos in the excursion set peak framework; the latter relies on the standard excursion set approach, but also includes the effects of a realistic filtering of the density field, a mass-dependent threshold for collapse, and the prescription from peak theory that halos tend to form around density maxima. We find that our approximations work excellently for diverse power spectra, collapse thresholds and density filters. Moreover, when adopting a cold dark matter power spectra, a tophat filtering and a mass-dependent collapse threshold (supplemented with conceivable scatter), our approximated halo mass function and halo bias represent very well the outcomes of cosmological N-body simulations.

  5. Dispersal of Tidal Debris in a Milky-Way-sized Dark Matter Halo

    NASA Astrophysics Data System (ADS)

    Ngan, Wayne; Carlberg, Raymond G.; Bozek, Brandon; Wyse, Rosemary F. G.; Szalay, Alexander S.; Madau, Piero

    2016-02-01

    We simulate the tidal disruption of a collisionless N-body globular star cluster in a total of 300 different orbits selected to have galactocentric radii between 10 and 30 kpc in four dark matter halos: (a) a spherical halo with no subhalos, (b) a spherical halo with subhalos, (c) a realistic halo with no subhalos, and (d) a realistic halo with subhalos. This allows us to isolate and study how the halo’s (lack of) dynamical symmetry and substructures affect the dispersal of tidal debris. The realistic halos are constructed from the snapshot of the Via Lactea II simulation at redshift zero. We find that the overall halo’s symmetry disperses tidal debris to make the streams fluffier, consistent with previous studies of tidal debris of dwarf galaxies in larger orbits than ours in this study. On the other hand, subhalos in realistic potentials can locally enhance the densities along streams, making streams denser than their counterparts in smooth potentials. We show that many long and thin streams can survive in a realistic and lumpy halo for a Hubble time. This suggests that upcoming stellar surveys will likely uncover more thin streams which may contain density gaps that have been shown to be promising probes for dark matter substructures.

  6. The behaviour of shape and velocity anisotropy in dark matter haloes

    SciTech Connect

    Sparre, Martin; Hansen, Steen H. E-mail: hansen@dark-cosmology.dk

    2012-10-01

    Dark matter haloes from cosmological N-body simulations typically have triaxial shapes and anisotropic velocity distributions. Recently it has been shown that the velocity anisotropy, β, of cosmological haloes and major merger remnants depend on direction in such a way that β is largest along the major axis and smallest along the minor axis. In this work we use a wide range of non-cosmological N-body simulations to examine halo shapes and direction-dependence of velocity anisotropy profiles. For each of our simulated haloes we define 48 cones pointing in different directions, and from the particles inside each cone we compute velocity anisotropy profiles. We find that elongated haloes can have very distinct velocity anisotropies. We group the behaviour of haloes into three different categories, that range from spherically symmetric profiles to a much more complex behaviour, where significant differences are found for β along the major and minor axes. We encourage future studies of velocity anisotropies in haloes from cosmological simulations to calculate β-profiles in cones, since it reveals information, which is hidden from a spherically averaged profile. Finally, we show that spherically averaged profiles often obey a linear relation between β and the logarithmic density slope in the inner parts of haloes, but this relation is not necessarily obeyed, when properties are calculated in cones.

  7. 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.

  8. Spin flips - II. Evolution of dark matter halo spin orientation, and its correlation with major mergers

    NASA Astrophysics Data System (ADS)

    Bett, Philip E.; Frenk, Carlos S.

    2016-09-01

    We expand our previous study on the relationship between changes in the orientation of the angular momentum vector of dark matter haloes (`spin flips') and changes in their mass, to cover the full range of halo masses in a simulation cube of length 100 h-1 Mpc. Since strong disturbances to a halo (such as might be indicated by a large change in the spin direction) are likely also to disturb the galaxy evolving within, spin flips could be a mechanism for galaxy morphological transformation without involving major mergers. We find that 35 per cent of haloes have, at some point in their lifetimes, had a spin flip of at least 45° that does not coincide with a major merger. Over 75 per cent of large spin flips coincide with non-major mergers; only a quarter coincide with major mergers. We find a similar picture for changes to the inner halo spin orientation, although here there is an increased likelihood of a flip occurring. Changes in halo angular momentum orientation, and other such measures of halo perturbation, are therefore very important quantities to consider, in addition to halo mergers, when modelling the formation and evolution of galaxies and confronting such models with observations.

  9. Puzzling outer-density profile of the dark matter halo in the Andromeda galaxy

    NASA Astrophysics Data System (ADS)

    Kirihara, Takanobu; Miki, Yohei; Mori, Masao

    2014-12-01

    The cold dark matter (CDM) cosmology, which is the standard theory of the structure formation in the universe, predicts that the outer density profile of dark matter halos decreases with the cube of distance from the center. However, so far not much effort has been expended in examining this hypothesis. In the halo of the Andromeda galaxy (M 31), large-scale stellar structures detected by the recent observations provide a potentially suitable window to investigate the mass-density distribution of the dark matter halo. We explore the density structure of the dark matter halo in M 31 using an N-body simulation of the interaction between an accreting satellite galaxy and M 31. To reproduce the Andromeda Giant Southern Stream and the stellar shells at the east and west sides of M 31, we find the sufficient condition for the power-law index α of the outer density distribution of the dark matter halo. The best-fitting parameter is α = -3.7, which is steeper than the CDM prediction.

  10. Lensing measurements of the ellipticity of luminous red galaxies dark matter haloes

    NASA Astrophysics Data System (ADS)

    Clampitt, Joseph; Jain, Bhuvnesh

    2016-04-01

    Lensing measurements of the shapes of dark matter haloes can provide tests of gravity theories and possible dark matter interactions. We measure the quadrupole weak lensing signal from the elliptical haloes of 70 000 Sloan Digital Sky Survey luminous red galaxies. We use a new estimator that nulls the spherical halo lensing signal, isolating the shear due to anisotropy in the dark matter distribution. One of the two Cartesian components of our estimator is insensitive to the primary systematic, a spurious alignment of lens and source ellipticities, allowing us to make robust measurements of halo ellipticity. Our best-fitting value for the ellipticity of the surface mass density is 0.24 ± 0.06, which translates to an axis ratio of 0.78. We rule out the hypothesis of no ellipticity at the 4σ confidence level, and ellipticity <0.12 (axis ratio >0.89) at the 2σ level. We discuss how our measurements of halo ellipticity are revised to higher values using estimates of the misalignment of mass and light from simulations. Finally, we apply the same techniques to a smaller sample of redMaPPer galaxy clusters and obtain a 3σ measurement of cluster ellipticity. We discuss how the improved signal-to-noise ratio properties of our estimator can enable studies of halo shapes for different galaxy populations with upcoming surveys.

  11. The Milky Way tomography with Sloan Digital Sky Survey. V. Mapping the dark matter halo

    SciTech Connect

    Loebman, Sarah R.; Ivezić, Željko; Quinn, Thomas R.; Governato, Fabio; Bovy, Jo; Christensen, Charlotte R.; Jurić, Mario; Roškar, Rok; Brooks, Alyson M.

    2014-10-20

    We present robust constraints from the Sloan Digital Sky Survey (SDSS) on the shape and distribution of the dark matter halo within the Milky Way (MW). Using the number density distribution and kinematics of SDSS halo stars, we probe the dark matter distribution to heliocentric distances exceeding ∼10 kpc and galactocentric distances exceeding ∼20 kpc. Our analysis utilizes Jeans equations to generate two-dimensional acceleration maps throughout the volume; this approach is thoroughly tested on a cosmologically derived N-body+SPH simulation of a MW-like galaxy. We show that the known accelerations (gradients of the gravitational potential) can be successfully recovered in such a realistic system. Leveraging the baryonic gravitational potential derived by Bovy and Rix, we show that the gravitational potential implied by the SDSS observations cannot be explained, assuming Newtonian gravity, by visible matter alone: the gravitational force experienced by stars at galactocentric distances of ∼20 kpc is as much as three times stronger than what can be attributed to purely visible matter. We also show that the SDSS data provide a strong constraint on the shape of the dark matter halo potential. Within galactocentric distances of ∼20 kpc, the dark matter halo potential is well described as an oblate halo with axis ratio q{sub DM}{sup Φ}=0.7±0.1; this corresponds to an axis ratio q{sub DM}{sup ρ}∼0.4±0.1 for the dark matter density distribution. Because of our precise two-dimensional measurements of the acceleration of the halo stars, we can reject several MOND models as an explanation of the observed behavior.

  12. Cosmic web alignments with the shape, angular momentum and peculiar velocities of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Forero-Romero, Jaime E.; Contreras, Sergio; Padilla, Nelson

    2014-09-01

    We study the alignment of dark matter haloes with the cosmic web characterized by the tidal and velocity shear fields. We focus on the alignment of their shape, angular momentum and peculiar velocities. We use a cosmological N-body simulation that allows us to study dark matter haloes spanning almost five orders of magnitude in mass (109-1014) h-1 M⊙ and spatial scales of (0.5-1.0) h-1 Mpc to define the cosmic web. The strongest alignment is measured for halo shape along the smallest tidal eigenvector, e.g. along filaments and walls, with a signal that gets stronger as the halo mass increases. In the case of the velocity shear field only massive haloes >1012 h-1 M⊙ tend to have their shapes aligned along the largest tidal eigenvector, i.e. perpendicular to filaments and walls. For the angular momentum we find alignment signals only for haloes more massive than 1012 h-1 M⊙ both in the tidal and velocity shear fields where the preferences is to be parallel to the middle eigenvector; perpendicular to filaments and parallel to walls. Finally, the peculiar velocities show a strong alignment along the smallest tidal eigenvector for all halo masses; haloes move along filaments and walls. The same alignment is present with the velocity shear, albeit weaker and only for haloes less massive than 1012 h-1 M⊙. Our results show that the two different algorithms used to define the cosmic web describe different physical aspects of non-linear collapse and should be used in a complementary way to understand the cosmic web influence on galaxy evolution.

  13. THE INTEGRATED STELLAR CONTENT OF DARK MATTER HALOS

    SciTech Connect

    Leauthaud, Alexie; Bundy, Kevin; Tanaka, Masayuki; George, Matthew R.; Behroozi, Peter S.; Wechsler, Risa H.; Tinker, Jeremy; Conroy, Charlie; Finoguenov, Alexis

    2012-02-10

    Measurements of the total amount of stars locked up in galaxies as a function of host halo mass contain key clues about the efficiency of processes that regulate star formation. We derive the total stellar mass fraction f{sub *} (excluding stars in the intracluster light) as a function of halo mass M{sub 500c} from z = 0.2 to z = 1 using two complementary methods. First, we derive f{sub *} using a statistical Halo Occupation Distribution model jointly constrained by data from lensing, clustering, and the stellar mass function. This method enables us to probe f{sub *} over a much wider halo mass range than with group or cluster catalogs. Second, we derive f{sub *} at group scales using a COSMOS X-ray group catalog and show that the two methods agree to within 30%. We quantify the systematic uncertainty on f{sub *} using abundance matching methods and show that the statistical uncertainty on f{sub *} ({approx}10%) is dwarfed by systematic uncertainties associated with stellar mass measurements ({approx}45% excluding initial mass function, IMF, uncertainties). Assuming a Chabrier IMF, we find 0.012 {<=} f{sub *} {<=} 0.025 at M{sub 500c} = 10{sup 13} M{sub Sun} and 0.0057 {<=} f{sub *} {<=} 0.015 at M{sub 500c} = 10{sup 14} M{sub Sun }. These values are significantly lower than previously published estimates. We investigate the cause of this difference and find that previous work has overestimated f{sub *} owing to a combination of inaccurate stellar mass estimators and/or because they have assumed that all galaxies in groups are early-type galaxies with a constant mass-to-light ratio. Contrary to previous claims, our results suggest that the mean value of f{sub *} is always significantly lower than f{sub gas} for halos above 10{sup 13} M{sub Sun }. Combining our results with recently published gas mass fractions, we find a shortfall in f{sub *} + f{sub gas} at R{sub 500c} compared to the cosmic mean. This shortfall varies with halo mass and becomes larger toward

  14. Are Halo-Like Solar Coronal Mass Ejections Merely a Matter of Geometric Projection Effect?

    NASA Astrophysics Data System (ADS)

    Kwon, Ryun Young; Vourlidas, Angelos; Zhang, Jie

    2015-04-01

    We investigated the physical nature of halo coronal mass ejections (CMEs) based on the stereoscopic observations from two STEREO Ahead and Behind (hereafter A and B) and SOHO spacecraft. There occurred 62 halo CMEs as observed by SOHO LASCO C2 for the three-year period from 2010 to 2012 during which the separation angles between SOHO and STEREOs were nearly 90 degrees. In such quadrature configuration, the coronagraphs of STEREOs, 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 the 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 only 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.

  15. Are Halo-like Solar Coronal Mass Ejections Merely a Matter of Geometric Projection Effects?

    NASA Astrophysics Data System (ADS)

    Kwon, Ryun-Young; Zhang, Jie; Vourlidas, Angelos

    2015-01-01

    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 the 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.

  16. ARE HALO-LIKE SOLAR CORONAL MASS EJECTIONS MERELY A MATTER OF GEOMETRIC PROJECTION EFFECTS?

    SciTech Connect

    Kwon, Ryun-Young; Zhang, Jie; Vourlidas, Angelos

    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 the 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.

  17. Imprint of primordial non-Gaussianity on dark matter halo profiles

    SciTech Connect

    Dizgah, Azadeh Moradinezhad; Dodelson, Scott; Riotto, Antonio

    2013-09-01

    We study the impact of primordial non-Gaussianity on the density profile of dark matter halos by using the semi-analytical model introduced recently by Dalal {\\it et al.} which relates the peaks of the initial linear density field to the final density profile of dark matter halos. Models with primordial non-Gaussianity typically produce an initial density field that differs from that produced in Gaussian models. We use the path-integral formulation of excursion set theory to calculate the non-Gaussian corrections to the peak profile and derive the statistics of the peaks of non-Gaussian density field. In the context of the semi-analytic model for halo profiles, currently allowed values for primordial non-Gaussianity would increase the shapes of the inner dark matter profiles, but only at the sub-percent level except in the very innermost regions.

  18. The stability of stellar discs in Milky Way-sized dark matter haloes

    NASA Astrophysics Data System (ADS)

    Yurin, Denis; Springel, Volker

    2015-09-01

    We employ an improved methodology to insert live stellar discs into high-resolution dark matter simulations of Milky Way-sized haloes, allowing us to investigate the fate of thin stellar discs in the tumultuous environment of cold dark matter structures. We study a set of eight different haloes, drawn from the Aquarius simulation project, in which stellar discs are adiabatically grown with a prescribed structure, and then allowed to self-consistently evolve. The initial velocity distribution is set-up in very good equilibrium with the help of the GALIC code. We find that the residual triaxiality of the haloes leads to significant disc tumbling, qualitatively confirming earlier work. We show that the disc turning motion is unaffected by structural properties of the galaxies such as the presence or absence of a bulge or bar. In typical Milky Way-sized dark matter haloes, we expect an average turning of the discs by about 40°between z = 1 and 0, over the course of 7.6 Gyr. We also investigate the impact of the discs on substructures, and conversely, the disc heating rate caused by the dark matter halo substructures. The presence of discs reduces the central subhalo abundance by a about a factor of 2, due to an increased evaporation rate by gravitational shocks from disc passages. We find that substructures are important for heating the outer parts of stellar discs but do not appear to significantly affect their inner parts.

  19. 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.

  20. Stochastic Model of the Spin Distribution of Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Kim, Juhan; Choi, Yun-Young; Kim, Sungsoo S.; Lee, Jeong-Eun

    2015-09-01

    We employ a stochastic approach to probing the origin of the log-normal distributions of halo spin in N-body simulations. After analyzing spin evolution in halo merging trees, it was found that a spin change can be characterized by a stochastic random walk of angular momentum. Also, spin distributions generated by random walks are fairly consistent with those directly obtained from N-body simulations. We derived a stochastic differential equation from a widely used spin definition and measured the probability distributions of the derived angular momentum change from a massive set of halo merging trees. The roles of major merging and accretion are also statistically analyzed in evolving spin distributions. Several factors (local environment, halo mass, merging mass ratio, and redshift) are found to influence the angular momentum change. The spin distributions generated in the mean-field or void regions tend to shift slightly to a higher spin value compared with simulated spin distributions, which seems to be caused by the correlated random walks. We verified the assumption of randomness in the angular momentum change observed in the N-body simulation and detected several degrees of correlation between walks, which may provide a clue for the discrepancies between the simulated and generated spin distributions in the voids. However, the generated spin distributions in the group and cluster regions successfully match the simulated spin distribution. We also demonstrated that the log-normality of the spin distribution is a natural consequence of the stochastic differential equation of the halo spin, which is well described by the Geometric Brownian Motion model.

  1. 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.

  2. EVIDENCE AGAINST DARK MATTER HALOS SURROUNDING THE GLOBULAR CLUSTERS MGC1 AND NGC 2419

    SciTech Connect

    Conroy, Charlie; Loeb, Abraham; Spergel, David N.

    2011-11-10

    The conjecture that the ancient globular clusters (GCs) formed at the center of their own dark matter (DM) halos was first proposed by Peebles in 1984 and has recently been revived to explain the puzzling abundance patterns observed within many GCs. In this paper, we demonstrate that the outer stellar density profile of isolated GCs is very sensitive to the presence of an extended dark halo. The GCs NGC 2419, located at 90 kpc from the center of our Galaxy, and MGC1, located at {approx}200 kpc from the center of M31, are ideal laboratories for testing the scenario that GCs formed at the centers of massive dark halos. Comparing analytic models to observations of these GCs, we conclude that these GCs cannot be embedded within dark halos with a virial mass greater than 10{sup 6} M{sub sun}, or, equivalently, the DM halo-mass-to-stellar mass ratio must be M{sub DM}/M{sub *} < 1. If these GCs have indeed orbited within weak tidal fields throughout their lifetimes, then these limits imply that these GCs did not form within their own dark halos. Recent observations of an extended stellar halo in the GC NGC 1851 are also interpreted in the context of our analytic models. Implications of these results for the formation of GCs are briefly discussed.

  3. The shape of dark matter haloes: dependence on mass, redshift, radius and formation

    NASA Astrophysics Data System (ADS)

    Allgood, Brandon; Flores, Ricardo A.; Primack, Joel R.; Kravtsov, Andrey V.; Wechsler, Risa H.; Faltenbacher, Andreas; Bullock, James S.

    2006-04-01

    Using six high-resolution dissipationless simulations with a varying box size in a flat Lambda cold dark matter (ΛCDM) universe, we study the mass and redshift dependence of dark matter halo shapes for Mvir= 9.0 × 1011- 2.0 × 1014h-1Msolar, over the redshift range z= 0-3, and for two values of σ8= 0.75 and 0.9. Remarkably, we find that the redshift, mass and σ8 dependence of the mean smallest-to-largest axis ratio of haloes is well described by the simple power-law relation = (0.54 +/- 0.02)(Mvir/M*)-0.050+/-0.003, where s is measured at 0.3Rvir, and the z and σ8 dependences are governed by the characteristic non-linear mass, M*=M*(z, σ8). We find that the scatter about the mean s is well described by a Gaussian with σ~ 0.1, for all masses and redshifts. We compare our results to a variety of previous works on halo shapes and find that reported differences between studies are primarily explained by differences in their methodologies. We address the evolutionary aspects of individual halo shapes by following the shapes of the haloes through ~100 snapshots in time. We determine the formation scalefactor ac as defined by Wechsler et al. and find that it can be related to the halo shape at z= 0 and its evolution over time.

  4. The First Billion Years project: dark matter haloes going from contraction to expansion and back again

    NASA Astrophysics Data System (ADS)

    Davis, Andrew J.; Khochfar, Sadegh; Dalla Vecchia, Claudio

    2014-09-01

    We study the effect of baryons on the inner dark matter profile of the first galaxies using the First Billion Years simulation between z = 16 and 6 before secular evolution sets in. Using a large statistical sample from two simulations of the same volume and cosmological initial conditions, one with and one without baryons, we are able to directly compare haloes with their baryon-free counterparts, allowing a detailed study of the modifications to the dark matter density profile due to the presence of baryons during the first billion years of galaxy formation. For each of the ≈5000 haloes in our sample (3 × 107 M⊙ ≤ Mtot ≤ 5 × 109 M⊙), we quantify the impact of the baryons using η, defined as the ratio of dark matter mass enclosed in 100 pc in the baryonic run to its counterpart without baryons. During this epoch of rapid growth of galaxies, we find that many haloes of these first galaxies show an enhancement of dark matter in the halo centre compared to the baryon-free simulation, while many others show a deficit. We find that the mean value of η is close to unity, but there is a large dispersion, with a standard deviation of 0.677. The enhancement is cyclical in time and tracks the star formation cycle of the galaxy; as gas falls to the centre and forms stars, the dark matter moves in as well. Supernova (SN) feedback then removes the gas, and the dark matter again responds to the changing potential. We study three physical models relating the motion of baryons to that of the dark matter: adiabatic contraction, dynamical friction, and rapid outflows. We find that dynamical friction plays only a very minor role, while adiabatic contraction and the rapid outflows due to feedback describe well the enhancement (or decrement) of dark matter. For haloes which show significant decrements of dark matter in the core, we find that to remove the dark matter requires an energy input between 1051 and 1053 erg. For our SN feedback proscription, this requires as a

  5. DARK MATTER HALOS IN GALAXIES AND GLOBULAR CLUSTER POPULATIONS

    SciTech Connect

    Hudson, Michael J.; Harris, Gretchen L.; Harris, William E.

    2014-05-20

    We combine a new, comprehensive database for globular cluster populations in all types of galaxies with a new calibration of galaxy halo masses based entirely on weak lensing. Correlating these two sets of data, we find that the mass ratio η ≡ M {sub GCS}/M {sub h} (total mass in globular clusters, divided by halo mass) is essentially constant at (η) ∼ 4 × 10{sup –5}, strongly confirming earlier suggestions in the literature. Globular clusters are the only known stellar population that formed in essentially direct proportion to host galaxy halo mass. The intrinsic scatter in η appears to be at most 0.2 dex; we argue that some of this scatter is due to differing degrees of tidal stripping of the globular cluster systems between central and satellite galaxies. We suggest that this correlation can be understood if most globular clusters form at very early stages in galaxy evolution, largely avoiding the feedback processes that inhibited the bulk of field-star formation in their host galaxies. The actual mean value of η also suggests that about one-fourth of the initial gas mass present in protogalaxies collected into giant molecular clouds large enough to form massive, dense star clusters. Finally, our calibration of (η) indicates that the halo masses of the Milky Way and M31 are (1.2 ± 0.5) × 10{sup 12} M {sub ☉} and (3.9 ± 1.8) × 10{sup 12} M {sub ☉}, respectively.

  6. Dark matter annihilation radiation in hydrodynamic simulations of Milky Way haloes

    NASA Astrophysics Data System (ADS)

    Schaller, Matthieu; Frenk, Carlos S.; Theuns, Tom; Calore, Francesca; Bertone, Gianfranco; Bozorgnia, Nassim; Crain, Robert A.; Fattahi, Azadeh; Navarro, Julio F.; Sawala, Till; Schaye, Joop

    2016-02-01

    We obtain predictions for the properties of cold dark matter annihilation radiation using high-resolution hydrodynamic zoom-in cosmological simulations of Milky Way-like galaxies (APOSTLE project) carried out as part of the `Evolution and Assembly of GaLaxies and their Environments' (EAGLE) programme. Galactic haloes in the simulation have significantly different properties from those assumed in the `standard halo model' often used in dark matter detection studies. The formation of the galaxy causes a contraction of the dark matter halo, whose density profile develops a steeper slope than the Navarro-Frenk-White (NFW) profile between r ≈ 1.5 kpc and r ≈ 10 kpc. At smaller radii, r ≲ 1.5 kpc, the haloes develop a flatter than NFW slope. This unexpected feature may be specific to our particular choice of subgrid physics model but nevertheless the dark matter density profiles agree within 30 per cent as the mass resolution is increased by a factor 150. The inner regions of the haloes are almost perfectly spherical (axis ratios b/a > 0.97 within r = 1 kpc) and there is no offset larger than 45 pc between the centre of the stellar distribution and the centre of the dark halo. The morphology of the predicted dark matter annihilation radiation signal is in broad agreement with γ-ray observations at large Galactic latitudes (b ≳ 3°). At smaller angles, the inferred signal in one of our four galaxies is similar to that which is observed but it is significantly weaker in the other three.

  7. Models of dark matter halos based on statistical mechanics: The classical King model

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri; Lemou, Mohammed; Méhats, Florian

    2015-03-01

    We consider the possibility that dark matter halos are described by the Fermi-Dirac distribution at finite temperature. This is the case if dark matter is a self-gravitating quantum gas made of massive neutrinos at statistical equilibrium. This is also the case if dark matter can be treated as a self-gravitating collisionless gas experiencing Lynden-Bell's type of violent relaxation. In order to avoid the infinite mass problem and carry out a rigorous stability analysis, we consider the fermionic King model. In this paper, we study the nondegenerate limit leading to the classical King model. This model was initially introduced to describe globular clusters. We propose to apply it also to large dark matter halos where quantum effects are negligible. We determine the caloric curve and study the thermodynamical stability of the different configurations. Equilibrium states exist only above a critical energy Ec in the microcanonical ensemble and only above a critical temperature Tc in the canonical ensemble. For E matter halos. Because of collisions and evaporation, the central density increases while the slope of the halo density profile decreases until an instability takes place. We show that large dark matter halos are relatively well described by the King model at, or close to, the point of marginal microcanonical stability. At that point, the King model generates a density profile that can be approximated by the modified Hubble profile. This profile has a flat core and decreases as r-3 at large distances, like the observational Burkert profile. Less steep halos are unstable. For large halos, the flat core is due to finite temperature effects, not to quantum mechanics. We argue that statistical

  8. 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.

  9. THE AVERAGE STAR FORMATION HISTORIES OF GALAXIES IN DARK MATTER HALOS FROM z = 0-8

    SciTech Connect

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

    2013-06-10

    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 10{sup 12} M{sub Sun} are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z {approx} 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z {approx} 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 {Lambda}CDM. Constraints on the stellar mass-halo mass relationship and SFRs are available for download online.

  10. Does the dark-matter halo induce chaos in the galactic disk?

    NASA Astrophysics Data System (ADS)

    Weinberg, Martin D.

    2013-07-01

    A three-dimensional galaxy disk will not have regular orbits (tori) everywhere. Therefore, there will be irregular, chaotic regions in addition to regular regions in the disk's phase space. In addition, galaxy formation in the standard LCDM scenario suggests a transition between disk-dominated and halo-dominated gravity at several disk scale lengths. These simple observations raise the following questions: 1) are there generic features of a exponential stellar disk induced by breaking of invariant tori? 2) do the chaotic regions in disks enable significant structural evolution in a galaxy lifetime? 3) does the orbital structure of disks indirectly depend on the dark matter halo especially in the transition region between the disk and dark-matter halo? In this talk, I present early results in my attempt to answer these questions using a new developed numerical technique based the mathematical construction used to prove the KAM theorem.

  11. Is Sextans dwarf galaxy in a scalar field dark matter halo?

    SciTech Connect

    Lora, V.; Magaña, Juan E-mail: juan.magana@uv.cl

    2014-09-01

    The Bose-Einstein condensate/scalar field dark matter model, considers that the dark matter is composed by spinless-ultra-light particles which can be described by a scalar field. This model is an alternative model to the Λ-cold dark matter paradigm, and therefore should be studied at galactic and cosmological scales. Dwarf spheroidal galaxies have been very useful when studying any dark matter theory, because the dark matter dominates their dynamics. In this paper we study the Sextans dwarf spheroidal galaxy, embedded in a scalar field dark matter halo. We explore how the dissolution time-scale of the stellar substructures in Sextans, constrain the mass, and the self-interacting parameter of the scalar field dark matter boson. We find that for masses in the range (0.12< m{sub φ}<8) ×10{sup -22} eV, scalar field dark halos without self-interaction would have cores large enough to explain the longevity of the stellar substructures in Sextans, and small enough mass to be compatible with dynamical limits. If the self-interacting parameter is distinct to zero, then the mass of the boson could be as high as m{sub φ}≈2×10{sup -21} eV, but it would correspond to an unrealistic low mass for the Sextans dark matter halo . Therefore, the Sextans dwarf galaxy could be embedded in a scalar field/BEC dark matter halo with a preferred self-interacting parameter equal to zero.

  12. Understanding the core-halo relation of quantum wave dark matter from 3D simulations.

    PubMed

    Schive, Hsi-Yu; Liao, Ming-Hsuan; Woo, Tak-Pong; Wong, Shing-Kwong; Chiueh, Tzihong; Broadhurst, Tom; Hwang, W-Y Pauchy

    2014-12-31

    We examine the nonlinear structure of gravitationally collapsed objects that form in our simulations of wavelike cold dark matter, described by the Schrödinger-Poisson (SP) equation with a particle mass ∼10(-22)  eV. A distinct gravitationally self-bound solitonic core is found at the center of every halo, with a profile quite different from cores modeled in the warm or self-interacting dark matter scenarios. Furthermore, we show that each solitonic core is surrounded by an extended halo composed of large fluctuating dark matter granules which modulate the halo density on a scale comparable to the diameter of the solitonic core. The scaling symmetry of the SP equation and the uncertainty principle tightly relate the core mass to the halo specific energy, which, in the context of cosmological structure formation, leads to a simple scaling between core mass (Mc) and halo mass (Mh), Mc∝a(-1/2)Mh(1/3), where a is the cosmic scale factor. We verify this scaling relation by (i) examining the internal structure of a statistical sample of virialized halos that form in our 3D cosmological simulations and by (ii) merging multiple solitons to create individual virialized objects. Sufficient simulation resolution is achieved by adaptive mesh refinement and graphic processing units acceleration. From this scaling relation, present dwarf satellite galaxies are predicted to have kiloparsec-sized cores and a minimum mass of ∼10(8)M⊙, capable of solving the small-scale controversies in the cold dark matter model. Moreover, galaxies of 2×10(12)M⊙ at z=8 should have massive solitonic cores of ∼2×10(9)M⊙ within ∼60  pc. Such cores can provide a favorable local environment for funneling the gas that leads to the prompt formation of early stellar spheroids and quasars. PMID:25615301

  13. EVIDENCE FOR A TRIAXIAL MILKY WAY DARK MATTER HALO FROM THE SAGITTARIUS STELLAR TIDAL STREAM

    SciTech Connect

    Law, David R.; Majewski, Steven R.; Johnston, Kathryn V. E-mail: srm4n@virginia.ed

    2009-09-20

    Observations of the lengthy tidal streams produced by the destruction of the Sagittarius dwarf spheroidal (Sgr dSph) are capable of providing strong constraints on the shape of the Galactic gravitational potential. However, previous work, based on modeling different stream properties in axisymmetric Galactic models, has yielded conflicting results: while the angular precession of the Sgr leading arm is most consistent with a spherical or slightly oblate halo, the radial velocities of stars in this arm are reproduced only by prolate halo models. We demonstrate that this apparent paradox can be resolved by instead adopting a triaxial potential. Our new Galactic halo model, which simultaneously fits all well-established phase space constraints from the Sgr stream, provides the first conclusive evidence for, and tentative measurement of, triaxiality in an individual dark matter halo. The Milky Way halo within {approx}60 kpc is best characterized by a minor/major axis ratio of the isovelocity contours c/a {approx} 0.67, intermediate/major axis ratio b/a {approx} 0.83, and triaxiality parameter T {approx} 0.56. In this model, the minor axis of the dark halo is coincident with the Galactic X-axis connecting the Sun and the Galactic center to within {approx}15 deg., while the major axis also lies in the Galactic plane, approximately along the Galactic Y-axis.

  14. Evidence for a Triaxial Milky Way Dark Matter Halo from the Sagittarius Stellar Tidal Stream

    NASA Astrophysics Data System (ADS)

    Law, David R.; Majewski, Steven R.; Johnston, Kathryn V.

    2009-09-01

    Observations of the lengthy tidal streams produced by the destruction of the Sagittarius dwarf spheroidal (Sgr dSph) are capable of providing strong constraints on the shape of the Galactic gravitational potential. However, previous work, based on modeling different stream properties in axisymmetric Galactic models, has yielded conflicting results: while the angular precession of the Sgr leading arm is most consistent with a spherical or slightly oblate halo, the radial velocities of stars in this arm are reproduced only by prolate halo models. We demonstrate that this apparent paradox can be resolved by instead adopting a triaxial potential. Our new Galactic halo model, which simultaneously fits all well-established phase space constraints from the Sgr stream, provides the first conclusive evidence for, and tentative measurement of, triaxiality in an individual dark matter halo. The Milky Way halo within ~60 kpc is best characterized by a minor/major axis ratio of the isovelocity contours c/a ≈ 0.67, intermediate/major axis ratio b/a ≈ 0.83, and triaxiality parameter T ~ 0.56. In this model, the minor axis of the dark halo is coincident with the Galactic X-axis connecting the Sun and the Galactic center to within ~15°, while the major axis also lies in the Galactic plane, approximately along the Galactic Y-axis.

  15. Models of dark matter halos based on statistical mechanics: The fermionic King model

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri; Lemou, Mohammed; Méhats, Florian

    2015-12-01

    We discuss the nature of phase transitions in the fermionic King model which describes tidally truncated quantum self-gravitating systems. This distribution function takes into account the escape of high-energy particles and has a finite mass. On the other hand, the Pauli exclusion principle puts an upper bound on the phase-space density of the system and stabilizes it against gravitational collapse. As a result, there exists a statistical equilibrium state for all accessible values of energy and temperature. We plot the caloric curves and investigate the nature of phase transitions as a function of the degeneracy parameter in both microcanonical and canonical ensembles, extending the work of Chavanis [Int. J. Mod. Phys. B 20, 3113 (2006)] for box-confined configurations. We consider stable and metastable states and emphasize the importance of the latter for systems with long-range interactions. Phase transitions can take place between a "gaseous" phase unaffected by quantum mechanics and a "condensed" phase dominated by quantum mechanics. The phase diagram exhibits two critical points, one in each ensemble, beyond which the phase transitions disappear. There also exists a region of negative specific heats and a situation of ensemble inequivalence for sufficiently large systems. In the microcanonical ensemble, gravitational collapse (gravothermal catastrophe) results in the formation of a small degenerate object containing a small mass. This is accompanied by the expulsion of a hot envelope containing a large mass. In the canonical ensemble, gravitational collapse (isothermal collapse) leads to a small degenerate object containing almost all the mass. It is surrounded by a tenuous envelope. We apply the fermionic King model to the case of dark matter halos made of massive neutrinos following the work of de Vega, Salucci, and Sanchez [Mon. Not. R. Astron. Soc. 442, 2717 (2014)]. The gaseous phase describes large halos and the condensed phase describes dwarf halos

  16. Tetrahedral collapse: a rotational toy model of simultaneous dark-matter halo, filament and wall formation

    NASA Astrophysics Data System (ADS)

    Neyrinck, Mark C.

    2016-07-01

    We discuss an idealized model of halo formation, in which a collapsing halo node is tetrahedral, with a filament extruding from each of its four faces, and with a wall connecting each pair of filaments. In the model, filaments generally spin when they form, and the halo spins if and only if there is some rotation in filaments. This is the simplest possible fully three-dimensional halo collapse in the `origami approximation', in which voids are irrotational, and the dark-matter sheet out of which dark-matter structures form is allowed to fold in position-velocity phase space, but not stretch (i.e. it cannot vary in density along a stream). Up to an overall scaling, the four filament directions, and only three other quantities, such as filament spins, suffice to determine all of the collapse's properties: the shape, mass, and spin of the halo; the densities per unit length and spins of all filaments; and masses per unit area of the walls. If the filaments are arranged regular-tetrahedrally, filament properties obey simple laws, reminiscent of angular-momentum conservation. The model may be most useful in understanding spin correlations between neighbouring galaxies joined by filaments; these correlations would give intrinsic alignments between galaxies, essential to understand for accurate cosmological weak-lensing measurements.

  17. Weakly Self-interacting Dark Matter and the Structure of Dark Halos

    NASA Astrophysics Data System (ADS)

    Yoshida, Naoki; Springel, Volker; White, Simon D. M.; Tormen, Giuseppe

    2000-12-01

    We study the formation of dark halos in a ΛCDM universe under the assumption that cold dark matter (CDM) particles have a finite cross section for elastic collisions. We compare evolution when CDM mean free paths are comparable to halo sizes with the collisionless and fluid limits. We show that a few collisions per particle per Hubble time at halo center can substantially affect the central density profile. Cross sections an order of magnitude larger produce sufficient relaxation for rich clusters to develop core radii in the range 100-200 h-1 kpc. The structural evolution of halos is a competition between collisional relaxation caused by individual particle interactions and violent relaxation resulting from the infall and merging processes by which clusters grow. Although our simulations concentrate on systems of cluster size, we can scale our results to address the halo structure expected for dwarf galaxies. We find that collision cross sections sufficiently large to significantly modify the cores of such galaxies produce cluster cores that are too large and/or too round to be consistent with observation. Thus, the simplest model for self-interacting dark matter is unable to improve fits to published dwarf galaxy rotation curves without violating other observational constraints.

  18. Tetrahedral collapse: a rotational toy model of simultaneous dark-matter halo, filament and wall formation

    NASA Astrophysics Data System (ADS)

    Neyrinck, Mark C.

    2016-04-01

    We discuss an idealized model of halo formation, in which a collapsing halo node is tetrahedral, with a filament extruding from each of its four faces, and with a wall connecting each pair of filaments. In the model, filaments generally spin when they form, and the halo spins if and only if there is some rotation in filaments. This is the simplest-possible fully three-dimensional halo collapse in the `origami approximation,' in which voids are irrotational, and the dark-matter sheet out of which dark-matter structures form is allowed to fold in position-velocity phase space, but not stretch (i.e., it cannot vary in density along a stream). Up to an overall scaling, the four filament directions, and only three other quantities, such as filament spins, suffice to determine all of the collapse's properties: the shape, mass, and spin of the halo; the densities per unit length and spins of all filaments; and masses per unit area of the walls. If the filaments are arranged regular-tetrahedrally, filament properties obey simple laws, reminiscent of angular-momentum conservation. The model may be most useful in understanding spin correlations between neighbouring galaxies joined by filaments; these correlations would give intrinsic alignments between galaxies, essential to understand for accurate cosmological weak-lensing measurements.

  19. Coming of age in the dark sector: how dark matter haloes grow their gravitational potential wells

    NASA Astrophysics Data System (ADS)

    van den Bosch, Frank C.; Jiang, Fangzhou; Hearin, Andrew; Campbell, Duncan; Watson, Douglas; Padmanabhan, Nikhil

    2014-12-01

    We present a detailed study of how dark matter haloes assemble their mass and grow their (central) potential well. We characterize these via their mass accretion histories (MAHs) and potential well growth histories (PWGHs), which we extract from the Bolshoi simulation and from semi-analytical merger trees supplemented with a method to compute the maximum circular velocity, Vmax, of progenitor haloes. The results of both methods are in excellent agreement, both in terms of the average and the scatter. We show that the MAH and PWGH are tightly correlated, and that growth of the central potential precedes the assembly of mass; the maximum circular velocity is already half the present-day value by the time the halo has accreted only 2 per cent of its final mass. Finally, we demonstrate that MAHs have a universal form, which we use to develop a new and improved universal model that can be used to compute the average or median MAH and PWGH for a halo of any mass in any Λ cold dark matter cosmology, without having to run a numerical simulation or a set of halo merger trees.

  20. The dark matter distribution function and halo thermalization from the Eddington equation in galaxies

    NASA Astrophysics Data System (ADS)

    de Vega, H. J.; Sanchez, N. G.

    2016-05-01

    We find the distribution function f(E) for dark matter (DM) halos in galaxies and the corresponding equation of state from the (empirical) DM density profiles derived from observations. We solve for DM in galaxies the analogous of the Eddington equation originally used for the gas of stars in globular clusters. The observed density profiles are a good realistic starting point and the distribution functions derived from them are realistic. We do not make any assumption about the DM nature, the methods developed here apply to any DM kind, though all results are consistent with warm dark matter (WDM). With these methods we find: (i) Cored density profiles behaving quadratically for small distances ρ(r)= r → 0ρ(0) ‑ Kr2 produce distribution functions which are finite and positive at the halo center while cusped density profiles always produce divergent distribution functions at the center. (ii) Cored density profiles produce approximate thermal Boltzmann distribution functions for r ≲ 3rh where rh is the halo radius. (iii) Analytic expressions for the dispersion velocity and the pressure are derived yielding at each halo point an ideal DM gas equation of state with local temperature T(r) ≡ mv2(r)/3. T(r) turns out to be constant in the same region where the distribution function is thermal and exhibits the same temperature within the percent. The self-gravitating DM gas can thermalize despite being collisionless because it is an ergodic system. (iv) The DM halo can be consistently considered at local thermal equilibrium with: (a) a constant temperature T(r) = T0 for r ≲ 3rh, (b) a space dependent temperature T(r) for 3rh < r ≲ Rvirial, which slowly decreases with r. That is, the DM halo is realistically a collisionless self-gravitating thermal gas for r ≲ Rvirial. (v) T(r) outside the halo radius nicely follows the decrease of the circular velocity squared.

  1. EVOLUTION OF THE GALAXY-DARK MATTER CONNECTION AND THE ASSEMBLY OF GALAXIES IN DARK MATTER HALOS

    SciTech Connect

    Yang Xiaohu; Zhang Youcai; Han Jiaxin; Mo, H. J.; Van den Bosch, Frank C.

    2012-06-10

    We present a new model to describe the galaxy-dark matter connection across cosmic time, which unlike the popular subhalo abundance-matching technique is self-consistent in that it takes account of the facts that (1) subhalos are accreted at different times and (2) the properties of satellite galaxies may evolve after accretion. Using observations of galaxy stellar mass functions (SMFs) out to z {approx} 4, the conditional SMF at z {approx} 0.1 obtained from Sloan Digital Sky Survey galaxy group catalogs, and the two-point correlation function (2PCF) of galaxies at z {approx} 0.1 as a function of stellar mass, we constrain the relation between galaxies and dark matter halos over the entire cosmic history from z {approx} 4 to the present. This relation is then used to predict the median assembly histories of different stellar mass components within dark matter halos (central galaxies, satellite galaxies, and halo stars). We also make predictions for the 2PCFs of high-z galaxies as function of stellar mass. Our main findings are the following: (1) Our model reasonably fits all data within the observational uncertainties, indicating that the {Lambda}CDM concordance cosmology is consistent with a wide variety of data regarding the galaxy population across cosmic time. (2) At low-z, the stellar mass of central galaxies increases with halo mass as M{sup 0.3} and M{sup {approx}>4.0} at the massive and low-mass ends, respectively. The ratio M{sub *,c}/M reveals a maximum of {approx}0.03 at a halo mass M {approx} 10{sup 11.8} h{sup -1} M{sub Sun }, much lower than the universal baryon fraction ({approx}0.17). At higher redshifts the maximum in M{sub *,c}/M remains close to {approx}0.03, but shifts to higher halo mass. (3) The inferred timescale for the disruption of satellite galaxies is about the same as the dynamical friction timescale of their subhalos. (4) The stellar mass assembly history of central galaxies is completely decoupled from the assembly history of its host

  2. Evolution of the Galaxy-Dark Matter Connection and the Assembly of Galaxies in Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Yang, Xiaohu; Mo, H. J.; van den Bosch, Frank C.; Zhang, Youcai; Han, Jiaxin

    2012-06-01

    We present a new model to describe the galaxy-dark matter connection across cosmic time, which unlike the popular subhalo abundance-matching technique is self-consistent in that it takes account of the facts that (1) subhalos are accreted at different times and (2) the properties of satellite galaxies may evolve after accretion. Using observations of galaxy stellar mass functions (SMFs) out to z ~ 4, the conditional SMF at z ~ 0.1 obtained from Sloan Digital Sky Survey galaxy group catalogs, and the two-point correlation function (2PCF) of galaxies at z ~ 0.1 as a function of stellar mass, we constrain the relation between galaxies and dark matter halos over the entire cosmic history from z ~ 4 to the present. This relation is then used to predict the median assembly histories of different stellar mass components within dark matter halos (central galaxies, satellite galaxies, and halo stars). We also make predictions for the 2PCFs of high-z galaxies as function of stellar mass. Our main findings are the following: (1) Our model reasonably fits all data within the observational uncertainties, indicating that the ΛCDM concordance cosmology is consistent with a wide variety of data regarding the galaxy population across cosmic time. (2) At low-z, the stellar mass of central galaxies increases with halo mass as M 0.3 and M gsim 4.0 at the massive and low-mass ends, respectively. The ratio M *, c /M reveals a maximum of ~0.03 at a halo mass M ~ 1011.8 h -1 M ⊙, much lower than the universal baryon fraction (~0.17). At higher redshifts the maximum in M *, c /M remains close to ~0.03, but shifts to higher halo mass. (3) The inferred timescale for the disruption of satellite galaxies is about the same as the dynamical friction timescale of their subhalos. (4) The stellar mass assembly history of central galaxies is completely decoupled from the assembly history of its host halo; the ratio M *, c /M initially increases rapidly with time until the halo mass reaches ~1012

  3. An accurate tool for the fast generation of dark matter halo catalogues

    NASA Astrophysics Data System (ADS)

    Monaco, P.; Sefusatti, E.; Borgani, S.; Crocce, M.; Fosalba, P.; Sheth, R. K.; Theuns, T.

    2013-08-01

    We present a new parallel implementation of the PINpointing Orbit Crossing-Collapsed HIerarchical Objects (PINOCCHIO) algorithm, a quick tool, based on Lagrangian Perturbation Theory, for the hierarchical build-up of dark matter (DM) haloes in cosmological volumes. To assess its ability to predict halo correlations on large scales, we compare its results with those of an N-body simulation of a 3 h-1 Gpc box sampled with 20483 particles taken from the MICE suite, matching the same seeds for the initial conditions. Thanks to the Fastest Fourier Transforms in the West (FFTW) libraries and to the relatively simple design, the code shows very good scaling properties. The CPU time required by PINOCCHIO is a tiny fraction (˜1/2000) of that required by the MICE simulation. Varying some of PINOCCHIO numerical parameters allows one to produce a universal mass function that lies in the range allowed by published fits, although it underestimates the MICE mass function of Friends-of-Friends (FoF) haloes in the high-mass tail. We compare the matter-halo and the halo-halo power spectra with those of the MICE simulation and find that these two-point statistics are well recovered on large scales. In particular, when catalogues are matched in number density, agreement within 10 per cent is achieved for the halo power spectrum. At scales k > 0.1 h Mpc-1, the inaccuracy of the Zel'dovich approximation in locating halo positions causes an underestimate of the power spectrum that can be modelled as a Gaussian factor with a damping scale of d = 3 h-1 Mpc at z = 0, decreasing at higher redshift. Finally, a remarkable match is obtained for the reduced halo bispectrum, showing a good description of non-linear halo bias. Our results demonstrate the potential of PINOCCHIO as an accurate and flexible tool for generating large ensembles of mock galaxy surveys, with interesting applications for the analysis of large galaxy redshift surveys.

  4. CONSTRAINING THE STAR FORMATION HISTORIES IN DARK MATTER HALOS. I. CENTRAL GALAXIES

    SciTech Connect

    Yang Xiaohu; Mo, H. J.; Lu Zhankui; Van den Bosch, Frank C.; Bonaca, Ana; Li Shijie; Lu Yi; Lu Yu

    2013-06-20

    Using the self-consistent modeling of the conditional stellar mass functions across cosmic time by Yang et al., we make model predictions for the star formation histories (SFHs) of central galaxies in halos of different masses. The model requires the following two key ingredients: (1) mass assembly histories of central and satellite galaxies and (2) local observational constraints of the star formation rates (SFRs) of central galaxies as a function of halo mass. We obtain a universal fitting formula that describes the (median) SFH of central galaxies as a function of halo mass, galaxy stellar mass, and redshift. We use this model to make predictions for various aspects of the SFRs of central galaxies across cosmic time. Our main findings are the following. (1) The specific star formation rate at high z increases rapidly with increasing redshift [{proportional_to}(1 + z){sup 2.5}] for halos of a given mass and only slowly with halo mass ({proportional_to}M{sub h}{sup 0.12}) at a given z, in almost perfect agreement with the specific mass accretion rate of dark matter halos. (2) The ratio between the SFR in the main branch progenitor and the final stellar mass of a galaxy peaks roughly at a constant value, {approx}10{sup -9.3} h {sup 2} yr{sup -1}, independent of the halo mass or the final stellar mass of the galaxy. However, the redshift at which the SFR peaks increases rapidly with halo mass. (3) More than half of the stars in the present-day universe were formed in halos with 10{sup 11.1} h {sup -1} M{sub Sun} < M{sub h} < 10{sup 12.3} h {sup -1} M{sub Sun} in the redshift range 0.4 < z < 1.9. (4) The star formation efficiencies (SFEs) of central galaxies reveal a ''downsizing'' behavior, in that the halo ''quenching'' mass, at which the SFE peaks, shifts from {approx}10{sup 12.5} h {sup -1} M{sub Sun} at z {approx}> 3.5 to {approx}10{sup 11.3} h {sup -1} M{sub Sun} at z = 0. (5) At redshift z {approx}> 2.5 more than 99% of the stars in the progenitors of massive

  5. ACCURATE UNIVERSAL MODELS FOR THE MASS ACCRETION HISTORIES AND CONCENTRATIONS OF DARK MATTER HALOS

    SciTech Connect

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

    2009-12-10

    A large amount of observations have constrained cosmological parameters and the initial density fluctuation spectrum to a very high accuracy. However, cosmological parameters change with time and the power index of the power spectrum dramatically varies with mass scale in the so-called concordance LAMBDACDM cosmology. Thus, any successful model for its structural evolution should work well simultaneously for various cosmological models and different power spectra. We use a large set of high-resolution N-body simulations of a variety of structure formation models (scale-free, standard CDM, open CDM, and LAMBDACDM) to study the mass accretion histories, the mass and redshift dependence of concentrations, and the concentration evolution histories of dark matter halos. We find that there is significant disagreement between the much-used empirical models in the literature and our simulations. Based on our simulation results, we find that the mass accretion rate of a halo is tightly correlated with a simple function of its mass, the redshift, parameters of the cosmology, and of the initial density fluctuation spectrum, which correctly disentangles the effects of all these factors and halo environments. We also find that the concentration of a halo is strongly correlated with the universe age when its progenitor on the mass accretion history first reaches 4% of its current mass. According to these correlations, we develop new empirical models for both the mass accretion histories and the concentration evolution histories of dark matter halos, and the latter can also be used to predict the mass and redshift dependence of halo concentrations. These models are accurate and universal: the same set of model parameters works well for different cosmological models and for halos of different masses at different redshifts, and in the LAMBDACDM case the model predictions match the simulation results very well even though halo mass is traced to about 0.0005 times the final mass

  6. Probing the structure of the cold dark matter halo using ancient mica

    SciTech Connect

    Baltz, E.A.; Westphal, A.J.; Snowden-Ifft, D.P.

    1999-01-01

    Mica can store (for {gt}1thinspGyr) etchable tracks caused by atoms recoiling from WIMPs. Ancient mica is a directional detector despite the complex motions it makes with respect to the WIMP {open_quotes}wind.{close_quotes} We can exploit the properties of directionality and long integration time to probe for structure in the dark matter halo of our galaxy. We compute a sample of possible signals in mica for a plausible model of halo structure. {copyright} {ital 1998} {ital The American Physical Society}

  7. Halo independent comparison of direct dark matter detection data

    SciTech Connect

    Gondolo, Paolo; Gelmini, Graciela B. E-mail: gelmini@physics.ucla.edu

    2012-12-01

    We extend the halo-independent method of Fox, Liu, and Weiner to include energy resolution and efficiency with arbitrary energy dependence, making it more suitable for experiments to use in presenting their results. Then we compare measurements and upper limits on the direct detection of low mass ( ∼ 10 GeV) weakly interacting massive particles with spin-independent interactions, including the upper limit on the annual modulation amplitude from the CDMS collaboration. We find that isospin-symmetric couplings are severely constrained both by XENON100 and CDMS bounds, and that isospin-violating couplings are still possible at the lowest energies, while the tension of the higher energy CoGeNT bins with the CDMS modulation constraint remains. We find the CRESST-II signal is not compatible with the modulation signals of DAMA and CoGeNT.

  8. Non-universality of Dark-matter Halos: Cusps, Cores, and the Central Potential

    NASA Astrophysics Data System (ADS)

    Hjorth, Jens; Williams, Liliya L. R.; Wojtak, Radosław; McLaughlin, Michael

    2015-09-01

    Dark-matter halos grown in cosmological simulations appear to have central Navarro–Frenk–White-like density cusps with mean values of d{log}ρ /d{log}r≈ -1, and some dispersion, which is generally parametrized by the varying index α in the Einasto density profile fitting function. Non-universality in profile shapes is also seen in observed galaxy clusters and possibly dwarf galaxies. Here we show that non-universality, at any given mass scale, is an intrinsic property of DARKexp, a theoretically derived model for collisionless self-gravitating systems. We demonstrate that DARKexp—which has only one shape parameter, ϕ0—fits the dispersion in profile shapes of massive simulated halos as well as observed clusters very well. DARKexp also allows for cored dark-matter profiles, such as those found for dwarf spheroidal galaxies. We provide approximate analytical relations between DARKexp ϕ0, Einasto α, or the central logarithmic slope in the Dehnen–Tremaine analytical γ-models. The range in halo parameters reflects a substantial variation in the binding energies per unit mass of dark-matter halos.

  9. Dark matter massive fermions and Einasto profiles in galactic haloes

    NASA Astrophysics Data System (ADS)

    Siutsou, I.; Argüelles, C. R.; Ruffini, R.

    2015-07-01

    On the basis of a fermionic dark matter model we fit rotation curves of The HI Nearby Galaxy Survey (THINGS) sample and compare our 3-parametric model to other models widely used in the literature: 2-parametric Navarro-Frenk-White, pseudoisothermal sphere, Burkhert models, and 3-parametric Einasto model, suggested as the new "standard dark matter profile" model in the paper by Chemin et al., Astron. J. 142 (2011) 109. The results from the fitting procedure provides evidence for an underlying fermionic nature of the dark matter candidate, with rest mass above the keV regime.

  10. MAGNIFICATION AS A PROBE OF DARK MATTER HALOS AT HIGH REDSHIFTS

    SciTech Connect

    Van Waerbeke, L.; Ford, J.; Milkeraitis, M.; Hildebrandt, H.

    2010-11-01

    We propose a new approach for measuring the mass profile of dark matter halos by stacking the lensing magnification of distant background galaxies behind groups and clusters of galaxies. The main advantage of lensing magnification is that, unlike lensing shear, it relies on accurate photometric redshifts only and not on galaxy shapes, thus enabling the study of the dark matter distribution with unresolved source galaxies. We present a feasibility study, using a real population of z {>=} 2.5 Lyman break galaxies as source galaxies, and where, similar to galaxy-galaxy lensing, foreground lenses are stacked in order to increase the signal-to-noise ratio. We find that there is an interesting new observational window for gravitational lensing as a probe of dark matter halos at high redshift, which does not require a measurement of galaxy shapes.

  11. HMFcalc: An online tool for calculating dark matter halo mass functions

    NASA Astrophysics Data System (ADS)

    Murray, S. G.; Power, C.; Robotham, A. S. G.

    2013-11-01

    The dark matter halo mass function (HMF) is a characteristic property of cosmological structure formation models, quantifying the number density of dark matter haloes per unit mass in the Universe. A key goal of current and planned large galaxy surveys is to measure the HMF and to use it to test theories of dark matter and dark energy. We present a new web application for calculating the HMF—the frontend HMFcalc and the engine hmf. HMFcalc has been designed to be flexible, efficient and easy to use, providing observational and theoretical astronomers alike with the means to explore standard functional forms of the HMF or to tailor their own. We outline the theoretical background needed to compute the HMF, we show how it has been implemented in hmf, and finally we provide worked examples that illustrate HMFcalc's versatility as an analysis tool.

  12. CONSTRAINTS ON THE SHAPE OF THE MILKY WAY DARK MATTER HALO FROM THE SAGITTARIUS STREAM

    SciTech Connect

    Vera-Ciro, Carlos; Helmi, Amina

    2013-08-10

    We propose a new model for the dark matter halo of the Milky Way that fits the properties of the stellar stream associated with the Sagittarius dwarf galaxy. Our dark halo is oblate with q{sub z} = 0.9 for r {approx}< 10 kpc, and can be made to follow the Law and Majewski model at larger radii. However, we find that the dynamical perturbations induced by the Large Magellanic Cloud on the orbit of Sgr cannot be neglected when modeling its streams. When taken into account, this leads us to constrain the Galaxy's outer halo shape to have minor-to-major axis ratio >(c/a){sub {Phi}} = 0.8 and intermediate-to-major axis ratio (b/a){sub {Phi}} = 0.9, in good agreement with cosmological expectations.

  13. Large-scale structure after COBE: Peculiar velocities and correlations of cold dark matter halos

    NASA Technical Reports Server (NTRS)

    Zurek, Wojciech H.; Quinn, Peter J.; Salmon, John K.; Warren, Michael S.

    1994-01-01

    Large N-body simulations on parallel supercomputers allow one to simultaneously investigate large-scale structure and the formation of galactic halos with unprecedented resolution. Our study shows that the masses as well as the spatial distribution of halos on scales of tens of megaparsecs in a cold dark matter (CDM) universe with the spectrum normalized to the anisotropies detected by Cosmic Background Explorer (COBE) is compatible with the observations. We also show that the average value of the relative pairwise velocity dispersion sigma(sub v) - used as a principal argument against COBE-normalized CDM models-is significantly lower for halos than for individual particles. When the observational methods of extracting sigma(sub v) are applied to the redshift catalogs obtained from the numerical experiments, estimates differ significantly between different observation-sized samples and overlap observational estimates obtained following the same procedure.

  14. Low-redshift Lyman-alpha absorption lines and the dark matter halos of disk galaxies

    NASA Technical Reports Server (NTRS)

    Maloney, Philip

    1992-01-01

    Ultraviolet observations of the low-redshift quasar 3C 273 using the Hubble Space Telescope have revealed many more Lyman-alpha absorption lines than would be expected from extrapolation of the absorption systems seen toward QSOs at z about 2. It is shown here that these absorption lines can plausibly be produced by gas at large radii in the disks of spiral and irregular galaxies; the gas is confined by the dark matter halos and ionized and heated by the extragalactic radiation field. This scenario does not require the extragalactic ionizing radiation field to decline as rapidly with decreasing z as the QSO emissivity. Observations of Ly-alpha absorption through the halos of known galaxies at low redshift will constrain both the extragalactic background and the properties of galactic halos.

  15. Constraints on baryonic dark matter in the Galactic halo and Local Group

    NASA Technical Reports Server (NTRS)

    Richstone, Douglas; Gould, Andrew; Guhathakurta, Puragra; Flynn, Chris

    1992-01-01

    A four-color method and deep CCD data are used to search for very faint metal-poor stars in the direction of the south Galactic pole. The results make it possible to limit the contribution of ordinary old, metal-poor stars to the dynamical halo of the Galaxy or to the Local Group. The ratio of the mass of the halo to its ordinary starlight must be more than about 2000, unless the halo is very small. For the Local Group, this ratio is greater than about 400. If this local dark matter is baryonic, the process of compact-object formation must produce very few 'impurities' in the form of stars similar to those found in globular clusters. The expected number of unbound stars with MV not greater than 6 within 100 pc of the sun is less than 1 based on the present 90-percent upper limit to the Local Group starlight.

  16. The Formation and Evolution of Galaxies Within Merging Dark Matter Haloes

    NASA Astrophysics Data System (ADS)

    Kauffmann, G.; White, S. D. M.; Guiderdoni, B.

    1993-09-01

    We construct semi-analytic models for galaxy formation within the framework of a hierarchical clustering scenario for structure formation in the Universe. We use the algorithm of Kauffmann & White to generate ensembles of merging histories for present-day dark matter haloes with a wide range of circular velocities. A galaxy is assumed to form from gas which cools and turns into stars at the centre of a halo until that halo merges with a more massive object. At this time the galaxy loses its source of new gas and becomes a non-dominant object within a larger group or cluster. Our methods thus enable us to `look inside' present dark matter haloes and investigate the formation, evolution and merging of the galaxies that they contain. We begin by investigating the properties of haloes with V_c_ = 220 km s^-1^, and use the observed properties of our Milky Way system to tune the free parameters that regulate star formation, hydrodynamic feedback from supernovae and the transformation of discs into spheroids by mergers. We then show that the same parameters lead to good agreement between the properties of galaxies in a V_c_ = 1000 km s^-1^ halo and observational data on the Virgo cluster of galaxies. This model correctly reproduces the observed trends in the luminosity, colour, gas content and morphology of galaxies. Turning to an investigation of the properties of the galaxy population as a whole, we highlight a problem that arises when applying this model to a `standard' cold dark matter universe. If the zero-point of the Tully-Fisher relation is set by the properties of our Milky Way system, we find that standard CDM predicts too many haloes and results in a B-band luminosity density of the Universe that is a factor of 2 too high. The only apparent solution to this problem is to assume that many haloes remain observationally undetectable. We also compute the gas mass-luminosity relation for galaxies, the variation in galaxy morphology as a function of luminosity, star

  17. THE CORRELATED FORMATION HISTORIES OF MASSIVE GALAXIES AND THEIR DARK MATTER HALOS

    SciTech Connect

    Tinker, Jeremy L.; George, Matthew R.; Leauthaud, Alexie; Bundy, Kevin; Finoguenov, Alexis; Massey, Richard; Rhodes, Jason; Wechsler, Risa H.

    2012-08-10

    Using observations in the COSMOS field, we report an intriguing correlation between the star formation activity of massive ({approx}10{sup 11.4} M{sub Sun }) central galaxies, their stellar masses, and the large-scale ({approx}10 Mpc) environments of their group-mass ({approx}10{sup 13.6} M{sub Sun }) dark matter halos. Probing the redshift range z = [0.2, 1.0], our measurements come from two independent sources: an X-ray-detected group catalog and constraints on the stellar-to-halo mass relation derived from a combination of clustering and weak lensing statistics. At z = 1, we find that the stellar mass in star-forming (SF) centrals is a factor of two less than in passive centrals at the same halo mass. This implies that the presence or lack of star formation in group-scale centrals cannot be a stochastic process. By z = 0, the offset reverses, probably as a result of the different growth rates of these objects. A similar but weaker trend is observed when dividing the sample by morphology rather than star formation. Remarkably, we find that SF centrals at z {approx} 1 live in groups that are significantly more clustered on 10 Mpc scales than similar mass groups hosting passive centrals. We discuss this signal in the context of halo assembly and recent simulations, suggesting that SF centrals prefer halos with higher angular momentum and/or formation histories with more recent growth; such halos are known to evolve in denser large-scale environments. If confirmed, this would be evidence of an early established link between the assembly history of halos on large scales and the future properties of the galaxies that form inside them.

  18. Simulations of isolated dwarf galaxies formed in dark matter halos with different mass assembly histories

    SciTech Connect

    González-Samaniego, A.; Avila-Reese, V.; Rodríguez-Puebla, A.; Valenzuela, O.; Colín, P.

    2014-04-10

    We present zoom-in N-body/hydrodynamics resimulations of dwarf galaxies formed in isolated cold dark matter (CDM) halos with the same virial mass (M{sub v} ≈ 2.5 × 10{sup 10} M {sub ☉}) at redshift z = 0. Our goals are to (1) study the mass assembly histories (MAHs) of the halo, stellar, and gaseous components; and (2) explore the effects of the halo MAHs on the stellar/baryonic assembly of simulated dwarfs. Overall, the dwarfs are roughly consistent with observations. More specific results include: (1) the stellar-to-halo mass ratio remains roughly constant since z ∼ 1, i.e., the stellar MAHs closely follow halo MAHs. (2) The evolution of the galaxy gas fractions, f{sub g} , are episodic, showing that the supernova-driven outflows play an important role in regulating f{sub g} —and hence, the star formation rate (SFR)—however, in most cases, a large fraction of the gas is ejected from the halo. (3) The star formation histories are episodic with changes in the SFRs, measured every 100 Myr, of factors of 2-10 on average. (4) Although the dwarfs formed in late assembled halos show more extended SF histories, their z = 0 specific SFRs are still below observations. (5) The inclusion of baryons most of the time reduces the virial mass by 10%-20% with respect to pure N-body simulations. Our results suggest that rather than increasing the strength of the supernova-driven outflows, processes that reduce the star formation efficiency could help to solve the potential issues faced by CDM-based simulations of dwarfs, such as low values of the specific SFR and high stellar masses.

  19. 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.

  20. THE DARK MATTER HALO CONCENTRATION AND STELLAR INITIAL MASS FUNCTION OF A CASSOWARY GROUP

    SciTech Connect

    Deason, A. J.; Auger, M. W.; Belokurov, V.; Evans, N. W.

    2013-08-10

    We exploit the group environment of the CAmbridge Sloan Survey Of Wide ARcs in the skY z = 0.3 lens J2158+0257 to measure the group dynamical mass as a complement to the central dynamical and lensing mass constraints. Follow-up spectroscopy of candidate group members is performed using VLT/FORS2. From the resulting N = 21 confirmed members, we measure the group dynamical mass by calibrating an analytic tracer mass estimator with cosmological simulations. The luminosity-weighted line-of-sight velocity dispersion and the Einstein radius of the lens are used as mass probes in the inner regions of the galaxy. Combining these three observational probes allows us to independently constrain the mass and concentration of the dark matter halo, in addition to the total stellar mass of the central galaxy. We find a dark matter halo in remarkably good agreement with simulations (log{sub 10} M{sub 200}/M{sub Sun} = 14.2 {+-} 0.2, c{sub 200}= 4.4{sup +1.6}{sub -1.4}) and a stellar mass-to-light ratio which favors a Salpeter initial mass function ((M/L)* = 5.7 {+-} 1.2). Our measurement of a normal halo concentration suggests that there is no discrepancy between simulations and observations at the group mass scale. This is in contrast to the cluster mass scale for which a number of studies have claimed over-concentrated halos. While the halo mass is robustly determined, and the halo concentration is not significantly affected by systematics, the resulting stellar mass-to-light ratio is sensitive to the choice of stellar parameters, such as density profile and velocity anisotropy.

  1. Simulations of Galaxies Formed in Warm Dark Matter Halos of Masses at the Filtering Scale

    NASA Astrophysics Data System (ADS)

    Colín, P.; Avila-Reese, V.; González-Samaniego, A.; Velázquez, H.

    2015-04-01

    We present zoom-in N-body + hydrodynamic simulations of dwarf central galaxies formed in warm dark matter (WDM) halos with present-day masses of 2-4 × {{10}10} M⊙. Two different cases are considered: the first one when halo masses are close to the corresponding half-mode filtering scale, Mf ({{m}WDM} = 1.2 keV), and the second when they are 20 to 30 times the corresponding Mf ({{m}WDM} = 3.0 keV). The WDM simulations are compared with the respective cold dark matter (CDM) simulations. The dwarfs formed in halos of masses (20-30)Mf have roughly similar properties and evolution to their CDM counterparts; on the contrary, those formed in halos of masses around Mf, are systematically different from their CDM counterparts. As compared to the CDM dwarfs, they assemble the dark and stellar masses later, having mass-weighted stellar ages 1.4-4.8 Gyr younger; their circular velocity profiles are shallower, with maximal velocities 20%-60% lower; their stellar distributions are much less centrally concentrated and with larger effective radii, by factors of 1.3-3. The WDM dwarfs at the filtering scale ({{m}WDM} = 1.2 keV) have disk-like structures, and end in most cases with higher gas fractions and lower stellar-to-total mass ratios than their CDM counterparts. The late halo assembly, low halo concentrations, and the absence of satellites of the former with respect to the latter are at the basis of the differences.

  2. Probing the halo dark matter. gamma. ray line from a lunar base

    SciTech Connect

    Salati, P.; Bouquet, A.; Silk, J. Department of Astronomy and Physics, University of California, Berkeley, CA )

    1990-03-15

    We study the possibility of detecting halo cold dark matter through the annihilation process {chi}{bar {chi}}{r arrow}{gamma}{gamma}. This process produces monoenergetic {gamma} rays, and may be a clear signature of particle dark matter. If there is a closure density of dark matter, we show that it will be very difficult to observe this annihilation line from a space station borne experiment. On the contrary, a large lunar based {gamma}-ray telescope could detect hundreds of events per year.

  3. WHAT DO DARK MATTER HALO PROPERTIES TELL US ABOUT THEIR MASS ASSEMBLY HISTORIES?

    SciTech Connect

    Wong, Anson W. C.; Taylor, James E. E-mail: taylor@uwaterloo.ca

    2012-09-20

    Individual dark matter halos in cosmological simulations vary widely in their detailed structural properties, properties such as concentration, shape, spin, and degree of internal relaxation. Recent non-parametric (principal component) analyses suggest that a few principal components explain a large fraction of the scatter in these structural properties. The main principal component is closely aligned with concentration, which in turn is known to be related to the mass accretion history (MAH) of the halo, as described by its merger tree. Here, we examine more generally the connection between the MAH and structural parameters. The space of mass accretion histories has principal components of its own. The strongest, accounting for almost 60% of the scatter between individual histories, can be interpreted as the age of the system. We give an analytic fit for this first component, which provides a rigorous way of defining the dynamical age of a halo. The second strongest component, representing acceleration or deceleration of growth at late times, accounts for 25% of the scatter. Relating structural parameters to formation history, we find that concentration correlates strongly with the early history of the halo, while shape and degree of relaxation or dynamical equilibrium correlate with the later history. We examine the inferences about formation history that can be drawn by splitting halos into sub-samples based on observable properties such as concentration and shape. Applications include the definition young and old samples of galaxy clusters in a quantitative way, or empirical tests of environmental processing rates in clusters.

  4. Systematic problems with using dark matter simulations to model stellar halos

    SciTech Connect

    Bailin, Jeremy; Bell, Eric F.; Valluri, Monica; Stinson, Greg S.; Debattista, Victor P.; Couchman, H. M. P.; Wadsley, James

    2014-03-10

    The limits of available computing power have forced models for the structure of stellar halos to adopt one or both of the following simplifying assumptions: (1) stellar mass can be 'painted' onto dark matter (DM) particles in progenitor satellites; (2) pure DM simulations that do not form a luminous galaxy can be used. We estimate the magnitude of the systematic errors introduced by these assumptions using a controlled set of stellar halo models where we independently vary whether we look at star particles or painted DM particles, and whether we use a simulation in which a baryonic disk galaxy forms or a matching pure DM simulation that does not form a baryonic disk. We find that the 'painting' simplification reduces the halo concentration and internal structure, predominantly because painted DM particles have different kinematics from star particles even when both are buried deep in the potential well of the satellite. The simplification of using pure DM simulations reduces the concentration further, but increases the internal structure, and results in a more prolate stellar halo. These differences can be a factor of 1.5-7 in concentration (as measured by the half-mass radius) and 2-7 in internal density structure. Given this level of systematic uncertainty, one should be wary of overinterpreting differences between observations and the current generation of stellar halo models based on DM-only simulations when such differences are less than an order of magnitude.

  5. Generating merger trees for dark matter haloes: a comparison of methods

    NASA Astrophysics Data System (ADS)

    Jiang, Fangzhou; van den Bosch, Frank C.

    2014-05-01

    Halo merger trees describe the hierarchical assembly of dark matter haloes, and are the backbone for modelling galaxy formation and evolution. Merger trees constructed using Monte Carlo algorithms based on the extended Press-Schechter (EPS) formalism are complementary to using N-body simulations and have the advantage that they are not trammelled by limited numerical resolution and uncertainties in identifying and linking (sub)haloes. This paper compares multiple EPS-based merger tree algorithms to simulation results using four diagnostics: progenitor mass function, mass assembly history (MAH), merger rate per descendant halo and the unevolved subhalo mass function. Spherical collapse-based methods typically overpredict major-merger rates, whereas ellipsoidal collapse dramatically overpredicts the minor-merger rate for massive haloes. The only algorithm in our comparison that yields results in good agreement with simulations is that by Parkinson et al. (P08). We emphasize, though, that the simulation results used as benchmarks in testing the merger trees are hampered by significant uncertainties themselves: MAHs and merger rates from different studies easily disagree by 50 per cent, even when based on the same simulation. Given this status quo, the P08 merger trees can be considered as accurate as those extracted from simulations.

  6. Bounds on Neutrino Non-Standard Interactions

    SciTech Connect

    Fernandez-Martinez, Enrique

    2010-03-30

    We review the present model independent bounds on neutrino non-standard interactions both at neutrino production and detection and in its interactions with matter. For matter non-standard interactions the direct bounds are rather weak. However, matter non-standard interactions are related by gauge invariance to the production and detection ones as well as to flavour changing processes involving charged leptons. Taking into account these relations much stronger bounds of at least O(10{sup -2}) can be derived unless significant fine tunings are implemented. Testing non-standard interactions at this level at future neutrino oscillation facilities is challenging but still feasible at very ambitious proposals such as the Neutrino Factory.

  7. The formation and evolution of dark matter halos early in cosmic history

    NASA Astrophysics Data System (ADS)

    Ernest, Alllan David; Collins, Matthew P.

    2015-08-01

    Observational evidence points to the formation of super-massive black holes, heavy elements and halo structure much earlier in cosmic history than expected [1], and this is challenging for Lambda Cold Dark Matter (LCDM) theory. However, if photon scattering cross sections were less than expected it becomes possible for halos to form at earlier times and relax the tensions that exist with LCDM theory. This may indeed be the case: it has recently been shown [2,3] that photon-particle scattering cross sections vary significantly with the eigenspectral distribution of the scattering particle in deep gravity wells, an effect that depends on the degree of localization of the particle wavefunction and the proximity of the halo to thermal equilibrium. Cross sections tend to be lower the larger and deeper the gravitational well. This purely quantum effect means that accepted cross sections, as measured on Earth and used to determine the rate and timing of halo formation, may not be applicable to deep gravity wells, not only at the present epoch but throughout cosmic history.By combining reduced photon scattering cross sections with Carr’s primordial black hole mass spectrum formulation[4] calculated at the last phase transition (t = 1 s), it is possible to provide a scenario of halo formation that enables galaxies and halos to form much earlier in cosmic history, yet maintain consistency with cosmic microwave background observations and primordial nucleosynthesis. In addition this scenario provides a unified model relating globular clusters, dwarf spheroidal galaxies and bulges, enables an understanding of the black hole-bulge/black hole-dark halo relations, and enables prediction of dark to visible matter, based on the physical parameters of a halo. This scenario will be presented and discussed.[1] Xue-Bing Wu et al, 2015, Nature, 518,512-515 doi: 10.1038/nature14241[2] Ernest A. D., 2009, J. Phys. A: Math. Theor. 42 115207, 115208[3] Ernest A. D, 2012, in Advances in

  8. Dark matter annihilation and decay from non-spherical dark halos in galactic dwarf satellites

    NASA Astrophysics Data System (ADS)

    Hayashi, Kohei; Ichikawa, Koji; Matsumoto, Shigeki; Ibe, Masahiro; Ishigaki, Miho N.; Sugai, Hajime

    2016-09-01

    The dwarf spheroidal galaxies (dSphs) in the Milky Way are the primary targets in the indirect searches for particle dark matter. To set robust constraints on candidate dark matter particles, understanding the dark halo structure of these systems is of substantial importance. In this paper, we first evaluate the astrophysical factors for dark matter annihilation and decay for 24 dSphs, taking into account a non-spherical dark halo, using generalized axisymmetric mass models based on axisymmetric Jeans equations. First, from a fitting analysis of the most recent kinematic data available, our axisymmetric mass models are a much better fit than previous spherical ones, thus, our work should be the most realistic and reliable estimator for astrophysical factors. Secondly, we find that among analysed dSphs, the ultra-faint dwarf galaxies Triangulum II and Ursa Major II are the most promising but large uncertain targets for dark matter annihilation while the classical dSph Draco is the most robust and detectable target for dark matter decay. It is also found that the non-sphericity of luminous and dark components influences the estimate of astrophysical factors, even though these factors largely depend on the sample size, the prior range of parameters and the spatial extent of the dark halo. Moreover, owing to these effects, the constraints on the dark matter annihilation cross-section are more conservative than those of previous spherical works. These results are important for optimizing and designing dark matter searches in current and future multi-messenger observations by space and ground-based telescopes.

  9. Positron line radiation from halo WIMP annihilations as a dark matter signature

    NASA Technical Reports Server (NTRS)

    Turner, Michael S.; Wilczek, Frank

    1989-01-01

    We suggest a new signature for dark matter annihilation in the halo: high energy positron line radiation. Because the cosmic ray positron spectrum falls rapidly with energy, e+'s from halo WIMP annihilations can be a significant, clean signal for very massive WIMP's (approx. greater than 30 GeV). In the case that the e+e- annihilation channel has an appreciable branch, the e+ signal should be above background in a future detector, such as have been proposed for ASTROMAG, and of potential importance as a dark matter signature. A significant e+e- branching ratio can occur for neutralinos or Dirac neutrinos. High-energy, continuum positron radiation may also be an important signature for massive neutralino annihilations, especially near or above the threshold of the W+W- and ZoZo annihilation channels.

  10. The Formation of Dark Matter Halos and High-Redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Genel, Shy

    2011-03-01

    In the concordance ΛCDMcosmological model, galaxies form in the centers of dark matter halos and merge with one another following the mergers of their host halos. Thus, we set out to quantify the growth mechanisms of dark matter halos. For this purpose, we analyze several large N-body simulations of the growth of cosmic structure. We devise a novel merger tree construction algorithm that properly takes into account halo fragmentations. We find that the merger rate evolves rapidly with redshift but depends weakly on mass, and that the proportions between mergers of different mass ratios, e.g.major and minor mergers, are universal. We also show that the merger rate per progenitor halo (related to future mergers and to galaxy pair counting) is smaller than that per descendant halo (related to past mergers and galaxy disturbed morphplogies), and that their redshift and mass dependencies are different. We find that only ~60%of the mass accreted onto halos arrives in mergers that are resolved in our simulations. Moreover, the functional form of the merger rate suggests that the merger contribution saturates at that value. Using full particle histories, we confirm that smoothly-accreted particles make a significant fraction of dark matter halos. This has important implications for the smoothness of gas accretion. Disk galaxies at z~2are rapidly star-forming, but show regular rotation, indicating little merger activity. We use a large dark matter simulation to show that even non-merging z~2 halos grow fast enough to explain observed high star-formation rates. We also follow those halos to z=0, finding that many do not undergo major mergers at all. The z~2disks also show high velocity dispersions and irregular clumpy morphologies. We run "zoom-in" cosmological hydrodynamical simulations focusing on the formation of individual z~2 galaxies. We find that the clumpy morphologies are a result of gravitational instability, where the high random motions make the (turbulent

  11. Finite temperature effects in Bose-Einstein condensed dark matter halos

    SciTech Connect

    Harko, Tiberiu; Madarassy, Enikö J.M. E-mail: eniko.madarassy@physics.uu.se

    2012-01-01

    Once the critical temperature of a cosmological boson gas is less than the critical temperature, a Bose-Einstein Condensation process can always take place during the cosmic history of the universe. Zero temperature condensed dark matter can be described as a non-relativistic, Newtonian gravitational condensate, whose density and pressure are related by a barotropic equation of state, with barotropic index equal to one. In the present paper we analyze the effects of the finite dark matter temperature on the properties of the dark matter halos. We formulate the basic equations describing the finite temperature condensate, representing a generalized Gross-Pitaevskii equation that takes into account the presence of the thermal cloud. The static condensate and thermal cloud in thermodynamic equilibrium is analyzed in detail, by using the Hartree-Fock-Bogoliubov and Thomas-Fermi approximations. The condensed dark matter and thermal cloud density and mass profiles at finite temperatures are explicitly obtained. Our results show that when the temperature of the condensate and of the thermal cloud are much smaller than the critical Bose-Einstein transition temperature, the zero temperature density and mass profiles give an excellent description of the dark matter halos. However, finite temperature effects may play an important role in the early stages of the cosmological evolution of the dark matter condensates.

  12. Constraints on the Galactic Halo Dark Matter from Fermi-LAT Diffuse Measurements

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Atwood, W. B.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Brandt, Theresa J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P A.; Casandjian, J. M.; Cecchi, C.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cuoco, A.; Guiriec, Sylvain Germain; McEnery, Julie E.; Scargle. J. D.; Troja, Eleonora

    2012-01-01

    We have performed an analysis of the diffuse gamma-ray emission with the Fermi Large Area Telescope (LAT) in the Milky Way halo region, searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We consider both gamma rays produced directly in the dark matter annihilation/decay and produced by inverse Compton scattering of the e+/e- produced in the annihilation/decay. Conservative limits are derived requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission. A second set of more stringent limits is derived based on modeling the foreground astrophysical diffuse emission using the GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the distribution of the cosmic-ray sources in the Galaxy, the index of the injection cosmic-ray electron spectrum, and the column density of the interstellar gas are taken into account using a profile likelihood formalism, while the parameters governing the cosmic-ray propagation have been derived from fits to local cosmic-ray data. The resulting limits impact the range of particle masses over which dark matter thermal production in the early universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as the annihilation of dark matter.

  13. Intrinsic Ellipticity Correlation of SDSS Luminous Red Galaxies and Misalignment with Their Host Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Okumura, Teppei; Jing, Y. P.; Li, Cheng

    2009-03-01

    We investigate the orientation correlation of giant elliptical galaxies by measuring the intrinsic ellipticity correlation function of 83,773 luminous red galaxies (LRGs) at redshifts 0.16-0.47 from the Sloan Digital Sky Survey. We have accurately determined the correlation up to 30 h-1 Mpc. Luminosity dependence of the ellipticity correlation is also detected although the error bars are large, while no evidence is found for its redshift evolution between z = 0.2 and z = 0.4. Then we use a cosmological N-body simulation to examine misalignment between the central LRGs and their parent dark matter halos. Central and satellite galaxies are assigned to simulated halos by employing a halo occupation distribution model for the LRGs. The ellipticity correlation is predicted to have the same shape as, but an amplitude about four times higher than, our observation if the central LRGs are perfectly aligned with their host halos. This indicates that the central LRG galaxies are preferentially but not perfectly aligned with their host halos. With the assumption that there is a misalignment angle between a central LRG and its host halo which follows a Gaussian distribution with a zero mean and a width σθ, we obtain a tight constraint on the misalignment parameter, σθ = 35.4+4.0 -3.3 deg. This type of intrinsic ellipticity correlation, if not corrected, can lead to contamination at 5% level to the shear power spectrum in weak lensing surveys of limiting magnitude RAB = 24.5 if the source central galaxies follow the same misalignment distribution as the LRGs.

  14. FastPM: a new scheme for fast simulations of dark matter and halos

    NASA Astrophysics Data System (ADS)

    Feng, Yu; Chu, Man-Yat; Seljak, Uroš; McDonald, Patrick

    2016-08-01

    We introduce FastPM, a highly-scalable approximated particle mesh N-body solver, which implements the particle mesh (PM) scheme enforcing correct linear displacement (1LPT) evolution via modified kick and drift factors. Employing a 2-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 3 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 halos 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.

  15. Dark matter halo properties from galaxy-galaxy lensing

    NASA Astrophysics Data System (ADS)

    Brimioulle, F.; Seitz, S.; Lerchster, M.; Bender, R.; Snigula, J.

    2013-06-01

    We present results for a galaxy-galaxy lensing study based on imaging data from the Canada-France-Hawaii Telescope Legacy Survey Wide. From a 12 million object multicolour catalogue for 124 deg2 of photometric data in the u*g'r'i'z' filters, we compute photometric redshifts (with a scatter of σΔz/(1 + z) = 0.033 and an outlier rate of η = 2.0 per cent for i' ≤ 22.5) and extract galaxy shapes down to i' = 24.0. We select a sample of lenses and sources with 0.05 < zd ≤ 1 and 0.05 < zs ≤ 2. We fit three different galaxy halo profiles to the lensing signal, a singular isothermal sphere (SIS), a truncated isothermal sphere (BBS) and a universal density profile (NFW). We derive velocity dispersions by fitting an SIS out to 100 h-1 kpc to the excess surface mass density ΔΣ and perform maximum likelihood analyses out to a maximum scale of 2 h-1 Mpc to obtain halo parameters and scaling relations. We find luminosity scaling relations of σred ∝ L0.24 ± 0.03 for the red lens sample, σblue ∝ L0.23 ± 0.03 for blue lenses and σ ∝ L0.29 ± 0.02 for the combined lens sample with zero-points of σ ^{*}_red=162± 2 {km s^{-1}}, σ ^{*}_blue=115± 3 {km s^{-1}} and σ* = 135 ± 2 km s-1 at a chosen reference luminosity L^{*}_{r^'=1.6 × 10^{10} h^{-2} L_{r^',⊙}. The steeper slope for the combined sample is due to the different zero-points of the blue and red lenses and the fact that blue lenses dominate at low luminosities and red lenses at high luminosities. The mean effective redshifts for the lens samples are = 0.28 for red lenses, = 0.35 for blue lenses and = 0.34 for the combined lens sample. The BBS maximum likelihood analysis yields for the combined sample a velocity dispersion of σ ^{*} = 131^{+2}_{-2} km s- 1 and a truncation radius of s^{*} = 184^{+17}_{+14} h^{-1} kpc, corresponding to a total mass of M^{*}_{total,BBS} = 2.32^{+0.28}_{-0.25} × 10^{12} h^{-1} M_{{⊙}} and a mass-to-light (M/L) ratio of M^{*}_total,BBS/L^{*}=178

  16. The Inner Structure of Dwarf-sized Halos in Warm and Cold Dark Matter Cosmologies

    NASA Astrophysics Data System (ADS)

    González-Samaniego, A.; Avila-Reese, V.; Colín, P.

    2016-03-01

    By means of N-body + hydrodynamic zoom-in simulations we study the evolution of the inner dark matter and stellar mass distributions of central dwarf galaxies formed in halos of virial masses Mv = (2-3) × 1010 h-1 M⊙ at z = 0, both in a warm dark matter (WDM) and cold dark matter (CDM) cosmology. The half-mode mass in the WDM power spectrum of our simulations is Mf = 2 × 1010 h-1 M⊙. In the dark matter (DM) only simulations halo density profiles are well described by the Navarro-Frenk-White parametric fit in both cosmologies, though the WDM halos have concentrations lower by factors of 1.5-2.0 than their CDM counterparts. In the hydrodynamic simulations, the effects of baryons significantly flatten the inner density, velocity dispersion, and pseudo phase space density profiles of the WDM halos but not of the CDM ones. The density slope, measured at ≈0.02Rv, α0.02, becomes shallow in periods of 2-5 Gyr in the WDM runs. We explore whether this flattening process correlates with the global star formation (SF), Ms/Mv ratio, gas outflow, and internal specific angular momentum histories. We do not find any clear trends, but when α0.02 is shallower than -0.5, Ms/Mv is always between 0.25% and 1%. We conclude that the main reason for the formation of the shallow core is the presence of strong gas mass fluctuations inside the inner halo, which are a consequence of the feedback driven by a very bursty and sustained SF history in shallow gravitational potentials. Our WDM halos, which assemble late and are less concentrated than the CDM ones, obey these conditions. There are also (rare) CDM systems with extended mass assembly histories that obey these conditions and form shallow cores. The dynamical heating and expansion processes behind the DM core flattening apply also to the stars in such a way that the stellar age and metallicity gradients of the dwarfs are softened, their stellar half-mass radii strongly grow with time, and their central surface densities

  17. PROGRESSIVELY MORE PROLATE DARK MATTER HALO IN THE OUTER GALAXY AS TRACED BY FLARING H I GAS

    SciTech Connect

    Banerjee, Arunima; Jog, Chanda J. E-mail: cjjog@physics.iisc.ernet.in

    2011-05-01

    A galactic disk in a spiral galaxy is generally believed to be embedded in an extended dark matter halo, which dominates its dynamics in the outer parts. However, the shape of the halo is not clearly understood. Here we show that the dark matter halo in the Milky Way is prolate in shape. Further, it is increasingly more prolate at larger radii, with the vertical-to-planar axis ratio monotonically increasing to 2.0 at 24 kpc. This is obtained by modeling the observed steeply flaring atomic hydrogen gas layer in the outer Galactic disk, where the gas is supported by pressure against the net gravitational field of the disk and the halo. The resulting prolate-shaped halo can explain several long-standing puzzles in galactic dynamics, for example, it permits long-lived warps thus explaining their ubiquitous nature.

  18. Dark radiation alleviates problems with dark matter halos.

    PubMed

    Chu, Xiaoyong; Dasgupta, Basudeb

    2014-10-17

    We show that a scalar and a fermion charged under a global U(1) symmetry can not only explain the existence and abundance of dark matter (DM) and dark radiation (DR), but can also imbue DM with improved scattering properties at galactic scales, while remaining consistent with all other observations. Delayed DM-DR kinetic decoupling eases the missing satellites problem, while scalar-mediated self-interactions of DM ease the cusp versus core and too big to fail problems. In this scenario, DM is expected to be pseudo-Dirac and have a mass 100 keV ≲ m(χ) ≲ 10 GeV. The predicted DR may be measurable using the primordial elemental abundances from big bang nucleosynthesis, and using the cosmic microwave background. PMID:25361246

  19. Dark Radiation Alleviates Problems with Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Chu, Xiaoyong; Dasgupta, Basudeb

    2014-10-01

    We show that a scalar and a fermion charged under a global U(1) symmetry can not only explain the existence and abundance of dark matter (DM) and dark radiation (DR), but can also imbue DM with improved scattering properties at galactic scales, while remaining consistent with all other observations. Delayed DM-DR kinetic decoupling eases the missing satellites problem, while scalar-mediated self-interactions of DM ease the cusp versus core and too big to fail problems. In this scenario, DM is expected to be pseudo-Dirac and have a mass 100 keV≲mχ≲10 GeV. The predicted DR may be measurable using the primordial elemental abundances from big bang nucleosynthesis, and using the cosmic microwave background.

  20. Distribution function approach to redshift space distortions. Part V: perturbation theory applied to dark matter halos

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    Numerical simulations show that redshift space distortions (RSD) introduce strong scale dependence in the power spectra of halos, with ten percent deviations relative to linear theory predictions even on relatively large scales (k < 0.1h/Mpc) and even in the absence of satellites (which induce Fingers-of-God, FoG, effects). If unmodeled these effects prevent one from extracting cosmological information from RSD surveys. In this paper we use Eulerian perturbation theory (PT) and Eulerian halo biasing model and apply it to the distribution function approach to RSD, in which RSD is decomposed into several correlators of density weighted velocity moments. We model each of these correlators using PT and compare the results to simulations over a wide range of halo masses and redshifts. We find that with an introduction of a physically motivated halo biasing, and using dark matter power spectra from simulations, we can reproduce the simulation results at a percent level on scales up to k ~ 0.15h/Mpc at z = 0, without the need to have free FoG parameters in the model.

  1. Distribution function approach to redshift space distortions. Part V: perturbation theory applied to dark matter halos

    SciTech Connect

    Vlah, Zvonimir; Seljak, Uroš; Okumura, Teppei; Desjacques, Vincent E-mail: seljak@physik.uzh.ch E-mail: Vincent.Desjacques@unige.ch

    2013-10-01

    Numerical simulations show that redshift space distortions (RSD) introduce strong scale dependence in the power spectra of halos, with ten percent deviations relative to linear theory predictions even on relatively large scales (k < 0.1h/Mpc) and even in the absence of satellites (which induce Fingers-of-God, FoG, effects). If unmodeled these effects prevent one from extracting cosmological information from RSD surveys. In this paper we use Eulerian perturbation theory (PT) and Eulerian halo biasing model and apply it to the distribution function approach to RSD, in which RSD is decomposed into several correlators of density weighted velocity moments. We model each of these correlators using PT and compare the results to simulations over a wide range of halo masses and redshifts. We find that with an introduction of a physically motivated halo biasing, and using dark matter power spectra from simulations, we can reproduce the simulation results at a percent level on scales up to k ∼ 0.15h/Mpc at z = 0, without the need to have free FoG parameters in the model.

  2. The hierarchical nature of the spin alignment of dark matter haloes in filaments

    NASA Astrophysics Data System (ADS)

    Aragon-Calvo, M. A.; Yang, Lin Forrest

    2014-05-01

    Dark matter haloes in cosmological filaments and walls have (in average) their spin vector aligned with their host structure. While haloes in walls are aligned with the plane of the wall independently of their mass, haloes in filaments present a mass-dependent two-regime orientation. Here, we show that the transition mass determining the change in the alignment regime (from parallel to perpendicular) depends on the hierarchical level in which the halo is located, reflecting the hierarchical nature of the Cosmic Web. By explicitly exposing the hierarchical structure of the Cosmic Web, we are able to identify the contributions of different components of the filament network to the alignment signal. We propose a unifying picture of angular momentum acquisition that is based on the results presented here and previous results found by other authors. In order to do a hierarchical characterization of the Cosmic Web, we introduce a new implementation of the multiscale morphology filter, the MMF-2, that significantly improves the identification of structures and explicitly describes their hierarchy. L36

  3. Accurate halo-model matter power spectra with dark energy, massive neutrinos and modified gravitational forces

    NASA Astrophysics Data System (ADS)

    Mead, A. J.; Heymans, C.; Lombriser, L.; Peacock, J. A.; Steele, O. I.; Winther, H. A.

    2016-06-01

    We present an accurate non-linear matter power spectrum prediction scheme for a variety of extensions to the standard cosmological paradigm, which uses the tuned halo model previously developed in Mead et al. We consider dark energy models that are both minimally and non-minimally coupled, massive neutrinos and modified gravitational forces with chameleon and Vainshtein screening mechanisms. In all cases, we compare halo-model power spectra to measurements from high-resolution simulations. We show that the tuned halo-model method can predict the non-linear matter power spectrum measured from simulations of parametrized w(a) dark energy models at the few per cent level for k < 10 h Mpc-1, and we present theoretically motivated extensions to cover non-minimally coupled scalar fields, massive neutrinos and Vainshtein screened modified gravity models that result in few per cent accurate power spectra for k < 10 h Mpc-1. For chameleon screened models, we achieve only 10 per cent accuracy for the same range of scales. Finally, we use our halo model to investigate degeneracies between different extensions to the standard cosmological model, finding that the impact of baryonic feedback on the non-linear matter power spectrum can be considered independently of modified gravity or massive neutrino extensions. In contrast, considering the impact of modified gravity and massive neutrinos independently results in biased estimates of power at the level of 5 per cent at scales k > 0.5 h Mpc-1. An updated version of our publicly available HMCODE can be found at https://github.com/alexander-mead/hmcode.

  4. Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John; Freeman, K. C.

    2015-04-01

    Dark matter (DM) halos of Sc-Im galaxies satisfy structural scaling laws analogous to the fundamental plane relations for elliptical galaxies. Halos in less luminous galaxies have smaller core radii rc , higher central densities ρ^, and smaller central velocity dispersions σ. If dwarf spheroidal (dSph) and dwarf Magellanic irregular (dIm) galaxies lie on the extrapolations of these correlations, then we can estimate their baryon loss relative to that of Sc-Im galaxies. We find that, if there had been no enhanced baryon loss relative to Sc-Im galaxies, typical dSph and dIm galaxies would be brighter by ΔMB ~= -4.0 mag and ΔMB ~= -3.5 mag, respectively. Instead, the galaxies lost or retained as gas (in dIm galaxies) baryons that could have formed stars. Also, dSph and dIm galaxies have DM halos that are more massive than we thought, with σ ~ 30 km s-1 or circular-orbit rotation velocities V circ ~ 42 km s-1. Comparison of DM and visible matter parameter correlations confirms that, at MV >~ -18, dSph and dIm galaxies form a sequence of decreasing baryon-to-DM mass ratios in smaller dwarfs. We show explicitly that galaxy baryon content goes to (almost) zero at V circ <~ 42 +/- 4 km s-1, in agreement with V circ as found from our estimate of baryon depletion. Our results suggest that there may be a large population of DM halos that are dark and undiscovered. This helps to solve the problem that the initial fluctuation spectrum of cold dark matter predicts more dwarf galaxies than we observe.

  5. Cold dark matter haloes in the Planck era: evolution of structural parameters for Einasto and NFW profiles

    NASA Astrophysics Data System (ADS)

    Dutton, Aaron A.; Macciò, Andrea V.

    2014-07-01

    We present the evolution of the structure of relaxed cold dark matter (CDM) haloes in the cosmology from the Planck satellite. Our simulations cover five decades in halo mass, from dwarf galaxies to galaxy clusters. Because of the increased matter density and power spectrum normalization the concentration-mass relation in the Planck cosmology has a ˜20 per cent higher normalization at redshift z = 0 compared to Wilkinson Microwave Anisotropy Probe cosmology. We confirm that CDM haloes are better described by the Einasto profile; for example, at scales near galaxy half-light radii CDM haloes have significantly steeper density profiles than implied by Navarro-Frenk-White (NFW) fits. There is a scatter of ˜0.2 dex in the Einasto shape parameter at fixed halo mass, adding further to the diversity of CDM halo profiles. The evolution of the concentration-mass relation in our simulations is not reproduced by any of the analytic models in the literature. We thus provide a simple fitting formula that accurately describes the evolution between redshifts z = 5 and 0 for both NFW and Einasto fits. Finally, the observed concentrations and halo masses of spiral galaxies, groups and clusters of galaxies at low redshifts are in good agreement with our simulations, suggesting only mild halo response to galaxy formation on these scales.

  6. The clustering of baryonic matter. II: halo model and hydrodynamic simulations

    SciTech Connect

    Fedeli, C.; Semboloni, E.; Velliscig, M.; Daalen, M. Van; Schaye, J.; Hoekstra, H. E-mail: sembolon@strw.leidenuniv.nl E-mail: daalen@strw.leidenuniv.nl E-mail: hoekstra@strw.leidenuniv.nl

    2014-08-01

    We recently developed a generalization of the halo model in order to describe the spatial clustering properties of each mass component in the Universe, including hot gas and stars. In this work we discuss the complementarity of the model with respect to a set of cosmological simulations including hydrodynamics of different kinds. We find that the mass fractions and density profiles measured in the simulations do not always succeed in reproducing the simulated matter power spectra, the reason being that the latter encode information from a much larger range in masses than that accessible to individually resolved structures. In other words, this halo model allows one to extract information on the growth of structures from the spatial clustering of matter, that is complementary with the information coming from the study of individual objects. We also find a number of directions for improvement of the present implementation of the model, depending on the specific application one has in mind. The most relevant one is the necessity for a scale dependence of the bias of the diffuse gas component, which will be interesting to test with future detections of the Warm-Hot Intergalactic Medium. This investigation confirms the possibility to gain information on the physics of galaxy and cluster formation by studying the clustering of mass, and our next work will consist of applying the halo model to use future high-precision cosmic shear surveys to this end.

  7. Dynamics of minimally coupled dark energy in spherical halos of dark matter

    NASA Astrophysics Data System (ADS)

    Novosyadlyj, Bohdan; Tsizh, Maksym; Kulinich, Yurij

    2016-03-01

    We analyse the evolution of scalar field dark energy in the spherical halos of dark matter at the late stages of formation of gravitationally bound systems in the expanding Universe. The dynamics of quintessential dark energy at the center of dark matter halo strongly depends on the value of effective sound speed c_s (in units of speed of light). If c_s˜ 1 (classical scalar field) then the dark energy in the gravitationally bound systems is only slightly perturbed and its density is practically the same as in cosmological background. The dark energy with small value of sound speed (c_s<0.1), on the contrary, is important dynamical component of halo at all stages of their evolution: linear, non-linear, turnaround, collapse, virialization and later up to current epoch. These properties of dark energy can be used for constraining the value of effective sound speed c_s by comparison the theoretical predictions with observational data related to the large scale gravitationally bound systems.

  8. The accretion history of dark matter haloes - I. The physical origin of the universal function

    NASA Astrophysics Data System (ADS)

    Correa, Camila A.; Wyithe, J. Stuart B.; Schaye, Joop; Duffy, Alan R.

    2015-06-01

    Understanding the universal accretion history of dark matter haloes is the first step towards determining the origin of their structure. We use the extended Press-Schechter formalism to derive the halo mass accretion history from the growth rate of initial density perturbations. We show that the halo mass history is well described by an exponential function of redshift in the high-redshift regime. However, in the low-redshift regime the mass history follows a power law because the growth of density perturbations is halted in the dark energy dominated era due to the accelerated expansion of the Universe. We provide an analytic model that follows the expression {M(z)=M0(1+z)^{af(M0)}e^{-f(M0)z}}, where M0 = M(z = 0), a depends on cosmology and f(M0) depends only on the linear matter power spectrum. The analytic model does not rely on calibration against numerical simulations and is suitable for any cosmology. We compare our model with the latest empirical models for the mass accretion history in the literature and find very good agreement. We provide numerical routines for the model online (available at https://bitbucket.org/astroduff/commah).

  9. Structure of dark matter halos in warm dark matter models and in models with long-lived charged massive particles

    SciTech Connect

    Kamada, Ayuki; Yoshida, Naoki; Kohri, Kazunori; Takahashi, Tomo E-mail: naoki.yoshida@phys.s.u-tokyo.ac.jp E-mail: tomot@cc.saga-u.ac.jp

    2013-03-01

    We study the formation of non-linear structures in warm dark matter (WDM) models and in a long-lived charged massive particle (CHAMP) model. CHAMPs with a decay lifetime of about 1 yr induce characteristic suppression in the matter power spectrum at subgalactic scales through acoustic oscillations in the thermal background. We explore structure formation in such a model. We also study three WDM models, where the dark matter particles are produced through the following mechanisms: i) WDM particles are produced in the thermal background and then kinematically decoupled; ii) WDM particles are fermions produced by the decay of thermal heavy bosons; and iii) WDM particles are produced by the decay of non-relativistic heavy particles. We show that the linear matter power spectra for the three models are all characterised by the comoving Jeans scale at the matter-radiation equality. Furthermore, we can also describe the linear matter power spectrum for the long-lived CHAMP model in terms of a suitably defined characteristic cut-off scale k{sub Ch}, similarly to the WDM models. We perform large cosmological N-body simulations to study the non-linear growth of structures in these four models. We compare the halo mass functions, the subhalo mass functions, and the radial distributions of subhalos in simulated Milky Way-size halos. For the characteristic cut-off scale k{sub cut} = 51 h Mpc{sup −1}, the subhalo abundance ( ∼ 10{sup 9}M{sub sun}) is suppressed by a factor of ∼ 10 compared with the standard ΛCDM model. We then study the models with k{sub cut} ≅ 51, 410, 820 h Mpc{sup −1}, and confirm that the halo and the subhalo abundances and the radial distributions of subhalos are indeed similar between the different WDM models and the long-lived CHAMP model. The result suggests that the cut-off scale k{sub cut} not only characterises the linear power spectra but also can be used to predict the non-linear clustering properties. The radial distribution of subhalos

  10. NIHAO IX: the role of gas inflows and outflows in driving the contraction and expansion of cold dark matter haloes

    NASA Astrophysics Data System (ADS)

    Dutton, Aaron A.; Macciò, Andrea V.; Dekel, Avishai; Wang, Liang; Stinson, Gregory; Obreja, Aura; Di Cintio, Arianna; Brook, Chris; Buck, Tobias; Kang, Xi

    2016-09-01

    We use ˜100 cosmological galaxy formation `zoom-in' simulations using the smoothed particle hydrodynamics code GASOLINE to study the effect of baryonic processes on the mass profiles of cold dark matter haloes. The haloes in our study range from dwarf (M200 ˜ 1010 M⊙) to Milky Way (M200 ˜ 1012 M⊙) masses. Our simulations exhibit a wide range of halo responses, primarily varying with mass, from expansion to contraction, with up to factor ˜10 changes in the enclosed dark matter mass at 1 per cent of the virial radius. Confirming previous studies, the halo response is correlated with the integrated efficiency of star formation: ɛSF ≡ (Mstar/M200)/(Ωb/Ωm). In addition, we report a new correlation with the compactness of the stellar system: ɛR ≡ r1/2/R200. We provide an analytic formula depending on ɛSF and ɛR for the response of cold dark matter haloes to baryonic processes. An observationally testable prediction is that, at fixed mass, larger galaxies experience more halo expansion, while the smaller galaxies more halo contraction. This diversity of dark halo response is captured by a toy model consisting of cycles of adiabatic inflow (causing contraction) and impulsive gas outflow (causing expansion). For net outflow, or equal inflow and outflow fractions, f, the overall effect is expansion, with more expansion with larger f. For net inflow, contraction occurs for small f (large radii), while expansion occurs for large f (small radii), recovering the phenomenology seen in our simulations. These regularities in the galaxy formation process provide a step towards a fully predictive model for the structure of cold dark matter haloes.

  11. The clustering of baryonic matter. I: a halo-model approach

    SciTech Connect

    Fedeli, C.

    2014-04-01

    In this paper I generalize the halo model for the clustering of dark matter in order to produce the power spectra of the two main baryonic matter components in the Universe: stars and hot gas. As a natural extension, this can be also used to describe the clustering of all mass. According to the design of the halo model, the large-scale power spectra of the various matter components are physically connected with the distribution of each component within bound structures and thus, ultimately, with the complete set of physical processes that drive the formation of galaxies and galaxy clusters. Besides being practical for cosmological and parametric studies, the semi-analytic model presented here has also other advantages. Most importantly, it allows one to understand on physical ground what is the relative contribution of each matter component to the total clustering of mass as a function of scale, and thus it opens an interesting new window to infer the distribution of baryons through high precision cosmic shear measurements. This is particularly relevant for future wide-field photometric surveys such as Euclid. In this work the concept of the model and its uncertainties are illustrated in detail, while in a companion paper we use a set of numerical hydrodynamic simulations to show a practical application and to investigate where the model itself needs to be improved.

  12. THE INTERGALACTIC STELLAR POPULATION FROM MERGERS OF ELLIPTICAL GALAXIES WITH DARK MATTER HALOS

    SciTech Connect

    Gonzalez-Garcia, A. Cesar; Stanghellini, Letizia; Manchado, Arturo

    2010-02-20

    We present simulations of dry-merger encounters between pairs of elliptical galaxies with dark matter halos. The aim of these simulations is to study the intergalactic (IG) stellar populations produced in both parabolic and hyperbolic encounters. We model progenitor galaxies with total-to-luminous mass ratios M{sub T} /M{sub L}= 3 and 11. The initial mass of the colliding galaxies are chosen so that M{sub 1}/M{sub 2} = 1 and 10. The model galaxies are populated by particles representing stars, as in Stanghellini et al., and dark matter. Merger remnants resulting from these encounters display a population of unbounded particles, both dark and luminous. The number of particles becoming unbounded depends on orbital configuration, with hyperbolic encounters producing a larger luminous intracluster population than parabolic encounters. Furthermore, in simulations with identical orbital parameters, a lower M{sub T} /M{sub L} of the colliding galaxies produces a larger fraction of unbounded luminous particles. For each modeled collision, the fraction of unbounded to initial stellar mass is the same in all mass bins considered, similarly to what we found previously by modeling encounters of galaxies without dark halos. The fraction of IG to total luminosity resulting from our simulations is {approx}4% and {approx}6% for dark-to-bright mass ratios of 10 and 2, respectively. These unbounded-to-total luminous fractions are down from the 17% that we had previously found in the case of no dark halos. Our results are in broad agreement with IG light observed in groups of galaxies, while the results of our previous models without dark halos better encompass observed intracluster populations. We suggest a possible formation scenario of IG stars.

  13. Halo-independent direct detection of momentum-dependent dark matter

    SciTech Connect

    Cherry, John F.; Frandsen, Mads T.; Shoemaker, Ian M. E-mail: frandsen@cp3-origins.net

    2014-10-01

    We show that the momentum dependence of dark matter interactions with nuclei can be probed in direct detection experiments without knowledge of the dark matter velocity distribution. This is one of the few properties of DM microphysics that can be determined with direct detection alone, given a signal of dark matter in multiple direct detection experiments with different targets. Long-range interactions arising from the exchange of a light mediator are one example of momentum-dependent DM. For data produced from the exchange of a massless mediator we find for example that the mediator mass can be constrained to be ∼< 10 MeV for DM in the 20-1000 GeV range in a halo-independent manner.

  14. THE SPACE MOTION OF LEO I: THE MASS OF THE MILKY WAY'S DARK MATTER HALO

    SciTech Connect

    Boylan-Kolchin, Michael; Bullock, James S.; Sohn, Sangmo Tony; Van der Marel, Roeland P.; Besla, Gurtina

    2013-05-10

    We combine our Hubble Space Telescope measurement of the proper motion of the Leo I dwarf spheroidal galaxy (presented in a companion paper) with the highest resolution numerical simulations of Galaxy-size dark matter halos in existence to constrain the mass of the Milky Way's dark matter halo (M{sub vir,MW}). Despite Leo I's large Galactocentric space velocity (200 km s{sup -1}) and distance (261 kpc), we show that it is extremely unlikely to be unbound if Galactic satellites are associated with dark matter substructure, as 99.9% of subhalos in the simulations are bound to their host. The observed position and velocity of Leo I strongly disfavor a low-mass Milky Way: if we assume that Leo I is the least bound of the Milky Way's classical satellites, then we find that M{sub vir,MW} > 10{sup 12} M{sub Sun} at 95% confidence for a variety of Bayesian priors on M{sub vir,MW}. In lower mass halos, it is vanishingly rare to find subhalos at 261 kpc moving as fast as Leo I. Should an additional classical satellite be found to be less bound than Leo I, this lower limit on M{sub vir,MW} would increase by 30%. Imposing a mass-weighted {Lambda}CDM prior, we find a median Milky Way virial mass of M{sub vir,MW} = 1.6 Multiplication-Sign 10{sup 12} M{sub Sun }, with a 90% confidence interval of [1.0-2.4] Multiplication-Sign 10{sup 12} M{sub Sun }. We also confirm a strong correlation between subhalo infall time and orbital energy in the simulations and show that proper motions can aid significantly in interpreting the infall times and orbital histories of satellites.

  15. Long GRBs as a tool to investigate star formation in dark matter halos

    NASA Astrophysics Data System (ADS)

    Wei, Jun-Jie; Hao, Jing-Meng; Wu, Xue-Feng; Yuan, Ye-Fei

    2016-03-01

    First stars can only form in structures that are suitably dense, which can be parametrized by the minimum dark matter halo mass Mmin. Mmin must play an important role in star formation. The connection of long gamma-ray bursts (LGRBs) with the collapse of massive stars has provided a good opportunity for probing star formation in dark matter halos. We place some constraints on Mmin using the latest Swift LGRB data. We conservatively consider that LGRB rate is proportional to the cosmic star formation rate (CSFR) and an additional evolution parametrized as (1 + z) α, where the CSFR model is a function of Mmin. Using the χ2 statistic, the contour constraints on the Mmin-α plane show that at the 1σ confidence level, we have Mmin <1010.5M⊙ from 118 LGRBs with redshift z < 4 and luminosity Liso > 1.8 ×1051 ergs-1. We also find that adding 12 high-z (4 < z < 5) LGRBs (consisting of 104 LGRBs with z < 5 and Liso > 3.1 ×1051 ergs-1) could result in much tighter constraints on Mmin, for which, 107.7M⊙ matter halos.

  16. The Space Motion of Leo I: The Mass of the Milky Way's Dark Matter Halo

    NASA Astrophysics Data System (ADS)

    Boylan-Kolchin, Michael; Bullock, James S.; Sohn, Sangmo Tony; Besla, Gurtina; van der Marel, Roeland P.

    2013-05-01

    We combine our Hubble Space Telescope measurement of the proper motion of the Leo I dwarf spheroidal galaxy (presented in a companion paper) with the highest resolution numerical simulations of Galaxy-size dark matter halos in existence to constrain the mass of the Milky Way's dark matter halo (M vir, MW). Despite Leo I's large Galactocentric space velocity (200 km s-1) and distance (261 kpc), we show that it is extremely unlikely to be unbound if Galactic satellites are associated with dark matter substructure, as 99.9% of subhalos in the simulations are bound to their host. The observed position and velocity of Leo I strongly disfavor a low-mass Milky Way: if we assume that Leo I is the least bound of the Milky Way's classical satellites, then we find that M vir, MW > 1012 M ⊙ at 95% confidence for a variety of Bayesian priors on M vir, MW. In lower mass halos, it is vanishingly rare to find subhalos at 261 kpc moving as fast as Leo I. Should an additional classical satellite be found to be less bound than Leo I, this lower limit on M vir, MW would increase by 30%. Imposing a mass-weighted ΛCDM prior, we find a median Milky Way virial mass of M vir, MW = 1.6 × 1012 M ⊙, with a 90% confidence interval of [1.0-2.4] × 1012 M ⊙. We also confirm a strong correlation between subhalo infall time and orbital energy in the simulations and show that proper motions can aid significantly in interpreting the infall times and orbital histories of satellites.

  17. Glow in the dark matter: observing galactic halos with scattered light.

    PubMed

    Davis, Jonathan H; Silk, Joseph

    2015-02-01

    We consider the observation of diffuse halos of light around the discs of spiral galaxies, as a probe of the interaction cross section between dark matter (DM) and photons. Using the galaxy M101 as an example, we show that for a scattering cross section at the level of 10(-23)(m/GeV)  cm(2) or greater dark matter in the halo will scatter light out from the more luminous center of the disc to larger radii, contributing to an effective increased surface brightness at the edges of the observed area on the sky. This allows us to set an upper limit on the DM-photon cross section using data from the Dragonfly instrument. We then show how to improve this constraint, and the potential for discovery, by combining the radial profile of DM-photon scattering with measurements at multiple wavelengths. Observation of diffuse light presents a new and potentially powerful way to probe the interactions of dark matter with photons, a way that is complementary to existing searches. PMID:25699431

  18. Glow in the Dark Matter: Observing Galactic Halos with Scattered Light

    NASA Astrophysics Data System (ADS)

    Davis, Jonathan H.; Silk, Joseph

    2015-02-01

    We consider the observation of diffuse halos of light around the discs of spiral galaxies, as a probe of the interaction cross section between dark matter (DM) and photons. Using the galaxy M101 as an example, we show that for a scattering cross section at the level of 10-23(m /GeV ) cm2 or greater dark matter in the halo will scatter light out from the more luminous center of the disc to larger radii, contributing to an effective increased surface brightness at the edges of the observed area on the sky. This allows us to set an upper limit on the DM-photon cross section using data from the Dragonfly instrument. We then show how to improve this constraint, and the potential for discovery, by combining the radial profile of DM-photon scattering with measurements at multiple wavelengths. Observation of diffuse light presents a new and potentially powerful way to probe the interactions of dark matter with photons, a way that is complementary to existing searches.

  19. Core formation in dwarf haloes with self-interacting dark matter: no fine-tuning necessary

    NASA Astrophysics Data System (ADS)

    Elbert, Oliver D.; Bullock, James S.; Garrison-Kimmel, Shea; Rocha, Miguel; Oñorbe, Jose; Peter, Annika H. G.

    2015-10-01

    We investigate the effect of self-interacting dark matter (SIDM) on the density profiles of Vmax ≃ 40km s-1 isolated dwarf dark matter haloes - the scale of relevance for the too big to fail problem (TBTF) - using very high resolution cosmological zoom simulations. Each halo has millions of particles within its virial radius. We find that SIDM models with cross-sections per unit mass spanning the range σ/m = 0.5-50 cm2 g-1 alleviate TBTF and produce constant-density cores of size 300-1000 pc, comparable to the half-light radii of M⋆ ˜ 105 - 7 M⊙ dwarfs. The largest, lowest density cores develop for cross-sections in the middle of this range, σ/m ˜ 5-10 cm2 g-1. Our largest SIDM cross-section run (σ/m = 50 cm2 g-1) develops a slightly denser core owing to mild core-collapse behaviour, but it remains less dense than the cold dark matter case and retains a constant-density core profile. Our work suggests that SIDM cross-sections as large or larger than 50 cm2 g-1 remain viable on velocity scales of dwarf galaxies (vrms ˜ 40 km s-1). The range of SIDM cross-sections that alleviate TBTF and the cusp/core problem spans at least two orders of magnitude and therefore need not be particularly fine-tuned.

  20. Some like it triaxial: the universality of dark matter halo shapes and their evolution along the cosmic time

    NASA Astrophysics Data System (ADS)

    Despali, Giulia; Giocoli, Carlo; Tormen, Giuseppe

    2014-10-01

    We present a detailed analysis of dark matter halo shapes, studying how the distributions of ellipticity, prolateness and axial ratios evolve as a function of time and mass. With this purpose in mind, we analysed the results of three cosmological simulations, running an ellipsoidal halo finder to measure triaxial halo shapes. The simulations have different scales, mass limits and cosmological parameters, which allows us to ensure a good resolution and statistics in a wide mass range, and to investigate the dependence of halo properties on the cosmological model. We confirm the tendency of haloes to be prolate at all times, even if they become more triaxial going to higher redshifts. Regarding the dependence on mass, more massive haloes are also less spherical at all redshifts, since they are the most recent forming systems and so still retain memory of their original shape at the moment of collapse. We then propose a rescaling of the shape-mass relations, using the variable ν = δc/σ to represent the mass, which absorbs the dependence on both cosmology and time, allowing us to find universal relations between halo masses and shape parameters (ellipticity, prolateness and the axial ratios) which hold at any redshift. This may be very useful to determine prior distributions of halo shapes for observational studies.

  1. Investigating the outer density profile of the dark matter halo of M31

    NASA Astrophysics Data System (ADS)

    Kirihara, Takanobu

    2015-08-01

    In the context of the hierarchical structure formation in the universe, cosmological N -body simulations predict that cold dark matter (CDM) halos have a universal mass-density profile(Navarro et al. 1996; Fukushige & Makino 1997; Moore et al. 1998).Especially, the density profile of CDM outer halos decreases with the cube of the radius from the galactic center. However, so far, not much effort has examined this hypothesis because it is extremely difficult to measure the mass distribution of the outer region of a galaxy.On the other hand, a recent observation discovered a giant stellar stream (GSS) and stellar shells in the halo of the Andromeda galaxy (M31). The GSS extends over 120 kpc further away along the line of sight from M31, and its spatial and velocity structure have been observed in detail. So far, N -body simulations of a galaxy merger between a satellite dwarf galaxy and M31 nicely reproduced these structures (Fardal et al. 2007; Mori & Rich 2008).We present the result of the N -body simulation of the galaxy merger to investigate the mass distribution of the DM halo in M31. We vary the power-law index of the outer-density profile and the total mass of the CDM halo of M31. To reproduce the observed structures, we find the sufficient condition for the power-law index x. The best-fit parameter is x=-3.7, which is steeper than the CDM prediction (x=-3).In addition, we also focus on the morphology of the progenitor galaxy. We perform large parameter surveys of the galaxy merger varying thickness and rotation velocity of a disk-like component of the progenitor. The result suggests that a rotating component of the progenitor is required to reproduce an asymmetric internal structure of the GSS. Using the parameter that reproduces the observed structures in detail, we discuss the evolution and relaxation of the dark matter component that initially associated with the progenitor.

  2. STELLAR MASS VERSUS STELLAR VELOCITY DISPERSION: WHICH IS BETTER FOR LINKING GALAXIES TO THEIR DARK MATTER HALOS?

    SciTech Connect

    Li Cheng; Wang Lixin; Jing, Y. P.

    2013-01-01

    It was recently suggested that compared to its stellar mass (M{sub *}), the central stellar velocity dispersion ({sigma}{sub *}) of a galaxy might be a better indicator for its host dark matter halo mass. Here we test this hypothesis by estimating the dark matter halo mass for central galaxies in groups as a function of M{sub *} and {sigma}{sub *}. For this we have estimated the redshift-space cross-correlation function (CCF) between the central galaxies at given M{sub *} and {sigma}{sub *} and a reference galaxy sample, from which we determine both the projected CCF, w{sub p} (r{sub p} ), and the velocity dispersion profile. A halo mass is then obtained from the average velocity dispersion within the virial radius. At fixed M{sub *}, we find very weak or no correlation between halo mass and {sigma}{sub *}. In contrast, strong mass dependence is clearly seen even when {sigma}{sub *} is limited to a narrow range. Our results thus firmly demonstrate that the stellar mass of central galaxies is still a good (if not the best) indicator for dark matter halo mass, better than the stellar velocity dispersion. The dependence of galaxy clustering on {sigma}{sub *} at fixed M{sub *}, as recently discovered by Wake et al., may be attributed to satellite galaxies, for which the tidal stripping occurring within halos has stronger effect on stellar mass than on central stellar velocity dispersion.

  3. ANISOTROPIC LOCATIONS OF SATELLITE GALAXIES: CLUES TO THE ORIENTATIONS OF GALAXIES WITHIN THEIR DARK MATTER HALOS

    SciTech Connect

    Agustsson, Ingolfur; Brainerd, Tereasa G. E-mail: brainerd@bu.ed

    2010-02-01

    We investigate the locations of the satellites of relatively isolated host galaxies in the Sloan Digital Sky Survey and the Millennium Run simulation. Provided we use two distinct prescriptions to embed luminous galaxies within the simulated dark matter halos (ellipticals share the shapes of their halos, while disks have angular momenta that are aligned with the net angular momenta of their halos), we find a fair agreement between observation and theory. Averaged over scales r{sub p} <= 500 kpc, the satellites of red, high-mass hosts with low star formation rates are found preferentially near the major axes of their hosts. In contrast, the satellites of blue, low-mass hosts with low star formation rates show little to no anisotropy when averaged over the same scale. The difference between the locations of the satellites of red and blue hosts cannot be explained by the effects of interlopers in the data. Instead, it is caused primarily by marked differences in the dependence of the mean satellite location, (phi), on the projected distance at which the satellites are found. We also find that the locations of red, high-mass satellites with low star formation rates show considerably more anisotropy than do the locations of blue, low-mass satellites with high star formation rates. There are two contributors to this result. First, the blue satellites have only recently arrived within their hosts' halos, while the red satellites arrived in the far distant past. Second, the sample of blue satellites is heavily contaminated by interlopers, which suppresses the measured anisotropy compared to the intrinsic anisotropy.

  4. Dark Matter annihilations in halos and high-redshift sources of reionization of the universe

    NASA Astrophysics Data System (ADS)

    Poulin, Vivian; Serpico, Pasquale D.; Lesgourgues, Julien

    2015-12-01

    It is well known that annihilations in the homogeneous fluid of dark matter (DM) can leave imprints in the cosmic microwave background (CMB) anisotropy power spectrum. However, the relevance of DM annihilations in halos for cosmological observables is still subject to debate, with previous works reaching different conclusions on this point. Also, all previous studies used a single type of parameterization for the astrophysical reionization, and included no astrophysical source for the heating of the intergalactic medium. In this work, we revisit these problems. When standard approaches are adopted, we find that the ionization fraction does exhibit a very particular (and potentially constraining) pattern, but the currently measurable τreio is left almost unchanged: in agreement with most of the previous literature, for plausible halo models we find that the modification of the signal with respect to the one coming from annihilations in the smooth background is tiny, below cosmic variance within currently allowed parameter space. However, if different and probably more realistic treatments of the astrophysical sources of reionization and heating are adopted, a more pronounced effect of the DM annihilation in halos is possible. We thus conclude that within currently adopted baseline models the impact of the virialised DM structures cannot be uncovered by CMB power spectra measurements, but a larger impact is possible if peculiar models are invoked for the redshift evolution of the DM annihilation signal or different assumptions are made for the astrophysical contributions. A better understanding (both theoretical and observational) of the reionization and temperature history of the universe, notably via the 21 cm signal, seems the most promising way for using halo formation as a tool in DM searches, improving over the sensitivity of current cosmological probes.

  5. WSRT HI imaging of candidate gas-bearing dark matter halos in the Local Group

    NASA Astrophysics Data System (ADS)

    Adams, Elizabeth A.; Oosterloo, Tom; Cannon, John M.; Giovanelli, Riccardo; Haynes, Martha P.

    2016-01-01

    A long standing problem in cosmology is the mismatch between the number of low mass dark matter halos predicted by simulations and the number of low mass galaxies observed in the Local Group. We recently presented a set of isolated ultra-compact high velocity clouds (UCHVCs) identified within the dataset of the Arecibo Legacy Fast ALFA (ALFALFA) HI line survey that are consistent with representing low mass gas-bearing dark matter halos within the Local Group (Adams+ 2013). At distances of ~1 Mpc, the UCHVCs have HI masses of ~10^5 Msun and indicative dynamical masses of ~10^7 Msun. The HI diameters of the UCHVCs range from 4' to 20', or 1 to 6 kpc at a distance of 1 Mpc. We have selected the most compact and isolated UCHVCs with the highest average column densities as representing the best galaxy candidates. These systems have been observed with the Westerbork Synthesis Radio Telescope (WSRT) to enable higher spatial resolution studies of the HI distribution. From these data, the sources break into two clear categories. Two of the sources maintain a smooth HI morphology at higher resolution, show a velocity gradient and have the highest peak column densities of the sample, indicating they are good candidates to represent gas in dark matter halos. In fact, one of these sources, AGC 198606, has a tentative stellar counterpart detection (Janesh+ 2015). Nine of the sources break into clumps at higher angular resolution, show no ordered velocity motion, and have significantly lower peak column densities, indicating they are likely Galactic halo HI clouds. One source straddles the two categories with a relatively smooth HI morphology and some evidence for ordered velocity motion while having a lower peak column density. These observations show that higher resolution HI data is a good way to address the galaxy hypothesis for isolated HI clouds, and future HI surveys with phased-array feeds on interferometers, such as Apertif, will be able to directly detect and

  6. Are Stellar Over-Densities in Dwarf Galaxies the ``Smoking Gun'' of Triaxial Dark Matter Haloes?

    NASA Astrophysics Data System (ADS)

    Peñarrubia, Jorge; Walker, Matthew G.; Gilmore, Gerard

    2010-06-01

    We use N-body simulations to study the tidal evolution of globular clusters (GCs) in dwarf spheroidal (dSph) galaxies. Our models adopt a cosmologically motivated scenario in which the dSph is approximated by a static NFW halo with a triaxial shape. For a large set of orbits and projection angles we examine the spatial and velocity distribution of stellar debris deposited during the complete disruption of stellar clusters. Our simulations show that such debris appears as shells, isolated clumps and elongated over-densities at low surface brightness (>=26 mag/arcsec2), reminiscent of substructure observed in several MW dSphs. Such features arise from the triaxiality of the galaxy potential and do not dissolve in time. Stellar over-densities reported in several MW dSphs may thus be the telltale evidence of dark matter haloes being triaxial in shape. We explore a number of kinematical signatures that would help to validate (or falsify) this scenario. The mean angular momentum of the cluster debris associated with box and resonant orbits, which are absent in spherical potentials, is null. As a result, we show that the line-of-sight velocity distribution may exhibit a characteristic ``double-peak'' depending on the oriention of the viewing angle with respect to the progenitor's orbital plane. Kinematic surveys of dSphs may help to detect and identify substructures associated with the disruption of stellar clusters, as well as to address the shape of the dark matter haloes in which dSphs are embedded.

  7. Collision of the Smith Cloud and its dark matter halo with the magnetized Galactic disk

    NASA Astrophysics Data System (ADS)

    Galyardt, Jason; Shelton, Robin L.

    2015-01-01

    The Smith Cloud is a massive High Velocity Cloud (HVC) that may have passed through the Milky Way disk in the recent past. Previous studies using hydrodynamic simulations suggest that a dark matter halo may have provided the confinement neccessary for the Smith Cloud to survive passage through the Galactic corona and disk. However, the models of the Galaxy that were used in these studies did not include a magnetic field, while magnetic fields are known to have confining properties. Other studies have shown that the Galactic magnetic field can inhibit mass exchange between the corona and the disk due to magnetic field compression. We extend upon these studies via FLASH magnetohydrodynamic simulations to consider the effects of a Galactic magnetic field on an infalling, dark matter confined HVC.

  8. TIDAL STREAM MORPHOLOGY AS AN INDICATOR OF DARK MATTER HALO GEOMETRY: THE CASE OF PALOMAR 5

    SciTech Connect

    Pearson, Sarah; Johnston, Kathryn V.; Price-Whelan, Adrian M.; Küpper, Andreas H. W.

    2015-01-20

    This paper presents an example where the morphology of a single stellar stream can be used to rule out a specific galactic potential form without the need for velocity information. We investigate the globular cluster Palomar 5 (Pal 5), which is tidally disrupting into a cold, thin stream mapped over 22 deg on the sky with a typical width of 0.7 deg. We generate models of this stream by fixing Pal 5's present-day position, distance, and radial velocity via observations, while allowing its proper motion to vary. In a spherical dark matter halo we easily find models that fit the observed morphology. However, no plausible Pal 5 model could be found in the triaxial potential of Law and Majewski, which has been proposed to explain the properties of the Sagittarius stream. In this case, the long, thin, and curved morphology of the Pal 5 stream alone can be used to rule out such a potential configuration. Pal 5-like streams in this potential are either too straight, missing the curvature of the observations, or show an unusual morphology which we dub stream-fanning: a signature sensitive to the triaxiality of a potential. We conclude that the mere existence of other thin tidal streams must provide broad constraints on the orientation and shape of the dark matter halo they inhabit.

  9. The shape of `dark matter' haloes of disc galaxies according to MOND

    NASA Astrophysics Data System (ADS)

    Milgrom, Mordehai

    2001-10-01

    Analyses of halo shapes for disc galaxies are said to give conflicting results. I point out that the modified dynamics (MOND) predicts for disc galaxies a distribution of fictitious dark matter that comprises two components: a pure disc and a rounder halo. The former dominates the true disc in regions of small accelerations, where it controls the z-dynamics in the disc (disc flaring etc.); it has a finite total mass. It also dominates the round component near the centre where the geometry is nearly planar. The second component controls motions far from the plane, has a total enclosed mass that diverges linearly with radius, and determines the rotation curve at large radii. Its ellipticity may be appreciable at small radii but vanishes asymptotically. This prediction of MOND differs from what one expects from galaxy formation scenarios with dark matter. Analyses to date, which, as they do, assume one component - usually with a constant ellipticity - perforce give conflicting results for the best value of ellipticity, depending on whether they probe the disc or the sphere, small radii or large ones.

  10. Enhanced tidal stripping of satellites in the galactic halo from dark matter self-interactions

    NASA Astrophysics Data System (ADS)

    Dooley, Gregory A.; Peter, Annika H. G.; Vogelsberger, Mark; Zavala, Jesús; Frebel, Anna

    2016-09-01

    We investigate the effects of self-interacting dark matter (SIDM) on the tidal stripping and evaporation of satellite galaxies in a Milky Way-like host. We use a suite of five zoom-in, dark-matter-only simulations, two with velocity-independent SIDM cross-sections, two with velocity-dependent SIDM cross-sections, and one cold dark matter (CDM) simulation for comparison. After carefully assigning stellar mass to satellites at infall, we find that stars are stripped at a higher rate in SIDM than in CDM. In contrast, the total bound dark matter mass-loss rate is minimally affected, with subhalo evaporation having negligible effects on satellites for viable SIDM models. Centrally located stars in SIDM haloes disperse out to larger radii as cores grow. Consequently, the half-light radius of satellites increases, stars become more vulnerable to tidal stripping, and the stellar mass function is suppressed. We find that the ratio of core radius to tidal radius accurately predicts the relative strength of enhanced SIDM stellar stripping. Velocity-independent SIDM models show a modest increase in the stellar stripping effect with satellite mass, whereas velocity-dependent SIDM models show a large increase in this effect towards lower masses, making observations of ultrafaint dwarfs prime targets for distinguishing between and constraining SIDM models. Due to small cores in the largest satellites of velocity-dependent SIDM, no identifiable imprint is left on the all-sky properties of the stellar halo. While our results focus on SIDM, the main physical mechanism of enhanced tidal stripping of stars apply similarly to satellites with cores formed via other means.

  11. Testing the self-consistency of the excursion set approach to predicting the dark matter halo mass function.

    PubMed

    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. PMID:24476252

  12. Dark matter mini-halo around the compact objects: the formation, evolution and possible contribution to the cosmic ray electrons/positrons

    SciTech Connect

    Yang, Rui-Zhi; Fan, Yi-Zhong; Chang, Jin; Waldman, Roni E-mail: yzfan@pmo.ac.cn E-mail: chang@pmo.ac.cn

    2012-01-01

    Dark matter particles may be captured by a star and then thermalized in the star's core. At the end of its life a massive star collapses suddenly and a compact object is formed. The dark matter particles redistribute accordingly. In the inelastic dark matter model, an extended dense dark matter mini-halo surrounding the neutron star may be formed. Such mini-halos may be common in the Galaxy. The electron/positron flux resulting in the annihilation of dark matter particles, however, is unable to give rise to observable signal unless a nascent mini-halo is within a distance ∼ a few 0.1 pc from the Earth.

  13. Connecting Massive Galaxies to Dark Matter Halos in BOSS. I: Is Galaxy Color a Stochastic Process in High Mass Halos?

    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.

    2016-05-01

    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 catalogs 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. (2013) at lower stellar masses. We construct two models, one in which galaxy color 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 colors are not a stochastic process in high-mass halos. Our results suggest that the colors of galaxies in high-mass halos 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.

  14. Revealing the network of periodic orbits in galaxy models with a prolate or an oblate dark matter halo component

    NASA Astrophysics Data System (ADS)

    Zotos, Euaggelos E.

    Locating the position of periodic orbits in galaxies is undoubtedly an issue of paramount importance. We reveal the position and the stability of periodic orbits of stars moving in the meridional plane (R,z) of an axially symmetric galactic model with a disk, a spherical nucleus, and a biaxial dark matter halo component. In particular, we study how all the involved parameters of the dynamical system influence the position and the stability of all resonant families. To locate the position and measure the stability of periodic orbits we use a highly sensitive numerical code which is able to identify resonant periodic orbits of the type n:m. Two cases are studied for every parameter: (i) the case where the dark matter halo component is prolate and (ii) the case where an oblate dark matter halo is present. Our numerical exploration reveals that all the dynamical quantities affect, more or less, the position and the stability of the periodic orbits. It is shown that the mass of the nucleus, the mass of the disk, the halo flattening parameter, the scale length of the halo, the angular momentum, and the total orbital energy are the most influential quantities, while the effect of all other parameters is much weaker.

  15. Light versus dark in strong-lens galaxies: dark matter haloes that are rounder than their stars

    NASA Astrophysics Data System (ADS)

    Bruderer, Claudio; Read, Justin I.; Coles, Jonathan P.; Leier, Dominik; Falco, Emilio E.; Ferreras, Ignacio; Saha, Prasenjit

    2016-02-01

    We measure the projected density profile, shape and alignment of the stellar and dark matter mass distribution in 11 strong-lens galaxies. We find that the projected dark matter density profile - under the assumption of a Chabrier stellar initial mass function - shows significant variation from galaxy to galaxy. Those with an outermost image beyond ˜10 kpc are very well fit by a projected Navarro-Frenk-White (NFW) profile; those with images within 10 kpc appear to be more concentrated than NFW, as expected if their dark haloes contract due to baryonic cooling. We find that over several half-light radii, the dark matter haloes of these lenses are rounder than their stellar mass distributions. While the haloes are never more elliptical than edm = 0.2, their stars can extend to e* > 0.2. Galaxies with high dark matter ellipticity and weak external shear show strong alignment between light and dark; those with strong shear (γ ≳ 0.1) can be highly misaligned. This is reassuring since isolated misaligned galaxies are expected to be unstable. Our results provide a new constraint on galaxy formation models. For a given cosmology, these must explain the origin of both very round dark matter haloes and misaligned strong-lens systems.

  16. Supermassive black holes do not correlate with dark matter haloes of galaxies.

    PubMed

    Kormendy, John; Bender, Ralf

    2011-01-20

    Supermassive black holes have been detected in all galaxies that contain bulge components when the galaxies observed were close enough that the searches were feasible. Together with the observation that bigger black holes live in bigger bulges, this has led to the belief that black-hole growth and bulge formation regulate each other. That is, black holes and bulges coevolve. Therefore, reports of a similar correlation between black holes and the dark matter haloes in which visible galaxies are embedded have profound implications. Dark matter is likely to be non-baryonic, so these reports suggest that unknown, exotic physics controls black-hole growth. Here we show, in part on the basis of recent measurements of bulgeless galaxies, that there is almost no correlation between dark matter and parameters that measure black holes unless the galaxy also contains a bulge. We conclude that black holes do not correlate directly with dark matter. They do not correlate with galaxy disks, either. Therefore, black holes coevolve only with bulges. This simplifies the puzzle of their coevolution by focusing attention on purely baryonic processes in the galaxy mergers that make bulges. PMID:21248846

  17. A novel approach to derive halo-independent limits on dark matter properties

    SciTech Connect

    Ferrer, Francesc; Ibarra, Alejandro; Wild, Sebastian

    2015-09-21

    We propose a method that allows to place an upper limit on the dark matter elastic scattering cross section with nucleons which is independent of the velocity distribution. Our approach combines null results from direct detection experiments with indirect searches at neutrino telescopes, and goes beyond previous attempts to remove astrophysical uncertainties in that it directly constrains the particle physics properties of the dark matter. The resulting halo-independent upper limits on the scattering cross section of dark matter are remarkably strong and reach σ{sub SI}{sup p}≲10{sup −43} (10{sup −42}) cm{sup 2} and σ{sub SD}{sup p}≲10{sup −37} (3×10{sup −37}) cm{sup 2}, for dark matter particles of m{sub DM}∼1 TeV annihilating into W{sup +}W{sup −} (bb-bar), assuming ρ{sub loc}=0.3 GeV/cm{sup 3}.

  18. VizieR Online Data Catalog: Surface density of dark matter haloes (Saburova+, 2014)

    NASA Astrophysics Data System (ADS)

    Saburova, A.; Del Popolo, A.

    2015-05-01

    In this article, we test the conclusion of the universality of the dark matter (DM) halo surface density μ0D={rho}0*r_0. According to our study, the dispersion of values of μ0D is twice as high as that found previously by other authors. We conclude that the DM surface density and its Newtonian acceleration are not constant but correlate with the luminosity, morphological type, (B-V)0 colour index and content of neutral hydrogen. These DM parameters are higher for more luminous systems of early types with red colour and low gas content. We also found that the correlation of DM parameters with colour index appears to be the manifestation of a stronger relation between DM halo mass and the colour of a galaxy. This finding is in agreement with cosmological simulations. These results leave little room for the recently claimed universality of DM column density. We also found that isolated galaxies in our sample (contained in the Analysis of the interstellar Medium of Isolated GAlaxies (AMIGA) catalogue) do not differ significantly in their value of μ0D from the entire sample. Thus, since the AMIGA catalogue gives a sample of galaxies that have not interacted with a significant mass neighbour in the past 3Gyr, the difference between systems with low and high values of μ0D is not related to merging events during this period of time. (1 data file).

  19. The derivation of constraints on the msugra parameter space from the entropy of dark matter halos

    SciTech Connect

    Cabral-Rosetti, L. G.; Mondragon, M.; Nellen, L.; Nunez, D.; Sussmann, R.; Zavala, J.

    2009-04-20

    We derive an expression for the entropy of a present dark matter halo described by a Navarro-Frenk-White modified model with a central core. We obtain an expression for the relic abundance of neutralinos by comparing this entropy of the halo with the value it had during the freeze-out era. Using WMAP observations, we constrain the parameter space for mSUGRA models. Combining our results with the usual abundance criteria, we are able to discriminate clearly among different validity regions for tan {beta} values. For this, we require both criteria to be consistent within a 2{sigma} bound of the WMAP observations for the relic density: 0.112<{omega}h{sup 2}<0.122. We find that for sgn {mu} = +1, small values of tan {beta} are not favored; only for tan {beta}{approx}50 are both criteria significantly consistent. Both criteria allow us to put a lower bound on the neutralino mass, m{sub {chi}}{>=}141 GeV.

  20. An empirical model to form and evolve galaxies in dark matter halos

    NASA Astrophysics Data System (ADS)

    Li, Shi-Jie; Zhang, You-Cai; Yang, Xiao-Hu; Wang, Hui-Yuan; Tweed, Dylan; Liu, Cheng-Ze; Yang, Lei; Shi, Feng; Lu, Yi; Luo, Wen-Tao; Wei, Jian-Wen

    2016-08-01

    Based on the star formation histories of galaxies in halos with different masses, we develop an empirical model to grow galaxies in dark matter halos. This model has very few ingredients, any of which can be associated with observational data and thus be efficiently assessed. By applying this model to a very high resolution cosmological N-body simulation, we predict a number of galaxy properties that are a very good match to relevant observational data. Namely, for both centrals and satellites, the galaxy stellar mass functions up to redshift z ≃ 4 and the conditional stellar mass functions in the local universe are in good agreement with observations. In addition, the two point correlation function is well predicted in the different stellar mass ranges explored by our model. Furthermore, after applying stellar population synthesis models to our stellar composition as a function of redshift, we find that the luminosity functions in the 0.1 u, 0.1 g, 0.1 r, 0.1 i and 0.1 z bands agree quite well with the SDSS observational results down to an absolute magnitude at about ‑17.0. The SDSS conditional luminosity function itself is predicted well. Finally, the cold gas is derived from the star formation rate to predict the HI gas mass within each mock galaxy. We find a remarkably good match to observed HI-to-stellar mass ratios. These features ensure that such galaxy/gas catalogs can be used to generate reliable mock redshift surveys.

  1. Particle Dark Matter in the galactic halo: results from DAMA/LIBRA

    SciTech Connect

    Bernabei, R.; Belli, P.; Nozzoli, F.; Montecchia, F.; Cappella, F.; D'Angelo, A.; Incicchitti, A.; Presperi, D.; Cerulli, R.; Dai, C. J.; He, H. L.; Kuang, H. H.; Ma, X. H.; Sheng, X. D.

    2010-02-10

    The DAMA/LIBRA experiment at the Gran Sasso National Laboratory of the I.N.F.N. has confirmed with higher sensitivity the model independent evidence for Dark Matter (DM) particles in the galactic halo obtained by the former DAMA/NaI experiment by investigating the DM annual modulation signature. Considering the data collected by DAMA/LIBRA together with the data collected by the former DAMA/NaI (cumulative exposure of 0.82 tonxyr) a confidence level of 8.2 sigma has been achieved. The experiment is in data taking; a first upgrading of the set-up has been carried out in Spetember 2008 and a second one--aiming to decrease the experimental energy threshold--is foreseen in September 2010.

  2. The Lyman-alpha glow of gas falling into the dark matter halo of a z = 3 galaxy.

    PubMed

    Weidinger, Michael; Møller, Palle; Fynbo, Johan Peter Uldall

    2004-08-26

    Quasars are the visible signatures of gas falling into the deep potential well of super-massive black holes in the centres of distant galaxies. It has been suggested that quasars are formed when two massive galaxies collide and merge, leading to the prediction that quasars should be found in the centres of regions of largest overdensity in the early Universe. In dark matter (DM)-dominated models of the early Universe, massive DM halos are predicted to attract the surrounding gas, which falls towards their centres. The neutral gas is not detectable in emission by itself, but gas falling into the ionizing cone of such a quasar will glow in the Lyman-alpha line of hydrogen, effectively imaging the DM halo. Here we present a Lyalpha image of a DM halo at redshift z = 3, along with a two-dimensional spectrum of the gaseous halo. Our observations are best understood in the context of the standard model for DM haloes; we infer a mass of (2 - 7) x 10(12) solar masses (M(\\circ)) for the halo. PMID:15329713

  3. Extended maximum likelihood halo-independent analysis of dark matter direct detection data

    SciTech Connect

    Gelmini, Graciela B.; Georgescu, Andreea; Gondolo, Paolo; Huh, Ji-Haeng

    2015-11-24

    We extend and correct a recently proposed maximum-likelihood halo-independent method to analyze unbinned direct dark matter detection data. Instead of the recoil energy as independent variable we use the minimum speed a dark matter particle must have to impart a given recoil energy to a nucleus. This has the advantage of allowing us to apply the method to any type of target composition and interaction, e.g. with general momentum and velocity dependence, and with elastic or inelastic scattering. We prove the method and provide a rigorous statistical interpretation of the results. As first applications, we find that for dark matter particles with elastic spin-independent interactions and neutron to proton coupling ratio f{sub n}/f{sub p}=−0.7, the WIMP interpretation of the signal observed by CDMS-II-Si is compatible with the constraints imposed by all other experiments with null results. We also find a similar compatibility for exothermic inelastic spin-independent interactions with f{sub n}/f{sub p}=−0.8.

  4. Extended maximum likelihood halo-independent analysis of dark matter direct detection data

    NASA Astrophysics Data System (ADS)

    Gelmini, Graciela B.; Georgescu, Andreea; Gondolo, Paolo; Huh, Ji-Haeng

    2015-11-01

    We extend and correct a recently proposed maximum-likelihood halo-independent method to analyze unbinned direct dark matter detection data. Instead of the recoil energy as independent variable we use the minimum speed a dark matter particle must have to impart a given recoil energy to a nucleus. This has the advantage of allowing us to apply the method to any type of target composition and interaction, e.g. with general momentum and velocity dependence, and with elastic or inelastic scattering. We prove the method and provide a rigorous statistical interpretation of the results. As first applications, we find that for dark matter particles with elastic spin-independent interactions and neutron to proton coupling ratio fn/fp=-0.7, the WIMP interpretation of the signal observed by CDMS-II-Si is compatible with the constraints imposed by all other experiments with null results. We also find a similar compatibility for exothermic inelastic spin-independent interactions with fn/fp=-0.8.

  5. Constraining the mSUGRA (minimal supergravity) parameter space using the entropy of dark matter halos

    SciTech Connect

    Nunez, Dario; Zavala, Jesus; Nellen, Lukas; Sussman, Roberto A; Cabral-Rosetti, Luis G; Mondragon, Myriam E-mail: jzavala@nucleares.unam.mx E-mail: lukas@nucleares.unam.mx E-mail: lgcabral@ciidet.edu.mx; Collaboration: For the Instituto Avanzado de Cosmologia, IAC

    2008-05-15

    We derive an expression for the entropy of a dark matter halo described using a Navarro-Frenk-White model with a core. The comparison of this entropy with that of dark matter in the freeze-out era allows us to constrain the parameter space in mSUGRA models. Moreover, combining these constraints with the ones obtained from the usual abundance criterion and demanding that these criteria be consistent with the 2{sigma} bounds for the abundance of dark matter: 0.112{<=}{Omega}{sub DM}h{sup 2}{<=}0.122, we are able to clearly identify validity regions among the values of tan{beta}, which is one of the parameters of the mSUGRA model. We found that for the regions of the parameter space explored, small values of tan{beta} are not favored; only for tan {beta} Asymptotically-Equal-To 50 are the two criteria significantly consistent. In the region where the two criteria are consistent we also found a lower bound for the neutralino mass, m{sub {chi}}{>=}141 GeV.

  6. The accretion history of dark matter haloes - III. A physical model for the concentration-mass relation

    NASA Astrophysics Data System (ADS)

    Correa, Camila A.; Wyithe, J. Stuart B.; Schaye, Joop; Duffy, Alan R.

    2015-09-01

    We present a semi-analytic, physically motivated model for dark matter halo concentration as a function of halo mass and redshift. The semi-analytic model combines an analytic model for the halo mass accretion history (MAH), based on extended Press-Schechter (EPS) theory, with an empirical relation between concentration and formation time obtained through fits to the results of numerical simulations. Because the semi-analytic model is based on EPS theory, it can be applied to wide ranges in mass, redshift and cosmology. The resulting concentration-mass (c-M) relations are found to agree with the simulations, and because the model applies only to relaxed haloes, they do not exhibit the upturn at high masses or high redshifts found by some recent works. We predict a change of slope in the z ˜ 0 c-M relation at a mass-scale of 1011 M⊙. We find that this is due to the change in the functional form of the halo MAH, which goes from being dominated by an exponential (for high-mass haloes) to a power law (for low-mass haloes). During the latter phase, the core radius remains approximately constant, and the concentration grows due to the drop of the background density. We also analyse how the c-M relation predicted by this work affects the power produced by dark matter annihilation, finding that at z = 0 the power is two orders of magnitude lower than that obtained from extrapolating best-fitting c-M relations. We provide fits to the c-M relations as well as numerical routines to compute concentrations and MAHs.†

  7. Dark matter and halo bispectrum in redshift space: theory and applications

    NASA Astrophysics Data System (ADS)

    Gil-Marín, Héctor; Wagner, Christian; Noreña, Jorge; Verde, Licia; Percival, Will

    2014-12-01

    We present a phenomenological modification of the standard perturbation theory prediction for the bispectrum in redshift space that allows us to extend the model to mildly non-linear scales over a wide range of redshifts, z<=1.5. Our model require 18 free parameters that are fitted to N-body simulations using the shapes k2/k1=1, 1.5, 2.0, 2.5. We find that we can describe the bispectrum of dark matter particles with ~5% accuracy for kilesssim0.10 h/Mpc at z=0, for kilesssim0.15 h/Mpc at z=0.5, for kilesssim0.17 h/Mpc at z=1.0 and for kilesssim0.20 h/Mpc at z=1.5. For very squeezed triangles with k1=k2gtrsim0.1 hMpc-1 and k3<=0.02 hMpc-1, however, neither SPT nor the proposed fitting formula are able to describe the measured dark matter bispectrum with this accuracy. We show that the fitting formula is sufficiently general that can be applied to other intermediate shapes such as k2/k1=1.25, 1.75, and 2.25. We also test that the fitting formula is able to describe with similar accuracy the bispectrum of cosmologies with different Ωm, in the range 0.2lesssim Ωm lesssim 0.4, and consequently with different values of the logarithmic grow rate f at z=0, 0.4lesssim f(z=0) lesssim 0.6. We apply this new formula to recover the bias parameters, f and σ8, by combining the redshift space power spectrum monopole and quadrupole with the bispectrum monopole for both dark matter particles and haloes. We find that the combination of these three statistics can break the degeneracy between b1, f and σ8. For dark matter particles the new model can be used to recover f and σ8 with ~1% accuracy. For dark matter haloes we find that f and σ8 present larger systematic shifts, ~10%. The systematic offsets arise because of limitations in the modelling of the interplay between bias and redshift space distortions, and represent a limitation as the statistical errors of forthcoming surveys reach this level. Conveniently, we find that these residual systematics are mitigated for

  8. Dark matter and halo bispectrum in redshift space: theory and applications

    SciTech Connect

    Gil-Marín, Héctor; Percival, Will; Wagner, Christian; Noreña, Jorge; Verde, Licia E-mail: cwagner@mpa-garching.mpg.de E-mail: liciaverde@icc.ub.edu

    2014-12-01

    We present a phenomenological modification of the standard perturbation theory prediction for the bispectrum in redshift space that allows us to extend the model to mildly non-linear scales over a wide range of redshifts, z≤1.5. Our model require 18 free parameters that are fitted to N-body simulations using the shapes k{sub 2}/k{sub 1}=1, 1.5, 2.0, 2.5. We find that we can describe the bispectrum of dark matter particles with ∼5% accuracy for k{sub i}∼<0.10 h/Mpc at z=0, for k{sub i}∼<0.15 h/Mpc at z=0.5, for k{sub i}∼<0.17 h/Mpc at z=1.0 and for k{sub i}∼<0.20 h/Mpc at z=1.5. For very squeezed triangles with k{sub 1}=k{sub 2}∼>0.1 hMpc{sup -1} and k{sub 3}≤0.02 hMpc{sup -1}, however, neither SPT nor the proposed fitting formula are able to describe the measured dark matter bispectrum with this accuracy. We show that the fitting formula is sufficiently general that can be applied to other intermediate shapes such as k{sub 2}/k{sub 1}=1.25, 1.75, and 2.25. We also test that the fitting formula is able to describe with similar accuracy the bispectrum of cosmologies with different Ω{sub m}, in the range 0.2∼< Ω{sub m} ∼< 0.4, and consequently with different values of the logarithmic grow rate f at z=0, 0.4∼< f(z=0) ∼< 0.6. We apply this new formula to recover the bias parameters, f and σ{sub 8}, by combining the redshift space power spectrum monopole and quadrupole with the bispectrum monopole for both dark matter particles and haloes. We find that the combination of these three statistics can break the degeneracy between b{sub 1}, f and σ{sub 8}. For dark matter particles the new model can be used to recover f and σ{sub 8} with ∼1% accuracy. For dark matter haloes we find that f and σ{sub 8} present larger systematic shifts, ∼10%. The systematic offsets arise because of limitations in the modelling of the interplay between bias and redshift space distortions, and represent a limitation as the statistical errors of

  9. Cosmology with massive neutrinos I: towards a realistic modeling of the relation between matter, haloes and galaxies

    SciTech Connect

    Villaescusa-Navarro, Francisco; Viel, Matteo; Marulli, Federico; Castorina, Emanuele; Sefusatti, Emiliano; Saito, Shun E-mail: federico.marulli3@unibo.it E-mail: branchin@fis.uniroma3.it E-mail: esefusat@ictp.it

    2014-03-01

    By using a suite of large box-size N-body simulations that incorporate massive neutrinos as an extra set of particles, with total masses of 0.15, 0.30, and 0.60 eV, we investigate the impact of neutrino masses on the spatial distribution of dark matter haloes and on the distribution of galaxies within the haloes. We compute the bias between the spatial distribution of dark matter haloes and the overall matter and cold dark matter distributions using statistical tools such as the power spectrum and the two-point correlation function. Overall we find a scale-dependent bias on large scales for the cosmologies with massive neutrinos. In particular, we find that the bias decreases with the scale, being this effect more important for higher neutrino masses and at high redshift. However, our results indicate that the scale-dependence in the bias is reduced if the latter is computed with respect to the cold dark matter distribution only. We find that the value of the bias on large scales is reasonably well reproduced by the Tinker fitting formula once the linear cold dark matter power spectrum is used, instead of the total matter power spectrum. We also investigate whether scale-dependent bias really comes from purely neutrino's effect or from nonlinear gravitational collapse of haloes. For this purpose, we address the Ω{sub ν}-σ{sub 8} degeneracy and find that such degeneracy is not perfect, implying that neutrinos imprint a slight scale dependence on the large-scale bias. Finally, by using a simple halo occupation distribution (HOD) model, we investigate the impact of massive neutrinos on the distribution of galaxies within dark matter haloes. We use the main galaxy sample in the Sloan Digital Sky Survey (SDSS) II Data Release 7 to investigate if the small-scale galaxy clustering alone can be used to discriminate among different cosmological models with different neutrino masses. Our results suggest that different choices of the HOD parameters can reproduce the

  10. A systematic halo-independent analysis of direct detection data within the framework of Inelastic Dark Matter

    SciTech Connect

    Scopel, Stefano; Yoon, Kook-Hyun E-mail: koreasds@naver.com

    2014-08-01

    We present a systematic halo-independent analysis of available Weakly Interacting Massive Particles (WIMP) direct detection data within the framework of Inelastic Dark Matter (IDM). We show that, when the smallest number of assumptions is made on the WIMP velocity distribution in the halo of our Galaxy, it is possible to find values of the WIMP mass and the IDM mass splitting for which compatibility between present constraints and any of the three experiments claiming to see a WIMP excess among DAMA, CDMS-Si and CRESST can be achieved.

  11. Mapping stellar content to dark matter haloes using galaxy clustering and galaxy-galaxy lensing in the SDSS DR7

    NASA Astrophysics Data System (ADS)

    Zu, Ying; Mandelbaum, Rachel

    2015-12-01

    The mapping between the distributions of the observed galaxy stellar mass and the underlying dark matter haloes provides the crucial link from theories of large-scale structure formation to interpreting the complex phenomena of galaxy formation and evolution. We develop a novel statistical method, based on the halo occupation distribution (HOD) model, to solve for this mapping by jointly fitting the galaxy clustering and the galaxy-galaxy lensing from the Sloan Digital Sky Survey (SDSS). The method, called the iHOD model, extracts maximum information from the survey by including ˜80 per cent more galaxies than the traditional HOD methods, accounting for the incompleteness of the stellar mass samples self-consistently. The derived stellar-to-halo mass relation (SHMR) explains the clustering and lensing of SDSS galaxies over four decades in stellar mass, while successfully predicting the observed stellar mass functions (SMFs). By modelling significantly more galaxies, the iHOD breaks the degeneracy between the logarithmic scatter in the stellar mass at fixed halo mass and the slope of the mean SHMR at high masses, without assuming a strong prior on the scatter and/or using the SMF as an input. We detect a decline of the scatter with halo mass, from 0.22_{-0.01}^{+0.02} dex below 1012 h-1 M⊙ to 0.18 ± 0.01 dex at 1014 h-1 M⊙. The model predicts a departure of satellite SMFs from the Schechter form in massive haloes and a linear scaling of satellite number with halo mass. The iHOD model can be easily applied to other spectroscopic data sets, greatly improving statistical constraints on the SHMR compared to traditional HOD methods within the same survey.

  12. Masses of high-z galaxy hosting haloes from angular clustering and their evolution in the cold dark matter model

    NASA Astrophysics Data System (ADS)

    Hamana, Takashi; Yamada, Toru; Ouchi, Masami; Iwata, Ikuru; Kodama, Tadayuki

    2006-07-01

    We examine masses of hosting haloes of two photometrically selected high-z galaxy samples: the old passively evolving galaxies (OPEGs) at z ~ 1 and Lyman break galaxies (LBGs) at z ~ 4 both taken from the Subaru/XMM-Newton Deep Survey (SXDS). The large survey area of the SXDS (1 deg2) allows us to measure the angular two-point correlation functions to a wide separation of >10 arcmin with a good statistical quality. We utilize the halo model prescription for estimating characteristic masses of hosting haloes from the measured large-scale clustering amplitudes. It is found that the hosting halo mass positively correlates with the luminosity of galaxies. Then, adopting the extended Press-Schechter (EPS) model, we compute the predictions for the mass evolution of the hosting haloes in the framework of the cold dark matter (CDM) cosmology in order to make an evolutionary link between the two galaxy samples at different redshifts and to identify their present-day descendants by letting their haloes evolve forward in time. It is found that, in the view of the mass evolution of hosting haloes in the CDM model, bright (i' <~ i'* + 1) LBGs are consistent with being the progenitor of the OPEGs, whereas it is less likely that the LBG population, as a whole, has evolved into the OPEG population. It is also found that the present-day descendants of both the bright LBGs and OPEGs are likely to be located in massive systems such as groups of galaxies or clusters of galaxies. Finally, we estimate the hosting halo mass of local early-type galaxy samples from the 2dF and Sloan Digital Sky Survey (SDSS) based on the halo model, and it turns out that their expected characteristic mass of hosting haloes is in good agreement with the EPS predictions for the descendant's mass of both the bright LBGs and OPEGs. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. E-mail: hamanatk@cc.nao.ac.jp ‡ Hubble fellow.

  13. "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)

  14. To be or not to be oblate: the shape of the dark matter halo in polar ring galaxies

    NASA Astrophysics Data System (ADS)

    Khoperskov, S. A.; Moiseev, A. V.; Khoperskov, A. V.; Saburova, A. S.

    2014-07-01

    With the aim of determining the spatial distribution of the dark matter halo, we investigate two polar ring galaxies, NGC 4262 and SPRC-7. For both galaxies, the stellar kinematics data for the central galaxy were obtained from optical spectroscopy at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Information about polar gaseous components was taken from optical three-dimensional spectroscopic observations of ionized gas (for SPRC-7) and from H I radio observations (for NGC 4262). SPRC-7 is a system with a relative angle δ = 73° towards the central galaxy and quite a massive stellar-gaseous polar component. Meanwhile, NGC 4262 is a classic polar case with δ = 88°, where the polar ring mainly consists of neutral gas with a negligible stellar contribution to the mass. Thus, we are dealing with two different systems, and the results are also diverse. The observed properties of both galaxies were compared with the results of self-consistent simulations of velocity fields of the polar component along with the rotation curve of the central lenticular galaxy. For SPRC-7, we have found a slightly flattened halo towards the polar plane with the axial ratio c/a ≃ 1.7 ± 0.2 for the isothermal halo model and c/a ≃ 1.5 ± 0.2 for the NFW model. NGC 4262 is more unusual, because the shape of the dark matter distribution varies strongly with radius. That is, the dark matter halo is flattened in the vicinity of the galactic disc (c/a ≈ 0.4 ± 0.1), but it is prolate far beyond the central galaxy (c/a ≈ 1.7 for the isothermal halo model and c/a ≈ 2.3 for the NFW model).

  15. Using Dark Matter Haloes to Learn about Cosmic Acceleration: A New Proposal for a Universal Mass Function

    NASA Technical Reports Server (NTRS)

    Prescod-Weinstein, Chanda; Afshordi, Niayesh

    2011-01-01

    Structure formation provides a strong test of any cosmic acceleration model because a successful dark energy model must not inhibit or overpredict the development of observed large-scale structures. Traditional approaches to studies of structure formation in the presence of dark energy or a modified gravity implement a modified Press-Schechter formalism, which relates the linear overdensities to the abundance of dark matter haloes at the same time. We critically examine the universality of the Press-Schechter formalism for different cosmologies, and show that the halo abundance is best correlated with spherical linear overdensity at 94% of collapse (or observation) time. We then extend this argument to ellipsoidal collapse (which decreases the fractional time of best correlation for small haloes), and show that our results agree with deviations from modified Press-Schechter formalism seen in simulated mass functions. This provides a novel universal prescription to measure linear density evolution, based on current and future observations of cluster (or dark matter) halo mass function. In particular, even observations of cluster abundance in a single epoch will constrain the entire history of linear growth of cosmological of perturbations.

  16. THE CORE-CUSP PROBLEM IN COLD DARK MATTER HALOS AND SUPERNOVA FEEDBACK: EFFECTS OF MASS LOSS

    SciTech Connect

    Ogiya, Go; Mori, Masao

    2011-07-20

    The core-cusp problem remains as one of the unsolved discrepancies between observations and theories predicted by the standard paradigm of cold dark matter (CDM) cosmology. To solve this problem, we perform N-body simulations to study the nonlinear response of CDM halos to the variance of the gravitational potential induced by gas removal from galaxy centers. In this study, we focus on the timescale of the gas ejection, which is strongly correlated with stellar activities, and demonstrate that it is one of the key factors in determining the dynamical response of CDM halos. The results of simulations show that the power-law index of the mass-density profile of the dark matter (DM) halo is correlated with the timescale of the mass loss and it is flatter when the mass loss occurs over a short time than when it occurs over a long time. However, it is still larger than typical observational values; in other words, the central cusp remains in the simulations for any mass-loss model. Moreover, for the slow mass-loss case, the final density profile of the DM halo recovers the universal density profiles predicted by the CDM cosmology. Therefore, the mass loss driven by stellar feedback may not be an effective mechanism to flatten the central cusp.

  17. The formation of massive black holes in z ˜ 30 dark matter haloes with large baryonic streaming velocities

    NASA Astrophysics Data System (ADS)

    Tanaka, Takamitsu L.; Li, Miao

    2014-03-01

    The origins of the ˜109 M⊙ quasar supermassive black holes (BHs) at redshifts z > 6 remain a theoretical puzzle. One possibility is that they grew from ˜105 M⊙ BHs formed in the `direct collapse' of pristine, atomic-cooling (temperatures ≳ 8000 K; PAC) gas that did not fragment to form ordinary stars due to a lack of molecular hydrogen and metals. We propose that baryonic streaming - the relic relative motion of gas with respect to dark matter from cosmological recombination - provides a natural mechanism for establishing the conditions necessary for direct collapse. This effect delays the formation of the first stars by inhibiting the infall of gas into dark matter haloes; streaming velocities more than twice the root-mean-square value could forestall star formation until halo virial temperatures ≳ 8000 K. The resulting PAC gas can proceed to form massive BHs by any of the mechanisms proposed in the literature to induce direct collapse in the absence of an ultraviolet background. This scenario produces haloes containing PAC gas at a characteristic redshift z ˜ 30. It can explain the abundance of the most luminous quasars at z ≈ 6, regardless of whether direct collapse occurs in nearly all or less than 1 per cent of PAC haloes.

  18. The halo Boltzmann equation

    NASA Astrophysics Data System (ADS)

    Biagetti, Matteo; Desjacques, Vincent; Kehagias, Alex; Racco, Davide; Riotto, Antonio

    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.

  19. Baryonic distributions in galaxy dark matter haloes - I. New observations of neutral and ionized gas kinematics

    NASA Astrophysics Data System (ADS)

    Richards, Emily E.; van Zee, L.; Barnes, K. L.; Staudaher, S.; Dale, D. A.; Braun, T. T.; Wavle, D. C.; Dalcanton, J. J.; Bullock, J. S.; Chandar, R.

    2016-07-01

    We present a combination of new and archival neutral hydrogen (H I) observations and new ionized gas spectroscopic observations for 16 galaxies in the statistically representative Extended Disk Galaxy Explore Science kinematic sample. H I rotation curves are derived from new and archival radio synthesis observations from the Very Large Array (VLA) as well as processed data products from the Westerbork Radio Synthesis Telescope (WSRT). The H I rotation curves are supplemented with optical spectroscopic integral field unit (IFU) observations using SparsePak on the WIYN 3.5 m telescope to constrain the central ionized gas kinematics in 12 galaxies. The full rotation curves of each galaxy are decomposed into baryonic and dark matter halo components using 3.6μm images from the Spitzer Space Telescope for the stellar content, the neutral hydrogen data for the atomic gas component, and, when available, CO data from the literature for the molecular gas component. Differences in the inferred distribution of mass are illustrated under fixed stellar mass-to-light ratio (M/L) and maximum disc/bulge assumptions in the rotation curve decomposition.

  20. Baryonic Distributions in Galaxy Dark Matter Haloes I: New Observations of Neutral and Ionized Gas Kinematics

    NASA Astrophysics Data System (ADS)

    Richards, Emily E.; van Zee, L.; Barnes, K. L.; Staudaher, S.; Dale, D. A.; Braun, T. T.; Wavle, D. C.; Dalcanton, J. J.; Bullock, J. S.; Chandar, R.

    2016-04-01

    We present a combination of new and archival neutral hydrogen (HI) observations and new ionized gas spectroscopic observations for sixteen galaxies in the statistically representative EDGES kinematic sample. HI rotation curves are derived from new and archival radio synthesis observations from the Very Large Array (VLA) as well as processed data products from the Westerbork Radio Synthesis Telescope (WSRT). The HI rotation curves are supplemented with optical spectroscopic integral field unit (IFU) observations using SparsePak on the WIYN 3.5 m telescope to constrain the central ionized gas kinematics in twelve galaxies. The full rotation curves of each galaxy are decomposed into baryonic and dark matter halo components using 3.6μm images from the Spitzer Space Telescope for the stellar content, the neutral hydrogen data for the atomic gas component, and, when available, CO data from the literature for the molecular gas component. Differences in the inferred distribution of mass are illustrated under fixed stellar mass-to-light ratio (M/L) and maximum disc/bulge assumptions in the rotation curve decomposition.

  1. AN OFF-CENTER DENSITY PEAK IN THE MILKY WAY'S DARK MATTER HALO?

    SciTech Connect

    Kuhlen, Michael; Guedes, Javiera; Pillepich, Annalisa; Madau, Piero; Mayer, Lucio

    2013-03-01

    We show that the position of the central dark matter (DM) density peak may be expected to differ from the dynamical center of the Galaxy by several hundred parsecs. In Eris, a high-resolution cosmological hydrodynamics simulation of a realistic Milky-Way-analog disk galaxy, this offset is 300-400 pc ({approx}3 gravitational softening lengths) after z = 1. In its dissipationless DM-only twin simulation ErisDark, as well as in the Via Lactea II and GHalo simulations, the offset remains below one softening length for most of its evolution. The growth of the DM offset coincides with a flattening of the central DM density profile in Eris inward of {approx}1 kpc, and the direction from the dynamical center to the point of maximum DM density is correlated with the orientation of the stellar bar, suggesting a bar-halo interaction as a possible explanation. A DM density offset of several hundred parsecs greatly affects expectations of the DM annihilation signals from the Galactic center. It may also support a DM annihilation interpretation of recent reports by Weniger and Su and Finkbeiner of highly significant 130 GeV gamma-ray line emission from a region 1. Degree-Sign 5 ({approx}200 pc projected) away from Sgr A* in the Galactic plane.

  2. MHF: MLAPM Halo Finder

    NASA Astrophysics Data System (ADS)

    Gill, Stuart P. D.; Knebe, Alexander

    2015-11-01

    MHF is a Dark Matter halo finder that is based on the refinement grids of MLAPM. The grid structure of MLAPM adaptively refines around high-density regions with an automated refinement algorithm, thus naturally "surrounding" the Dark Matter halos, as they are simply manifestations of over-densities within (and exterior) to the underlying host halo. Using this grid structure, MHF restructures the hierarchy of nested isolated MLAPM grids into a "grid tree". The densest cell in the end of a tree branch marks center of a prospective Dark Matter halo. All gravitationally bound particles about this center are collected to obtain the final halo catalog. MHF automatically finds halos within halos within halos.

  3. Bright gamma-ray Galactic Center excess and dark dwarfs: Strong tension for dark matter annihilation despite Milky Way halo profile and diffuse emission uncertainties

    NASA Astrophysics Data System (ADS)

    Abazajian, Kevork N.; Keeley, Ryan E.

    2016-04-01

    We incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center Extended gamma-ray excess (GCE) detected by the Fermi Gamma Ray Space Telescope. The range of particle annihilation rate and masses expand when including these unknowns. However, two of the most precise empirical determinations of the Milky Way halo's local density and density profile leave the signal region to be in considerable tension with dark matter annihilation searches from combined dwarf galaxy analyses for single-channel dark matter annihilation models. The GCE and dwarf tension can be alleviated if: one, the halo is very highly concentrated or strongly contracted; two, the dark matter annihilation signal differentiates between dwarfs and the GC; or, three, local stellar density measures are found to be significantly lower, like that from recent stellar counts, increasing the local dark matter density.

  4. Discussion on the energy content of the galactic dark matter Bose-Einstein condensate halo in the Thomas-Fermi approximation

    SciTech Connect

    De Souza, J.C.C.; Pires, M.O.C. E-mail: marcelo.pires@ufabc.edu.br

    2014-03-01

    We show that the galactic dark matter halo, considered composed of an axionlike particles Bose-Einstein condensate [6] trapped by a self-graviting potential [5], may be stable in the Thomas-Fermi approximation since appropriate choices for the dark matter particle mass and scattering length are made. The demonstration is performed by means of the calculation of the potential, kinetic and self-interaction energy terms of a galactic halo described by a Boehmer-Harko density profile. We discuss the validity of the Thomas-Fermi approximation for the halo system, and show that the kinetic energy contribution is indeed negligible.

  5. Dark matter halo properties of GAMA galaxy groups from 100 square degrees of KiDS weak lensing data

    NASA Astrophysics Data System (ADS)

    Viola, M.; Cacciato, M.; Brouwer, M.; Kuijken, K.; Hoekstra, H.; Norberg, P.; Robotham, A. S. G.; van Uitert, E.; Alpaslan, M.; Baldry, I. K.; Choi, A.; de Jong, J. T. A.; Driver, S. P.; Erben, T.; Grado, A.; Graham, Alister W.; Heymans, C.; Hildebrandt, H.; Hopkins, A. M.; Irisarri, N.; Joachimi, B.; Loveday, J.; Miller, L.; Nakajima, R.; Schneider, P.; Sifón, C.; Verdoes Kleijn, G.

    2015-10-01

    The Kilo-Degree Survey is an optical wide-field survey designed to map the matter distribution in the Universe using weak gravitational lensing. In this paper, we use these data to measure the density profiles and masses of a sample of ˜1400 spectroscopically identified galaxy groups and clusters from the Galaxy And Mass Assembly survey. We detect a highly significant signal (signal-to-noise-ratio ˜120), allowing us to study the properties of dark matter haloes over one and a half order of magnitude in mass, from M ˜ 1013-1014.5 h-1 M⊙. We interpret the results for various subsamples of groups using a halo model framework which accounts for the mis-centring of the brightest cluster galaxy (used as the tracer of the group centre) with respect to the centre of the group's dark matter halo. We find that the density profiles of the haloes are well described by an NFW profile with concentrations that agree with predictions from numerical simulations. In addition, we constrain scaling relations between the mass and a number of observable group properties. We find that the mass scales with the total r-band luminosity as a power law with slope 1.16 ± 0.13 (1σ) and with the group velocity dispersion as a power law with slope 1.89 ± 0.27 (1σ). Finally, we demonstrate the potential of weak lensing studies of groups to discriminate between models of baryonic feedback at group scales by comparing our results with the predictions from the Cosmo-OverWhelmingly Large Simulations project, ruling out models without AGN feedback.

  6. A universality of dark-halo surface density for the Milky Way and Andromeda dwarf satellites as a probe of the coldness of dark matter

    NASA Astrophysics Data System (ADS)

    Hayashi, Kohei; Chiba, Masashi

    2016-08-01

    We propose a new astrophysical test on the nature of dark matter based on the properties of dark halos associated with dwarf spheroidal galaxies. The method adopts a mean surface density of a dark halo defined within a radius of maximum circular velocity, which is derivable for a wide variety of galaxies with any dark-matter density profiles. We find that even though dark halo density profiles are derived based on the different assumptions for each galaxy sample, this surface density is generally constant across a wide mass range of galaxy. We find that at higher halo-mass scales, this constancy for real galaxies can be naturally reproduced by both cold and warm dark matter (CDM and WDM) models. However, at low-mass scales, for which we have estimated from the Milky Way and Andromeda dwarf satellites, the mean surface density derived from WDM models largely deviates from the observed constancy, whereas CDM models are in reasonable agreement with observations.

  7. The rise and fall of galaxy activity in dark matter haloes

    NASA Astrophysics Data System (ADS)

    Pasquali, Anna; van den Bosch, Frank C.; Mo, H. J.; Yang, Xiaohu; Somerville, Rachel

    2009-03-01

    We use the catalogue of galaxy groups constructed from the Sloan Digital Sky Survey (SDSS DR4) by Yang et al. to study the dependence of galaxy activity on stellar mass, M*, halo mass, Mh, and group hierarchy (central versus satellite galaxies). The wealth of data provided by the SDSS allows us to split the sample on the basis of galaxy activity in star-forming galaxies, galaxies with optical active galactic nuclei (AGN), composite galaxies (both star formation and optical AGN activity) and radio sources. We find a smooth transition in halo mass as the activity of central galaxies changes from star formation to optical AGN activity to radio emission. Star-forming centrals preferentially reside in haloes with Mh < 1012h-1Msolar, central galaxies with optical AGN activity typically inhabit haloes with Mh ~ 1013h-1Msolar and centrals emitting in the radio mainly reside in haloes more massive than 1014h-1Msolar. Although this seems to suggest that the environment (halo mass) determines the type of activity of its central galaxy, we find a similar trend with stellar mass: central star formers typically have stellar masses less than 1010h-2Msolar, while optical AGN hosts and central radio sources have characteristic stellar masses of ~1010.8 and ~1011.6h-2Msolar, respectively. Since more massive haloes typically host more massive centrals, it is unclear whether the activity of a central galaxy is causally connected to its stellar mass or to its halo mass. In general, satellite galaxies have their activity suppressed with respect to central galaxies of the same stellar mass. This holds not only for star formation activity, but also for AGN activity in the optical and the radio. At fixed stellar mass, we find that the activity of satellite galaxies depends only weakly on halo mass. In fact, using a set of reduced conditional probability functions, we find that for satellite galaxies the dependence of galaxy activity on halo mass is more than four times weaker than the

  8. DARK MATTER CORES IN THE FORNAX AND SCULPTOR DWARF GALAXIES: JOINING HALO ASSEMBLY AND DETAILED STAR FORMATION HISTORIES

    SciTech Connect

    Amorisco, N. C.; Zavala, J.; De Boer, T. J. L.

    2014-02-20

    We combine the detailed star formation histories of the Fornax and Sculptor dwarf spheroidals with the mass assembly history of their dark matter (DM) halo progenitors to estimate if the energy deposited by Type II supernovae (SNe II) is sufficient to create a substantial DM core. Assuming the efficiency of energy injection of the SNe II into DM particles is ε{sub gc} = 0.05, we find that a single early episode, z ≳ z {sub infall}, that combines the energy of all SNe II due to explode over 0.5 Gyr is sufficient to create a core of several hundred parsecs in both Sculptor and Fornax. Therefore, our results suggest that it is energetically plausible to form cores in cold dark matter (CDM) halos via early episodic gas outflows triggered by SNe II. Furthermore, based on CDM merger rates and phase-space density considerations, we argue that the probability of a subsequent complete regeneration of the cusp is small for a substantial fraction of dwarf-size halos.

  9. Dynamics of groups around interacting double ellipticals: Measuring dark matter haloes

    NASA Technical Reports Server (NTRS)

    Quintana, H.

    1990-01-01

    Binary galaxies, as binary stars, are important to measure masses, as suggested by Page (1952). Because three orbit parameters are measurable for galaxies at one instant of time, severe uncertainties remain in the orbit and mass determinations. These uncertainties can partly be overcome by statistical studies of selected samples and/or n-body simulations. Close double galaxies (and isolated galaxies) could also be useful to estimate dynamical masses if we can find test particles around them. Interacting elliptical pairs or dumb-bell galaxies are found with a large range, between 0-1200 km s(exp -1), of relative radial velocities. Standard 2-body orbit calculations, highly uncertain due to projection factors, suggest for the largest velocity differences very large galaxy masses, if the systems are bound and stationary. However, recent n-body simulations model these binaries as galaxies captured from hyperbolic orbits, requiring masses of order a few times 10(exp 11) solar maximum (Borne et al. 1988), but producing systems that are short lived. A different picture appears when we study observationally the dynamical mass of interacting double ellipticals using faint satellite galaxies. These satellites contribute little luminosity and, presumably, little mass to the system. The authors present results of two such groups, basically forming systems of test particles, around the dumb-bells NGC 4782/3 and IC 5049. They also briefly discuss the satellite group around the central dumb-bell in the cluster Sersic 40/6. Apparently, they detect large quantities of dark matter in the vicinity of these dumb-bell galaxies, because the system masses of approx. 4.5 times 10(exp 13) solar mass and 8 times 10(exp 13) solar mass for NGC 4782/3 and IC 5049, respectively, are quite high. Likewise, the mass of the Sersic 40/6 inner core is 7 times 10(exp 13) solar mass. The possibility that a common massive dark matter halo increases the merging times of these types of galaxies is

  10. Unveiling hidden black holes in the cosmic web: Dark matter halos of WISE quasars from Planck CMB lensing

    NASA Astrophysics Data System (ADS)

    Hickox, Ryan

    The WISE and Planck surveys have now produced groundbreaking data sets which, in concert, can be exploited to obtain revolutionary constraints on the evolution of structure in the Universe. One particularly powerful application of WISE has been to uncover millions of the previously "hidden" obscured quasars, rapidly growing supermassive black holes that are shrouded in gas and dust and so are not detectable using traditional ground-based optical and near-IR techniques. Recently, Planck has produced the most precise all-sky map to date of dark matter structures via the lensing of the cosmic microwave background (CMB). We propose to combine these data sets to obtain a uniquely powerful measurement of the link between rapidly growing black holes and their host dark matter structures, by cross-correlating the density field of WISE-selected quasars with the CMB lensing convergence maps obtained from Planck. This proposal will build on our current ADAP program (NNX12AE38G), which studies the host dark matter halos of WISE-selected quasars via spatial clustering. NNX12AE38G involves a detailed characterization of the redshifts, luminosities, and spectral energy distributions of WISE-selected quasars and uses new techniques to measure how quasars cluster around themselves. NNX12AE38G has contributed to more than 10 journal articles and 5 conference proceedings. Building on our current work, an even more complete understanding of the link between black holes and their host dark matter structures is possible if we employ an independent method for measuring the clustering bias (and thus characteristic halo mass) of the quasar population. This has recently become possible using CMB lensing maps. In the past two years, our team has conducted an initial analysis covering 2500 square degrees using WISE-selected quasars and lensing maps from the South Pole Telescope (Geach, Hickox, Myers et al., 2013), and have implemented this technique with Planck over part of the SDSS region

  11. The link between the assembly of the inner dark matter halo and the angular momentum evolution of galaxies in the EAGLE simulation

    NASA Astrophysics Data System (ADS)

    Zavala, Jesús; Frenk, Carlos S.; Bower, Richard; Schaye, Joop; Theuns, Tom; Crain, Robert A.; Trayford, James W.; Schaller, Matthieu; Furlong, Michelle

    2016-08-01

    We explore the co-evolution of the specific angular momentum of dark matter haloes and the cold baryons that comprise the galaxies within. We study over 2000 galaxies within the reference cosmological hydrodynamical simulation of the `Evolution and Assembly of GaLaxies and their Environments' (EAGLE) project. We employ a methodology within which the evolutionary history of a system is specified by the time-evolving properties of the Lagrangian particles that define it at z = 0. We find a strong correlation between the evolution of the specific angular momentum of today's stars (cold gas) and that of the inner (whole) dark matter halo they are associated with. This link is particularly strong for the stars formed before the epoch of maximum expansion and subsequent collapse of the central dark matter halo (turnaround). Spheroids are assembled primarily from stars formed prior to turnaround, and suffer a net loss of angular momentum associated with the strong merging activity during the assembly of the inner dark matter halo. Stellar discs retain their specific angular momentum since they are comprised of stars formed mainly after turnaround, from gas that mostly preserves the high specific angular momentum it acquired by tidal torques during the linear growth of the halo. Since the specific angular momentum loss of the stars is tied to the galaxy's morphology today, it may be possible to use our results to predict, statistically, the maximum loss of specific angular momentum of the inner part of a halo given the morphology of the galaxy it hosts.

  12. The link between the assembly of the inner dark matter halo and the angular momentum evolution of galaxies in the EAGLE simulation

    NASA Astrophysics Data System (ADS)

    Zavala, Jesús; Frenk, Carlos S.; Bower, Richard; Schaye, Joop; Theuns, Tom; Crain, Robert A.; Trayford, James W.; Schaller, Matthieu; Furlong, Michelle

    2016-08-01

    We explore the co-evolution of the specific angular momentum of dark matter haloes and the cold baryons that comprise the galaxies within. We study over two thousand central galaxies within the reference cosmological hydrodynamical simulation of the "Evolution and Assembly of GaLaxies and their Environments" (EAGLE) project. We employ a methodology within which the evolutionary history of a system is specified by the time-evolving properties of the Lagrangian particles that define it at z=0. We find a strong correlation between the evolution of the specific angular momentum of today's stars (cold gas) and that of the inner (whole) dark matter halo they are associated with. This link is particularly strong for the stars formed before the epoch of maximum expansion and subsequent collapse of the central dark matter halo (turnaround). Spheroids are typically assembled primarily from stars formed prior to turnaround, and are therefore destined to suffer a net loss of angular momentum associated with the strong merging activity during the assembly of the inner dark matter halo. Stellar discs retain their specific angular momentum since they are comprised of stars formed mainly after turnaround, from gas that mostly preserves the high specific angular momentum it acquired by tidal torques during the linear growth of the halo. Since the specific angular momentum loss of the stars is tied to the galaxy's morphology today, it may be possible to use our results to predict, statistically, the assembly history of a halo given the morphology of the galaxy it hosts.

  13. Dynamical flows through dark matter haloes - II. One- and two-point statistics at the virial radius

    NASA Astrophysics Data System (ADS)

    Aubert, Dominique; Pichon, Christophe

    2007-01-01

    In a series of three papers, the dynamical interplay between environments and dark matter haloes is investigated, while focusing on the dynamical flows through the virtual virial sphere. It relies on both cosmological simulations, to constrain the environments, and an extension to the classical matrix method to derive the responses of the halo. A companion paper (Paper I) showed how perturbation theory allows us to propagate the statistical properties of the environment to an ensemble description of the dynamical response of the embedded halo. The current paper focuses on the statistical characterization of the environments surrounding haloes, using a set of large-scale simulations; the large statistic of environments presented here allows us to put quantitative and statistically significant constrains on the properties of flows accreted by haloes. The description chosen in this paper relies on a `fluid' halocentric representation. The interactions between the halo and its environment are investigated in terms of a time-dependent external tidal field and a source term characterizing the infall. The former accounts for fly bys and interlopers. The latter stands for the distribution function of the matter accreted through the virial sphere. The method of separation of variables is used to decouple the temporal evolution of these two quantities from their angular and velocity dependence by means of projection on a 5D basis. It is shown that how the flux densities of mass, momentum and energy can provide an alternative description to the 5D projection of the source. Such a description is well suited to regenerate synthetic time lines of accretion which are consistent with environments found in simulations as discussed in the Appendix. The method leading to the measurements of these quantities in simulations is presented in detail and applied to 15000 haloes, with masses between 5 × 1012 and 1014Msolar evolving between z = 1 and 0. The influence of resolution, class of

  14. 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⊙.

  15. The galaxy-dark matter halo connection: which galaxy properties are correlated with the host halo mass?

    NASA Astrophysics Data System (ADS)

    Contreras, S.; Baugh, C. M.; Norberg, P.; Padilla, N.

    2015-09-01

    We demonstrate how the properties of a galaxy depend on the mass of its host dark matter subhalo, using two independent models of galaxy formation. For the cases of stellar mass and black hole mass, the median property value displays a monotonic dependence on subhalo mass. The slope of the relation changes for subhalo masses for which heating by active galactic nuclei becomes important. The median property values are predicted to be remarkably similar for central and satellite galaxies. The two models predict considerable scatter around the median property value, though the size of the scatter is model dependent. There is only modest evolution with redshift in the median galaxy property at a fixed subhalo mass. Properties such as cold gas mass and star formation rate, however, are predicted to have a complex dependence on subhalo mass. In these cases, subhalo mass is not a good indicator of the value of the galaxy property. We illustrate how the predictions in the galaxy property-subhalo mass plane differ from the assumptions made in some empirical models of galaxy clustering by reconstructing the model output using a basic subhalo abundance matching scheme. In its simplest form, abundance matching generally does not reproduce the clustering predicted by the models, typically resulting in an overprediction of the clustering signal. Using the predictions of the galaxy formation model for the correlations between pairs of galaxy properties, the basic abundance matching scheme can be extended to reproduce the model predictions more faithfully for a wider range of galaxy properties. Our results have implications for the analysis of galaxy clustering, particularly for low abundance samples.

  16. Multipole analysis of IceCube data to search for dark matter accumulated in the Galactic halo

    NASA Astrophysics Data System (ADS)

    Aartsen, M. G.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Ahrens, M.; Altmann, D.; Anderson, T.; Arguelles, C.; Arlen, T. C.; Auffenberg, J.; Bai, X.; Barwick, S. W.; Baum, V.; Beatty, J. J.; Becker Tjus, J.; Becker, K.-H.; BenZvi, S.; Berghaus, P.; Berley, D.; Bernardini, E.; Bernhard, A.; Besson, D. Z.; Binder, G.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Bos, F.; Bose, D.; Böser, S.; Botner, O.; Brayeur, L.; Bretz, H.-P.; Brown, A. M.; Casey, J.; Casier, M.; Chirkin, D.; Christov, A.; Christy, B.; Clark, K.; Classen, L.; Clevermann, F.; Coenders, S.; Cowen, D. F.; Cruz Silva, A. H.; Danninger, M.; Daughhetee, J.; Davis, J. C.; Day, M.; de André, J. P. A. M.; De Clercq, C.; De Ridder, S.; Desiati, P.; de Vries, K. D.; de With, M.; DeYoung, T.; Díaz-Vélez, J. C.; Dunkman, M.; Eagan, R.; Eberhardt, B.; Eichmann, B.; Eisch, J.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feintzeig, J.; Felde, J.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Flis, S.; Franckowiak, A.; Frantzen, K.; Fuchs, T.; Gaisser, T. K.; Gallagher, J.; Gerhardt, L.; Gier, D.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Golup, G.; Gonzalez, J. G.; Goodman, J. A.; Góra, D.; Grandmont, D. T.; Grant, D.; Gretskov, P.; Groh, J. C.; Groß, A.; Ha, C.; Haack, C.; Haj Ismail, A.; Hallen, P.; Hallgren, A.; Halzen, F.; Hanson, K.; Hebecker, D.; Heereman, D.; Heinen, D.; Helbing, K.; Hellauer, R.; Hellwig, D.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Homeier, A.; Hoshina, K.; Huang, F.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobi, E.; Jacobsen, J.; Jagielski, K.; Japaridze, G. S.; Jero, K.; Jlelati, O.; Jurkovic, M.; Kaminsky, B.; Kappes, A.; Karg, T.; Karle, A.; Kauer, M.; Kelley, J. L.; Kheirandish, A.; Kiryluk, J.; Kläs, J.; Klein, S. R.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Koob, A.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Kriesten, A.; Krings, K.; Kroll, G.; Kroll, M.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Larsen, D. T.; Larson, M. J.; Lesiak-Bzdak, M.; Leuermann, M.; Leute, J.; Lünemann, J.; Macías, O.; Madsen, J.; Maggi, G.; Maruyama, R.; Mase, K.; Matis, H. S.; McNally, F.; Meagher, K.; Medici, M.; Meli, A.; Meures, T.; Miarecki, S.; Middell, E.; Middlemas, E.; Milke, N.; Miller, J.; Mohrmann, L.; Montaruli, T.; Morse, R.; Nahnhauer, R.; Naumann, U.; Niederhausen, H.; Nowicki, S. C.; Nygren, D. R.; Obertacke, A.; Odrowski, S.; Olivas, A.; Omairat, A.; O'Murchadha, A.; Palczewski, T.; Paul, L.; Penek, Ö.; Pepper, J. A.; Pérez de los Heros, C.; Pfendner, C.; Pieloth, D.; Pinat, E.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Pütz, J.; Quinnan, M.; Rädel, L.; Rameez, M.; Rawlins, K.; Redl, P.; Rees, I.; Reimann, R.; Resconi, E.; Rhode, W.; Richman, M.; Riedel, B.; Robertson, S.; Rodrigues, J. P.; Rongen, M.; Rott, C.; Ruhe, T.; Ruzybayev, B.; Ryckbosch, D.; Saba, S. M.; Sander, H.-G.; Sandroos, J.; Santander, M.; Sarkar, S.; Schatto, K.; Scheriau, F.; Schmidt, T.; Schmitz, M.; Schoenen, S.; Schöneberg, S.; Schönwald, A.; Schukraft, A.; Schulte, L.; Schulz, O.; Seckel, D.; Sestayo, Y.; Seunarine, S.; Shanidze, R.; Sheremata, C.; Smith, M. W. E.; Soldin, D.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stanisha, N. A.; Stasik, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Strahler, E. A.; Ström, R.; Strotjohann, N. L.; Sullivan, G. W.; Taavola, H.; Taboada, I.; Tamburro, A.; Tepe, A.; Ter-Antonyan, S.; Terliuk, A.; Tešić, G.; Tilav, S.; Toale, P. A.; Tobin, M. N.; Tosi, D.; Tselengidou, M.; Unger, E.; Usner, M.; Vallecorsa, S.; van Eijndhoven, N.; Vandenbroucke, J.; van Santen, J.; Vehring, M.; Voge, M.; Vraeghe, M.; Walck, C.; Wallraff, M.; Weaver, Ch.; Wellons, M.; Wendt, C.; Westerhoff, S.; Whelan, B. J.; Whitehorn, N.; Wichary, C.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, D. L.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Ziemann, J.; Zierke, S.; Zoll, M.

    2015-01-01

    Dark matter which is bound in the Galactic halo might self-annihilate and produce a flux of stable final state particles, e.g. high energy neutrinos. These neutrinos can be detected with IceCube, a cubic-kilometer sized Cherenkov detector. Given IceCube's large field of view, a characteristic anisotropy of the additional neutrino flux is expected. In this paper we describe a multipole method to search for such a large-scale anisotropy in IceCube data. This method uses the expansion coefficients of a multipole expansion of neutrino arrival directions and incorporates signal-specific weights for each expansion coefficient. We apply the technique to a high-purity muon neutrino sample from the Northern Hemisphere. The final result is compatible with the null-hypothesis. As no signal was observed, we present limits on the self-annihilation cross-section averaged over the relative velocity distribution down to for a dark matter particle mass of 700-1,000 GeV and direct annihilation into . The resulting exclusion limits come close to exclusion limits from -ray experiments, that focus on the outer Galactic halo, for high dark matter masses of a few TeV and hard annihilation channels.

  17. Taking Halo-independent dark matter methods out of the bin

    SciTech Connect

    Fox, Patrick J.; Kahn, Yonatan; McCullough, Matthew E-mail: ykahn@mit.edu

    2014-10-01

    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 between 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.

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

    SciTech Connect

    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 between 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.

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

    DOE PAGESBeta

    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

  20. Dark Matter Halos as Particle Colliders: Unified Solution to Small-Scale Structure Puzzles from Dwarfs to Clusters.

    PubMed

    Kaplinghat, Manoj; Tulin, Sean; Yu, Hai-Bo

    2016-01-29

    Astrophysical observations spanning dwarf galaxies to galaxy clusters indicate that dark matter (DM) halos are less dense in their central regions compared to expectations from collisionless DM N-body simulations. Using detailed fits to DM halos of galaxies and clusters, we show that self-interacting DM (SIDM) may provide a consistent solution to the DM deficit problem across all scales, even though individual systems exhibit a wide diversity in halo properties. Since the characteristic velocity of DM particles varies across these systems, we are able to measure the self-interaction cross section as a function of kinetic energy and thereby deduce the SIDM particle physics model parameters. Our results prefer a mildly velocity-dependent cross section, from σ/m≈2  cm^{2}/g on galaxy scales to σ/m≈0.1  cm^{2}/g on cluster scales, consistent with the upper limits from merging clusters. Our results dramatically improve the constraints on SIDM models and may allow the masses of both DM and dark mediator particles to be measured even if the dark sector is completely hidden from the standard model, which we illustrate for the dark photon model. PMID:26871320

  1. Dark-matter halo mergers as a fertile environment for low-mass Population III star formation

    NASA Astrophysics Data System (ADS)

    Bovino, S.; Latif, M. A.; Grassi, T.; Schleicher, D. R. G.

    2014-07-01

    While Population III (Pop III) stars are typically thought to be massive, pathways towards lower mass Pop III stars may exist when the cooling of the gas is particularly enhanced. A possible route is enhanced HD cooling during the merging of dark-matter haloes. The mergers can lead to a high ionization degree catalysing the formation of HD molecules and may cool the gas down to the cosmic microwave background temperature. In this paper, we investigate the merging of mini-haloes with masses of a few 105 M⊙ and explore the feasibility of this scenario. We have performed three-dimensional cosmological hydrodynamics calculations with the ENZO code, solving the thermal and chemical evolution of the gas by employing the astrochemistry package KROME. Our results show that the HD abundance is increased by two orders of magnitude compared to the no-merging case and the halo cools down to ˜60 K triggering fragmentation. Based on Jeans estimates, the expected stellar masses are about 10 M⊙. Our findings show that the merging scenario is a potential pathway for the formation of low-mass stars.

  2. The most luminous quasars do not live in the most massive dark matter haloes at any redshift

    NASA Astrophysics Data System (ADS)

    Fanidakis, N.; Macciò, A. V.; Baugh, C. M.; Lacey, C. G.; Frenk, C. S.

    2013-11-01

    Quasars (QSOs) represent the brightest active galactic nuclei (AGN) in the Universe and are thought to indicate the location of prodigiously growing black holes (BHs), with luminosities as high as 1048 erg s-1. It is often expected though that such an extremely energetic process takes place in the most massive bound structures in the dark matter (DM) distribution. We show that in contrast to this expectation, in a galaxy formation model which includes AGN feedback, QSOs are predicted to live in DM haloes with typical masses of a few times 1012 M⊙. Such an environment is considered to be average in the low-redshift universe (z ≲ 2-3) and almost comparable to a Milky Way halo. This fundamental prediction arises from the fact that QSO activity (i.e. BH accretion with luminosity greater than 1046 erg s-1) is inhibited in more massive DM haloes, where AGN feedback operates. The galactic hosts of QSOs in our simulations have typical stellar masses of 1010-1011 M⊙, and represent remnants of massive disc galaxies that have undergone a disc instability or galaxy merger. Interestingly, we find no dependence of QSO activity on environment; thus, the typical QSO halo mass remains constant over two orders of magnitude in luminosity. We further show that the z ˜ 6 QSOs do not inhabit the largest DM haloes at that time as these environments are already subject to feedback. Their descendants at z = 0 span a wide range of morphologies and galaxy masses, and their BHs typically grow only by a modest factor between z ˜ 6 and the present day. We predict that there should be an enhancement in the abundance of galaxies around QSOs at z ˜ 5. However, these enhancements are considerably weaker compared to the overdensities expected at the extreme peaks of the DM distribution. Given that high-z QSO descendants are typically found in rich clusters (˜1014 M⊙) and very seldom in the most massive haloes, we conclude that it is very unlikely that QSOs observed at z ≳ 5 trace the

  3. Structure Formation inside Triaxial Dark Matter Halos: Galactic Disks, Bulges, and Bars

    NASA Astrophysics Data System (ADS)

    Heller, Clayton H.; Shlosman, Isaac; Athanassoula, E.

    2007-12-01

    We investigate formation and evolution of galactic disks immersed in assembling live DM halos. Models have been evolved from cosmological initial conditions and represent the collapse of an isolated density perturbation. The baryons include gas participating in star formation (SF) and stars with the energy feedback onto the ISM. We find that (1) the triaxial halo figure tumbling is insignificant and the angular momentum (J) is channeled into the internal circulation, while the baryonic collapse is stopped by the centrifugal barrier; (2) density response of the (disk) baryons is out of phase with DM, thus washing out the inner halo ellipticity; (3) the total J is neatly conserved, even in models accounting for stellar feedback; (4) the specific J for DM is nearly constant, while that for baryons is decreasing; (5) early stage of disk formation resembles the cat's cradle-a small amorphous disk fueled via radial string patterns-followed by growing oval disk whose shape varies with its orientation to the halo major axis; (6) the disk gas layer thins when the SF rate drops below ~5 Msolar yr-1 (7) about half of the baryons remain outside the disk SF region or in the halo as a hot gas; (8) rotation curves appear to be flat and account for the observed disk/halo contributions; (9) a range of bulge-dominated to bulgeless disks was obtained, depending on the stellar feedback parameter, ɛSF: smaller ɛSF leads to a larger and earlier bulge; lower density threshold for SF leads to a smaller, thicker disk; gas gravitational softening mimics a number of intrinsic processes within the ISM; (10) models are characterized by an extensive bar-forming activity; (11) nested bars form in response to the gas inflow along the primary bars, as shown by Heller, Shlosman, and Athanassoula.

  4. Interpreting short gamma-ray burst progenitor kicks and time delays using the host galaxy-dark matter halo connection

    SciTech Connect

    Behroozi, Peter S.; Ramirez-Ruiz, Enrico; Fryer, Christopher L.

    2014-09-10

    Nearly 20% of short gamma-ray bursts (sGRBs) have no observed host galaxies. Combining this finding with constraints on galaxies' dark matter halo potential wells gives strong limits on the natal kick velocity distribution for sGRB progenitors. For the best-fitting velocity distribution, one in five sGRB progenitors receives a natal kick above 150 km s{sup –1}, consistent with merging neutron star models but not with merging white dwarf binary models. This progenitor model constraint is robust to a wide variety of systematic uncertainties, including the sGRB progenitor time-delay model, the Swift redshift sensitivity, and the shape of the natal kick velocity distribution. We also use constraints on the galaxy-halo connection to determine the host halo and host galaxy demographics for sGRBs, which match extremely well with available data. Most sGRBs are expected to occur in halos near 10{sup 12} M {sub ☉} and in galaxies near 5 × 10{sup 10} M {sub ☉} (L {sub *}); unobserved faint and high-redshift host galaxies contribute a small minority of the observed hostless sGRB fraction. We find that sGRB redshift distributions and host galaxy stellar masses weakly constrain the progenitor time-delay model; the active versus passive fraction of sGRB host galaxies may offer a stronger constraint. Finally, we discuss how searches for gravitational wave optical counterparts in the local universe can reduce follow-up times using these findings.

  5. Universality of dark matter haloes shape over six decades in mass: insights from the Millennium XXL and SBARBINE simulations

    NASA Astrophysics Data System (ADS)

    Bonamigo, Mario; Despali, Giulia; Limousin, Marceau; Angulo, Raul; Giocoli, Carlo; Soucail, Geneviève

    2015-05-01

    For the last 30 yr many observational and theoretical evidences have shown that galaxy clusters are not spherical objects, and that their shape is much better described by a triaxial geometry. With the advent of multiwavelength data of increasing quality, triaxial investigations of galaxy clusters is gathering a growing interest from the community, especially in the time of `precision cosmology'. In this work, we aim to provide the first statistically significant predictions in the unexplored mass range above 3 × 1014 M⊙h-1, using haloes from two redshift snapshots (z = 0 and z = 1) of the Millennium XXL simulation. The size of this cosmological dark matter-only simulation (4.1 Gpc) allows the formation of a statistically significant number of massive cluster scale haloes (≈500 with M > 2× 1015 M⊙ h-1, and 780 000 with M > 1014 M⊙ h-1). Besides, we aim to extend this investigation to lower masses in order to look for universal predictions across nearly six orders of magnitude in mass, from 1010 to almost 1016 M⊙ h-1. For this purpose we use the SBARBINE simulations, allowing us to model haloes of masses starting from ≈1010 M⊙ h-1. We use an elliptical overdensity method to select haloes and compute the shapes of the unimodal ones (approximately 50 per cent), while we discard the more unrelaxed. The minor to major and intermediate to major axis ratio distributions are found to be well described by simple universal functional forms that do not depend on cosmology or redshift. Our results extend the findings of Jing & Suto to a higher precision and a wider range of mass. This `recipe' is made available to the community in this paper and in a dedicated web page.

  6. Small scale anisotropies of UHECRs from super-heavy halo dark matter

    SciTech Connect

    P. Blasi; R. K. Sheth

    2001-10-23

    The decay of very heavy metastable relics of the Early Universe can produce ultra-high energy cosmic rays (UHECRs) in the halo of our own Galaxy. In this model, no Greisen-Zatsepin-Kuzmin cutoff is expected because of the short propagation distances. They show here that, as a consequence of the hierarchical build up of the halo, this scenario predicts the existence of small scale anisotropies in the arrival directions of UHECRs, in addition to a large scale anisotropy, known from previous studies. They also suggest some other observable consequences of this scenario which will be testable with upcoming experiments, as Auguer, EUSO and OWL.

  7. Dark Matter Halo Models of Stellar Mass-dependent Galaxy Clustering in PRIMUS+DEEP2 at 0.2>z>1.2

    NASA Astrophysics Data System (ADS)

    Skibba, Ramin A.; Coil, Alison L.; Mendez, Alexander J.; Blanton, Michael R.; Bray, Aaron D.; Cool, Richard J.; Eisenstein, Daniel J.; Guo, Hong; Miyaji, Takamitsu; Moustakas, John; Zhu, Guangtun

    2015-07-01

    We utilize ΛCDM halo occupation models of galaxy clustering to investigate the evolving stellar mass dependent clustering of galaxies in the PRIsm MUlti-object Survey (PRIMUS) and DEEP2 Redshift Survey over the past eight billion years of cosmic time, between 0.2\\lt z\\lt 1.2. These clustering measurements provide new constraints on the connections between dark matter halo properties and galaxy properties in the context of the evolving large-scale structure of the universe. Using both an analytic model and a set of mock galaxy catalogs, we find a strong correlation between central galaxy stellar mass and dark matter halo mass over the range {M}{halo}˜ {10}11-{10}13 {h}-1 {M}⊙ , approximately consistent with previous observations and theoretical predictions. However, the stellar-to-halo mass relation and the mass scale where star formation efficiency reaches a maximum appear to evolve more strongly than predicted by other models, including models based primarily on abundance-matching constraints. We find that the fraction of satellite galaxies in halos of a given mass decreases significantly from z˜ 0.5 to z˜ 0.9, partly due to the fact that halos at fixed mass are rarer at higher redshift and have lower abundances. We also find that the {M}1/{M}{min} ratio, a model parameter that quantifies the critical mass above which halos host at least one satellite, decreases from ≈ 20 at z˜ 0 to ≈ 13 at z˜ 0.9. Considering the evolution of the subhalo mass function vis-à-vis satellite abundances, this trend has implications for relations between satellite galaxies and halo substructures and for intracluster mass, which we argue has grown due to stripped and disrupted satellites between z˜ 0.9 and z˜ 0.5.

  8. The dark matter haloes of moderate luminosity X-ray AGN as determined from weak gravitational lensing and host stellar masses

    NASA Astrophysics Data System (ADS)

    Leauthaud, Alexie; J. Benson, Andrew; Civano, Francesca; L. Coil, Alison; Bundy, Kevin; Massey, Richard; Schramm, Malte; Schulze, Andreas; Capak, Peter; Elvis, Martin; Kulier, Andrea; Rhodes, Jason

    2015-01-01

    Understanding the relationship between galaxies hosting active galactic nuclei (AGN) and the dark matter haloes in which they reside is key to constraining how black hole fuelling is triggered and regulated. Previous efforts have relied on simple halo mass estimates inferred from clustering, weak gravitational lensing, or halo occupation distribution modelling. In practice, these approaches remain uncertain because AGN, no matter how they are identified, potentially live a wide range of halo masses with an occupation function whose general shape and normalization are poorly known. In this work, we show that better constraints can be achieved through a rigorous comparison of the clustering, lensing, and cross-correlation signals of AGN hosts to the fiducial stellar-to-halo mass relation (SHMR) derived for all galaxies, irrespective of nuclear activity. Our technique exploits the fact that the global SHMR can be measured with much higher accuracy than any statistic derived from AGN samples alone. Using 382 moderate luminosity X-ray AGN at z < 1 from the COSMOS field, we report the first measurements of weak gravitational lensing from an X-ray-selected sample. Comparing this signal to predictions from the global SHMR, we find that, contrary to previous results, most X-ray AGN do not live in medium size groups - nearly half reside in relatively low mass haloes with M200b ˜ 1012.5 M⊙. The AGN occupation function is well described by the same form derived for all galaxies but with a lower normalization - the fraction of haloes with AGN in our sample is a few per cent. The number of AGN satellite galaxies scales as a power law with host halo mass with a power-law index α = 1. By highlighting the relatively `normal' way in which moderate luminosity X-ray AGN hosts occupy haloes, our results suggest that the environmental signature of distinct fuelling modes for luminous quasars compared to moderate luminosity X-ray AGN is less obvious than previously claimed.

  9. 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

  10. The redshift evolution of the distribution of star formation among dark matter halos as seen in the infrared

    NASA Astrophysics Data System (ADS)

    Béthermin, Matthieu; Wang, Lingyu; Doré, Olivier; Lagache, Guilaine; Sargent, Mark; Daddi, Emanuele; Cousin, Morgane; Aussel, Hervé

    2013-09-01

    Recent studies have revealed a strong correlation between the star formation rate (SFR) and stellar mass of the majority of star-forming galaxies, the so-called star-forming main sequence. An empirical modeling approach (the 2-SFM framework) that distinguishes between the main sequence and rarer starburst galaxies is capable of reproducing most statistical properties of infrared galaxies, such as number counts, luminosity functions, and redshift distributions. In this paper, we extend this approach by establishing a connection between stellar mass and halo mass with the technique of abundance matching. Based on a few simple assumptions and a physically motivated formalism, our model successfully predicts the (cross-)power spectra of the cosmic infrared background (CIB), the cross-correlation between CIB and cosmic microwave background (CMB) lensing, and the correlation functions of bright, resolved infrared galaxies measured by Herschel, Planck, ACT, and SPT. We use this model to infer the redshift distribution of CIB-anisotropies and of the CIB × CMB lensing signal, as well as the level of correlation between CIB-anisotropies at different wavelengths. We study the link between dark matter halos and star-forming galaxies in the framework of our model. We predict that more than 90% of cosmic star formation activity occurs in halos with masses between 1011.5 and 1013.5 M⊙. If taking subsequent mass growth of halos into account, this implies that the majority of stars were initially (at z > 3) formed in the progenitors of clusters (Mh(z = 0) > 1013.5 M⊙), then in groups (1012.5 < Mh(z = 0) < 1013.5 M⊙) at 0.5 < z < 3, and finally in Milky-Way-like halos (1011.5 < Mh(z = 0) < 1012.5 M⊙) at z < 0.5. At all redshifts, the dominant contribution to the SFR density stems from halos of mass ~1012 M⊙, in which the instantaneous star formation efficiency - defined here as the ratio between SFR and baryonic accretion rate - is maximal (~70%). The strong redshift

  11. Study of the X-ray Source Population and the Dark Matter Halo in Dwarf Spheroidal Galaxiess

    NASA Astrophysics Data System (ADS)

    Sasaki, Manami; Saeedi, Sara; Ducci, Lorenzo

    2015-09-01

    The Local Group of galaxies consists of the large spiral galaxies Milky Way, M31, and M33, and a large number of dwarf galaxies. Most of the galaxies are dwarf spheroidal (dSph) galaxies, which are the least luminous galaxies with the largest mass-to-light ratios. In general, dSphs show no recent star formation, which means that they are ideal laboratories to study the old, pristine stellar populations formed in the earliest epochs of chemical enrichment of the Universe. Observations with today's X-ray telescopes have revealed X-ray sources in the fields of the dSphs that are satellites of our Milky Way. The study of X-ray source population in these galaxies and their X-ray luminosity function will help us to understand the source population in galaxies at the early stages of galaxy evolution. Moreover, the existence of X-ray binaries in these galaxies, if confirmed, would indicate that these galaxies are able to retain their compact objects, which are believed to obtain high kick-velocities at their birth in asymmetric supernova explosions. Therefore, the search for and the study of X-ray sources in dSph galaxies in the Local Group will enable us to constrain the mass of dark matter in these galaxies and test different models of the formation and growth of galaxies out of primordial dark-matter halos.I will discuss, how, owing to the large effective area, large field of view and high spatial and time resolution, Athena and its WFI will make it possible to obtain unprecedented observational data of the stellar populations in primordial galaxies and dark-matter halo distribution in our Local Group through the study of high-energy sources.

  12. The Formation and Evolution of Young Low-mass Stars within Halos with High Concentration of Dark Matter Particles

    NASA Astrophysics Data System (ADS)

    Casanellas, Jordi; Lopes, IlíDio

    2009-11-01

    The formation and evolution of low-mass stars within dense halos of dark matter (DM) leads to evolution scenarios quite different from the classical stellar evolution. As a result of our detailed numerical work, we describe these new scenarios for a range of DM densities on the host halo, for a range of scattering cross sections of the DM particles considered, and for stellar masses from 0.7 to 3 M sun. For the first time, we also computed the evolution of young low-mass stars in their Hayashi track in the pre-main-sequence phase and found that, for high DM densities, these stars stop their gravitational collapse before reaching the main sequence, in agreement with similar studies on first stars. Such stars remain indefinitely in an equilibrium state with lower effective temperatures (|ΔT eff|>103 K for a star of one solar mass), the annihilation of captured DM particles in their core being the only source of energy. In the case of lower DM densities, these protostars continue their collapse and progress through the main-sequence burning hydrogen at a lower rate. A star of 1 M sun will spend a time period greater than the current age of the universe consuming all the hydrogen in its core if it evolves in a halo with DM density ρχ = 109 GeV cm-3. We also show the strong dependence of the effective temperature and luminosity of these stars on the characteristics of the DM particles and how this can be used as an alternative method for DM research.

  13. Updated measurements of the dark matter halo masses of obscured quasars with improved WISE and Planck data

    NASA Astrophysics Data System (ADS)

    DiPompeo, M. A.; Hickox, R. C.; Myers, A. D.

    2016-02-01

    Using the most recent releases of WISE and Planck data, we perform updated measurements of the bias and typical dark matter halo mass of infrared (IR)-selected obscured and unobscured quasars, using the angular autocorrelation function and cosmic microwave background lensing cross-correlations. Since our recent work of this kind, the WISE ALLWISE catalogue was released with improved photometry, and the Planck mission was completed and released improved products. These new data provide a more reliable measurement of the quasar bias and provide an opportunity to explore the role of changing survey pipelines in results downstream. We present a comparison of IR colour-selected quasars, split into obscured and unobscured populations based on optical-IR colours, selected from two versions of the WISE data. Which combination of data is used impacts the final results, particularly for obscured quasars, both because of mitigation of some systematics and because the newer catalogue provides a slightly different sample. We show that ALLWISE data is superior in several ways, though there may be some systematic trends with Moon contamination that were not present in the previous catalogue. We opt currently for the most conservative sample that meet our selection criteria in both the previous and new WISE catalogues. We measure a higher bias and halo mass for obscured quasars (bobsc ˜ 2.1, bunob ˜ 1.8) - at odds with simple orientation models - but at a reduced significance (˜1.5σ) as compared to our work with previous survey data.

  14. The link between the assembly of the inner dark matter halo and the angular momentum evolution of galaxies in the EAGLE simulation

    NASA Astrophysics Data System (ADS)

    Zavala, Jesús; Frenk, Carlos S.; Bower, Richard; Schaye, Joop; Theuns, Tom; Crain, Robert A.; Trayford, James W.; Schaller, Matthieu; Furlong, Michelle

    2016-05-01

    We explore the co-evolution of the specific angular momentum of dark matter haloes and the cold baryons that comprise the galaxies within. We study over two thousand galaxies within the reference cosmological hydrodynamical simulation of the "Evolution and Assembly of GaLaxies and their Environments" (EAGLE) project. We employ a methodology within which the evolutionary history of a system is specified by the time-evolving properties of the Lagrangian particles that define it at z = 0. We find a strong correlation between the evolution of the specific angular momentum of today's stars (cold gas) and that of the inner (whole) dark matter halo they are associated with. This link is particularly strong for the stars formed before the epoch of maximum expansion and subsequent collapse of the central dark matter halo (turnaround). Spheroids are assembled primarily from stars formed prior to turnaround, and suffer a net loss of angular momentum associated with the strong merging activity during the assembly of the inner dark matter halo. Stellar discs retain their specific angular momentum since they are comprised of stars formed mainly after turnaround, from gas that mostly preserves the high specific angular momentum it acquired by tidal torques during the linear growth of the halo. Since the specific angular momentum loss of the stars is tied to the galaxy's morphology today, it may be possible to use our results to predict, statistically, the maximum loss of specific angular momentum of the inner part of a halo given the morphology of the galaxy it hosts.

  15. Dark-ages reionization and galaxy formation simulation - II. Spin and concentration parameters for dark matter haloes during the epoch of reionization

    NASA Astrophysics Data System (ADS)

    Angel, Paul W.; Poole, Gregory B.; Ludlow, Aaron D.; Duffy, Alan R.; Geil, Paul M.; Mutch, Simon J.; Mesinger, Andrei; Wyithe, J. Stuart B.

    2016-06-01

    We use high-resolution N-body simulations to study the concentration and spin parameters of dark matter haloes in the mass range 108 M⊙ h-1 < M < 1011 M⊙ h-1 and redshifts 5 < z < 10, corresponding to the haloes of galaxies thought to be responsible for reionization. We build a subsample of equilibrium haloes and contrast their properties to the full population that also includes unrelaxed systems. Concentrations are calculated by fitting both NFW and Einasto profiles to the spherically averaged density profiles of individual haloes. After removing haloes that are out of equilibrium, we find a z > 5 concentration-mass (c(M)) relation that is almost flat and well described by a simple power law for both NFW and Einasto fits. The intrinsic scatter around the mean relation is Δcvir ˜ 1 (or 20 per cent) at z = 5. We also find that the analytic model proposed by Ludlow et al. reproduces the mass and redshift dependence of halo concentrations. Our best-fitting Einasto shape parameter, α, depends on peak height, ν, in a manner that is accurately described by α = 0.0070ν2 + 0.1839. The distribution of the spin parameter, λ, has a weak dependence on equilibrium state; λ peaks at roughly ˜0.033 for our relaxed sample, and at ˜0.04 for the full population. The spin-virial mass relation has a mild negative correlation at high redshift.

  16. Cosmic-ray antiprotons, positrons, and gamma rays from halo dark matter annihilation

    NASA Technical Reports Server (NTRS)

    Rudaz, S.; Stecker, F. W.

    1988-01-01

    The subject of cosmic ray antiproton production is reexamined by considering other choices for the nature of the Majorana fermion chi other than the photino considered in a previous article. The calculations are extended to include cosmic-ray positrons and cosmic gamma rays as annihilation products. Taking chi to be a generic higgsino or simply a heavy Majorana neutrino with standard couplings to the Z-zero boson allows the previous interpretation of the cosmic antiproton data to be maintained. In this case also, the annihilation cross section can be calculated independently of unknown particle physics parameters. Whereas the relic density of photinos with the choice of parameters in the previous paper turned out to be only a few percent of the closure density, the corresponding value for Omega in the generic higgsino or Majorana case is about 0.2, in excellent agreement with the value associated with galaxies and one which is sufficient to give the halo mass.

  17. WEAK GRAVITATIONAL LENSING AS A PROBE OF PHYSICAL PROPERTIES OF SUBSTRUCTURES IN DARK MATTER HALOS

    SciTech Connect

    Shirasaki, Masato

    2015-02-01

    We propose a novel method to select satellite galaxies in outer regions of galaxy groups or clusters using weak gravitational lensing. The method is based on the theoretical expectation that the tangential shear pattern around satellite galaxies would appear with negative values at an offset distance from the center of the main halo. We can thus locate the satellite galaxies statistically with an offset distance of several lensing smoothing scales by using the standard reconstruction of surface mass density maps from weak lensing observation. We test the idea using high-resolution cosmological simulations. We show that subhalos separated from the center of the host halo are successfully located even without assuming the position of the center. For a number of such subhalos, the characteristic mass and offset length can be also estimated on a statistical basis. We perform a Fisher analysis to show how well upcoming weak lensing surveys can constrain the mass density profile of satellite galaxies. In the case of the Large Synoptic Survey Telescope with a sky coverage of 20,000 deg{sup 2}, the mass of the member galaxies in the outer region of galaxy clusters can be constrained with an accuracy of ∼0.1 dex for galaxy clusters with mass 10{sup 14} h {sup –1} M {sub ☉} at z = 0.15. Finally we explore the detectability of tidal stripping features for subhalos having a wide range of masses of 10{sup 11}-10{sup 13} h {sup –1} M {sub ☉}.

  18. About non standard Lagrangians in cosmology

    SciTech Connect

    Dimitrijevic, Dragoljub D.; Milosevic, Milan

    2012-08-17

    A review of non standard Lagrangians present in modern cosmological models will be considered. Well known example of non standard Lagrangian is Dirac-Born-Infeld (DBI) type Lagrangian for tachyon field. Another type of non standard Lagrangian under consideration contains scalar field which describes open p-adic string tachyon and is called p-adic string theory Lagrangian. We will investigate homogenous cases of both DBI and p-adic fields and obtain Lagrangians of the standard type which have the same equations of motions as aforementioned non standard one.

  19. A 14.6 Arcsecond Quasar Lens Split by a Massive Dark Matter Halo

    SciTech Connect

    Inada, N; Oguri, M; Pindor, B; Hennawi, J; Chiu, K; Zheng, W; Ichikawa, S; Gregg, M; Becker, R; Suto, Y; Strauss, M; Turner, E; Keeton, C; Annis, J; Castander, F; Eisenstein, D; Frieman, J; Fukugita, M; Gunn, J; Johnston, D; Kent, S; Nichol, R; Richards, G; Rix, H; Sheldon, E; Bahcall, N; Brinkmann, J; Ivezic, Z; Lamb, D; Mckay, T; Schneider, D; York, D

    2003-12-04

    Gravitational lensing is a powerful tool to study the distribution of dark matter in the universe. The cold dark matter model of structure formation predicts the existence of quasars gravitationally lensed by concentrations of dark matter so massive that the quasar images would be split by over 7 inches. However, numerous searches for large-separation lensed quasars have been unsuccessful; all of the roughly 70 lensed quasars known to date, such as Q0957+561, have smaller splittings, and can be explained in terms of galaxy scale concentrations of baryonic matter that have undergone dissipative collapse. Here they report the discovery of the first large-separation lensed quasar, SDSS J1004+4112, with a maximum separation of 14.62 inches; at this separation, the lensing object must be dominated by dark matter. While gravitationally lensed galaxies of even large separation are known, large-separation quasars are more useful cosmological probes because of the simplicity of the resulting lens systems. The discovery in their current quasar sample is fully consistent with the theoretical expectations based on the cold dark matter model.

  20. Dark-matter halo assembly bias: Environmental dependence in the non-Markovian excursion-set theory

    SciTech Connect

    Zhang, Jun; Ma, Chung-Pei; Riotto, Antonio

    2014-02-10

    In the standard excursion-set model for the growth of structure, the statistical properties of halos are governed by the halo mass and are independent of the larger-scale environment in which the halos reside. Numerical simulations, however, have found the spatial distributions of halos to depend not only on their mass but also on the details of their assembly history and environment. Here we present a theoretical framework for incorporating this 'assembly bias' into the excursion-set model. Our derivations are based on modifications of the path-integral approach of Maggiore and Riotto that models halo formation as a non-Markovian random-walk process. The perturbed density field is assumed to evolve stochastically with the smoothing scale and exhibits correlated walks in the presence of a density barrier. We write down conditional probabilities for multiple barrier crossings and derive from them analytic expressions for descendant and progenitor halo mass functions and halo merger rates as a function of both halo mass and the linear overdensity δ {sub e} of the larger-scale environment of the halo. Our results predict a higher halo merger rate and higher progenitor halo mass function in regions of higher overdensity, consistent with the behavior seen in N-body simulations.

  1. 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.

  2. Pathways to massive black holes and compact star clusters in pre-galactic dark matter haloes with virial temperatures >~10000K

    NASA Astrophysics Data System (ADS)

    Regan, John A.; Haehnelt, Martin G.

    2009-06-01

    Large dynamic range numerical simulations of atomic cooling driven collapse of gas in pre-galactic dark matter haloes with Tvir ~ 10000 K show that the gas loses 90 per cent and more of its angular momentum before rotational support sets in. In a fraction of these haloes where the metallicity is low and ultraviolet (UV) radiation suppresses H2 cooling, conditions are thus very favourable for the rapid build-up of massive black holes. Depending on the progression of metal enrichment, the continued suppression of H2 cooling by external and internal UV radiation and the ability to trap the entropy produced by the release of gravitational energy, the gas at the centre of the halo is expected to form a supermassive star, a stellar-mass black hole accreting at super-Eddington accretion rates or a compact star-cluster undergoing collisional run-away of massive stars at its centre. In all three cases, a massive black hole of initially modest mass finds itself at the centre of a rapid inflow of gas with inflow rates of >~1Msolaryr-1. The massive black hole will thus grow quickly to a mass of 105- 106Msolar until further inflow is halted either by consumption of gas by star formation or by the increasing energy and momentum feedback from the growing massive black hole. Conditions for the formation of massive seed black holes in this way are most favourable in haloes with Tvir ~ 15000K and Vvir ~ 20 km s-1 with less massive haloes not allowing collapse of gas by atomic cooling and more massive haloes being more prone to fragmentation. This should imprint a characteristic mass on the mass spectrum of an early population of massive black hole seeds in pre-galactic haloes which will later grow into the observed population of supermassive black holes in galactic bulges.

  3. Non-standard neutrino interactions in IceCube

    NASA Astrophysics Data System (ADS)

    Day, Melanie; IceCube Collaboration

    2016-05-01

    Neutrinos interact weakly with matter mediated by the W and Z bosons. For example, neutrino interactions with electrons in the earth interferes with the propagation of neutrinos, producing a measurable effect called the “MSW effect” [2]. These types of interactions are the “standard interactions” of neutrinos in standard matter. Some non-standard model theories predict the existence of heavy TeV-scale bosons. Recent ATLAS results have 3.4 sigma significance for a resonance in the diboson channel around 2 TeV [1], which could be caused by non-standard bosons interacting with matter. The neutrino interaction rate in matter would then fluctuate from the standard prediction due to interactions with these bosons in addition to the standard W and Z. Like the MSW effect, the fluctuation of neutrinos detected compared to those produced on the opposite side of the earth would be measurable. This analysis aims to measure this effect in the IceCube experiment using the event selection from the DeepCore three-year muon disappearance result. Because of the wide range of neutrino energies it can observe IceCube has the potential to set world leading limits for this measurement. The limits that can be set on the NSI parameters from interactions of muon neutrinos with non-standard bosons will be discussed.

  4. Constraining the Cosmic Ray Electron Distribution and the Halo Dark Matter from the High Energy Gamma-Ray Background

    NASA Astrophysics Data System (ADS)

    Chary, R.; Wright, E. L.

    2000-10-01

    We present an independent estimate of the high latitude (|b|>20 deg) contribution to the E>30 MeV gamma-ray background from Galactic nucleon-nucleon, electron bremsstrahlung and inverse Compton processes. In particular, the inverse Compton contribution has been estimated for different cosmic ray electron distributions and after factoring in the anisotropy in the interstellar radiation field and the anisotropic Klein-Nishina scattering cross section. We find that the emission from the inverse Compton process when the anisotropy in the radiation field is included can be higher by up to 50% when compared to estimates that adopt an isotropic radiation field. Simulated inverse Compton maps with a cosmic ray electron distribution represented by a ``pill box'' extending up to a distance of 5 kpc above the Galactic plane provide better fits to the EGRET intensity maps suggesting that the cosmic ray halo may be larger than previously thought. Fitting for the Galactic components of gamma-ray emission confirms the existence of an isotropic component with an intensity that can be represented by the form 27.7*(E/MeV)-2.16 ph m-2 s-1 sr-1 MeV-1, in excellent agreement with previous estimates. The spectrum of the isotropic component further argues strongly in favor of unresolved gamma-ray blazars being the source of this emission. Introduction of an anisotropic component improves the quality of the fits. However, this component, which could potentially arise from the dark matter in the Galactic halo, is not well characterized by a single power law which might be associated with any single dark matter candidate. It has an intensity of about a third of the isotropic background above E > 100 MeV at the level of 3*10-2 ph m-2 s-1 sr-1. The best fit power law spectrum to this component has a photon index of -1.7. Based on the intensity and spectrum of the anisotropic component we derive upper limits of 109Msun for the mass of cold, baryonic gas within the solar circle and a primordial

  5. A halo-independent lower bound on the dark matter capture rate in the Sun from a direct detection signal

    SciTech Connect

    Blennow, Mattias; Herrero-Garcia, Juan; Schwetz, Thomas

    2015-05-21

    We show that a positive signal in a dark matter (DM) direct detection experiment can be used to place a lower bound on the DM capture rate in the Sun, independent of the DM halo. For a given particle physics model and DM mass we obtain a lower bound on the capture rate independent of the local DM density, velocity distribution, galactic escape velocity, as well as the scattering cross section. We illustrate this lower bound on the capture rate by assuming that upcoming direct detection experiments will soon obtain a significant signal. When comparing the lower bound on the capture rate with limits on the high-energy neutrino flux from the Sun from neutrino telescopes, we can place upper limits on the branching fraction of DM annihilation channels leading to neutrinos. With current data from IceCube and Super-Kamiokande non-trivial limits can be obtained for spin-dependent interactions and direct annihilations into neutrinos. In some cases also annihilations into ττ or bb start getting constrained. For spin-independent interactions current constraints are weak, but they may become interesting for data from future neutrino telescopes.

  6. Transonic galactic outflows in a dark matter halo with a central black hole and its application to the Sombrero galaxy

    NASA Astrophysics Data System (ADS)

    Igarashi, Asuka; Mori, Masao; Nitta, Shin-ya

    2014-10-01

    We have classified possible transonic solutions of galactic outflows in the gravitational potential of the dark matter halo (DMH) and supermassive black hole (SMBH) under the assumptions of isothermal, spherically symmetric and steady state. It is clarified that the gravity of SMBH adds a new branch of transonic solutions with the transonic point in very close proximity to the centre in addition to the outer transonic point generated by the gravity of DMH. Because these two transonic solutions have substantially different mass fluxes and starting points, these solutions may have different influences on the evolution of galaxies and the release of metals into intergalactic space. We have applied our model to the Sombrero galaxy and obtained a new type of galactic outflow: a slowly accelerated transonic outflow through the transonic point at very distant region (≃126 kpc). In this galaxy, previous works reported that although the trace of the galactic outflow is observed by X-ray, the gas density distribution is consistent with the hydrostatic state. We have clarified that the slowly accelerating outflow has a gas density profile quite similar to that of the hydrostatic solution in the widely spread subsonic region. Thus, the slowly accelerating transonic solution cannot be distinguished from the hydrostatic solution in the observed region (≤25 kpc) even if slow transonic flow exists. Our model provides a new perspective of galactic outflows and is applicable even to quiescent galaxies with inactive star formation.

  7. Dark-matter halos and evolution of high-z early-type galaxies

    NASA Astrophysics Data System (ADS)

    Koopmans, Leon

    2004-07-01

    Gravitational lensing and stellar dynamics provide two complementary methods to determine the mass distribution and evolution of luminous and dark-matter in early-type {E/S0} galaxies. The combined study of stellar dynamics and gravitational lensing allows one to break degeneracies inherent to each method separately, providing a clean probe of the internal structure of massive galaxies. Since most lens galaxies are at redshifts z=0.1-1.0, they also provide the required look-back time to study their structural and stellar-population evolution. We recently analyzed 5 E/S0 lens galaxies between z=0.5 and 1.0, combining exquisite Hubble Space Telescope imaging data with kinematic data from ground-based Keck spectroscopy, placing the first precise constraints on the dark-matter mass fraction and its inner slope beyond the local Universe. To expand the sample to 30 systems - required to study potential trends and evolution in the E/S0 mass profiles - we propose to target the 49 E/S0 lens-galaxy candidates discovered by Bolton et al. {2004} from the Sloan Digital Sky Survey {SDSS}. With the average lens rate being 40% and some systems having a lensing probability close to unity, we expect to discover 20 strong gravitational lenses from the sample. This will triple the current sample of 9 E/S0 systems, with data in hand. With the sample of 30 systems, we will be able to determine the average slope of the dark-matter and total mass profile of E/S0 galaxies to 10% and 4% accuracy, respectively. If present, we can simultaneously detect 10% evolution in the total mass slope with 95% confidence. This will provide unprecedented constraints on E/S0 galaxies beyond the local Universe and allow a stringent test of their formation scenarios and the standard cosmological model.

  8. Gamma rays from dark matter annihilations strongly constrain the substructure in halos.

    PubMed

    Pinzke, Anders; Pfrommer, Christoph; Bergström, Lars

    2009-10-30

    To fit recent data, e(+/-) from dark matter (DM) needs a boosted annihilation rate. This may imply an observable level of gamma rays from nearby galaxy clusters for the Fermi satellite. Using EGRET data, we limit the minimum mass of DM substructures to be about 5x10(3) times larger than for cold DM, meaning a cutoff similar to, e.g., warm DM. We numerically simulate clusters to reliably model the background. If we assume no anomalous boost factor, we find comparable levels of gamma-ray emission from DM and cosmic ray interactions, giving a chance with future data to characterize the DM. PMID:19905798

  9. Linking X-ray AGN with dark matter halos: a model compatible with AGN luminosity function and large-scale clustering properties

    NASA Astrophysics Data System (ADS)

    Hütsi, Gert; Gilfanov, Marat; Sunyaev, Rashid

    2014-01-01

    Aims: Our goal is to find a minimalistic model that describes the luminosity function and large-scale clustering bias of X-ray-selected active galactic nuclei in the general framework of the concordance ΛCDM model. Methods: We assume that a simple population-averaged scaling relation between the AGN X-ray luminosity LX and the host dark matter halo mass Mh exists. With such a relation, the AGN X-ray luminosity function can be computed from the halo mass function. Using the concordance ΛCDM halo mass function for the latter, we obtain the Mh - LX relation required to match the redshift-dependent AGN X-ray luminosity function known from X-ray observations. Results: We find that with a simple power-law-scaling Mh ∝ LΓ(z), our model can successfully reproduce the observed X-ray luminosity function. Furthermore, we automatically obtain predictions for the large-scale AGN clustering amplitudes and their dependence on the luminosity and redshift, which seem to be compatible with AGN clustering measurements. Our model also includes the redshift-dependent AGN duty cycle, which peaks at the redshift z ≃ 1, and its peak value is consistent with unity, suggesting that on average there is no more than one AGN per dark matter halo. For a typical X-ray-selected AGN at z ~ 1, our best-fit Mh - LX scaling implies low Eddington ratio LX/LEdd ~ 10-4 - 10-3 (2-10 keV band, no bolometric correction applied) and correspondingly high mass-growth e-folding times, suggesting that typical X-ray AGN are dominantly fueled via relatively inefficient "hot-halo" accretion mode.

  10. Caustics of 1/rn binary gravitational lenses: from galactic haloes to exotic matter

    NASA Astrophysics Data System (ADS)

    Bozza, V.; Melchiorre, C.

    2016-03-01

    We investigate the caustic topologies for binary gravitational lenses made up of two objects whose gravitational potential declines as 1/rn. With n<1 this corresponds to power-law dust distributions like the singular isothermal sphere. The n>1 regime can be obtained with some violations of the energy conditions, one famous example being the Ellis wormhole. Gravitational lensing provides a natural arena to distinguish and identify such exotic objects in our Universe. We find that there are still three topologies for caustics as in the standard Schwarzschild binary lens, with the main novelty coming from the secondary caustics of the close topology, which become huge at higher n. After drawing caustics by numerical methods, we derive a large amount of analytical formulae in all limits that are useful to provide deeper insight in the mathematics of the problem. Our study is useful to better understand the phenomenology of galaxy lensing in clusters as well as the distinct signatures of exotic matter in complex systems.

  11. Submillimetre galaxies reside in dark matter haloes with masses greater than 3 × 10(11) solar masses.

    PubMed

    Amblard, Alexandre; Cooray, Asantha; Serra, Paolo; Altieri, B; Arumugam, V; Aussel, H; Blain, A; Bock, J; Boselli, A; Buat, V; Castro-Rodríguez, N; Cava, A; Chanial, P; Chapin, E; Clements, D L; Conley, A; Conversi, L; Dowell, C D; Dwek, E; Eales, S; Elbaz, D; Farrah, D; Franceschini, A; Gear, W; Glenn, J; Griffin, M; Halpern, M; Hatziminaoglou, E; Ibar, E; Isaak, K; Ivison, R J; Khostovan, A A; Lagache, G; Levenson, L; Lu, N; Madden, S; Maffei, B; Mainetti, G; Marchetti, L; Marsden, G; Mitchell-Wynne, K; Nguyen, H T; O'Halloran, B; Oliver, S J; Omont, A; Page, M J; Panuzzo, P; Papageorgiou, A; Pearson, C P; Pérez-Fournon, I; Pohlen, M; Rangwala, N; Roseboom, I G; Rowan-Robinson, M; Portal, M Sánchez; Schulz, B; Scott, Douglas; Seymour, N; Shupe, D L; Smith, A J; Stevens, J A; Symeonidis, M; Trichas, M; Tugwell, K; Vaccari, M; Valiante, E; Valtchanov, I; Vieira, J D; Vigroux, L; Wang, L; Ward, R; Wright, G; Xu, C K; Zemcov, M

    2011-02-24

    The extragalactic background light at far-infrared wavelengths comes from optically faint, dusty, star-forming galaxies in the Universe with star formation rates of a few hundred solar masses per year. These faint, submillimetre galaxies are challenging to study individually because of the relatively poor spatial resolution of far-infrared telescopes. Instead, their average properties can be studied using statistics such as the angular power spectrum of the background intensity variations. A previous attempt at measuring this power spectrum resulted in the suggestion that the clustering amplitude is below the level computed with a simple ansatz based on a halo model. Here we report excess clustering over the linear prediction at arcminute angular scales in the power spectrum of brightness fluctuations at 250, 350 and 500 μm. From this excess, we find that submillimetre galaxies are located in dark matter haloes with a minimum mass, M(min), such that log(10)[M(min)/M(⊙)] = 11.5(+0.7)(-0.2) at 350 μm, where M(⊙) is the solar mass. This minimum dark matter halo mass corresponds to the most efficient mass scale for star formation in the Universe, and is lower than that predicted by semi-analytical models for galaxy formation. PMID:21326201

  12. Core Formation And Gravothermal Collapse Of Self-interacting Dark Matter Halos: Monte Carlo N-body simulation versus Conducting Fluid Model

    NASA Astrophysics Data System (ADS)

    Koda, Jun; Shapiro, P. R.

    2007-12-01

    Self-interacting dark matter (SIDM) has been proposed to solve the cuspy core problem of dark matter halos in standard CDM. There are two ways to investigate the effect of the 2-body, non-gravitational, elastic collisions of SIDM, Monte-Carlo N-body simulation and a conducting fluid model. The former is a gravitational N-body simulation with a Monte Carlo algorithm for the SIDM scattering that changes the direction of N-body particles randomly according to a given scattering cross section. The latter is a system of fluid conservation equations with a thermal conduction that describes the collisional effect, which was originally invented to describe the gravothermal collapse of globular clusters. Our previous work found a significant disagreement as regards the strength of collisionality required to solve cuspy core problem. However the two methods have not been properly tested against each other. Here, we make direct comparisons between Monte Carlo N-body simulations and analytic and numerical solutions of the conducting fluid (gaseous) model, for various isolated self-interacting dark matter halos. The N-body simulations reproduce the analytical self-similar solution of gravothermal collapse in the fluid model when one free parameter, the coefficient of heat conduction C, is chosen to be 0.75. The gravothermal collapse results of the simulations agrees well with our 1D numerical hydro solutions of the fluid model within 20% for other initial conditions, including Plummer model, Hernquist profile and NFW profile. In conclusion the conducting fluid model is in reasonably good agreement with the Monte Carlo simulations for isolated halos. We will pursue the origin of the reported disagreement between two methods in a cosmological environment by comparing new N-body simulations with fully cosmological initial conditions.

  13. Constraining Dark Matter Halo Profiles and Galaxy Formation Models Using Spiral Arm Morphology. II. Dark and Stellar Mass Concentrations for 13 Nearby Face-on Galaxies

    NASA Astrophysics Data System (ADS)

    Seigar, Marc S.; Davis, Benjamin L.; Berrier, Joel; Kennefick, Daniel

    2014-11-01

    We investigate the use of spiral arm pitch angles as a probe of disk galaxy mass profiles. We confirm our previous result that spiral arm pitch angles (P) are well correlated with the rate of shear (S) in disk galaxy rotation curves. We use this correlation to argue that imaging data alone can provide a powerful probe of galactic mass distributions out to large look-back times. We then use a sample of 13 galaxies, with Spitzer 3.6 μm imaging data and observed Hα rotation curves, to demonstrate how an inferred shear rate coupled with a bulge-disk decomposition model and a Tully-Fisher-derived velocity normalization can be used to place constraints on a galaxy's baryon fraction and dark matter halo profile. Finally, we show that there appears to be a trend (albeit a weak correlation) between spiral arm pitch angle and halo concentration. We discuss implications for the suggested link between supermassive black hole (SMBH) mass and dark halo concentration, using pitch angle as a proxy for SMBH mass.

  14. Constraining dark matter halo profiles and galaxy formation models using spiral arm morphology. II. Dark and stellar mass concentrations for 13 nearby face-on galaxies

    SciTech Connect

    Seigar, Marc S.; Davis, Benjamin L.; Berrier, Joel; Kennefick, Daniel

    2014-11-01

    We investigate the use of spiral arm pitch angles as a probe of disk galaxy mass profiles. We confirm our previous result that spiral arm pitch angles (P) are well correlated with the rate of shear (S) in disk galaxy rotation curves. We use this correlation to argue that imaging data alone can provide a powerful probe of galactic mass distributions out to large look-back times. We then use a sample of 13 galaxies, with Spitzer 3.6 μm imaging data and observed Hα rotation curves, to demonstrate how an inferred shear rate coupled with a bulge-disk decomposition model and a Tully-Fisher-derived velocity normalization can be used to place constraints on a galaxy's baryon fraction and dark matter halo profile. Finally, we show that there appears to be a trend (albeit a weak correlation) between spiral arm pitch angle and halo concentration. We discuss implications for the suggested link between supermassive black hole (SMBH) mass and dark halo concentration, using pitch angle as a proxy for SMBH mass.

  15. How to calculate dark matter direct detection exclusion limits that are consistent with gamma rays from annihilation in the Milky Way halo

    NASA Astrophysics Data System (ADS)

    Cerdeño, David G.; Fornasa, Mattia; Green, Anne M.; Peiró, Miguel

    2016-08-01

    When comparing constraints on the weakly interacting massive particle (WIMP) properties from direct and indirect detection experiments it is crucial that the assumptions made about the dark matter (DM) distribution are realistic and consistent. For instance, if the Fermi-LAT Galactic center GeV gamma-ray excess was due to WIMP annihilation, its morphology would be incompatible with the standard halo model that is usually used to interpret data from direct detection experiments. In this article, we calculate exclusion limits from direct detection experiments using self-consistent velocity distributions, derived from mass models of the Milky Way where the DM halo has a generalized Navarro-Frenk-White profile. We use two different methods to make the mass model compatible with a DM interpretation of the Galactic center gamma-ray excess. First, we fix the inner slope of the DM density profile to the value that best fits the morphology of the excess. Second, we allow the inner slope to vary and include the morphology of the excess in the data sets used to constrain the gravitational potential of the Milky Way. The resulting direct detection limits differ significantly from those derived using the standard halo model, in particular for light WIMPs, due to the differences in both the local DM density and velocity distribution.

  16. Signature of primordial non-Gaussianity of {phi}{sup 3} type in the mass function and bias of dark matter haloes

    SciTech Connect

    Desjacques, Vincent; Seljak, Uros

    2010-01-15

    We explore the effect of a cubic correction g{sub NL{phi}}{sup 3} on the mass function and bias of dark matter haloes extracted from a series of large N-body simulations and compare it to theoretical predictions. Such cubic terms can be motivated in scenarios like the curvaton model, in which a large cubic correction can be produced while simultaneously keeping the quadratic f{sub NL{phi}}{sup 2} correction small. The deviation from the Gaussian halo mass function is in reasonable agreement with the theoretical predictions. The scale-dependent bias correction {Delta}b{sub {kappa}}(k,g{sub NL}) measured from the auto- and cross-power spectrum of haloes, is similar to the correction in f{sub NL} models, but the amplitude is lower than theoretical expectations. Using the compilation of LSS data in [A. Slosar et al., J. Cosmol. Astropart. Phys. 08 (2008) 031], we obtain for the first time a limit on g{sub NL} of -3.5x10{sup 5}

  17. Large-scale clustering measurements with photometric redshifts: comparing the dark matter haloes of X-ray AGN, star-forming and passive galaxies at z ≈ 1

    NASA Astrophysics Data System (ADS)

    Georgakakis, A.; Mountrichas, G.; Salvato, M.; Rosario, D.; Pérez-González, P. G.; Lutz, D.; Nandra, K.; Coil, A.; Cooper, M. C.; Newman, J. A.; Berta, S.; Magnelli, B.; Popesso, P.; Pozzi, F.

    2014-10-01

    We combine multi-wavelength data in the AEGIS-XD and C-COSMOS surveys to measure the typical dark matter halo mass of X-ray selected active galactic nuclei (AGN) [LX(2-10 keV) > 1042 erg s- 1] in comparison with far-infrared selected star-forming galaxies detected in the Herschel/PEP survey (PACS Evolutionary Probe; LIR > 1011 L⊙) and quiescent systems at z ≈ 1. We develop a novel method to measure the clustering of extragalactic populations that uses photometric redshift probability distribution functions in addition to any spectroscopy. This is advantageous in that all sources in the sample are used in the clustering analysis, not just the subset with secure spectroscopy. The method works best for large samples. The loss of accuracy because of the lack of spectroscopy is balanced by increasing the number of sources used to measure the clustering. We find that X-ray AGN, far-infrared selected star-forming galaxies and passive systems in the redshift interval 0.6 < z < 1.4 are found in haloes of similar mass, log MDMH/(M⊙ h-1) ≈ 13.0. We argue that this is because the galaxies in all three samples (AGN, star-forming, passive) have similar stellar mass distributions, approximated by the J-band luminosity. Therefore, all galaxies that can potentially host X-ray AGN, because they have stellar masses in the appropriate range, live in dark matter haloes of log MDMH/(M⊙ h-1) ≈ 13.0 independent of their star formation rates. This suggests that the stellar mass of X-ray AGN hosts is driving the observed clustering properties of this population. We also speculate that trends between AGN properties (e.g. luminosity, level of obscuration) and large-scale environment may be related to differences in the stellar mass of the host galaxies.

  18. Chaotic motion and the evolution of morphological components in a time-dependent model of a barred galaxy within a dark matter halo

    NASA Astrophysics Data System (ADS)

    Machado, R. E. G.; Manos, T.

    2016-06-01

    Studies of dynamical stability (chaotic versus regular motion) in galactic dynamics often rely on static analytical models of the total gravitational potential. Potentials based upon self-consistent N-body simulations offer more realistic models, fully incorporating the time-dependent nature of the systems. Here we aim at analysing the fractions of chaotic motion within different morphological components of the galaxy. We wish to investigate how the presence of chaotic orbits evolves with time, and how their spatial distribution is associated with morphological features of the galaxy. We employ a time-dependent analytical potential model that was derived from an N-body simulation of a strongly barred galaxy. With this analytical potential, we may follow the dynamical evolution of ensembles of orbits. Using the Generalized Alignment Index (GALI) chaos detection method, we study the fraction of chaotic orbits, sampling the dynamics of both the stellar disc and of the dark matter halo. Within the stellar disc, the global trend is for chaotic motion to decrease in time, specially in the region of the bar. We scrutinized the different changes of regime during the evolution (orbits that are permanently chaotic, permanently regular, those that begin regular and end chaotic, and those that begin chaotic and end regular), tracing the types of orbits back to their common origins. Within the dark matter halo, chaotic motion also decreases globally in time. The inner halo (r < 5 kpc) is where most chaotic orbits are found and it is the only region where chaotic orbits outnumber regular orbits, in the early evolution.

  19. X-ray surveys - Weighting the dark matter haloes of X-ray AGN: towards a physical description of the accretion history of the Universe

    NASA Astrophysics Data System (ADS)

    Georgakakis, Antonis; Mountrichas, G.; Fanidakis, N.; Finoguenov, A.; Aegis Collaboration

    2012-09-01

    The masses of the dark matter haloes in which AGN live is powerful diagnostic of the conditions under which supermassive black holes form and evolve across cosmic time. A new clustering estimation method will be presented which requires spectroscopy only for the AGN and uses photometric redshift probability density functions for galaxies to determine the projected real-space AGN/galaxy cross-correlation function. Our method is superior to traditional AGN clustering estimators (e.g. auto-correlation function) because (i) random errors are significantly suppressed when counting AGN/galaxy pairs, (ii) the impact of sample variance is minimized, and (iii) the requirements for spectroscopy are minimal; only spectroscopic redshift measurements for the AGN are needed. This method is applied to the combined AEGIS, COSMOS and ECDFS fields to infer the bias and dark matter halo mass of moderate luminosity (Lx~10^43 erg/s/cm^2) X-ray AGN at z~1 (total of 400). Predictions from the GALFORM semi-analytic model will be compared to the observations to show that a combination of hot and cold-gas accretion (the latter triggered by disk instabilities in spirals rather than mergers) reproduce well the clustering properties of X-ray AGN over a range of redshifts and luminosities.

  20. Balloon-borne direct search for ionizing massive particles as a component of the galactic halo dark matter (The Arizona-IMAX Collaboration)

    NASA Astrophysics Data System (ADS)

    McGuire, P. C.; Bowen, T.; Barker, D. L.; Halverson, P. G.; Kendall, K. R.; Metcalfe, T. S.; Norton, R. S.; Pifer, A. E.; Barbier, L. M.; Christian, E. R.; Krombel, K. E.; Mitchell, J. W.; Ormes, J. F.; Streitmatter, R. E.; Davis, A. J.; Labrador, A. W.; Mewaldt, R. A.; Schindler, S. M.; Golden, R. L.; Stochaj, S. J.; Webber, W. R.; Arizona-IMAX Collaboration

    1995-07-01

    A dark matter (DM) search experiment was flown on the IMAX balloon payload to search for a possible minor component of the dark matter in the Galactic halo: ionizing massive particles (IMPs) (mx>~104 GeV/c2) that cannot penetrate the atmosphere due to their low-velocities and high energy-loss. The DM search experiment consisted of a delayed coincidence between four large plastic scintillation detectors arranged in a vertical stack. In order to search for ultra-slow particles which do not slow down in the IMAX telescope, the experiment contained TDCs which measured the time-delay Ti,i+1∈(0.3, 14.0) μs between hits in successive counters to ~2% precision. We present IMP flux limits for non-slowing IMPs and also for IMPs which slow down significantly within the IMAX telescope. This experiment effectively closes much of a previously unconstrained ``window'' in the mass/cross-section joint parameter spaces for massive particles as the dominant halo DM.

  1. Analyzing Direct Dark Matter Detection Data by the AMIDAS Website

    NASA Astrophysics Data System (ADS)

    Shan, C.-L.

    2012-02-01

    In this talk I have presented the data analysis results of extracting properties of halo WIMPs: the mass and the (ratios between the) spin-independent and spin-dependent couplings/cross sections on nucleons by the amidas website. Although non-standard astronomical setup has been used to generate pseudodata sets for our analyses, it has been found that, without prior information/assumption about the local density and velocity distribution of halo Dark Matter, these WIMP properties have been reconstructed with ~5% to ≲40% deviations from the input values.

  2. The SL2S Galaxy-scale Lens Sample. V. Dark Matter Halos and Stellar IMF of Massive Early-type Galaxies Out to Redshift 0.8

    NASA Astrophysics Data System (ADS)

    Sonnenfeld, Alessandro; Treu, Tommaso; Marshall, Philip J.; Suyu, Sherry H.; Gavazzi, Raphaël; Auger, Matthew W.; Nipoti, Carlo

    2015-02-01

    We investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the universe. We perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the Strong Lensing Legacy Survey and Sloan ACS Lens Survey and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar initial mass function (IMF) across the population of massive early-type galaxies. Lensing selection effects are taken into account. We find that the dark matter mass projected within the inner 5 kpc increases for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of a Navarro-Frenk-White profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at log M * = 11.5 and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.

  3. Artificial halos

    NASA Astrophysics Data System (ADS)

    Selmke, Markus

    2015-09-01

    Judged by their frequency and beauty, ice halos easily rival rainbows as a prominent atmospheric optics phenomenon. This article presents experimental halo demonstrations of varying complexity. Using a single commercially available hexagonal glass prism, a variety of artificial halos can be simulated. The experiments include laser beam path analysis, a modified classic spinning prism experiment, and a novel Monte-Carlo machine for three-dimensional rotations. Each of these experiments emulates different conditions of certain halo displays, and in combination, they allow a thorough understanding of these striking phenomena.

  4. Status of non-standard neutrino interactions.

    PubMed

    Ohlsson, Tommy

    2013-04-01

    The phenomenon of neutrino oscillations has been established as the leading mechanism behind neutrino flavor transitions, providing solid experimental evidence that neutrinos are massive and lepton flavors are mixed. Here we review sub-leading effects in neutrino flavor transitions known as non-standard neutrino interactions (NSIs), which is currently the most explored description for effects beyond the standard paradigm of neutrino oscillations. In particular, we report on the phenomenology of NSIs and their experimental and phenomenological bounds as well as an outlook for future sensitivity and discovery reach. PMID:23481442

  5. Non-standard symmetries and quantum anomalies

    SciTech Connect

    Visinescu, Anca; Visinescu, Mihai

    2008-08-31

    Quantum anomalies are investigated on curved spacetimes. The intimate relation between Killing-Yano tensors and non-standard symmetries is pointed out. The gravitational anomalies are absent if the hidden symmetry is associated to a Killing-Yano tensor. The axial anomaly in a background gravitational field is directly related with the index of the Dirac operator. In the Dirac theory on curved spaces, Killing-Yano tensors generate Dirac-type operators involved in interesting algebraic structures. The general results are applied to the 4-dimensional Euclidean Taub-NUT space.

  6. Statistical Analysis of Fly-by Encounters between Milky Way-sized Dark Matter Halos in Cosmological Simulations

    NASA Astrophysics Data System (ADS)

    An, Sung-Ho; Kim, Jeonghwan; Yun, Kiyun; Kim, Juhan; Yoon, Suk-Jin

    2015-08-01

    We present a statistical analysis of gravitational interactions between two Milky Way-sized halos (0.3 - 2.0 MMW) by performing cosmological N-body simulations. We take the total energy (E12) of two halos as the classifier of the halo pairs into mergers (E12 < 0) and flyby encounters (E12 > 0). The relative velocity distribution of galaxy pairs in clusters show that, regardless of redshift, the mean relative velocity is as high as ~600 km s-1 with a long high-velocity tail (up to ~ 1500 km s-1). The mean relative velocity in fields is, regardless of redshift, ~ 300 km s-1 with relatively narrow spread (100 ~ 500 km s-1). This leads to the flyby fraction in clusters being as high as the merger fraction and to the flyby fractions in fields being lower than the merger fraction. On the other hand, the statistics of the redshift evolution show that the number of flybys is, regardless of the environment, comparable to that of mergers at z ~ 1, yet N(flyby)/N(merger) decreases till z ~ 0. It is concluded that the flyby interactions have played a critical role in evolution of Milky Way-sized galaxies, particularly in clusters and at high redshift (z ~ 1).

  7. Low-background balloon-borne direct search for ionizing massive particles as a component of the dark galactic halo matter

    NASA Astrophysics Data System (ADS)

    McGuire, Patrick Charles

    A dark matter (DM) search experiment was flown on the IMAX balloon payload, which tested the hypothesis that a minor component of the dark matter in the Galactic halo is composed of ionizing (dE/dx greater than 1 MeV/g/cm2 or sigma greater than 2 x 10-20 sq cm supermassive particles (mx is an element of (104, 1012)GeV/c2 that cannot penetrate the atmosphere due to their low velocities (beta belongs to (0.0003, 0.00025)). The DM search experiment consisted of a delayed coincidence between four approximately 2400 cm2 plastic scintillation detectors, with a total acceptance of approximately 100 cm2 sr. In order to search for ultra-slow particles which do not slow down in the IMAX telescope, the experiment contained TDCs which measured the time-delays Ti,i+1is an element of (0.3, 14.0)microseconds between hits in a successive counters to approximately 1 percent precision. Using the first 5 hours of data at float altitude (5 g/sq cm residual atmosphere), we observed approximately 5 candidate non-slowing dark matter events, consistent with the background from accidental coincidences of 4 events. This implies that the DM flux is less than 6.5 x 10-6 cm-2s-1sr-1 (95 percent C.L.). Similar results were also obtained for particles which slow down in the counter telescope. This experiment effectively closes much of a previously unconstrained 'window' in the mass/cross-section joint parameter space for massive particles as the dominant halo DM, and implies that for certain regions of this parameter space massive particles cannot be more than one part in 105 by mass of all the DM. These results can also directly constrain 'light' magnetic monopoles and neutra CHAMPs in a previously unconstrained mass region mx belongs to (106, 109) GeV.

  8. Where are the Luminous Red Galaxies (LRGs)? Using correlation measurements and lensing to relate LRGs to dark matter haloes

    NASA Astrophysics Data System (ADS)

    Hikage, Chiaki; Mandelbaum, Rachel; Takada, Masahiro; Spergel, David N.

    2013-11-01

    Non-linear redshift-space distortions, the Finger-of-God (FoG) effect, can complicate the interpretation of the galaxy power spectrum. Here, we demonstrate the method proposed by Hikage, Takada & Spergel to use complimentary observations to directly constrain this effect on the data. We use catalogues of Luminous Red Galaxies (LRGs) and photometric galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) to measure the redshift-space power spectrum of LRGs, the cross-correlation of LRGs with the shapes of background photometric galaxies (galaxy-galaxy weak lensing) and the projected cross-correlation of LRGs with photometric galaxies having similar photometric redshifts to the LRG spectroscopic redshift. All of these measurements use a reconstructed halo field. While we use the position of each LRG for single LRG systems, we compare the measurements using different halo-centre proxies for multiple-LRG systems (4.5 per cent of all the haloes): the brightest LRG position (BLRG), the faintest LRG position (FLRG) and their arithmetical mean position (Mean), respectively, in each system. We find significant differences in the measured correlations of different centres, showing consistent off-centring effects in the three observables. By comparing the measurements with a halo model that treats the satellite photometric galaxies as being distributed according to a generalized Navarro, Frenk and White profile, we find that ˜40 (70) per cent of BLRGs (FLRGs) are off-centred satellite galaxies in the multiple-LRG systems. The satellite LRGs have typical off-centring radius of ˜400 kpc h-1, and velocity dispersion of about 500 km s-1 in host haloes with a mean mass of 1.6 × 1014 M⊙ h-1. We show that, if LRGs in the single LRG systems have similar offsets, the residual FoG contamination in the LRG power spectrum can be significant at k ≳ 0.1 h Mpc-1, which may cause a bias in cosmological parameters determined by the shape of the power spectrum, such as

  9. Sunyaev-Zel'dovich effects from annihilating dark matter in the Milky Way: Smooth halo, subhalos, and intermediate-mass black holes

    NASA Astrophysics Data System (ADS)

    Lavalle, Julien

    2010-10-01

    We study the Sunyaev-Zel’dovich effect potentially generated by relativistic electrons injected from dark matter annihilation or decay in the Galaxy, and check whether it could be observed by Planck or the Atacama Large Millimeter Array (ALMA), or even imprint the current CMB data as, e.g., the specific fluctuation excess claimed from an recent reanalysis of the WMAP-5 data. We focus on high-latitude regions to avoid contamination of the Galactic astrophysical electron foreground, and consider the annihilation or decay coming from the smooth dark matter halo as well as from subhalos, further extending our analysis to a generic modeling of spikes arising around intermediate-mass black holes. We show that all these dark Galactic components are unlikely to produce any observable Sunyaev-Zel’dovich effect. For a self-annihilating dark matter particle of 10 GeV with canonical properties, the largest optical depth we find is τe≲10-7 for massive isolated subhalos hosting intermediate-mass black holes. We conclude that dark matter annihilation or decay on the Galactic scale cannot lead to significant Sunyaev-Zel’dovich distortions of the CMB spectrum.

  10. THE INFLUENCE OF DARK MATTER HALOS ON DYNAMICAL ESTIMATES OF BLACK HOLE MASS: 10 NEW MEASUREMENTS FOR HIGH-{sigma} EARLY-TYPE GALAXIES

    SciTech Connect

    Rusli, S. P.; Thomas, J.; Saglia, R. P.; Fabricius, M.; Erwin, P.; Bender, R.; Nowak, N.; Lee, C. H.; Riffeser, A.; Sharp, R.

    2013-09-15

    Adaptive optics assisted SINFONI observations of the central regions of 10 early-type galaxies are presented. Based primarily on the SINFONI kinematics, 10 black hole (BH) masses occupying the high-mass regime of the M{sub BH}-{sigma} relation are derived using three-integral Schwarzschild models. The effect of dark matter (DM) inclusion on the BH mass is explored. The omission of a DM halo in the model results in a higher stellar mass-to-light ratio, especially when extensive kinematic data are used in the model. However, when the diameter of the sphere of influence-computed using the BH mass derived without a dark halo-is at least 10 times the point-spread function FWHM during the observations, it is safe to exclude a DM component in the dynamical modeling, i.e., the change in BH mass is negligible. When the spatial resolution is marginal, restricting the mass-to-light ratio to the right value returns the correct M{sub BH} although a dark halo is not present in the model. Compared to the M{sub BH}-{sigma} and M{sub BH}-L relations of McConnell et al., the 10 BHs are all more massive than expected from the luminosities and 7 BH masses are higher than expected from the stellar velocity dispersions of the host bulges. Using new fitted relations, which include the 10 galaxies, we find that the space density of the most massive BHs (M{sub BH} {approx}> 10{sup 9} M{sub Sun }) estimated from the M{sub BH}-L relation is higher than the estimate based on the M{sub BH}-{sigma} relation and the latter is higher than model predictions based on quasar counts, each by about an order of magnitude.

  11. An Unusual Lunar Halo

    ERIC Educational Resources Information Center

    Cardon, Bartley L.

    1977-01-01

    Discusses a photograph of an unusual combination of lunar halos: the 22-degree refraction halo, the circumscribed halo, and a reflection halo. Deduces the form and orientations of the ice crystals responsible for the observed halo features. (MLH)

  12. In the Dusty Recesses: Characterizing the Dark Matter Halos of Obscured Quasars via Clustering and CMB Lensing

    NASA Astrophysics Data System (ADS)

    Myers, Adam D.; DiPompeo, Michael A.; Hickox, Ryan C.; Runnoe, Jessie C.

    2016-06-01

    The spatial clustering of obscured and unobscured quasars provides an interesting constraint on the connection between the growth of supermassive black holes and the evolution of galaxies and large-scale structure. In pursuit of these constraints, we update our recent measurements of quasar clustering using WISE and Planck data. We carefully assess how alterations in these missions' data reduction pipelines result in different systematics on a range of angular scales, and define samples of WISE-selected quasars that appear to be least-influenced by differences in data calibration. With these samples we analyze quasar clustering via two complementary methods; the angular autocorrelation function and cosmic microwave background lensing cross-correlations. We measure a higher bias and halo mass for obscured quasars (b ~ 2.1) as compared to unobscured quasars (b ~ 1.8). This is at odds with simple orientation models but at a reduced significance (1.5σ) as compared to our work with previous survey data. Assuming that some fraction (as high as 75%) of obscured quasars are intrinsically similar to unobscured quasars but viewed through a "dusty torus," we infer that the remaining non-torus obscured quasar population must have a large clustering bias of ~3, and inhabit typical halo masses of ~3 × 1013 h-1M⊙ at a redshift of z ~ 1. These massive halos are likely the descendants of high-mass unobscured quasars at high redshift, and will evolve into members of galaxy groups by z ~ 0. This work was supported in part by NSF grants 1211112, 1515404 and 1515364.

  13. Testing Sunyaev-Zel'dovich measurements of the hot gas content of dark matter haloes using synthetic skies

    NASA Astrophysics Data System (ADS)

    Le Brun, Amandine M. C.; McCarthy, Ian G.; Melin, Jean-Baptiste

    2015-08-01

    The thermal Sunyaev-Zel'dovich (tSZ) effect offers a means of probing the hot gas in and around massive galaxies and galaxy groups and clusters, which is thought to constitute a large fraction of the baryon content of the Universe. The Planck collaboration recently performed a stacking analysis of a large sample of `locally brightest galaxies' (LBGs) and, surprisingly, inferred an approximately self-similar relation between the tSZ flux and halo mass. At face value, this implies that the hot gas mass fraction is independent of halo mass, a result which is in apparent conflict with resolved X-ray observations. We test the robustness of the inferred trend using synthetic tSZ maps generated from cosmological hydrodynamical simulations and using the same tools and assumptions applied in the Planck study. We show that, while the detection and the estimate of the `total' flux (within 5r500) is reasonably robust, the inferred flux originating from within r500 (i.e. the limiting radius to which X-ray observations typically probe) is highly sensitive to the assumed pressure distribution of the gas. Using our most realistic simulations with AGN feedback, that reproduce a wide variety of X-ray and optical properties of groups and clusters, we estimate that the derived tSZ flux within r500 is biased high by up to an order of magnitude for haloes with masses M500 ˜ 1013 M⊙. Moreover, we show that the AGN simulations are consistent with the total tSZ flux-mass relation observed with Planck, whereas a self-similar model is ruled out.

  14. Non-standard analysis and embedded software

    NASA Technical Reports Server (NTRS)

    Platek, Richard

    1995-01-01

    One model for computing in the future is ubiquitous, embedded computational devices analogous to embedded electrical motors. Many of these computers will control physical objects and processes. Such hidden computerized environments introduce new safety and correctness concerns whose treatment go beyond present Formal Methods. In particular, one has to begin to speak about Real Space software in analogy with Real Time software. By this we mean, computerized systems which have to meet requirements expressed in the real geometry of space. How to translate such requirements into ordinary software specifications and how to carry out proofs is a major challenge. In this talk we propose a research program based on the use of no-standard analysis. Much detail remains to be carried out. The purpose of the talk is to inform the Formal Methods community that Non-Standard Analysis provides a possible avenue to attack which we believe will be fruitful.

  15. Renormalized halo bias

    SciTech Connect

    Assassi, Valentin; Baumann, Daniel; Green, Daniel; Zaldarriaga, Matias E-mail: dbaumann@damtp.cam.ac.uk E-mail: matiasz@ias.edu

    2014-08-01

    This paper provides a systematic study of renormalization in models of halo biasing. Building on work of McDonald, we show that Eulerian biasing is only consistent with renormalization if non-local terms and higher-derivative contributions are included in the biasing model. We explicitly determine the complete list of required bias parameters for Gaussian initial conditions, up to quartic order in the dark matter density contrast and at leading order in derivatives. At quadratic order, this means including the gravitational tidal tensor, while at cubic order the velocity potential appears as an independent degree of freedom. Our study naturally leads to an effective theory of biasing in which the halo density is written as a double expansion in fluctuations and spatial derivatives. We show that the bias expansion can be organized in terms of Galileon operators which aren't renormalized at leading order in derivatives. Finally, we discuss how the renormalized bias parameters impact the statistics of halos.

  16. Attitudes towards Non-Standard English in Singapore

    ERIC Educational Resources Information Center

    Tan, Peter K. W.; Tan, Daniel K. H.

    2008-01-01

    This paper examines the problem of a curriculum which promotes a standard linguistic variety in a context where non-standardisms are common in the learners' milieu. There have been curricula which try to incorporate the non-standard and have its function discussed; some have considered the non-standard a stepping-stone towards the standard; and…

  17. Is the misalignment of the Local Group velocity and the dipole generated by the 2MASS Redshift Survey typical in {lambda} cold dark matter and the halo model of galaxies?

    SciTech Connect

    Erdogdu, Pirin; Lahav, Ofer

    2009-08-15

    We predict the acceleration of the Local Group generated by the 2MASS Redshift Survey within the framework of {lambda} cold dark matter and the halo model of galaxies. We show that as the galaxy fluctuations derived from the halo model have more power on small scales compared with the mass fluctuations, the misalignment angle between the CMB velocity vector and the 2MASS Redshift Survey dipole is in reasonable agreement with the observed 21 deg. This statistical analysis suggests that it is not necessary to invoke a hypothetical nearby galaxy or a distant cluster to explain this misalignment.

  18. Effects of center offset and noise on weak-lensing derived concentration-mass relation of dark matter halos

    SciTech Connect

    Du, Wei; Fan, Zuhui

    2014-04-10

    With the halo catalog from the Millennium Simulation, we analyze the weak-lensing measured density profiles for clusters of galaxies, paying attention to the determination of the concentration-mass (c-M) relation, which can be biased by the center offset, selection effect, and shape noise from intrinsic ellipticities of background galaxies. Several different methods of locating the center of a cluster from weak-lensing effects alone are explored. We find that, for intermediate redshift clusters, the highest peak from our newly proposed two-scale smoothing method applied to the reconstructed convergence field, first with a smoothing scale of 2' and then 0.'5, corresponds best to the true center. Assuming the parameterized Navarro-Frenk-White profile, we fit the reduced tangential shear signals around different centers identified by different methods. It is shown that, for the ensemble median values, a center offset larger than one scale radius r{sub s} can bias the derived mass and concentration significantly lower than the true values, especially for low-mass halos. However, the existence of noise can compensate for the offset effect and reduce the systematic bias, although the scatter of mass and concentration becomes considerably larger. Statistically, the bias effect of center offset on the c-M relation is insignificant if an appropriate center finding method is adopted. On the other hand, noise from intrinsic ellipticities can bias the c-M relation derived from a sample of weak-lensing analyzed clusters if a simple χ{sup 2} fitting method is used. To properly account for the scatter and covariance between c and M, we apply a Bayesian method to improve the statistical analysis of the c-M relation. It is shown that this new method allows us to derive the c-M relation with significantly reduced biases.

  19. Non-standard neutrino interactions at DUNE

    NASA Astrophysics Data System (ADS)

    de Gouvêa, André; Kelly, Kevin J.

    2016-07-01

    We explore the effects of non-standard neutrino interactions (NSI) and how they modify neutrino propagation in the Deep Underground Neutrino Experiment (DUNE). We find that NSI can significantly modify the data to be collected by the DUNE experiment as long as the new physics parameters are large enough. For example, if the DUNE data are consistent with the standard three-massive-neutrinos paradigm, order 0.1 (in units of the Fermi constant) NSI effects will be ruled out. On the other hand, if large NSI effects are present, DUNE will be able to not only rule out the standard paradigm but also measure the new physics parameters, sometimes with good precision. We find that, in some cases, DUNE is sensitive to new sources of CP-invariance violation. We also explored whether DUNE data can be used to distinguish different types of new physics beyond nonzero neutrino masses. In more detail, we asked whether NSI can be mimicked, as far as the DUNE setup is concerned, by the hypothesis that there is a new light neutrino state.

  20. Non-standard symmetries and Killing tensors

    NASA Astrophysics Data System (ADS)

    Visinescu, Mihai

    2009-10-01

    Higher order symmetries corresponding to Killing tensors are investigated. The intimate relation between Killing-Yano tensors and non-standard supersymmetries is pointed out. The gravitational anomalies are absent if the hidden symmetry is associated with a Killing-Yano tensor. In the Dirac theory on curved spaces, Killing-Yano tensors generate Dirac type operators involved in interesting algebraic structures as dynamical algebras or even infinite dimensional algebras or superalgebras. The general results are applied to space-times which appear in modern studies. The 4-dimensional Euclidean Taub-NUT space and its generalizations introduced by Iwai and Katayama are analyzed from the point of view of hidden symmetries. One presents the infinite dimensional superalgebra of Dirac type operators on Taub-NUT space that can be seen as a twisted loop algebra. The axial anomaly, interpreted as the index of the Dirac operator, is computed for the generalized Taub-NUT metrics. The existence of the conformal Killing-Yano tensors is investigated for some spaces with mixed Sasakian structures.

  1. 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

  2. Analyzing direct dark matter detection data with unrejected background events by the AMIDAS website

    NASA Astrophysics Data System (ADS)

    Shan, Chung-Lin

    2012-09-01

    In this talk I have presented the data analysis results of extracting properties of halo WIMPs: the mass and the (ratios between the) spin-independent and spin-dependent couplings/cross sections on nucleons by the AMIDAS website by taking into account possible unrejected background events in the analyzed data sets. Although non-standard astronomical setup has been used to generate pseudodata sets for our analyses, it has been found that, without prior information/assumption about the local density and velocity distribution of halo Dark Matter, these WIMP properties have been reconstructed with ~ 2% to lesssim 30% deviations from the input values.

  3. THE STRIKINGLY SIMILAR RELATION BETWEEN SATELLITE AND CENTRAL GALAXIES AND THEIR DARK MATTER HALOS SINCE z = 2

    SciTech Connect

    Watson, Douglas F.; Conroy, Charlie

    2013-08-01

    Satellite galaxies in rich clusters are subject to numerous physical processes that can significantly influence their evolution. However, the typical L* satellite galaxy resides in much lower mass galaxy groups, where the processes capable of altering their evolution are generally weaker and have had less time to operate. To investigate the extent to which satellite and central galaxy evolution differs, we separately model the stellar mass-halo mass (M{sub *}-M{sub h} ) relation for these two populations over the redshift interval 0 < z < 1. This relation for central galaxies is constrained by the galaxy stellar mass function while the relation for satellite galaxies is constrained against recent measurements of the galaxy two-point correlation function (2PCF). Our approach does not rely on the abundance matching technique but instead adopts a flexible functional form for the relation between satellite galaxy stellar mass and subhalo mass, where subhalo mass is considered as the maximum mass that a subhalo has ever reached in its merger history, M{sub peak}. At z {approx} 0 the satellites, on average, have {approx}10% larger stellar masses at fixed M{sub peak} compared to central galaxies of the same halo mass (although the two relations are consistent at 2{sigma}-3{sigma} for M{sub peak} {approx}> 10{sup 13} M{sub Sun }). This is required in order to reproduce the observed stellar mass-dependent 2PCF and satellite fractions. At low masses our model slightly under-predicts the correlation function at {approx}1 Mpc scales. At z {approx} 1 the satellite and central galaxy M{sub *}-M{sub h} relations are consistent within the errors, and the model provides an excellent fit to the clustering data. At present, the errors on the clustering data at z {approx} 2 are too large to constrain the satellite model. A simple model in which satellite and central galaxies share the same M{sub *}-M{sub h} relation is able to reproduce the extant z {approx} 2 clustering data. We

  4. Non-Standard Neutrino Physics Probed by Tokai-To Two-Detector Complex

    NASA Astrophysics Data System (ADS)

    Ribeiro, Nei Cipriano; Kajita, Takaaki; Ko, Pyungwon; Minakata, Hisakazu; Nakayama, Shoei; Nunokawa, Hiroshi

    2009-01-01

    The discovery potentials of non-standard physics (NSP) which might be possessed by neutrinos are examined by taking a concrete setting of Tokai-to-Kamioka-Korea (T2KK) two detector complex which receives neutrino superbeam from J-PARC. We restrict ourselves into νμ and {bar v}μ disappearance measurement. We describe here only the non-standard interactions (NSI) of neutrinos with matter and the quantum decoherence. It is shown in some favorable cases T2KK can significantly improve the current bounds on NSP. For NSI, for example, ɛμτ < 0.03, which is a factor 5 severer than the current one.

  5. Quasar-microlensing versus star-microlensing evidence of small-planetary-mass objects as the dominant inner-halo galactic dark matter

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.; Schild, Rudolph E.

    2011-11-01

    We examine recent results of two kinds of microlensing experiments intended to detect galactic dark matter objects, and we suggest that the lack of short period star-microlensing events observed for stars near the Galaxy does not preclude either the "rogue planets" identified from quasar-microlensing by Schild 1996 as the missing-mass of a lens galaxy, or the "Primordial Fog Particles" (PFPs) in Proto-Globular-star-Cluster (PGC) clumps predicted by Gibson 1996 - 2000 as the dominant inner-halo galactic dark matter component from a new hydrodynamic gravitational structure formation theory. We point out that hydro-gravitational processes acting on a massive population of such micro-brown-dwarfs in their nonlinear accretional cascades to form stars gives intermittent lognormal number density np distributions for the PFPs within the PGC gas-stabilized-clumps. Hence, star-microlensing searches that focus on a small fraction of the sky assuming a uniform distribution for np are subject to vast underestimates of the mean ⟨np⟩mean. Sparse independent samples give modes 10-4 - 10-6 smaller than means of the highly skewed lognormal distributions expected. Quasar-microlensing searches with higher optical depths are less affected by np intermittency. We attempt to reconcile the results of the star-microlensing and quasar-microlensing studies, with particular reference to the necessarily hydrogenous and primordial small-planetary-mass range. We conclude that star microlensing searches cannot exclude and are unlikely even to detect these low-mass candidate-galactic-dark-matter-objects so easily observed by quasar-microlensing and so robustly predicted by the new theory.

  6. Halo model and halo properties in Galileon gravity cosmologies

    SciTech Connect

    Barreira, Alexandre; Li, Baojiu; Hellwing, Wojciech A.; Baugh, Carlton M.; Lombriser, Lucas; Pascoli, Silvia E-mail: baojiu.li@durham.ac.uk E-mail: llo@roe.ac.uk E-mail: silvia.pascoli@durham.ac.uk

    2014-04-01

    We investigate the performance of semi-analytical modelling of large-scale structure in Galileon gravity cosmologies using results from N-body simulations. We focus on the Cubic and Quartic Galileon models that provide a reasonable fit to CMB, SNIa and BAO data. We demonstrate that the Sheth-Tormen mass function and linear halo bias can be calibrated to provide a very good fit to our simulation results. We also find that the halo concentration-mass relation is well fitted by a power law. The nonlinear matter power spectrum computed in the halo model approach is found to be inaccurate in the mildly nonlinear regime, but captures reasonably well the effects of the Vainshtein screening mechanism on small scales. In the Cubic model, the screening mechanism hides essentially all of the effects of the fifth force inside haloes. In the case of the Quartic model, the screening mechanism leaves behind residual modifications to gravity, which make the effective gravitational strength time-varying and smaller than the standard value. Compared to normal gravity, this causes a deficiency of massive haloes and leads to a weaker matter clustering on small scales. For both models, we show that there are realistic halo occupation distributions of Luminous Red Galaxies that can match both the observed large-scale clustering amplitude and the number density of these galaxies.

  7. Reionization histories of Milky Way mass halos

    SciTech Connect

    Li, Tony Y.; Wechsler, Risa H.; Abel, Tom; Alvarez, Marcelo A. E-mail: rwechsler@stanford.edu E-mail: malvarez@cita.utoronto.ca

    2014-04-20

    We investigate the connection between the reionization era and the present-day universe by examining the mass reionization histories of z = 0 dark matter halos. In a 600{sup 3} Mpc{sup 3} volume, we combine a dark matter N-body simulation with a three-dimensional seminumerical reionization model. This tags each particle with a reionization redshift, so that individual present-day halos can be connected to their reionization histories and environments. We find that the vast majority of present-day halos with masses larger than ∼ few × 10{sup 11} M {sub ☉} reionize earlier than the rest of the universe. We also find significant halo-to-halo diversity in mass reionization histories, and find that in realistic inhomogeneous models, the material within a given halo is not expected to reionize at the same time. In particular, the scatter in reionization times within individual halos is typically larger than the scatter among halos. From our fiducial reionization model, we find that the typical 68% scatter in reionization times within halos is ∼115 Myr for 10{sup 12±0.25} M {sub ☉} halos, decreasing slightly to ∼95 Myr for 10{sup 15±0.25} M {sub ☉} halos. We find a mild correlation between reionization history and environment: halos with shorter reionization histories are typically in more clustered environments, with the strongest trend on a scale of ∼20 Mpc. Material in Milky Way mass halos with short reionization histories is preferentially reionized in relatively large H II regions, implying reionization mostly by sources external to the progenitors of the present-day halo. We investigate the impact on our results of varying the reionization model parameters, which span a range of reionization scenarios with varying timing and morphology.

  8. Halotools: Galaxy-Halo connection models

    NASA Astrophysics Data System (ADS)

    Hearin, Andrew; Tollerud, Erik; Robitaille, Thomas; Droettboom, Michael; Zentner, Andrew; Bray, Erik; Craig, Matt; Bradley, Larry; Barbary, Kyle; Deil, Christoph; Tan, Kevin; Becker, Matthew R.; More, Surhud; Günther, Hans Moritz; Sipocz, Brigitta

    2016-04-01

    Halotools builds and tests models of the galaxy-halo connection and analyzes catalogs of dark matter halos. The core functions of the package include fast generation of synthetic galaxy populations using HODs, abundance matching, and related methods; efficient algorithms for calculating galaxy clustering, lensing, z-space distortions, and other astronomical statistics; a modular, object-oriented framework for designing galaxy evolution models; and end-to-end support for reducing halo catalogs and caching them as hdf5 files.

  9. Smooth halos in the cosmic web

    NASA Astrophysics Data System (ADS)

    Gaite, José

    2015-04-01

    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 of 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.

  10. Lepton flavor violating non-standard interactions via light mediators

    NASA Astrophysics Data System (ADS)

    Farzan, Yasaman; Shoemaker, Ian M.

    2016-07-01

    Non-Standard neutral current Interactions (NSIs) of neutrinos with matter can alter the pattern of neutrino oscillation due to the coherent forward scattering of neutrinos on the medium. This effect makes long-baseline neutrino experiments such as NO νA and DUNE a sensitive probe of beyond standard model (BSM) physics. We construct light mediator models that can give rise to both lepton flavor conserving as well as Lepton Flavor Violating (LFV) neutral current NSI. We outline the present phenomenological viability of these models and future prospects to test them. We predict a lower bound on Br( H → μτ ) in terms of the parameters that can be measured by DUNE and NO νA, and show that the hint for H → μτ in current LHC data can be accommodated in our model. A large part of the parameter space of the model is already constrained by the bound on Br( τ → Z ' μ) and by the bounds on rare meson decays and can be in principle fully tested by improving these bounds.

  11. Neutrino physics with non-standard interactions at INO

    NASA Astrophysics Data System (ADS)

    Choubey, Sandhya; Ghosh, Anushree; Ohlsson, Tommy; Tiwari, Deepak

    2015-12-01

    Non-standard neutrino interactions (NSI) involved in neutrino propagation inside Earth matter could potentially alter atmospheric neutrino fluxes. In this work, we look at the impact of these NSI on the signal at the ICAL detector to be built at the India-based Neutrino Observatory (INO). We show how the sensitivity to the neutrino mass hierarchy of ICAL changes in the presence of NSI. The mass hierarchy sensitivity is shown to be rather sensitive to the NSI parameters ɛ eμ and ɛ eτ , while the dependence on ɛ μτ and ɛ τ τ is seen to be very mild, once the χ 2 is marginalised over oscillation and NSI parameters. If the NSI are large enough, the event spectrum at ICAL is expected to be altered and this can be used to discover new physics. We calculate the lower limit on NSI parameters above which ICAL could discover NSI at a given C.L. from 10 years of data. If NSI were too small, the null signal at ICAL can constrain the NSI parameters. We give upper limits on the NSI parameters at any given C.L. that one is expected to put from 10 years of running of ICAL. Finally, we give C.L. contours in the NSI parameter space that is expected to be still allowed from 10 years of running of the experiment.

  12. Halo-independent tests of dark matter direct detection signals: local DM density, LHC, and thermal freeze-out

    SciTech Connect

    Blennow, Mattias; Herrero-Garcia, Juan; Schwetz, Thomas; Vogl, Stefan

    2015-08-19

    From an assumed signal in a Dark Matter (DM) direct detection experiment a lower bound on the product of the DM-nucleon scattering cross section and the local DM density is derived, which is independent of the local DM velocity distribution. This can be combined with astrophysical determinations of the local DM density. Within a given particle physics model the bound also allows a robust comparison of a direct detection signal with limits from the LHC. Furthermore, the bound can be used to formulate a condition which has to be fulfilled if the particle responsible for the direct detection signal is a thermal relic, regardless of whether it constitutes all DM or only part of it. We illustrate the arguments by adopting a simplified DM model with a Z{sup ′} mediator and assuming a signal in a future xenon direct detection experiment.

  13. Search for a dark matter annihilation signal from the galactic center halo with H.E.S.S.

    PubMed

    Abramowski, A; Acero, F; Aharonian, F; Akhperjanian, A G; Anton, G; Barnacka, A; de Almeida, U Barres; Bazer-Bachi, A R; Becherini, Y; Becker, J; Behera, B; Bernlöhr, K; Bochow, A; Boisson, C; Bolmont, J; Bordas, P; Borrel, V; Brucker, J; Brun, F; Brun, P; Bulik, T; Büsching, I; Carrigan, S; Casanova, S; Cerruti, M; Chadwick, P M; Charbonnier, A; Chaves, R C G; Cheesebrough, A; Chounet, L-M; Clapson, A C; Coignet, G; Conrad, J; Dalton, M; Daniel, M K; Davids, I D; Degrange, B; Deil, C; Dickinson, H J; Djannati-Ataï, A; Domainko, W; Drury, L O'C; Dubois, F; Dubus, G; Dyks, J; Dyrda, M; Egberts, K; Eger, P; Espigat, P; Fallon, L; Farnier, C; Fegan, S; Feinstein, F; Fernandes, M V; Fiasson, A; Fontaine, G; Förster, A; Füssling, M; Gallant, Y A; Gast, H; Gérard, L; Gerbig, D; Giebels, B; Glicenstein, J F; Glück, B; Goret, P; Göring, D; Hague, J D; Hampf, D; Hauser, M; Heinz, S; Heinzelmann, G; Henri, G; Hermann, G; Hinton, J A; Hoffmann, A; Hofmann, W; Hofverberg, P; Horns, D; Jacholkowska, A; de Jager, O C; Jahn, C; Jamrozy, M; Jung, I; Kastendieck, M A; Katarzyński, K; Katz, U; Kaufmann, S; Keogh, D; Kerschhaggl, M; Khangulyan, D; Khélifi, B; Klochkov, D; Kluźniak, W; Kneiske, T; Komin, Nu; Kosack, K; Kossakowski, R; Laffon, H; Lamanna, G; Lennarz, D; Lohse, T; Lopatin, A; Lu, C-C; Marandon, V; Marcowith, A; Masbou, J; Maurin, D; Maxted, N; McComb, T J L; Medina, M C; Méhault, J; Moderski, R; Moulin, E; Naumann, C L; Naumann-Godo, M; de Naurois, M; Nedbal, D; Nekrassov, D; Nguyen, N; Nicholas, B; Niemiec, J; Nolan, S J; Ohm, S; Olive, J-F; Wilhelmi, E de Oña; Opitz, B; Ostrowski, M; Panter, M; Arribas, M Paz; Pedaletti, G; Pelletier, G; Petrucci, P-O; Pita, S; Pühlhofer, G; Punch, M; Quirrenbach, A; Raue, M; Rayner, S M; Reimer, A; Reimer, O; Renaud, M; de los Reyes, R; Rieger, F; Ripken, J; Rob, L; Rosier-Lees, S; Rowell, G; Rudak, B; Rulten, C B; Ruppel, J; Ryde, F; Sahakian, V; Santangelo, A; Schlickeiser, R; Schöck, F M; Schönwald, A; Schwanke, U; Schwarzburg, S; Schwemmer, S; Shalchi, A; Sikora, M; Skilton, J L; Sol, H; Spengler, G; Stawarz, Ł; Steenkamp, R; Stegmann, C; Stinzing, F; Sushch, I; Szostek, A; Tavernet, J-P; Terrier, R; Tibolla, O; Tluczykont, M; Valerius, K; van Eldik, C; Vasileiadis, G; Venter, C; Vialle, J P; Viana, A; Vincent, P; Vivier, M; Völk, H J; Volpe, F; Vorobiov, S; Vorster, M; Wagner, S J; Ward, M; Wierzcholska, A; Zajczyk, A; Zdziarski, A A; Zech, A; Zechlin, H-S

    2011-04-22

    A search for a very-high-energy (VHE; ≥100  GeV) γ-ray signal from self-annihilating particle dark matter (DM) is performed towards a region of projected distance r∼45-150  pc from the Galactic center. The background-subtracted γ-ray spectrum measured with the High Energy Stereoscopic System (H.E.S.S.) γ-ray instrument in the energy range between 300 GeV and 30 TeV shows no hint of a residual γ-ray flux. Assuming conventional Navarro-Frenk-White and Einasto density profiles, limits are derived on the velocity-weighted annihilation cross section (σv) as a function of the DM particle mass. These are among the best reported so far for this energy range and in particular differ only little between the chosen density profile parametrizations. In particular, for the DM particle mass of ∼1  TeV, values for (σv) above 3×10(-25)  cm(3) s(-1) are excluded for the Einasto density profile. PMID:21599352

  14. THE PSEUDO-EVOLUTION OF HALO MASS

    SciTech Connect

    Diemer, Benedikt; Kravtsov, Andrey V.; More, Surhud

    2013-03-20

    A dark matter halo is commonly defined as a spherical overdensity of matter with respect to a reference density, such as the critical density or the mean matter density of the universe. Such definitions can lead to a spurious pseudo-evolution of halo mass simply due to redshift evolution of the reference density, even if its physical density profile remains constant over time. We estimate the amount of such pseudo-evolution of mass between z = 1 and 0 for halos identified in a large N-body simulation, and show that it accounts for almost the entire mass evolution of the majority of halos with M{sub 200{rho}-bar} Less-Than-Or-Equivalent-To 10{sup 12} h{sup -1} M{sub Sun} and can be a significant fraction of the apparent mass growth even for cluster-sized halos. We estimate the magnitude of the pseudo-evolution assuming that halo density profiles remain static in physical coordinates, and show that this simple model predicts the pseudo-evolution of halos identified in numerical simulations to good accuracy, albeit with significant scatter. We discuss the impact of pseudo-evolution on the evolution of the halo mass function and show that the non-evolution of the low-mass end of the halo mass function is the result of a fortuitous cancellation between pseudo-evolution and the absorption of small halos into larger hosts. We also show that the evolution of the low-mass end of the concentration-mass relation observed in simulations is almost entirely due to the pseudo-evolution of mass. Finally, we discuss the implications of our results for the interpretation of the evolution of various scaling relations between the observable properties of galaxies and galaxy clusters and their halo masses.

  15. Alignments between galaxies, satellite systems and haloes

    NASA Astrophysics Data System (ADS)

    Shao, Shi; Cautun, Marius; Frenk, Carlos S.; Gao, Liang; Crain, Robert A.; Schaller, Matthieu; Schaye, Joop; Theuns, Tom

    2016-08-01

    The spatial distribution of the satellite populations of the Milky Way and Andromeda are puzzling in that they are nearly perpendicular to the disks of their central galaxies. To understand the origin of such configurations we study the alignment of the central galaxy, satellite system and dark matter halo in the largest of the "Evolution and Assembly of GaLaxies and their Environments" (EAGLE) simulation. We find that centrals and their satellite systems tend to be well aligned with their haloes, with a median misalignment angle of $33^{\\circ}$ in both cases. While the centrals are better aligned with the inner $10$ kpc halo, the satellite systems are better aligned with the entire halo indicating that satellites preferentially trace the outer halo. The central - satellite alignment is weak (median misalignment angle of $52^{\\circ}$) and we find that around $20\\%$ of systems have a misalignment angle larger than $78^{\\circ}$, which is the value for the Milky Way. The central - satellite alignment is a consequence of the tendency of both components to align with the dark matter halo. As a consequence, when the central is parallel to the satellite system, it also tends to be parallel to the halo. In contrast, if the central is perpendicular to the satellite system, as in the case of the Milky Way and Andromeda, then the central - halo alignment is much weaker. Dispersion-dominated (spheroidal) centrals have a stronger alignment with both their halo and their satellites than rotation-dominated (disk) centrals. We also found that the halo, the central galaxy and the satellite system tend to be aligned with the surrounding large-scale distribution of matter, with the halo being the better aligned of the three.

  16. Alignments between galaxies, satellite systems and haloes

    NASA Astrophysics Data System (ADS)

    Shao, Shi; Cautun, Marius; Frenk, Carlos S.; Gao, Liang; Crain, Robert A.; Schaller, Matthieu; Schaye, Joop; Theuns, Tom

    2016-08-01

    The spatial distribution of the satellite populations of the Milky Way and Andromeda are puzzling in that they are nearly perpendicular to the discs of their central galaxies. To understand the origin of such configurations we study the alignment of the central galaxy, satellite system and dark matter halo in the largest of the `Evolution and Assembly of GaLaxies and their Environments' (EAGLE) simulation. We find that centrals and their satellite systems tend to be well aligned with their haloes, with a median misalignment angle of 33° in both cases. While the centrals are better aligned with the inner 10 kpc halo, the satellite systems are better aligned with the entire halo indicating that satellites preferentially trace the outer halo. The central-satellite alignment is weak (median misalignment angle of 52°) and we find that around 20 per cent of systems have a misalignment angle larger than 78°, which is the value for the Milky Way. The central-satellite alignment is a consequence of the tendency of both components to align with the dark matter halo. As a consequence, when the central is parallel to the satellite system, it also tends to be parallel to the halo. In contrast, if the central is perpendicular to the satellite system, as in the case of the Milky Way and Andromeda, then the central-halo alignment is much weaker. Dispersion-dominated (spheroidal) centrals have a stronger alignment with both their halo and their satellites than rotation-dominated (disc) centrals. We also found that the halo, the central galaxy and the satellite system tend to be aligned with the surrounding large-scale distribution of matter, with the halo being the better aligned of the three.

  17. Halo modelling in chameleon theories

    SciTech Connect

    Lombriser, Lucas; Koyama, Kazuya; Li, Baojiu E-mail: kazuya.koyama@port.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 local 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.

  18. A Lyα blob and zabs ≈ zem damped Lyα absorber in the dark matter halo of the binary quasar Q 0151+048

    NASA Astrophysics Data System (ADS)

    Zafar, T.; Møller, P.; Ledoux, C.; Fynbo, J. P. U.; Nilsson, K. K.; Christensen, L.; D'Odorico, S.; Milvang-Jensen, B.; Michałowski, M. J.; Ferreira, D. D. M.

    2011-08-01

    Context. Q 0151+048 is a physical quasar (QSO) pair at z ~ 1.929 with a separation of 3.3 arcsec on the sky. In the spectrum of the brighter member of this pair, Q 0151+048A, a damped Lyα absorber (DLA) is observed at a higher redshift. We have previously detected the host galaxies of both QSOs, as well as a Lyα blob whose emission surrounding Q 0151+048A extends over 5 × 3.3 arcsec. Aims: We seek to constrain the geometry of the system and understand the possible relations between the DLA, the Lyα blob, and the two QSOs. We also aim at characterizing the former two objects in more detail. Methods: To study the nature of the Lyα blob, we performed low-resolution, long-slit spectroscopy with the slit aligned with the extended emission. We also observed the whole system using the medium-resolution VLT/X-shooter spectrograph and the slit aligned with the two QSOs. The systemic redshift of both QSOs was determined from rest-frame optical emission lines redshifted into the NIR. We employed line-profile fitting technique, to measure metallicities and the velocity width of low-ionization metal absorption lines associated to the DLA and photo-ionization modeling to characterize the DLA further. Results: We measure systemic redshifts of zem(A) = 1.92924 ± 0.00036 and zem(B) = 1.92863 ± 0.00042 from the H β and H α emission lines, respectively. In other words, the two QSOs have identical redshifts within 2σ. From the width of Balmer emission lines and the strength of the rest-frame optical continuum, we estimate the masses of the black holes of the two QSOs to be 109.33 M⊙ and 108.38 M⊙ for Q 0151+048A and Q 0151+048B, respectively. We then use the correlation between black hole mass and dark matter halo mass to infer the mass of the dark matter halos hosting the two QSOs: 1013.74 M⊙ and 1013.13 M⊙ for Q 0151+048A and Q 0151+048B, respectively. We observe a velocity gradient along the major axis of the Lyα blob consistent with the rotation curve of a large

  19. Linking Galaxies to Dark Matter Halos at z ~ 1 : Dependence of Galaxy Clustering on Stellar Mass and Specific Star Formation Rate

    NASA Astrophysics Data System (ADS)

    Kim, Jae-Woo; Im, Myungshin; Lee, Seong-Kook; Edge, Alastair C.; Wake, David A.; Merson, Alexander I.; Jeon, Yiseul

    2015-06-01

    We study the dependence of angular two-point correlation functions on stellar mass (M*) and specific star formation rate (sSFR) of {M}*\\gt {10}10{M}ȯ galaxies at z∼ 1. The data from the UK Infrared Telescope Infrared Deep Sky Survey Deep eXtragalactic Survey and Canada–France–Hawaii Telescope Legacy Survey cover 8.2 deg2 sample scales larger than 100 {h}-1 {Mpc} at z∼ 1, allowing us to investigate the correlation between clustering, M*, and star formation through halo modeling. Based on halo occupation distributions (HODs) of M* threshold samples, we derive HODs for M* binned galaxies, and then calculate the {M}*/{M}{halo} ratio. The ratio for central galaxies shows a peak at {M}{halo}∼ {10}12{h}-1{M}ȯ , and satellites predominantly contribute to the total stellar mass in cluster environments with {M}*/{M}{halo} values of 0.01–0.02. Using star-forming galaxies split by sSFR, we find that main sequence galaxies ({log} {sSFR}/{{yr}}-1∼ -9) are mainly central galaxies in ∼ {10}12.5{h}-1{M}ȯ halos with the lowest clustering amplitude, while lower sSFR galaxies consist of a mixture of both central and satellite galaxies where those with the lowest M* are predominantly satellites influenced by their environment. Considering the lowest {M}{halo} samples in each M* bin, massive central galaxies reside in more massive halos with lower sSFRs than low mass ones, indicating star-forming central galaxies evolve from a low M*–high sSFR to a high M*–low sSFR regime. We also find that the most rapidly star-forming galaxies ({log} {sSFR}/{{yr}}-1\\gt -8.5) are in more massive halos than main sequence ones, possibly implying galaxy mergers in dense environments are driving the active star formation. These results support the conclusion that the majority of star-forming galaxies follow secular evolution through the sustained but decreasing formation of stars.

  20. Interpretation of MINOS data in terms of non-standard neutrino interactions

    SciTech Connect

    Kopp, Joachim; Machado, Pedro A.N.; Parke, Stephen J.; /Fermilab

    2010-09-01

    The MINOS experiment at Fermilab has recently reported a tension between the oscillation results for neutrinos and anti-neutrinos. We show that this tension, if it persists, can be understood in the framework of non-standard neutrino interactions (NSI). While neutral current NSI (non-standard matter effects) are disfavored by atmospheric neutrinos, a new charged current coupling between tau neutrinos and nucleons can fit the MINOS data without violating other constraints. In particular, we show that loop-level contributions to flavor-violating {tau} decays are sufficiently suppressed. However, conflicts with existing bounds could arise once the effective theory considered here is embedded into a complete renormalizable model. We predict the future sensitivity of the T2K and NOvA experiments to the NSI parameter region favored by the MINOS fit, and show that both experiments are excellent tools to test the NSI interpretation of the MINOS data.

  1. The scale-dependence of halo assembly bias

    NASA Astrophysics Data System (ADS)

    Sunayama, Tomomi; Hearin, Andrew P.; Padmanabhan, Nikhil; Leauthaud, Alexie

    2016-05-01

    The two-point clustering of dark matter haloes is influenced by halo properties besides mass, a phenomenon referred to as halo assembly bias. Using the depth of the gravitational potential well, Vmax, as our secondary halo property, in this paper, we present the first study of the scale-dependence of assembly bias. In the large-scale linear regime, r ≥ 10 h-1 Mpc, our findings are in keeping with previous results. In particular, at the low-mass end (haloes with high Vmax show stronger large-scale clustering relative to haloes with low Vmax of the same mass; this trend weakens and reverses for Mvir ≳ Mcoll. In the non-linear regime, assembly bias in low-mass haloes exhibits a pronounced scale-dependent `bump' at 500 kpc h-1-5 Mpc h-1. This feature weakens and eventually vanishes for haloes of higher mass. We show that this scale-dependent signature can primarily be attributed to a special subpopulation of ejected haloes, defined as present-day host haloes that were previously members of a higher mass halo at some point in their past history. A corollary of our results is that galaxy clustering on scales of r ˜ 1-2 Mpc h-1 can be impacted by up to ˜15 per cent by the choice of the halo property used in the halo model, even for stellar mass-limited samples.

  2. CARS: the CFHTLS-Archive-Research Survey. II. Weighing dark matter halos of Lyman-break galaxies at z = 3-5

    NASA Astrophysics Data System (ADS)

    Hildebrandt, H.; Pielorz, J.; Erben, T.; van Waerbeke, L.; Simon, P.; Capak, P.

    2009-05-01

    Aims: We measure the clustering properties for a large samples of u- (z˜3), g- (z˜4), and r- (z˜5) dropouts from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) Deep fields. Methods: Photometric redshift distributions along with simulations allow us to de-project the angular correlation measurements and estimate physical quantities such as the correlation length, halo mass, galaxy bias, and halo occupation as a function of UV luminosity. Results: For the first time we detect a significant one-halo term in the correlation function at z˜5. The comoving correlation lengths and halo masses of LBGs are found to decrease with decreasing rest-frame UV-luminosity. No significant redshift evolution is found in either quantity. The typical halo mass hosting an LBG is M⪆1012~h-1~M_⊙ and the halos are typically occupied by less than one galaxy. Clustering segregation with UV luminosity is clearly observed in the dropout samples, however redshift evolution cannot clearly be disentangled from systematic uncertainties introduced by the redshift distributions. We study a range of possible redshift distributions to illustrate the effect of this choice. Spectroscopy of representative subsamples is required to make high-accuracy absolute measurements of high-z halo masses. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Based on zCOSMOS and VVDS observations carried out using the Very Large Telescope at the ESO Paranal Observatory under Programme IDs: LP175.A

  3. Dark matter axions and caustic rings

    SciTech Connect

    Sikivie, P.

    1997-11-01

    This report contains discussions on the following topics: the strong CP problem; dark matter axions; the cavity detector of galactic halo axions; and caustic rings in the density distribution of cold dark matter halos.

  4. Higher Education in Non-Standard Wage Contracts

    ERIC Educational Resources Information Center

    Rosti, Luisa; Chelli, Francesco

    2012-01-01

    Purpose: The purpose of this paper is to verify whether higher education increases the likelihood of young Italian workers moving from non-standard to standard wage contracts. Design/methodology/approach: The authors exploit a data set on labour market flows, produced by the Italian National Statistical Office, by interviewing about 85,000…

  5. CP-violation and non-standard interactions at the MOMENT

    NASA Astrophysics Data System (ADS)

    Bakhti, Pouya; Farzan, Yasaman

    2016-07-01

    To measure the last unknown 3 ν oscillation parameter ( δ), several long baseline neutrino experiments have been designed or proposed. Recently it has been shown that turning on neutral current Non-Standard Interactions (NSI) of neutrinos with matter can induce degeneracies that may even hinder the proposed state-of-the-art DUNE long baseline experiment from measuring the value of δ. We study how the result of the proposed MOMENT experiment with a baseline of 150 km and 200 MeV < E ν < 600 MeV can help to solve the degeneracy induced by NSI and determine the true value of δ.

  6. The Dependence of Subhalo Abundance on Halo Concentration

    NASA Astrophysics Data System (ADS)

    Mao, Yao-Yuan; Williamson, Marc; Wechsler, Risa H.

    2015-09-01

    Hierarchical structure formation implies that the number of subhalos within a dark matter halo depends not only on halo mass, but also on the formation history of the halo. This dependence on the formation history, which is highly correlated with halo concentration, can account for the super-Poissonian scatter in subhalo occupation at a fixed halo mass that has been previously measured in simulations. Here we propose a model to predict the subhalo abundance function for individual host halos that incorporates both halo mass and concentration. We combine results of cosmological simulations with a new suite of zoom-in simulations of Milky Way-mass halos to calibrate our model. We show that the model can successfully reproduce the mean and the scatter of subhalo occupation in these simulations. The implications of this correlation between subhalo abundance and halo concentration are further investigated. We also discuss cases in which inferences about halo properties can be affected if this correlation between subhalo abundance and halo concentration is ignored; in these cases, our model would give a more accurate inference. We propose that with future deep surveys, satellite occupation in the low-mass regime can be used to verify the existence of halo assembly bias.

  7. Can MACHOs probe the shape of the galaxy halo ?

    NASA Technical Reports Server (NTRS)

    Frieman, Joshua; Scoccimarro, Roman

    1994-01-01

    Microlensing searches in our galaxy have recently discovered several candidates in the direction of the Large Magellanic Cloud (LMC). We study the prospects for such searches to yield useful information about the flattening of the Galaxy dark matter halo, using a self-consistent oblate halo model and allowing for the possibility of misalignment between the disk and halo symmetry axes. The microlensing optical depth for the LMC, tau(LMC), depends sensitively on the disk-halo tilt angle in the Milky Way, as does the ratio tau(SMC)/tau(LMC). If the tilt angle is as large as 30 deg, a much larger spread in values for tau(LMC) is consistent with rotation curve constraints than previously thought. Disk-halo tilt and halo flattening do not significantly affect the massive compact halo object (MACHO) masses inferred from event durations.

  8. Separate universe consistency relation and calibration of halo bias

    NASA Astrophysics Data System (ADS)

    Li, Yin; Hu, Wayne; Takada, Masahiro

    2016-03-01

    The linear halo bias is the response of the dark matter halo number density to a long-wavelength fluctuation in the dark matter density. Using abundance matching between separate universe simulations which absorb the latter into a change in the background, we test the consistency relation between the change in a one-point function, the halo mass function, and a two-point function, the halo-matter cross-correlation in the long-wavelength limit. We find excellent agreement between the two at the 1%-2% level for average halo biases between 1 ≲b¯ 1≲4 and no statistically significant deviations at the 4%-5% level out to b¯1≈8 . The halo bias inferred assuming instead a universal mass function is significantly different and inaccurate at the 10% level or more. The separate universe technique provides a way of calibrating the linear halo bias efficiently for even highly biased rare halos in the Λ cold dark matter model. Observational violation of the consistency relation would indicate new physics, e.g. in the dark matter, dark energy, or primordial non-Gaussianity sectors.

  9. Non-standard Space Weather Products and Services from NOAA

    NASA Astrophysics Data System (ADS)

    Denig, W. F.; Viereck, R. A.

    2012-12-01

    The NOAA National Geophysical Data Center (NGDC) and Space Weather Prediction Center (SWPC) have developed and are continuing to develop a variety of "non-standard" data products for near real-time space weather applications. Core space weather services provided by SWPC include access to space environmental data from NOAA operational satellites and leveraged data from NASA and USAF assets. Core services also include operational space weather model results providing environmental specifications and forecasts. Non-standard products to be discussed include space weather services and applications that have either not yet reached operational maturity or are being released as beta-version test products. Included are the Forecasting Ionospheric Real-time Scintillation Tool (FIRST), the Ovation Prime Real-Time product, the Space Environment Anomaly Expert System Real Time (SEAESRT) and the PEople Empowered Product (PEEP). The status of these products, including how to access and provide comments, will be presented.

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

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    2016-04-01

    Observations of the nearby universe fail to locate about half of the normal matter (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.

  11. Halo formation and evolution: unification of structure and physical properties

    NASA Astrophysics Data System (ADS)

    Ernest, Allan D.; Collins, Matthew P.

    2016-08-01

    The assembly of matter in the universe proliferates a wide variety of halo structures, often with enigmatic consequences. Giant spiral galaxies, for example, contain both dark matter and hot gas, while dwarf spheroidal galaxies, with weaker gravity, contain much larger fractions of dark matter, but little gas. Globular clusters, superficially resembling these dwarf spheroidals, have little or no dark matter. Halo temperatures are also puzzling: hot cluster halos contain cooler galaxy halos; dwarf galaxies have no hot gas at all despite their similar internal processes. Another mystery is the origin of the gas that galaxies require to maintain their measured star formation rates (SFRs). We outline how gravitational quantum theory solves these problems, and enables baryons to function as weakly-interacting-massive-particles (WIMPs) in Lambda Cold Dark Matter (LCDM) theory. Significantly, these dark-baryon ensembles may also be consistent with primordial nucleosynthesis (BBN) and cosmic microwave background (CMB) anisotropies.

  12. Halo Microlensing and Dark Baryons

    NASA Astrophysics Data System (ADS)

    Crotts, A. P. S.

    1993-12-01

    (While Pierce lectures review past accomplishments, customarily, this talk concerns efforts which we have pursued for some years and which are now reaching fruition. We present elsewhere at this meeting results from research cited for the Prize.) Dark matter exists in the halos of spiral galaxies, and the least radical alternative for its identity is normal matter produced by primordial nucleosynthesis. This matter could easily be hidden in large, condensed objects. Paczynski pointed out in 1986 that if condensations of Galactic halo matter are sufficiently massive, they will produce detectable amplification of background starlight by gravitational lensing. Several groups recently reported possible detections of this effect after surveying large numbers of stars in the Galactic Bulge and LMC. The connection between these events and massive, dark halos is unclear and likely to remain so for some time, given the rate at which they are detected. Following Paczynski's realization, we stressed that a much higher event rate, a statistical control sample, sensitivity to a much broader mass range, and modulation of the predicted lensing rate with galactocentric distance can all be realized by a different experiment: observing the halo of M31 (and the Galaxy) using stars in M31. In some ways, M31 is a more difficult target than the LMC or the Bulge, given the faintness of its stars, but our observations in 1991 and 1993 indicate that these problems have been surmounted. We can detect stellar variability even under extremely crowded conditions like those in M31's inner disk, and can monitor a sufficient number of stars to study halo lensing. We present results from our initial survey which indicates that the required sensitivity can be reached to confirm or reject the hypothesis that sub-solar masses like those detected in our Galaxy make up the missing spiral galaxy mass. It is possible that we may use the data already obtained (and still being analyzed) to place

  13. Halo mass distribution reconstruction across the cosmic web

    NASA Astrophysics Data System (ADS)

    Zhao, Cheng; Kitaura, Francisco-Shu; Chuang, Chia-Hsun; Prada, Francisco; Yepes, Gustavo; Tao, Charling

    2015-08-01

    We study the relation between halo mass and its environment from a probabilistic perspective. We find that halo mass depends not only on local dark matter density, but also on non-local quantities such as the cosmic web environment and the halo-exclusion effect. Given these accurate relations, we have developed the HADRON-code (Halo mAss Distribution ReconstructiON), a technique which permits us to assign halo masses to a distribution of haloes in three-dimensional space. This can be applied to the fast production of mock galaxy catalogues, by assigning halo masses, and reproducing accurately the bias for different mass cuts. The resulting clustering of the halo populations agree well with that drawn from the BigMultiDark N-body simulation: the power spectra are within 1σ up to scales of k = 0.2 h Mpc-1, when using augmented Lagrangian perturbation theory based mock catalogues. Only the most massive haloes show a larger deviation. For these, we find evidence of the halo-exclusion effect. A clear improvement is achieved when assigning the highest masses to haloes with a minimum distance separation. We also compute the two- and three-point correlation functions, and find an excellent agreement with N-body results. Our work represents a quantitative application of the cosmic web classification. It can have further interesting applications in the multitracer analysis of the large-scale structure for future galaxy surveys.

  14. The Local Dark Matter

    SciTech Connect

    Helfer, H.L.

    2005-10-21

    The observations of the extended rotation curves of some galaxies provide important constraints upon the nature of the local dark matter present in the halos of these galaxies. Using these constraints, one can show that the halo dark matter cannot be some population of conventional astronomical objects and (most probably) cannot be a population of exotic non-interacting particles. We suggest that the halos can be regarded as large spatial fluctuations in a classic scalar field.

  15. The Impact of Stellar Feedback on the Structure, Size, and Morphology of Galaxies in Milky-Way-sized Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Agertz, Oscar; Kravtsov, Andrey V.

    2016-06-01

    We use cosmological zoom-in simulations of galaxy formation in a Milky-Way-sized halo started from identical initial conditions to investigate the evolution of galaxy sizes, baryon fractions, morphologies, and angular momenta in runs with different parameters of the star formation–feedback cycle. Our fiducial model with a high local star formation efficiency, which results in efficient feedback, produces a realistic late-type galaxy that matches the evolution of basic properties of late-type galaxies: stellar mass, disk size, morphology dominated by a kinematically cold disk, stellar and gas surface density profiles, and specific angular momentum. We argue that feedback’s role in this success is twofold: (1) removal of low angular momentum gas, and (2) maintaining a low disk-to-halo mass fraction, which suppresses disk instabilities that lead to angular momentum redistribution and a central concentration of baryons. However, our model with a low local star formation efficiency, but large energy input per supernova, chosen to produce a galaxy with a similar star formation history as our fiducial model, leads to a highly irregular galaxy with no kinematically cold component, overly extended stellar distribution, and low angular momentum. This indicates that only when feedback is allowed to become vigorous via locally efficient star formation in dense cold gas do resulting galaxy sizes, gas/stellar surface density profiles, and stellar disk angular momenta agree with observed z = 0 galaxies.

  16. A halo bias function measured deeply into voids without stochasticity

    NASA Astrophysics Data System (ADS)

    Neyrinck, Mark C.; Aragón-Calvo, Miguel A.; Jeong, Donghui; Wang, Xin

    2014-06-01

    We study the relationship between dark-matter haloes and matter in the MIP (multum in parvo) N-body simulation ensemble, which allows precision measurements of this relationship, even deeply into voids. What enables this is a lack of discreteness, stochasticity, and exclusion, achieved by averaging over hundreds of possible sets of initial small-scale modes, while holding fixed large-scale modes that give the cosmic web. We find (i) that dark-matter-halo formation is greatly suppressed in voids; there is an exponential downturn at low densities in the otherwise power-law matter-to-halo density bias function. Thus, the rarity of haloes in voids is akin to the rarity of the largest clusters, and their abundance is quite sensitive to cosmological parameters. The exponential downturn appears both in an excursion-set model, and in a model in which fluctuations evolve in voids as in an open universe with an effective Ωm proportional to a large-scale density. We also find that (ii) haloes typically populate the average halo-density field in a super-Poisson way, i.e. with a variance exceeding the mean; and (iii) the rank-order-Gaussianized halo and dark-matter fields are impressively similar in Fourier space. We compare both their power spectra and cross-correlation, supporting the conclusion that one is roughly a strictly increasing mapping of the other. The MIP ensemble especially reveals how halo abundance varies with `environmental' quantities beyond the local matter density; (iv) we find a visual suggestion that at fixed matter density, filaments are more populated by haloes than clusters.

  17. Updated constraints on non-standard neutrino interactions from Planck

    NASA Astrophysics Data System (ADS)

    Archidiacono, Maria; Hannestad, Steen

    2014-07-01

    We provide updated bounds on non-standard neutrino interactions based on data from the Planck satellite as well as auxiliary cosmological measurements. Two types of models are studied - A Fermi-like 4-point interaction and an interaction mediated by a light pseudoscalar - and we show that these two models are representative of models in which neutrinos either decouple or recouple in the early Universe. Current cosmological data constrain the effective 4-point coupling to be GX <= (0.06 GeV)-2, corresponding to GX <= 2.5 × 107 GF. For non-standard pseudoscalar interactions we set a limit on the diagonal elements of the dimensionless coupling matrix, gij, of gii <= 1.2 × 10-7. For the off-diagonal elements which induce neutrino decay the bound is significantly stronger, corresponding to gij <= 2.3 × 10-11(m/0.05 eV)-2, or a lifetime constraint of τ >= 1.2 × 109 s (m/0.05 eV)3 . This is currently the strongest known bound on this particular type of neutrino decay. We finally note that extremely strong neutrino self-interactions which completely suppress anisotropic stress over all of cosmic history are very highly disfavored by current data Δ χ2 ~ 104).

  18. On detecting halo assembly bias with galaxy populations

    NASA Astrophysics Data System (ADS)

    Lin, Yen-Ting; Mandelbaum, Rachel; Huang, Yun-Hsin; Huang, Hung-Jin; Dalal, Neal; Diemer, Benedikt; Kravtsov, Andrey

    2016-01-01

    The fact that the clustering and concentration of dark matter halos depend not only on their mass, but also the formation epoch, is a prominent, albeit subtle, feature of the cold dark matter structure formation theory, and is known as assembly bias. At low mass scales (~1012 Msun), early-forming halos are predicted to be more strongly clustered than the late-forming ones. In this study we aim to robustly detect the signature of assembly bias observationally, making use of formation time indicators of central galaxies in low mass halos as a proxy for the halo formation history. Weak gravitational lensing is employed to ensure our early- and late-forming halo samples have similar masses, and are free of contamination of satellites from more massive halos. For the two formation time indicators used (resolved star formation history and current specific star formation rate), we do not find convincing evidence of assembly bias. We attribute the lack of detection to the possibility that these indicators do not correlate well with the halo formation history, and suggest alternatives that should perform better for future studies. In addition, we have developed a method to constrain the probability distribution function of halo mass of a given galaxy sample, and also demonstrate that the abundance matching-based halo mass assignments to galaxy groups and clusters may be biased, likely due to interlopers from more massive galactic systems.

  19. The First Six Months of the LLNL-CfPA-MSSSO Search for Baryonic Dark Matter in the Galaxy's Halo via its Gravitational Microlensing Signature

    NASA Astrophysics Data System (ADS)

    Cook, K.; Alcock, C.; Allsman, R.; Axelrod, T.; Bennett, D.; Marshall, S.; Stubbs, C.; Griest, K.; Perlmutter, S.; Sutherland, W.; Freeman, K.; Peterson, B.; Quinn, P.; Rodgers, A.

    1992-12-01

    This collaboration, dubbed the MACHO Project (an acronym for MAssive Compact Halo Objects), has refurbished the 1.27-m, Great Melbourne Telescope at Mt. Stromlo and equipped it with a corrected {1°} FOV. The prime focus corrector yields a red and blue beam for simultaneous imaging in two passbands, 4500{ Angstroms}--6100{ Angstroms} and 6100{ Angstroms}--7900{ Angstroms}. Each beam is imaged by a 2x2 array of 2048x2048 pixel CCDs which are simultaneously read out from two amplifiers on each CCD. A 32 Megapixel dual-color image of 0.5 square degree is clocked directly into computer memory in less than 70 seconds. We are using this system to monitor more than 10(7) stars in the Magellanic Clouds for gravitational microlensing events and will soon monitor an additional 10(7) stars in the bulge of our galaxy. Image data goes directly into a reduction pipeline where photometry for stars in an image is determined and stored in a database. An early version of this pipeline has used a simple aperture photometry code and results from this will be presented. A more sophisticated PSF fitting photometry code is currently being installed in the pipeline and results should also be available at the meeting. The PSF fitting code has also been used to produce ~ 10(7) photometric measurements outside of the pipeline. This poster will present details of the instrumentation, data pipeline, observing conditions (weather and seeing), reductions and analyses for the first six months of dual-color observing. Eventually, we expect to be able to determine whether MACHOs are a significant component of the galactic halo in the mass range of \\(10^{-6} M_{\\sun} < M \\ {lower .5exhbox {\\: \\buildrel < \\over \\sim ;}} \\ 100 M_{\\sun}\\).

  20. 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.

  1. A Universal Model for Halo Concentrations

    NASA Astrophysics Data System (ADS)

    Diemer, Benedikt; Kravtsov, Andrey V.

    2015-01-01

    We present a numerical study of dark matter halo concentrations in ΛCDM and self-similar cosmologies. We show that the relation between concentration, c, and peak height, ν, exhibits the smallest deviations from universality if halo masses are defined with respect to the critical density of the universe. These deviations can be explained by the residual dependence of concentration on the local slope of the matter power spectrum, n, which affects both the normalization and shape of the c-ν relation. In particular, there is no well-defined floor in the concentration values. Instead, the minimum concentration depends on redshift: at fixed ν, halos at higher z experience steeper slopes n, and thus have lower minimum concentrations. We show that the concentrations in our simulations can be accurately described by a universal seven-parameter function of only ν and n. This model matches our ΛCDM results to <~ 5% accuracy up to z = 6, and matches scale-free Ωm = 1 models to <~ 15%. The model also reproduces the low concentration values of Earth-mass halos at z ≈ 30, and thus correctly extrapolates over 16 orders of magnitude in halo mass. The predictions of our model differ significantly from all models previously proposed in the literature at high masses and redshifts. Our model is in excellent agreement with recent lensing measurements of cluster concentrations.

  2. A ''LIGHT'', CENTRALLY CONCENTRATED MILKY WAY HALO?

    SciTech Connect

    Rashkov, Valery; Pillepich, Annalisa; Deason, Alis J.; Madau, Piero; Rockosi, Constance M.; Mayer, Lucio

    2013-08-20

    We discuss a novel approach to ''weighing'' the Milky Way (MW) dark matter halo, one that combines the latest samples of halo stars selected from the Sloan Digital Sky Survey (SDSS) with state of the art numerical simulations of MW analogs. The fully cosmological runs employed in the present study include ''Eris'', one of the highest resolution hydrodynamical simulations of the formation of a M{sub vir} = 8 Multiplication-Sign 10{sup 11} M{sub Sun} late-type spiral, and the dark-matter-only M{sub vir} = 1.7 Multiplication-Sign 10{sup 12} M{sub Sun} ''Via Lactea II'' (VLII) simulation. Eris provides an excellent laboratory for creating mock SDSS samples of tracer halo stars, and we successfully compare their density, velocity anisotropy, and radial velocity dispersion profiles with the observational data. Most mock SDSS realizations show the same ''cold veil'' recently observed in the distant stellar halo of the MW, with tracers as cold as {sigma}{sub los} Almost-Equal-To 50 km s{sup -1} between 100 and 150 kpc. Controlled experiments based on the integration of the spherical Jeans equation as well as a particle tagging technique applied to VLII show that a ''heavy'' M{sub vir} Almost-Equal-To 2 Multiplication-Sign 10{sup 12} M{sub Sun} realistic host produces a poor fit to the kinematic SDSS data. We argue that these results offer added evidence for a ''light'', centrally concentrated MW halo.

  3. A UNIVERSAL MODEL FOR HALO CONCENTRATIONS

    SciTech Connect

    Diemer, Benedikt; Kravtsov, Andrey V.

    2015-01-20

    We present a numerical study of dark matter halo concentrations in ΛCDM and self-similar cosmologies. We show that the relation between concentration, c, and peak height, ν, exhibits the smallest deviations from universality if halo masses are defined with respect to the critical density of the universe. These deviations can be explained by the residual dependence of concentration on the local slope of the matter power spectrum, n, which affects both the normalization and shape of the c-ν relation. In particular, there is no well-defined floor in the concentration values. Instead, the minimum concentration depends on redshift: at fixed ν, halos at higher z experience steeper slopes n, and thus have lower minimum concentrations. We show that the concentrations in our simulations can be accurately described by a universal seven-parameter function of only ν and n. This model matches our ΛCDM results to ≲ 5% accuracy up to z = 6, and matches scale-free Ω{sub m} = 1 models to ≲ 15%. The model also reproduces the low concentration values of Earth-mass halos at z ≈ 30, and thus correctly extrapolates over 16 orders of magnitude in halo mass. The predictions of our model differ significantly from all models previously proposed in the literature at high masses and redshifts. Our model is in excellent agreement with recent lensing measurements of cluster concentrations.

  4. Stellar halos: a rosetta stone for galaxy formation and cosmology

    NASA Astrophysics Data System (ADS)

    Inglis Read, Justin

    2015-08-01

    Stellar halos make up about a percent of the total stellar mass in galaxies. Yet their old age and long phase mixing times make them living fossil records of galactic history. In this talk, I review the latest simulations of structure formation in our standard Lambda Cold Dark Matter cosmology. I discuss the latest predictions for stellar halos and the relationship between the stellar halo light and the underlying dark matter. Finally, I discuss how these simulations compare to observations of the Milky Way and Andromeda and, ultimately, what this means for our cosmological model and the formation history of the Galaxy.

  5. Oscillation degeneracy in non-standard neutrino interactions

    NASA Astrophysics Data System (ADS)

    Wright, Warren

    2016-06-01

    The standard theory describing neutrino oscillations only uses the interactions predicted by the Standard Model of particle physics. However, there is plenty of room for non-standard interactions (NSI) to exist. This is because extra interactions are allowed by experimental error bars and even expected at some level from effective theory arguments. This research is focused on examining the phenomenological consequences of the new physics of NSI at large atmospheric neutrino detectors like IceCube DeepCore. Of particular focus are the degeneracies between and within the standard neutrino oscillation parameters and the NSI parameters. These degeneracies will be explored both analytically and numerically, and strategies to lift them will also be discussed. This research is largely based on [1].

  6. Proton affinity of several basic non-standard amino acids

    NASA Astrophysics Data System (ADS)

    Rožman, Marko

    2012-08-01

    The structures and absolute proton affinities of several arginine (2-amino-3-guanidinopropionic acid, 2-amino-4-guanidinobutyric acid, homoarginine, citrulline and canavanine), histidine (1-methylhistidine and 3-methylhistidine) and lysine (2,3-diaminopropanoic acid, 2,4-diaminobutanoic acid, ornithine, 5-hydroxylysine, canaline and thialysine) homologues and analogues have been estimated using composite G3MP2B3 computational protocol. For a majority of here studied non-standard amino acids the gas-phase proton affinities were established for the first time, while for the others obtained values are used to improve the accuracy of the computational and experimental proton affinities reported previously. In addition, structures and proton affinities are discussed in order to rationalize their biological activity.

  7. Non-standard isotope production and applications at Washington University

    NASA Astrophysics Data System (ADS)

    McCarthy, Timothy J.; McCarthy, Deborah W.; Laforest, Richard; Bigott, Heather M.; Wüst, Frank; Reichert, David E.; Lewis, Michael R.; Welch, Michael J.

    2001-07-01

    The positron emitting radionuclides, oxygen-15, nitrogen-13, carbon-11, and fluorine-18 have been produced at Washington University for many years utilizing two biomedical cyclotrons; a Cyclotron Corporation CS15 and a Japan Steel Works 16/8 cyclotron. In recent years we have become interested in the production of non-standard PET isotopes. We were initially interested in copper-64 production using the 64Ni(p,n)64Cu nuclear reaction, but now apply this technique to other positron emitting copper isotopes, copper-60 and copper-61. Copper-64 is being produced routinely and made available to other institutions. In 1999 over ten Curies of copper-64 were produced, making copper available to thirteen institutions, as well as research groups at Washington University. We are currently developing methods for the routine productions of other PET radioisotopes of interest, these include; bromine-76, bromine-77, iodine-124, gallium-66, and technetium-94m.

  8. THE EFFECTS OF HALO-TO-HALO VARIATION ON SUBSTRUCTURE LENSING

    SciTech Connect

    Chen, Jacqueline; Koushiappas, Savvas M.; Zentner, Andrew R. E-mail: koushiappas@brown.edu

    2011-11-10

    We explore the halo-to-halo variation of dark matter (DM) substructure in galaxy-sized DM halos, focusing on its implications for strongly gravitational lensed systems. We find that the median value for projected substructure mass fractions within projected radii of 3% of the host halo virial radius is approximately f{sub sub} Almost-Equal-To 0.25%, but that the variance is large with a 95 percentile range of 0 {<=} f{sub sub} {<=} 1%. We quantify possible effects of substructure on quadruply imaged lens systems using the cusp relation and the simple statistic, R{sub cusp}. We estimate that the probability of obtaining the large values of the R{sub cusp} which have been observed from substructure effects is roughly {approx}10{sup -3} to {approx}10{sup -2}. We consider a variety of possible correlations between host halo properties and substructure properties in order to probe possible sample biases. In particular, low-concentration host DM halos have more large substructures and give rise to large values of R{sub cusp} more often. However, there is no known observational bias that would drive observed quadruply imaged quasars to be produced by low-concentration lens halos. Finally, we show that the substructure mass fraction is a relatively reliable predictor of the value of R{sub cusp}.

  9. Updated constraints on non-standard neutrino interactions from Planck

    SciTech Connect

    Archidiacono, Maria; Hannestad, Steen E-mail: sth@phys.au.dk

    2014-07-01

    We provide updated bounds on non-standard neutrino interactions based on data from the Planck satellite as well as auxiliary cosmological measurements. Two types of models are studied - A Fermi-like 4-point interaction and an interaction mediated by a light pseudoscalar - and we show that these two models are representative of models in which neutrinos either decouple or recouple in the early Universe. Current cosmological data constrain the effective 4-point coupling to be G{sub X} ≤ (0.06 GeV){sup -2}, corresponding to G{sub X} ≤ 2.5 × 10{sup 7} G{sub F}. For non-standard pseudoscalar interactions we set a limit on the diagonal elements of the dimensionless coupling matrix, g{sub ij}, of g{sub ii} ≤ 1.2 × 10{sup -7}. For the off-diagonal elements which induce neutrino decay the bound is significantly stronger, corresponding to g{sub ij} ≤ 2.3 × 10{sup -11}(m/0.05 eV){sup -2}, or a lifetime constraint of τ ≥ 1.2 × 10{sup 9} s (m/0.05 eV){sup 3} . This is currently the strongest known bound on this particular type of neutrino decay. We finally note that extremely strong neutrino self-interactions which completely suppress anisotropic stress over all of cosmic history are very highly disfavored by current data Δ χ{sup 2} ∼ 10{sup 4})

  10. Non-standard Hubbard models in optical lattices: a review

    NASA Astrophysics Data System (ADS)

    Dutta, Omjyoti; Gajda, Mariusz; Hauke, Philipp; Lewenstein, Maciej; Lühmann, Dirk-Sören; Malomed, Boris A.; Sowiński, Tomasz; Zakrzewski, Jakub

    2015-06-01

    Originally, the Hubbard model was derived for describing the behavior of strongly correlated electrons in solids. However, for over a decade now, variations of it have also routinely been implemented with ultracold atoms in optical lattices, allowing their study in a clean, essentially defect-free environment. Here, we review some of the vast literature on this subject, with a focus on more recent non-standard forms of the Hubbard model. After giving an introduction to standard (fermionic and bosonic) Hubbard models, we discuss briefly common models for mixtures, as well as the so-called extended Bose-Hubbard models, that include interactions between neighboring sites, next-neighbor sites, and so on. The main part of the review discusses the importance of additional terms appearing when refining the tight-binding approximation for the original physical Hamiltonian. Even when restricting the models to the lowest Bloch band is justified, the standard approach neglects the density-induced tunneling (which has the same origin as the usual on-site interaction). The importance of these contributions is discussed for both contact and dipolar interactions. For sufficiently strong interactions, the effects related to higher Bloch bands also become important even for deep optical lattices. Different approaches that aim at incorporating these effects, mainly via dressing the basis, Wannier functions with interactions, leading to effective, density-dependent Hubbard-type models, are reviewed. We discuss also examples of Hubbard-like models that explicitly involve higher p orbitals, as well as models that dynamically couple spin and orbital degrees of freedom. Finally, we review mean-field nonlinear Schrödinger models of the Salerno type that share with the non-standard Hubbard models nonlinear coupling between the adjacent sites. In that part, discrete solitons are the main subject of consideration. We conclude by listing some open problems, to be addressed in the future.

  11. Non-standard Hubbard models in optical lattices: a review.

    PubMed

    Dutta, Omjyoti; Gajda, Mariusz; Hauke, Philipp; Lewenstein, Maciej; Lühmann, Dirk-Sören; Malomed, Boris A; Sowiński, Tomasz; Zakrzewski, Jakub

    2015-06-01

    Originally, the Hubbard model was derived for describing the behavior of strongly correlated electrons in solids. However, for over a decade now, variations of it have also routinely been implemented with ultracold atoms in optical lattices, allowing their study in a clean, essentially defect-free environment. Here, we review some of the vast literature on this subject, with a focus on more recent non-standard forms of the Hubbard model. After giving an introduction to standard (fermionic and bosonic) Hubbard models, we discuss briefly common models for mixtures, as well as the so-called extended Bose-Hubbard models, that include interactions between neighboring sites, next-neighbor sites, and so on. The main part of the review discusses the importance of additional terms appearing when refining the tight-binding approximation for the original physical Hamiltonian. Even when restricting the models to the lowest Bloch band is justified, the standard approach neglects the density-induced tunneling (which has the same origin as the usual on-site interaction). The importance of these contributions is discussed for both contact and dipolar interactions. For sufficiently strong interactions, the effects related to higher Bloch bands also become important even for deep optical lattices. Different approaches that aim at incorporating these effects, mainly via dressing the basis, Wannier functions with interactions, leading to effective, density-dependent Hubbard-type models, are reviewed. We discuss also examples of Hubbard-like models that explicitly involve higher p orbitals, as well as models that dynamically couple spin and orbital degrees of freedom. Finally, we review mean-field nonlinear Schrödinger models of the Salerno type that share with the non-standard Hubbard models nonlinear coupling between the adjacent sites. In that part, discrete solitons are the main subject of consideration. We conclude by listing some open problems, to be addressed in the future

  12. Is the Milky Way's Hot Halo Convectively Unstable?

    NASA Astrophysics Data System (ADS)

    Henley, David B.; Shelton, Robin L.

    2014-03-01

    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. Using 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.

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

    SciTech Connect

    Henley, David B.; Shelton, Robin L.

    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. Using 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.

  14. Probing the CP violation signal at DUNE in the presence of non-standard neutrino interactions

    NASA Astrophysics Data System (ADS)

    Masud, Mehedi; Chatterjee, Animesh; Mehta, Poonam

    2016-09-01

    We discuss the impact of non-standard neutrino matter interactions (NSIs) in propagation on the determination of the CP phase in the context of long baseline accelerator experiments such as the Deep Underground Neutrino Experiment (DUNE). DUNE will mainly address the issue of CP violation in the leptonic sector. Here we study the role of NSI and its impact on observing the CP violation signal at DUNE. We consider two scenarios of oscillation with three active neutrinos in the absence and presence of NSI. We elucidate the importance of ruling out subdominant new physics effects introduced by NSI in inferring the CP violation signal at DUNE by considering NSI terms collectively as well as by exploiting the non-trivial interplay of moduli and phases of the NSI terms. We demonstrate the existence of NSI-SI degeneracies which need to be eliminated in reliable manner in order to make conclusive statements about the CP phase.

  15. The halo model in a massive neutrino cosmology

    SciTech Connect

    Massara, Elena; Villaescusa-Navarro, Francisco; Viel, Matteo E-mail: villaescusa@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 in 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.

  16. Rockstar: Phase-space halo finder

    NASA Astrophysics Data System (ADS)

    Behroozi, Peter; Wechsler, Risa; Wu, Hao-Yi

    2012-10-01

    Rockstar (Robust Overdensity Calculation using K-Space Topologically Adaptive Refinement) identifies dark matter halos, substructure, and tidal features. The approach is based on adaptive hierarchical refinement of friends-of-friends groups in six phase-space dimensions and one time dimension, which allows for robust (grid-independent, shape-independent, and noise-resilient) tracking of substructure. Our method is massively parallel (up to 10^5 CPUs) and runs on the largest current simulations (>10^10 particles) with high efficiency (10 CPU hours and 60 gigabytes of memory required per billion particles analyzed). Rockstar offers significant improvement in substructure recovery as compared to several other halo finders.

  17. 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

  18. On Detecting Halo Assembly Bias with Galaxy Populations

    NASA Astrophysics Data System (ADS)

    Lin, Yen-Ting; Mandelbaum, Rachel; Huang, Yun-Hsin; Huang, Hung-Jin; Dalal, Neal; Diemer, Benedikt; Jian, Hung-Yu; Kravtsov, Andrey

    2016-03-01

    The fact that the clustering of dark matter halos depends not only on their mass, but also the formation epoch is a prominent, albeit subtle, feature of the cold dark matter structure formation theory and is known as assembly bias. At low-mass scales (˜ {10}12 {h}-1 {M}⊙ ), early-forming halos are predicted to be more strongly clustered than the late-forming ones. In this study, we aim to robustly detect the signature of assembly bias observationally, making use of formation time indicators of central galaxies in low-mass halos as a proxy for the halo formation history. Weak gravitational lensing is employed to ensure our early- and late-forming halo samples have similar masses, and are free of contamination of satellites from more massive halos. For the two formation time indicators used (resolved star formation history and current specific star formation rate), we do not find convincing evidence of assembly bias. For a pair of early- and late-forming galaxy samples with mean mass {M}200c≈ 9× {10}11 {h}-1 {M}⊙ , the relative bias is 1.00 ± 0.12. We attribute the lack of detection to the possibilities that either the current measurements of these indicators are too noisy, or they do not correlate well with the halo formation history. Alternative proxies for the halo formation history that should perform better are suggested for future studies.

  19. Halo-independent direct detection analyses without mass assumptions

    NASA Astrophysics Data System (ADS)

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

    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 mχ-σn plane. Recently methods which are independent of the DM halo velocity distribution have been developed which present results in the vmin-tilde 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 vmin to nuclear recoil momentum (pR), 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(pR). The entire family of conventional halo-independent tilde g(vmin) plots for all DM masses are directly found from the single tilde h(pR) plot through a simple rescaling of axes. By considering results in tilde h(pR) 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(vmin) 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.

  20. Halo-independent direct detection analyses without mass assumptions

    SciTech Connect

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

    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{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 momentum (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-til-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.

  1. Halo-independent direct detection analyses without mass assumptions

    SciTech Connect

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

    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 mχ – σn plane. Recently methods which are independent of the DM halo velocity distribution have been developed which present results in the vmin – 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 vmin to nuclear recoil momentum (pR), 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(pR). The entire family of conventional halo-independent tilde g~(vmin) plots for all DM masses are directly found from the single tilde h~(pR) plot through a simple rescaling of axes. By considering results in tildeh~(pR) 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~(vmin) 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.

  2. Halo-independent direct detection analyses without mass assumptions

    DOE PAGESBeta

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

    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 mχ – σn plane. Recently methods which are independent of the DM halo velocity distribution have been developed which present results in the vmin – 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 vmin to nuclear recoil momentum (pR),more » 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(pR). The entire family of conventional halo-independent tilde g~(vmin) plots for all DM masses are directly found from the single tilde h~(pR) plot through a simple rescaling of axes. By considering results in tildeh~(pR) 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~(vmin) 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

  3. Structure of relativistic accretion disk with non-standard model

    NASA Astrophysics Data System (ADS)

    Khesali, A. R.; Salahshoor, K.

    2016-07-01

    The structure of stationary, axisymmetric advection-dominated accretion disk (ADAF) around rotating black hole, using non-standard model, was examined. In this model, the transport efficiency of the angular momentum α was dependent on the magnetic Prandtl number α ∝ Pm^{δ } . The full relativistic shear stress recently obtained by a new manner, was used. By considering black hole spin and Prandtl number instantaneously, the structure of ADAFs was changed in inner and outer region of the disk. It was discovered that the accretion flow was denser and hotter in the inner region, due to the black hole spin, and in the outer region, due to the presence of Prandtl parameter. Inasmuch as the rotation of the black hole affected the transport efficiency of angular momentum in parts of the disk very close to the even horizon, then in these regions, the viscosity depended on the rotation of black hole. Also, it was discovered that the effect of the black hole spin on the structure of the disk was related to the presence of Prandtl parameter.

  4. Tokamak halo currents

    SciTech Connect

    Boozer, Allen H.

    2013-08-15

    A halo current flows for part of its path through the plasma edge and for part through the chamber walls and 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. Two discordant constraints are central to the theory: (1) Halo currents must produce the magnetic field distribution required to maintain plasma force balance—a distribution that depends on the two angular coordinates of a torus. (2) Halo currents must flow along the magnetic field lines in the plasma, which implies a dependence on a linear combination of the two angular coordinates—only one angular coordinate is free. The physics basis of these two constraints is explained as is their application to the calculation of the properties of halo currents, such as their broad toroidal spectrum. Existing codes could be used to (1) provide detailed comparisons with experiments to validate that the critical elements of physics are adequately included, (2) allow more complete predictions for future machines such as ITER, and (3) design shunts and resistive elements to ensure halo currents follow paths that are the least damaging to the machine. The physics of halo currents implies that it may be possible to feedback stabilize resistive wall modes beyond the ideal-wall limit.

  5. Modelling galactic conformity with the colour-halo age relation in the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Bray, Aaron D.; Pillepich, Annalisa; Sales, Laura V.; Zhu, Emily; Genel, Shy; Rodriguez-Gomez, Vicente; Torrey, Paul; Nelson, Dylan; Vogelsberger, Mark; Springel, Volker; Eisenstein, Daniel J.; Hernquist, Lars

    2016-01-01

    Comparisons between observational surveys and galaxy formation models find that dark matter haloes' mass can largely explain their galaxies' stellar mass. However, it remains uncertain whether additional environmental variables, known as assembly bias, are necessary to explain other galaxy properties. We use the Illustris simulation to investigate the role of assembly bias in producing galactic conformity by considering 18 000 galaxies with Mstellar > 2 × 109 M⊙. We find a significant signal of galactic conformity: out to distances of about 10 Mpc, the mean red fraction of galaxies around redder galaxies is higher than around bluer galaxies at fixed stellar mass. Dark matter haloes exhibit an analogous conformity signal, in which the fraction of haloes formed at earlier times (old haloes) is higher around old haloes than around younger ones at fixed halo mass. A plausible interpretation of galactic conformity is the combination of the halo conformity signal with the galaxy colour-halo age relation: at fixed stellar mass, particularly towards the low-mass end, Illustris' galaxy colours correlate with halo age, with the reddest galaxies (often satellites) preferentially found in the oldest haloes. We explain the galactic conformity effect with a simple semi-empirical model, assigning stellar mass via halo mass (abundance matching) and galaxy colour via halo age (age matching). Regarding comparison to observations, we conclude that the adopted selection/isolation criteria, projection effects, and stacking techniques can have a significant impact on the measured amplitude of the conformity signal.

  6. Using accurate phase space coordinates of ~100,00 halo field stars to constrain the Milky Way halo

    NASA Astrophysics Data System (ADS)

    Valluri, Monica

    2015-08-01

    The current cosmological paradigm predicts that dark matter halos are triaxial overall, but oblate in regions where baryons dominate. However recent measurements of the shape of the Milky Way dark matter halo find it to be very triaxial with a shape and orientation that are significantly at odds with theoretical predictions. The ESA’s Gaia satellite will soon map the entire Milky Way giving us six phase-space coordinates, ages and abundances for hundreds of thousands of halo stars. I will report progress on a new code based on the Schwarzschild orbit superposition method and orbital frequency mapping, to determine the global shape of the Milky Way's dark matter halo using field stars from Gaia. This technique will simultaneously yield the self-consistent phase-space distribution function of the stellar halo in the inner 20-30kpc region. Detailed analysis of correlations between the chemical abundances, ages and orbits of halo stars in this distribution function will enable us to extract clues to the formation history of the Milky Way that are encoded in orbital properties of halo stars.

  7. ASSEMBLY OF THE OUTER GALACTIC STELLAR HALO IN THE HIERARCHICAL MODEL

    SciTech Connect

    Murante, Giuseppe; Curir, Anna; Poglio, Eva; Villalobos, Alvaro E-mail: curir@oato.inaf.i E-mail: villalobos@oats.inaf.i

    2010-06-20

    We provide a set of numerical N-body simulations for studying the formation of the outer Milky Ways' stellar halo through accretion events. After simulating minor mergers of prograde and retrograde orbiting satellite halos with a dark matter main halo, we analyze the signal left by satellite stars in the rotation velocity distribution. The aim is to explore the orbital conditions where a retrograde signal in the outer part of the halo can be obtained, in order to give a possible explanation of the observed rotational properties of the Milky Way stellar halo. Our results show that, for satellites more massive than {approx}1/40 of the main halo, the dynamical friction has a fundamental role in assembling the final velocity distributions resulting from different orbits and that retrograde satellites moving on low-inclination orbits deposit more stars in the outer halo regions and therefore can produce the counter-rotating behavior observed in the outer Milky Way halo.

  8. The Impact of Theoretical Uncertainties in the Halo Mass Function and Halo

    SciTech Connect

    Wu, Hao-Yi; Zentner, Andrew R.; Wechsler, Risa H.; /KIPAC, Menlo Park /SLAC /Pittsburgh U. /KIPAC, Menlo Park /SLAC

    2010-06-04

    We study the impact of theoretical uncertainty in the dark matter halo mass function and halo bias on dark energy constraints from imminent galaxy cluster surveys. We find that for an optical cluster survey like the Dark Energy Survey, the accuracy required on the predicted halo mass function to make it an insignificant source of error on dark energy parameters is {approx}1%. The analogous requirement on the predicted halo bias is less stringent ({approx}5%), particularly if the observable-mass distribution can be well constrained by other means. These requirements depend upon survey area but are relatively insensitive to survey depth. The most stringent requirements are likely to come from a survey over a significant fraction of the sky that aims to observe clusters down to relatively low mass, M{sub th}{approx} 10{sup 13.7} h{sup -1} M{sub sun}; for such a survey, the mass function and halo bias must be predicted to accuracies of {approx}0.5% and {approx}1%, respectively. These accuracies represent a limit on the practical need to calibrate ever more accurate halo mass and bias functions. We find that improving predictions for the mass function in the low-redshift and low-mass regimes is the most effective way to improve dark energy constraints.

  9. Cosmology with massive neutrinos II: on the universality of the halo mass function and bias

    NASA Astrophysics Data System (ADS)

    Castorina, Emanuele; Sefusatti, Emiliano; Sheth, Ravi K.; Villaescusa-Navarro, Francisco; Viel, Matteo

    2014-02-01

    We use a large suite of N-body simulations to study departures from universality in halo abundances and clustering in cosmologies with non-vanishing neutrino masses. To this end, we study how the halo mass function and halo bias factors depend on the scaling variable σ2(M,z), the variance of the initial matter fluctuation field, rather than on halo mass M and redshift z themselves. We show that using the variance of the cold dark matter rather than the total mass field, i.e., σ2cdm(M,z) rather than σ2m(M,z), yields more universal results. Analysis of halo bias yields similar conclusions: when large-scale halo bias is defined with respect to the cold dark matter power spectrum, the result is both more universal, and less scale- or k-dependent. These results are used extensively in Papers I and III of this series.

  10. Study of fusion probabilities with halo nuclei using different proximity based potentials

    NASA Astrophysics Data System (ADS)

    Kumari, Raj

    2013-11-01

    We study fusion of halo nuclei with heavy targets using proximity based potentials due to Aage Winther (AW) 95, Bass 80 and Proximity 2010. In order to consider the extended matter distribution of halo nuclei, the nuclei radii borrowed from cross section measurements are included in these potentials. Our study reveals that the barrier heights are effectively reduced and fusion cross sections are appreciably enhanced by including extended radii of these nuclei. We also find that the extended sizes of halos contribute towards enhancement of fusion probabilities in case of proton halo nuclei, but, contribute to transfer or break-up process rather than fusion yield in case of neutron halo nuclei.

  11. Non-Gaussian halo mass function and non-spherical halo collapse: theory vs. simulations

    SciTech Connect

    Achitouv, Ixandra E.; Corasaniti, Pier Stefano E-mail: Pier-Stefano.Corasaniti@obspm.fr

    2012-02-01

    The mass distribution of dark matter halos is a sensitive probe of primordial non-Gaussianity (NG). We derive an analytical formula of the halo mass function by perturbatively computing excursion set path-integrals for a non-Gaussian density field with non-vanishing skewness, f{sub NL}. We assume a stochastic barrier model which captures the main features of the ellipsoidal collapse of halos. Contrary to previous results based on extensions of the Press-Schechter formalism to NG initial conditions, we find that the non-spherical collapse of halos directly alter the signature of primordial NG. This points toward a potential degeneracy between the effect of primordial non-Gaussianity and that of non-linear halo collapse. The inferred mass function is found to be in remarkable agreement with N-body simulations of NG local type. Deviations are well within numerical uncertainties for all values of f{sub NL}{sup loc} in the range of validity of the perturbative calculation (|f{sub nl}{sup loc}|∼<200). Moreover, the comparison with simulation results suggests that for |f{sub NL}|∼>30 the non-linear collapse of halos, as described by our barrier model, strongly deviates from that of Gaussian initial conditions. This is not surprising since the effect of non-linear gravitational processes may be altered by initially large NG. Hence, in the lack of prior theoretical knowledge, halo collapse model parameters should be included in statistical halo mass function data analysis which aim to constrain the signature of primordial NG.

  12. 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.

  13. Sterile Neutrinos in Non-Standard Cosmologies and Particle Models

    NASA Astrophysics Data System (ADS)

    Osoba, Efunwande

    2010-12-01

    The discovery of neutrino masses suggests that the Standard Model should be supplemented with new gauge-singlet fermions, often called sterile neutrinos. These sterile neutrinos can shed new light on open questions in cosmology. I will highlight some interesting contributions that sterile neutrinos bring to the understanding of cosmology. In this dissertation, I will show a novel way in which sterile neutrinos could be a dark matter candidate in the form of "Inert-Sterile" neutrinos. In usual particle models, sterile neutrinos can account for the dark matter of the Universe only if they have niasses in the keV range and are warm dark matter. Stringent cosmological and astrophysical bounds, in particular imposed by X-ray observations, apply to them. I will point out that in a particular variation of the Inert Doublet Model, sterile neutrinos can account for the dark matter in the Universe and may be either cold or warm dark matter candidates, even for masses much larger than the keV range. These "Inert-Sterile" neutrinos, produced non-thermally in the early Universe, would be stable and have very small couplings to Standard Model particles, rendering very difficult their detection in either direct or indirect dark matter searches. They could be, in principle, revealed in colliders by discovering other particles in the model. I also show how the existence of the sterile neutrino may force us to rethink the standard cosmology. It is commonly assumed that the cosmological and astrophysical bounds on the mixings of sterile with active neutrinos are much more stringent than those obtained from laboratory measurements. In this dissertation, I show that in scenarios with a very low reheating temperature at the end of (the last episode of) inflation or entropy creation, the abundance of heavy (> 1 MeV) sterile neutrinos becomes largely suppressed with respect to that obtained within the standard framework. Thus, in this case cosmological bounds become much less stringent

  14. Spherical collapse and halo mass function in the symmetron model

    NASA Astrophysics Data System (ADS)

    Taddei, Laura; Catena, Riccardo; Pietroni, Massimo

    2014-01-01

    We study the gravitational clustering of spherically symmetric overdensities and the statistics of the resulting dark matter halos in the "symmetron model," in which a new long range force is mediated by a Z2 symmetric scalar field. Depending on the initial radius of the overdensity, we identify two distinct regimes: for small initial radii the symmetron mediated force affects the spherical collapse at all redshifts; for initial radii larger than some critical size this force vanishes before collapse because of the symmetron screening mechanism. As a consequence, halos with initial radii smaller than some critical value collapse earlier than in the ΛCDM and statistically tend to form more massive dark matter halos. Regarding the halo mass function of these objects, we observe departures from standard ΛCDM predictions at the few percent level. The formalism developed here can be easily applied to other models where fifth forces participate to the dynamics of the gravitational collapse.

  15. MASS-DEPENDENT BARYON ACOUSTIC OSCILLATION SIGNAL AND HALO BIAS

    SciTech Connect

    Wang Qiao; Zhan Hu

    2013-05-10

    We characterize the baryon acoustic oscillations (BAO) feature in halo two-point statistics using N-body simulations. We find that nonlinear damping of the BAO signal is less severe for halos in the mass range we investigate than for dark matter. The amount of damping depends weakly on the halo mass. The correlation functions show a mass-dependent drop of the halo clustering bias below roughly 90 h {sup -1} Mpc, which coincides with the scale of the BAO trough. The drop of bias is 4% for halos with mass M > 10{sup 14} h {sup -1} M{sub Sun} and reduces to roughly 2% for halos with mass M > 10{sup 13} h {sup -1} M{sub Sun }. In contrast, halo biases in simulations without BAO change more smoothly around 90 h {sup -1} Mpc. In Fourier space, the bias of M > 10{sup 14} h {sup -1} M{sub Sun} halos decreases smoothly by 11% from wavenumber k = 0.012 h Mpc{sup -1} to 0.2 h Mpc{sup -1}, whereas that of M > 10{sup 13} h {sup -1} M{sub Sun} halos decreases by less than 4% over the same range. By comparing the halo biases in pairs of otherwise identical simulations, one with and the other without BAO, we also observe a modulation of the halo bias. These results suggest that precise calibrations of the mass-dependent BAO signal and scale-dependent bias on large scales would be needed for interpreting precise measurements of the two-point statistics of clusters or massive galaxies in the future.

  16. Non-standard D region usage by human TCRB sequences

    SciTech Connect

    Bowman, S.J.; Lanchbury, J.S.

    1996-06-01

    T-cell receptor P (TCRB) chain variability is primarily created by a specific process of rearrangement of three sets of gene segments, V D, and J regions, with deletion of the intervening DNA. This process utilizes one of at least 51 TCRBV gene segments, downstream of which are two clusters of D, J, and C region genes. The TCRBC1 cluster contains a TCRBD1 (DB1) gene, six TCRBJ1 genes and the TCRBC1 (CB1) gene. The TCRBC2 cluster is similar, with a TCRBD2 (DB2) gene, seven TCRBJ2 genes, and the TCRBC2 (CB2) gene. The TCRBD genes are unusual in that they can be translated in all three reading frames. The region between the V and J region segments (the junctional region) shows the greatest sequence variability and there is good evidence that this region contacts the major histocompatibility complex peptide complex. Complexity at the V-D and D-J junctions is enhanced by exonuclease activity, the addition of a variable number of template-independent N nucleotides by terminal deoxynucleotidyl transferase, and by P nucleotide addition by a DNA polymerase. As a result of these processes and the sequence similarity between the germline TCRBD1 and TCRBD2 segments, it is not always possible to clearly assign TCRBD gene segment usage to either TCRBD1 or TCRBD2. Where TCRBD1 is used, {open_quotes}standard{close_quotes} downstream rearrangement can occur either to the TCRBJ1-CB1 cluster or the TCRBJ2-CB2 cluster. Only the TCRBJ2-CB2 cluster is downstream of TCRBD2, and hence is generally utilized in sequences containing TCRBD2. In the TCRD locus, however, multiple TCRDD segment usage is not uncommon. Sequences have also been reported for the TCRB locus in which both TCRBD1 and TCRBD2 were used in a single sequence, and more recently, TCRBD2 - TCRBJ1, and occasional TCRBD2 - TCRBD1 - TCRBJ1 and TCRBD1 - TCRBD2 - TCRBJ1 {open_quotes}non-standard{close_quotes} rearrangements have been reported. 11 refs., 1 fig.

  17. The chosen few: the low-mass haloes that host faint galaxies

    NASA Astrophysics Data System (ADS)

    Sawala, Till; Frenk, Carlos S.; Fattahi, Azadeh; Navarro, Julio F.; Theuns, Tom; Bower, Richard G.; Crain, Robert A.; Furlong, Michelle; Jenkins, Adrian; Schaller, Matthieu; Schaye, Joop

    2016-02-01

    Since reionization prevents star formation in most haloes less massive than 3 × 109 M⊙, dwarf galaxies only populate a fraction of existing dark matter haloes. We use hydrodynamic cosmological simulations of the Local Group to study the discriminating factors for galaxy formation in the early Universe and connect them to the present-day properties of galaxies and haloes. A combination of selection effects related to reionization, and the subsequent evolution of haloes in different environments, introduces strong biases between the population of haloes that host dwarf galaxies, and the total halo population. Haloes that host galaxies formed earlier and are more concentrated. In addition, haloes more affected by tidal stripping are more likely to host a galaxy for a given mass or maximum circular velocity, vmax, today. Consequently, satellite haloes are populated more frequently than field haloes, and satellite haloes of 108-109 M⊙ or vmax of 12-20 km s-1, compatible with stellar kinematics of Local Group dwarf spheroidals, have experienced a greater than average reduction in both mass and vmax after infall. They are on closer, more radial orbits with higher infall velocities and earlier infall times. Together, these effects make dwarf galaxies highly biased tracers of the underlying dark matter distribution.

  18. The gamma-ray-flux PDF from galactic halo substructure

    NASA Astrophysics Data System (ADS)

    Lee, Samuel K.; Ando, Shin'ichiro; Kamionkowski, Marc

    2009-07-01

    One of the targets of the recently launched Fermi Gamma-ray Space Telescope is a diffuse gamma-ray background from dark-matter annihilation or decay in the Galactic halo. N-body simulations and theoretical arguments suggest that the dark matter in the Galactic halo may be clumped into substructure, rather than smoothly distributed. Here we propose the gamma-ray-flux probability distribution function (PDF) as a probe of substructure in the Galactic halo. We calculate this PDF for a phenomenological model of halo substructure and determine the regions of the substructure parameter space in which the PDF may be distinguished from the PDF for a smooth distribution of dark matter. In principle, the PDF allows a statistical detection of substructure, even if individual halos cannot be detected. It may also allow detection of substructure on the smallest microhalo mass scales, ~ M⊕, for weakly-interacting massive particles (WIMPs). Furthermore, it may also provide a method to measure the substructure mass function. However, an analysis that assumes a typical halo substructure model and a conservative estimate of the diffuse background suggests that the substructure PDF may not be detectable in the lifespan of Fermi in the specific case that the WIMP is a neutralino. Nevertheless, for a large range of substructure, WIMP annihilation, and diffuse background models, PDF analysis may provide a clear signature of substructure.

  19. HOW WELL DO COSMOLOGICAL SIMULATIONS REPRODUCE INDIVIDUAL HALO PROPERTIES?

    SciTech Connect

    Trenti, Michele; Smith, Britton D.; Hallman, Eric J.; Skillman, Samuel W.; Shull, J. Michael

    2010-03-10

    Cosmological simulations of galaxy formation often rely on prescriptions for star formation and feedback that depend on halo properties such as halo mass, central overdensity, and virial temperature. In this paper, we address the convergence of individual halo properties, based on their number of particles N, focusing, in particular, on the mass of halos near the resolution limit of a simulation. While it has been established that the halo mass function is sampled on average down to N {approx} 20-30 particles, we show that individual halo properties exhibit significant scatter, and some systematic biases, as one approaches the resolution limit. We carry out a series of cosmological simulations using the Gadget2 and Enzo codes with N{sub p} = 64{sup 3} to N{sub p} = 1024{sup 3} total particles, keeping the same large-scale structure in the simulation box. We consider boxes of small (l{sub box} = 8 Mpc h {sup -1}), medium (l{sub box} = 64 Mpc h {sup -1}), and large (l{sub box} = 512 Mpc h {sup -1}) size to probe different halo masses and formation redshifts. We cross-identify dark matter halos in boxes at different resolutions and measure the scatter in their properties. The uncertainty in the mass of single halos depends on the number of particles (scaling approximately as N {sup -1/3}), but the rarer the density peak, the more robust its identification. The virial radius of halos is very stable and can be measured without bias for halos with N {approx}> 30. In contrast, the average density within a sphere containing 25% of the total halo mass is severely underestimated (by more than a factor 2) and the halo spin is moderately overestimated for N {approx}< 100. If sub-grid physics is implemented upon a cosmological simulation, we recommend that rare halos ({approx}3sigma peaks) be resolved with N {approx}> 100 particles and common halos ({approx}1sigma peaks) with N {approx}> 400 particles to avoid excessive numerical noise and possible systematic biases in the

  20. PARAMETERS FOR QUANTIFYING BEAM HALO

    SciTech Connect

    C.K. ALLEN; T.P. WANGLER

    2001-06-01

    Two different parameters for the quantitative description of beam halo are introduced, both based on moments of the particle distribution. One parameter is a measure of spatial halo formation and has been defined previously by Wangler and Crandall [3], termed the profile parameter. The second parameter relies on kinematic invariants to quantify halo formation in phase space; we call it the halo parameter. The profile parameter can be computed from experimental beam profile data. The halo parameter provides a theoretically more complete description of halo in phase space, but is difficult to obtain experimentally.

  1. Remarks on Several Non-standard Location Methods

    NASA Astrophysics Data System (ADS)

    Jih, R.

    2004-05-01

    In this study, several non-standard location procedures are reviewed, contrasted, and compared. Though independently developed, two methods among those been tested, the "Induced Perpendicular Bisector" [IPB] (or,equivalently, the "Yin Zhong Zian" [YZX] in Chinese) method and Jih's (PEPI, 1999) "J0" method, appear to be extremely similar in concept. For several decades, i.e., since before the advent of digital computers, Asian seismic network operators have been locating earthquakes by triangulation using the IPB technique. In the ideal case where two seismographs happen to report identical arrival times of the same seismic phase, then under the assumption of a uniform earth structure, the hypocenter should lie on the perpendicular bisector of the line segment (great circle) which connects these two specific seismographs. Depending on the epicentral distances, the perpendicular bisector itself could be a great circle along the Earth's surface or a normal section cutting through the Earth. If two or more such perpendicular bisectors are available, then the hypocenter or epicenter can be determined via triangulation. The challenge lies in how the perpendicular bisector is derived for the more general situation when arrival times vary from station to station, which is more typically the case. An advantage of the technique is that it can be used when waveform data are not available, thus rendering techniques based on full waveforms (such as correlation analysis, polarization analysis and frequency-wavenumber [FK] technique) not applicable. The so-called YZX algorithm, is a variation of IPB procedure, in which one computes an IPB (via interpolation) for each group of three seismographs. Also relying on azimuth triangulation for seismic location, Jih (1999) proposed a procedure J0 to derive the backazimuth with a large aperture network where all seismographs are on one side of the event. Any standard Geiger-type of least-squares inversion routine can be applied to

  2. 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.

  3. Gaseous Halos and the Interstellar Disk-Halo Connection

    NASA Astrophysics Data System (ADS)

    Dettmar, Ralf Jurgen

    The presence of diffuse ionized gas (DIG) in the halos of spiral galaxies is discussed in the framework of the disk-halo interaction. The halo DIG is typically correlated with the presence of other components of the ISM in the halo including X-ray hot gas, cosmic rays, and magnetic fields. All these tracers of an extraplanar ISM correlate well with star formation in the disk thus corroborating the paradigm of an ISM driven by multiple and clustered supernovae.

  4. Non-standard models and the sociology of cosmology

    NASA Astrophysics Data System (ADS)

    López-Corredoira, Martín

    2014-05-01

    I review some theoretical ideas in cosmology different from the standard "Big Bang": the quasi-steady state model, the plasma cosmology model, non-cosmological redshifts, alternatives to non-baryonic dark matter and/or dark energy, and others. Cosmologists do not usually work within the framework of alternative cosmologies because they feel that these are not at present as competitive as the standard model. Certainly, they are not so developed, and they are not so developed because cosmologists do not work on them. It is a vicious circle. The fact that most cosmologists do not pay them any attention and only dedicate their research time to the standard model is to a great extent due to a sociological phenomenon (the "snowball effect" or "groupthink"). We might well wonder whether cosmology, our knowledge of the Universe as a whole, is a science like other fields of physics or a predominant ideology.

  5. Unraveling the History of the Milky Way's Halo

    NASA Astrophysics Data System (ADS)

    Valluri, Monica; Debattista, V. P.

    2010-01-01

    One of the key predictions of Lambda-CDM cosmological simulations is that the dark matter halos of galaxies, such as the Milky Way, are strongly prolate or triaxial. However simulations with gas show that both the shapes and density profiles of dark matter halos can be dramatically altered by the condensation of baryons into a disk or spheroidal component. Current and future astrometric mission (e.g. RAVE, Segue, Gaia and NASA's SIM Lite Astrometric Observatory) are expected to obtain the full 6 dimensional phase space information of several thousands of halo stars. We describes a novel method to analyze this phase-space information that be used to set constrains, not just on the present shape and phase space distribution of the Milky Way halo, but also on its past shape history. We exploit a technique for revealing the phase space structure and orbital content of galaxies: "The Laskar Frequency Map". The power of this technique is demonstrated by applying it to a series of controlled simulations in which dynamically realistic disks are grown in isolated triaxial dark matter halos. We show that even when the growth of a baryonic disk causes the halo's shape to become oblate or close to spherical, it is possible to determine if it was originally prolate or triaxial as predicted by cosmological N-body simulations. It is also possible to determine if the original halo's major axis was perpendicular to the major axis or the minor axis of the disk. The technique can yield valuable information on the shape history of the halo form as few as a 1000- 5000 orbits.

  6. The Outer Halo -- Halo Origins and Mass of the Galaxy

    NASA Astrophysics Data System (ADS)

    Morrison, Heather; Arabadjis, John; Dohm-Palmer, Robbie; Freeman, Ken; Harding, Paul; Mateo, Mario; Norris, John; Olszewski, Ed; Sneden, Chris

    2000-02-01

    Through our detection of distant halo stars, we are now well placed to map the regions of the Galactic halo where previously only satellite galaxies and a few globular clusters were known. Mapping this region is crucial for answering questions like: How and over what timescales was the Milky Way's stellar halo assembled? What is the total mass and shape of its dark halo? The Sagittarius dwarf has demonstrated that at least some of the stellar halo was accreted. But, HOW MUCH of the halo was accreted? Our previous efforts have proven that the Washington photometric system, in conjuction with spectroscopy, is capable of efficiently and unambiguously identifying halo stars out to 100 kpc or more. We require followup spectroscopy to map velocity substructure, which is more likely visible in the outer halo because of the long dynamical timescales, and to identify the rare objects in the extreme outer halo which will constrain the shape and size of its dark halo. We are applying for 4m/RCSP time at both CTIO and KPNO to observe faint outer-halo giant and BHB candidates.

  7. Halo formation and evolution: unifying physical properties with structure

    NASA Astrophysics Data System (ADS)

    Ernest, Alllan David; Collins, Matthew P.

    2015-08-01

    The assembly of matter in the universe proliferates a variety of structures with diverse properties. For example, massive halos of clusters of galaxies have temperatures often an order of magnitude or more higher than the individual galaxy halos within the cluster, or the temperatures of isolated galaxy halos. Giant spiral galaxies contain large quantities of both dark matter and hot gas while other structures like globular clusters appear to have little or no dark matter or gas. Still others, like the dwarf spheroidal galaxies have low gravity and little hot gas, but ironically contain some of the largest fractions of dark matter in the universe. Star forming rates (SFRs) also vary: compare for example the SFRs of giant elliptical galaxies, globular clusters, spiral and starburst galaxies. Furthermore there is evidence that the various structure types have existed over a large fraction of cosmic history. How can this array of variation in properties be reconciled with galaxy halo formation and evolution?We propose a model of halo formation [1] and evolution [2] that is consistent with both primordial nucleosynthesis (BBN) and the isotropies in the cosmic microwave background (CMB). The model uses two simple parameters, the total mass and size of a structure, to (1) explain why galaxies have the fractions of dark matter that they do (including why dwarf spheroidals are so dark matter dominated despite their weak gravity), (2) enable an understanding of the black hole-bulge/black hole-dark halo relations, (3) explain how fully formed massive galaxies can occur so early in cosmic history, (4) understand the connection between spiral and elliptical galaxies (5) unify the nature of globular clusters, dwarf spheroidal galaxies and bulges and (6) predict the temperatures of hot gas halos and understand how cool galaxy halos can remain stable in the hot environments of cluster-galaxy halos.[1] Ernest, A. D., 2012, in Prof. Ion Cotaescu (Ed) Advances in Quantum Theory, pp

  8. Scaling Limit Analysis of Borromean Halos

    NASA Astrophysics Data System (ADS)

    Souza, L. A.; Bellotti, F. F.; Frederico, T.; Yamashita, M. T.; Tomio, Lauro

    2016-05-01

    The analysis of the core recoil momentum distribution of neutron-rich isotopes of light exotic nuclei is performed within a model of halo nuclei described by a core and two neutrons dominated by the s-wave channel. We adopt the renormalized three-body model with a zero-range force, which accounts for the Efimov physics. This model is applicable to nuclei with large two-neutron halos compared to the core size, and a neutron-core scattering length larger than the interaction range. The halo wave function in momentum space is obtained by using as inputs the two-neutron separation energy and the energies of the singlet neutron-neutron and neutron-core virtual states. Within our model, we obtain the momentum probability densities for the Borromean exotic nuclei Lithium-11 (^{11}Li), Berylium-14 (^{14}Be) and Carbon-22 (^{22}C). A fair reproduction of the experimental data was obtained in the case of the core recoil momentum distribution of ^{11}Li and ^{14}Be, without free parameters. By extending the model to ^{22}C, the combined analysis of the core momentum distribution and matter radius suggest (i) a ^{21}C virtual state well below 1 MeV; (ii) an overestimation of the extracted matter ^{22}C radius; and (iii) a two-neutron separation energy between 100 and 400 keV.

  9. THE HALO OCCUPATION DISTRIBUTION OF SDSS QUASARS

    SciTech Connect

    Richardson, Jonathan; Chatterjee, Suchetana; Nagai, Daisuke; Zheng Zheng; Shen Yue

    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 measurements 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{sub q

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

    SciTech Connect

    Rahaman, Farook; Salucci, P.; Kuhfittig, P.K.F.; Ray, Saibal; Rahaman, Mosiur

    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 the 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.

  11. Building Blocks of the Milky Way's Stellar Halo

    NASA Astrophysics Data System (ADS)

    van Oirschot, Pim; Starkenburg, Else; Helmi, Amina; Nelemans, Gijs

    2016-08-01

    We study the assembly history of the stellar halo of Milky Way-like galaxies using the six high-resolution Aquarius dark matter simulations combined with the Munich-Groningen semi-analytic galaxy formation model. Our goal is to understand the stellar population contents of the building blocks of the Milky Way halo, including their star formation histories and chemical evolution, as well as their internal dynamical properties. We are also interested in how they relate or are different from the surviving satellite population. Finally, we will use our models to compare to observations of halo stars in an attempt to reconstruct the assembly history of the Milky Way's stellar halo itself.

  12. Dark Halo and Disk Galaxy Scaling Laws

    NASA Astrophysics Data System (ADS)

    Navarro, J. F.

    I highlight recent progress in our understanding of the origin of disk galaxy scaling laws in a hierarchically clustering universe. Numerical simulations of galaxy formation in Cold Dark Matter (CDM) dominated universes indicate that the slope and scatter of the I-band Tully-Fisher (TF) relation are well reproduced in this model, although not, as proposed in recent work, because of the cosmological equivalence between halo mass and circular velocity, but rather as a result of the dynamical response of the halo to the assembly of the luminous component of the galaxy. The zero-point of the TF relation is determined mainly by the stellar mass-to-light ratio (ΥI) as well as by the concentration (c) of the dark halo. For c ~ 10, as is typical of halos formed in the `concordance' ΛCDM model, we find that this requires ΥI ~ 1.5, in reasonable agreement with the mass-to-light ratios expected of stellar populations with colors similar to those of TF galaxies. This conclusion supersedes that of Navarro & Steinmetz (2000a,b), who claimed the ΛCDM halos were too concentrated to be consistent with the observed TF relation. The disagreement can be traced to an incorrect normalization of the power spectrum used in that work. Our new results show that simulated disk galaxies in the ΛCDM scenario are not clearly inconsistent with the observed I-band Tully-Fisher relation. On the other hand, their angular momenta is much lower than observed. Accounting simultaneously for the spin, size and luminosity of disk galaxies remains a challenge for hierarchical models of galaxy formation.

  13. 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.

  14. The Red Halos of Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Zackrisson, E.; Bergvall, N.; Flynn, C.; Caldwell, B.; Östlin, G.; Micheva, G.

    2008-10-01

    Deep optical/near-IR surface photometry of galaxies outside the Local Group have revealed the existence of faint and very red halos around objects as diverse as spirals and blue compact galaxies. The colors of these structures are much too extreme to be reconciled with resolved stellar populations like those seen in the halos of the Milky Way or M 31, and alternative explanations like dust reddening, high metallicities or nebular emission are also disfavored. A stellar population obeying an extremely bottom-heavy initial mass function, similar to that recently reported for the LMC field population, is on the other hand consistent with all available data. Because of its high mass-to-light ratio, such a population would effectively behave as baryonic dark matter and could account for some of the baryons still missing from local inventories. Here, we report on a number of recent developments in this field.

  15. Probing the Shape and History of the Milky Way Halo with Stellar Orbits

    NASA Astrophysics Data System (ADS)

    Valluri, Monica

    2010-05-01

    One of the key predictions of Lambda-CDM cosmological simulations is that the dark matter halos of galaxies such as the Milky Way are prolate or triaxial. However simulations show that both the shapes and density profiles of dark matter halos can be dramatically altered by the condensation of baryons. I will describe how Laskar's Frequency mapping technique can be used to analyze the phase-space structure of the Milky Way's halo with halo stellar orbits. From Frequency Maps of halo stars it is possible to set constrains, not just on the present shape and phase space distribution of the Milky Way halo, but also on its past shape history. The power of this technique is demonstrated by applying it to a series of controlled simulations in which dynamically realistic disks are grown in isolated triaxial dark matter halos. I will demonstrate that even when the growth of a baryonic disk causes the halo's shape to become oblate or close to spherical, it is possible to determine if it was originally prolate or triaxial as predicted by cosmological N-body simulations. Current and future Galactic surveys (e.g. RAVE, Segue, Gaia and LAMOST) are expected to obtain the full 6 dimensional phase space orbits of hundreds of thousands of halo stars. This technique will be a new and valuable tool that will complement on-going efforts to constrain the shape of the halo with tidal streams. Reliable indicators of the halo's shape can be obtained with as few as 5000-10000 halo stellar orbits.

  16. Assembly history of subhalo populations in galactic and cluster sized dark haloes

    NASA Astrophysics Data System (ADS)

    Xie, Lizhi; Gao, Liang

    2015-12-01

    We make use of two suits of ultrahigh resolution N-body simulations of individual dark matter haloes from the Phoenix and the Aquarius Projects to investigate systematics of assembly history of subhaloes in dark matter haloes differing by a factor of 1000 in the halo mass. We have found that real progenitors which built up present-day subhalo population are relatively more abundant for high-mass haloes, in contrast to previous studies claiming a universal form independent of the host halo mass. That is mainly because of repeated counting of the `re-accreted' (progenitors passed through and were later re-accreted to the host more than once) and inclusion of the `ejected' progenitor population (progenitors were accreted to the host in the past but no longer members at present day) in previous studies. The typical accretion time for all progenitors vary strongly with the host halo mass, which is typical about z ˜ 5 for the galactic Aquarius and about z ˜ 3 for the cluster sized Phoenix haloes. Once these progenitors start to orbit their parent haloes, they rapidly lose their original mass but not their identifiers, more than 55 (50) per cent of them survive to present day for the Phoenix (Aquarius) haloes. At given redshift, survival fraction of the accreted subhalo is independent of the parent halo mass, whilst the mass-loss of the subhalo is more efficient in high-mass haloes. These systematics results in similarity and difference in the subhalo population in dark matter haloes of different masses at present day.

  17. Non-Standard v-Interactions at a Neutrino Factory: Correlation and CP violation effects

    SciTech Connect

    Lopez-Pavon, Jacobo

    2011-10-06

    The so-called Non-Standard v-Interactions in propagation is a widely studied topic in the Neutrino Factory literature. However, special attention has not been paid to the possible correlation effects among the whole set of parameters arising in this context (standard and non-standard ones). Here we will focus on these correlation effects analysing the performance of three different Neutrino Factory setups. In addition, we explore the new avenues of CP violation coming from this sort of Non-Standard v-Interactions with the same perspective, in other words, studying the relation among the several CP-phases involved.

  18. 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.

  19. A Speeding Binary in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    cool (4,800 K) companion star in a wide orbit, likely separated by several AU.An Unknown Past and FutureWhy are these new observations of J1211 such a big deal? Because all the acceleration scenarios for a star originating in the Galactic disk fail in the case of J1211. The authors find by modeling J1211s motion that the system cant have originated in the Galactic center, so interactions with the supermassive black hole are out. And supernova explosions or dynamical interactions would tear the wide binary apart in the process of accelerating it. Nmeth and collaborators suggest instead that J1211 was either born in the halo population or accreted later from the debris of a destroyed satellite galaxy.J1211s speed is so extreme that its orbit could be either bound or unbound. Interestingly, when the authors model the binarys orbit, they find that the assumed mass of the Milky Ways dark-matter halo determines whether J1211s orbit is bound. This means that future observations of J1211 may provide a new way to probe the Galactic potential and determine the mass of the dark matter halo, in addition to revealing unexpected origins of high-velocity halo stars.CitationPter Nmeth et al 2016 ApJ 821 L13. doi:10.3847/2041-8205/821/1/L13

  20. Towards a self-consistent halo model for the nonlinear large-scale structure

    NASA Astrophysics Data System (ADS)

    Schmidt, Fabian

    2016-03-01

    The halo model is a theoretically and empirically well-motivated framework for predicting the statistics of the nonlinear matter distribution in the Universe. However, current incarnations of the halo model suffer from two major deficiencies: (i) they do not enforce the stress-energy conservation of matter; (ii) they are not guaranteed to recover exact perturbation theory results on large scales. Here, we provide a formulation of the halo model (EHM) that remedies both drawbacks in a consistent way, while attempting to maintain the predictivity of the approach. In the formulation presented here, mass and momentum conservation are guaranteed on large scales, and results of the perturbation theory and the effective field theory can, in principle, be matched to any desired order on large scales. We find that a key ingredient in the halo model power spectrum is the halo stochasticity covariance, which has been studied to a much lesser extent than other ingredients such as mass function, bias, and profiles of halos. As written here, this approach still does not describe the transition regime between perturbation theory and halo scales realistically, which is left as an open problem. We also show explicitly that, when implemented consistently, halo model predictions do not depend on any properties of low-mass halos that are smaller than the scales of interest.

  1. Halo Star Lithium Depletion

    SciTech Connect

    Pinsonneault, M. H.; Walker, T. P.; Steigman, G.; Narayanan, Vijay K.

    1999-12-10

    The depletion of lithium during the pre-main-sequence and main-sequence phases of stellar evolution plays a crucial role in the comparison of the predictions of big bang nucleosynthesis with the abundances observed in halo stars. Previous work has indicated a wide range of possible depletion factors, ranging from minimal in standard (nonrotating) stellar models to as much as an order of magnitude in models that include rotational mixing. Recent progress in the study of the angular momentum evolution of low-mass stars permits the construction of theoretical models capable of reproducing the angular momentum evolution of low-mass open cluster stars. The distribution of initial angular momenta can be inferred from stellar rotation data in young open clusters. In this paper we report on the application of these models to the study of lithium depletion in main-sequence halo stars. A range of initial angular momenta produces a range of lithium depletion factors on the main sequence. Using the distribution of initial conditions inferred from young open clusters leads to a well-defined halo lithium plateau with modest scatter and a small population of outliers. The mass-dependent angular momentum loss law inferred from open cluster studies produces a nearly flat plateau, unlike previous models that exhibited a downward curvature for hotter temperatures in the 7Li-Teff plane. The overall depletion factor for the plateau stars is sensitive primarily to the solar initial angular momentum used in the calibration for the mixing diffusion coefficients. Uncertainties remain in the treatment of the internal angular momentum transport in the models, and the potential impact of these uncertainties on our results is discussed. The 6Li/7Li depletion ratio is also examined. We find that the dispersion in the plateau and the 6Li/7Li depletion ratio scale with the absolute 7Li depletion in the plateau, and we use observational data to set bounds on the 7Li depletion in main-sequence halo

  2. Bounds on halo-particle interactions from interstellar calorimetry

    NASA Technical Reports Server (NTRS)

    Chivukula, Sekhar R.; Cohen, Andrew G.; Dimopoulos, Savas; Walker, Terry P.

    1990-01-01

    It is shown that the existence of neutral interstellar clouds constrains the interaction of any particulate dark-matter candidate with atomic hydrogen to be quite small. Even for a halo particle of mass 1 PeV (10 to the 6 GeV), it is shown that the cross section with hydrogen must be smaller than the typical atomic cross section that is expected for a positively charged particle bound to an electron. The argument presented is that if the clouds are in equilibrium, then the rate at which energy is deposited by collisions with dark-matter particles must be smaller than the rate at which the cloud can cool. This argument is used to constrain the interaction cross section of dark matter with hydrogen. Remarks are made on the general viability of charged dark matter. Comments are also made on a bound which derives from the dynamical stability of the halo.

  3. Expanded haloes, abundance matching and too-big-to-fail in the Local Group

    NASA Astrophysics Data System (ADS)

    Brook, Chris B.; Di Cintio, Arianna

    2015-07-01

    Observed kinematical data of 40 Local Group (LG) members are used to derive the dark matter halo mass of such galaxies. Haloes are selected from the theoretically expected LG mass function and two different density profiles are assumed, a standard universal cuspy model and a mass-dependent profile which accounts for the effects of baryons in modifying the dark matter distribution within galaxies. The resulting relations between stellar and halo mass are compared with expectations from abundance matching. Using a universal cuspy profile, the ensemble of LG galaxies is fit in relatively low-mass haloes, leaving `dark' many massive haloes of Mhalo ≳ 1010 M⊙: this reflects the `too-big-to-fail' problem and results in a Mstar-Mhalo relation that differs from abundance matching predictions. Moreover, the star formation efficiency of isolated LG galaxies increases with decreasing halo mass when adopting a cuspy model. By contrast, using the mass-dependent density profile, dwarf galaxies with Mstar ≳ 106 M⊙ are assigned to more massive haloes, which have a central cored distribution of dark matter: the `too-big-to-fail' problem is alleviated, the resultant Mstar-Mhalo relation follows abundance matching predictions down to the completeness limit of current surveys, and the star formation efficiency of isolated members decreases with decreasing halo mass, in agreement with theoretical expectations. Finally, the cusp/core space of LG galaxies is presented, providing a framework to understand the non-universality of their density profiles.

  4. The discovery reach of CP violation in neutrino oscillation with non-standard interaction effects

    NASA Astrophysics Data System (ADS)

    Rahman, Zini; Dasgupta, Arnab; Adhikari, Rathin

    2015-06-01

    We have studied the CP violation discovery reach in a neutrino oscillation experiment with superbeam, neutrino factory and monoenergetic neutrino beam from the electron capture process. For NSI satisfying model-dependent bound for shorter baselines (like CERN-Fréjus set-up) there is insignificant effect of NSI on the the discovery reach of CP violation due to δ. Particularly, for the superbeam and neutrino factory we have also considered relatively longer baselines for which there could be significant NSI effects on CP violation discovery reach for higher allowed values of NSI. For the monoenergetic beam only shorter baselines are considered to study CP violation with different nuclei as neutrino sources. Interestingly for non-standard interactions—{{\\varepsilon }eμ } and {{\\varepsilon }eτ } of neutrinos with matter during propagation in longer baselines in the superbeam, there is the possibility of better discovery reach of CP violation than that with only Standard Model interactions of neutrinos with matter. For complex NSI we have shown the CP violation discovery reach in the plane of Dirac phase δ and NSI phase {{φ }ij}. The CP violation due to some values of δ remain unobservable with present and near future experimental facilities in the superbeam and neutrino factory. However, in the presence of some ranges of off-diagonal NSI phase values there are some possibilities of discovering total CP violation for any {{δ }CP} value even at 5σ confidence level for neutrino factory. Our analysis indicates that for some values of NSI phases total CP violation may not be at all observable for any values of δ. Combination of shorter and longer baselines could indicate in some cases the presence of NSI. However, in general for NSIs ≲ 1 the CP violation discovery reach is better in neutrino factory set-ups. Using a neutrino beam from the electron capture process for nuclei 50110Sn and 152Yb, we have shown the discovery reach of CP violation in a neutrino

  5. The importance of the cosmic web and halo substructure for power spectra

    NASA Astrophysics Data System (ADS)

    Pace, Francesco; Manera, Marc; Bacon, David J.; Crittenden, Robert; Percival, Will J.

    2015-11-01

    In this work, we study the relevance of the cosmic web and substructures on the matter and lensing power spectra measured from halo mock catalogues extracted from the N-body simulations. Since N-body simulations are computationally expensive, it is common to use faster methods that approximate the dark matter field as a set of haloes. In this approximation, we replace mass concentrations in N-body simulations by a spherically symmetric Navarro-Frenk-White halo density profile. We also consider the full mass field as the sum of two distinct fields: dark matter haloes (M > 9 × 1012 M⊙ h-1) and particles not included into haloes. Mock haloes reproduce well the matter power spectrum, but underestimate the lensing power spectrum on large and small scales. For sources at zs = 1 the lensing power spectrum is underestimated by up to 40 per cent at ℓ ≈ 104 with respect to the simulated haloes. The large-scale effect can be alleviated by combining the mock catalogue with the dark matter distribution outside the haloes. In addition, to evaluate the contribution of substructures we have smeared out the intrahalo substructures in an N-body simulation while keeping the halo density profiles unchanged. For the matter power spectrum the effect of this smoothing is only of the order of 5 per cent, but for lensing substructures and ellipticity are much more important: for ℓ ≈ 104 modifications to the internal structure contribute to 30 per cent of the total spectrum. These findings have important implications in the way mock catalogues have to be created, suggesting that some approximate methods currently used for galaxy surveys will be inadequate for future weak lensing surveys.

  6. Subhalo statistics of galactic haloes: beyond the resolution limit

    NASA Astrophysics Data System (ADS)

    Cautun, Marius; Hellwing, Wojciech A.; van de Weygaert, Rien; Frenk, Carlos S.; Jones, Bernard J. T.; Sawala, Till

    2014-12-01

    We study the substructure population of Milky Way (MW)-mass haloes in the Λ cold dark matter (ΛCDM) cosmology using a novel procedure to extrapolate subhalo number statistics beyond the resolution limit of N-body simulations. The technique recovers the mean and the variance of the subhalo abundance, but not its spatial distribution. It extends the dynamic range over which precise statistical predictions can be made by the equivalent of performing a simulation with 50 times higher resolution, at no additional computational cost. We apply this technique to MW-mass haloes, but it can easily be applied to haloes of any mass. We find up to 20 per cent more substructures in MW-mass haloes than found in previous studies. Our analysis lowers the mass of the MW halo required to accommodate the observation that the MW has only three satellites with a maximum circular velocity Vmax ≥ 30 km s- 1 in the ΛCDM cosmology. The probability of having a subhalo population similar to that in the MW is 20 per cent for a virial mass, M200 = 1 × 1012 M⊙ and practically zero for haloes more massive than M200 = 2 × 1012 M⊙.

  7. Methods for Identifying Pair Halos

    NASA Astrophysics Data System (ADS)

    Wells, Brendan; Caputo, Regina; Atwood, William; Ritz, Steven M.

    2016-01-01

    The flux of very high energy gamma rays from active galactic nuclei (AGN) is attenuated via interactions with extragalactic background photons and is converted into e+e- pairs. With non-zero intergalactic magnetic fields, the electrons and positrons will deflect as they propagate and simultaneously lose energy by upscattering cosmic microwave background photons. "Pair halos," the visible consequences of these electromagnetic cascades, are faint and difficult to observe against their AGN counterparts. We investigate three methods for indirectly identifying pair halos, using a two-component approach to model the AGN core/halo image. We estimate each method's sensitivity by utilizing a new, detailed Monte Carlo pair-halo simulation.

  8. Constraining the halo mass function with observations

    NASA Astrophysics Data System (ADS)

    Castro, Tiago; Marra, Valerio; Quartin, Miguel

    2016-08-01

    The abundances of dark matter halos in the universe are described by the halo mass function (HMF). It enters most cosmological analyses and parametrizes how the linear growth of primordial perturbations is connected to these abundances. Interestingly, this connection can be made approximately cosmology independent. This made it possible to map in detail its near-universal behavior through large-scale simulations. However, such simulations may suffer from systematic effects, especially if baryonic physics is included. In this paper we ask how well observations can constrain directly the HMF. The observables we consider are galaxy cluster number counts, galaxy cluster power spectrum and lensing of type Ia supernovae. Our results show that DES is capable of putting the first meaningful constraints on the HMF, while both Euclid and J-PAS can give stronger constraints, comparable to the ones from state-of-the-art simulations. We also find that an independent measurement of cluster masses is even more important for measuring the HMF than for constraining the cosmological parameters, and can vastly improve the determination of the halo mass function. Measuring the HMF could thus be used to cross-check simulations and their implementation of baryon physics. It could even, if deviations cannot be accounted for, hint at new physics.

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

    SciTech Connect

    Baushev, A. N.

    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 not 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.

  10. Galaxy Halo Formation in the Absence of Violent Relaxation and a Universal Density Profile of the Halo Center

    NASA Astrophysics Data System (ADS)

    Baushev, A. N.

    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 not 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.

  11. The Making of the Milky Way Halo

    NASA Astrophysics Data System (ADS)

    1999-02-01

    The VLT Watches a Dissolving Stellar Cluster A group of ESO astronomers [1] has used new observations, obtained with the first 8.2-m VLT Unit Telescope (UT1) during the "Science Verification" programme, to show that a globular cluster in the Milky Way galaxy is "evaporating" and has already lost its faintest stars. This is the first observational result of its kind and has important implications for future studies. It may be explained by a gradual loss of such stars from the cluster into the Milky Way halo, a roughly spherical region around the much flatter, spiral structure in which most of the stars and nebulae are located. The new result lends strong support to current theories about the evolution of the structure of this halo and also provides insights into the formation of the galaxy in which we live. Globular clusters and the halo of the Milky Way The stars that we observe in the halo of the Milky Way represent only a small fraction of the total mass in this region. Investigations of the motions of stars in our Galaxy have shown that this halo must harbour much more matter, which is hidden from our view. The same phenomenon has been observed in other galaxies, and astronomers refer to it as "dark matter". It is at this moment not known what this matter consists of. The brightest objects in the halo are the globular clusters . They are large groupings of stars that were formed together in the very early evolutionary phases of the Milky Way, some 12,000 - 14,000 million years ago. This happened soon after the moment when the first structures emerged in the large cloud of primordial hydrogen in which our Galaxy was born. A popular scenario describes the first build-up of galactic structure, i.e. of stars and gas, as when normal matter began to collect inside the dark-matter halo, due to its strong gravitational attraction. The globular clusters were most probably the first denizens of this protogalaxy . It is believed that the Milky Way Galaxy subsequently

  12. Scale dependence of halo and galaxy bias: Effects in real space

    SciTech Connect

    Smith, Robert E.; Scoccimarro, Roman; Sheth, Ravi K.

    2007-03-15

    We examine the scale dependence of dark matter halo and galaxy clustering on very large scales (0.01halo bias. We pursue a two line offensive: high-resolution numerical simulations are used to establish some old and some new results, and an analytic model is developed to understand their origins. Our simulations show: (i) that the z=0 dark matter power spectrum is suppressed relative to linear theory by {approx}5% on scales 0.05halo bias is nonlinear over the scales we probe and that the scale dependence is a strong function of halo mass. High mass haloes show no suppression of power on scales k<0.07[h Mpc{sup -1}], and only show amplification on smaller scales, whereas low mass haloes show strong, {approx}5%-10%, suppression over the range 0.05matter and haloes, which circumvents the thorny issue of shot-noise correction. The halo-halo power spectrum, however, is highly sensitive to the shot-noise correction; we show that halo exclusion effects make this sub-Poissonian and a new correction is presented. Our results have special relevance for studies of the baryon acoustic oscillation features in the halo power spectra. Nonlinear mode-mode coupling: (i) damps these features on progressively larger scales as halo mass increases; (ii) produces small shifts in the positions of the peaks and troughs which depend on halo mass. We show that these effects on halo clustering are important over the redshift range relevant to such studies (0halo model.' The halo-halo clustering term is propagated into the nonlinear regime using '1-loop' perturbation theory and a nonlinear

  13. 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

  14. Adiabatic Halo Formation

    SciTech Connect

    Bazzani, A.; Turchetti, G.; Benedetti, C.; Rambaldi, S.; Servizi, G.

    2005-06-08

    In a high intensity circular accelerator the synchrotron dynamics introduces a slow modulation in the betatronic tune due to the space-charge tune depression. When the transverse motion is non-linear due to the presence of multipolar effects, resonance islands move in the phase space and change their amplitude. This effect introduces the trapping and detrapping phenomenon and a slow diffusion in the phase space. We apply the neo-adiabatic theory to describe this diffusion mechanism that can contribute to halo formation.

  15. Halo abundances within the cosmic web

    NASA Astrophysics Data System (ADS)

    Alonso, D.; Eardley, E.; Peacock, J. A.

    2015-03-01

    We investigate the dependence of the mass function of dark-matter haloes on their environment within the cosmic web of large-scale structure. A dependence of the halo mass function on large-scale mean density is a standard element of cosmological theory, allowing mass-dependent biasing to be understood via the peak-background split. On the assumption of a Gaussian density field, this analysis can be extended to ask how the mass function depends on the geometrical environment: clusters, filaments, sheets and voids, as classified via the tidal tensor (the Hessian matrix of the gravitational potential). In linear theory, the problem can be solved exactly, and the result is attractively simple: the conditional mass function has no explicit dependence on the local tidal field, and is a function only of the local density on the filtering scale used to define the tidal tensor. There is nevertheless a strong implicit predicted dependence on geometrical environment, because the local density couples statistically to the derivatives of the potential. We compute the predictions of this model and study the limits of their validity by comparing them to results deduced empirically from N-body simulations. We have verified that, to a good approximation, the abundance of haloes in different environments depends only on their densities, and not on their tidal structure. In this sense we find relative differences between halo abundances in different environments with the same density which are smaller than ˜13 per cent. Furthermore, for sufficiently large filtering scales, the agreement with the theoretical prediction is good, although there are important deviations from the Gaussian prediction at small, non-linear scales. We discuss how to obtain improved predictions in this regime, using the `effective-universe' approach.

  16. The Caterpillar Project: A Large Suite of Milky Way Sized Halos

    NASA Astrophysics Data System (ADS)

    Griffen, Brendan F.; Ji, Alexander P.; Dooley, Gregory A.; Gómez, Facundo A.; Vogelsberger, Mark; O'Shea, Brian W.; Frebel, Anna

    2016-02-01

    We present the largest number of Milky Way sized dark matter halos simulated at very high mass (˜104{M}⊙ /particle) and temporal resolution (5 Myr/snapshot) done to date, quadrupling what is currently available in the literature. This initial suite consists of the first 24 halos of the Caterpillar Project whose project goal of 60-70 halos will be made public when complete. We do not bias our halo selection by the size of the Lagrangian volume. We resolve ˜20,000 gravitationally bound subhalos within the virial radius of each host halo. Improvements were made upon current state-of-the-art halo finders to better identify substructure at such high resolutions, and on average we recover ˜4 subhalos in each host halo above 108 {M}⊙ which would have otherwise not been found. The density profiles of relaxed host halos are reasonably fit by Einasto profiles (α = 0.169 ± 0.023) with dependence on the assembly history of a given halo. Averaging over all halos, the substructure mass fraction is {f}m,{subs}\\quad =\\quad 0.121+/- 0.041, and mass function slope is dN/dM\\propto {M}-1.88+/- 0.10. We find concentration-dependent scatter in the normalizations at fixed halo mass. Our detailed contamination study of 264 low-resolution halos has resulted in unprecedentedly large high-resolution regions around our host halos for our fiducial resolution (sphere of radius ˜ 1.4+/- 0.4 Mpc). This suite will allow detailed studies of low mass dwarf galaxies out to large galactocentric radii and the very first stellar systems at high redshift (z ≥slant 15).

  17. The universality of the virial halo mass function and models for non-universality of other halo definitions

    NASA Astrophysics Data System (ADS)

    Despali, Giulia; Giocoli, Carlo; Angulo, Raul E.; Tormen, Giuseppe; Sheth, Ravi K.; Baso, Giacomo; Moscardini, Lauro

    2016-03-01

    The abundance of galaxy clusters can constrain both the geometry and growth of structure in our Universe. However, this probe could be significantly complicated by recent claims of non-universality-non-trivial dependences with respect to the cosmological model and redshift. In this work, we analyse the dependence of the mass function on the way haloes are identified and establish if this can cause departures from universality. In order to explore this dependence, we use a set of different N-body cosmological simulations (Le SBARBINE simulations), with the latest cosmological parameters from the Planck collaboration; this first suite of simulations is followed by a lower resolution set, carried out with different cosmological parameters. We identify dark matter haloes using a spherical overdensity algorithm with varying overdensity thresholds (virial, 2000, 1000, 500, 200 ρc and 200 ρb) at all redshifts. We notice that, when expressed in terms of the rescaled variable ν, the mass function for virial haloes is a nearly universal as a function of redshift and cosmology, while this is clearly not the case for the other overdensities we considered. We provide fitting functions for the halo mass function parameters as a function of overdensity, that allow us to predict, to within a few per cent accuracy, the halo mass function for a wide range of halo definitions, redshifts and cosmological models. We then show how the departures from universality associated with other halo definitions can be derived by combining the universality of the virial definition with the expected shape of the density profile of haloes.

  18. 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.

  19. Stellar halos and the link to galaxy formation

    NASA Astrophysics Data System (ADS)

    Helmi, Amina

    2016-08-01

    I present a brief overview of how stellar halos may be used to constrain the process of galaxy formation. In particular, streams and substructure in stellar halos trace merger events but can also be used to determine the mass distribution of the host galaxy and hence put constraints on the nature of dark matter. Much of the focus of this contribution is on the Milky Way, but I also present an attempt to understand the kinematics of the globular cluster system of M31.

  20. Toward a universal formulation of the halo mass function.

    PubMed

    Corasaniti, P S; Achitouv, I

    2011-06-17

    We compute the dark matter halo mass function using the excursion set formalism for a diffusive barrier with linearly drifting average which captures the main features of the ellipsoidal collapse model. We evaluate the non-Markovian corrections due to the sharp filtering of the linear density field in real space with a path-integral method. We find an unprecedented agreement with N-body simulation data with deviations ≲5% over the range of masses probed by the simulations. This indicates that the excursion set in combination with a realistic modeling of the collapse threshold can provide a robust estimation of the halo mass function. PMID:21770562

  1. The Highly Flattened Dark Halo of NGC 4244

    NASA Astrophysics Data System (ADS)

    Olling, R. P.

    1995-12-01

    In a previous paper (Olling 1995, AJ, 110, 591) a method was developed to determine the shapes of dark matter halos of spiral galaxies from an accurate determination of the rotation curve and the flaring of the gas layer. Here this method is applied to the almost edge-on spiral NGC 4244. I present sensitive high resolution VLA B, C, and D array observations in the 21-cm spectral line of neutral atomic hydrogen of the nearby Scd galaxy NGC 4244. The observed flaring of the HI beyond the optical disk puts significant constraints on the dark matter halo, which are almost independent of the stellar mass-to-light ratio. I find that NGC 4244's dark matter halo is highly flattened: c/a=0.1 - 0.5. Alternatively, the measured flaring curve is consistent with a round halo if the gaseous velocity dispersion ellipsoid is anisotropic. In that case the vertical dispersion of the gas is 50 - 70% of the measured tangential velocity dispersion. A new technique is presented to determine simultaneously the inclination and the thickness of the gas layer from high resolution HI observations. This procedure uses the apparent widths at many azimuths rather than just the edge channels, and can be used at inclinations as low as 60^o .

  2. The influence of halo evolution on galaxy structure

    NASA Astrophysics Data System (ADS)

    White, Simon

    2015-03-01

    If Einstein-Newton gravity holds on galactic and larger scales, then current observations demonstrate that the stars and interstellar gas of a typical bright galaxy account for only a few percent of its total nonlinear mass. Dark matter makes up the rest and cannot be faint stars or any other baryonic form because it was already present and decoupled from the radiation plasma at z = 1000, long before any nonlinear object formed. The weak gravito-sonic waves so precisely measured by CMB observations are detected again at z = 4 as order unity fluctuations in intergalactic matter. These subsequently collapse to form today's galaxy/halo systems, whose mean mass profiles can be accurately determined through gravitational lensing. High-resolution simulations link the observed dark matter structures seen at all these epochs, demonstrating that they are consistent and providing detailed predictions for all aspects of halo structure and growth. Requiring consistency with the abundance and clustering of real galaxies strongly constrains the galaxy-halo relation, both today and at high redshift. This results in detailed predictions for galaxy assembly histories and for the gravitational arena in which galaxies live. Dark halos are not expected to be passive or symmetric but to have a rich and continually evolving structure which will drive evolution in the central galaxy over its full life, exciting warps, spiral patterns and tidal arms, thickening disks, producing rings, bars and bulges. Their growth is closely related to the provision of new gas for galaxy building.

  3. Non-standard interactions in propagation at the Deep Underground Neutrino Experiment

    NASA Astrophysics Data System (ADS)

    Coloma, Pilar

    2016-03-01

    We study the sensitivity of current and future long-baseline neutrino oscillation experiments to the effects of dimension six operators affecting neutrino propagation through Earth, commonly referred to as Non-Standard Interactions (NSI). All relevant parameters entering the oscillation probabilities (standard and non-standard) are considered at once, in order to take into account possible cancellations and degeneracies between them. We find that the Deep Underground Neutrino Experiment will significantly improve over current constraints for most NSI parameters. Most notably, it will be able to rule out the so-called LMA-dark solution, still compatible with current oscillation data, and will be sensitive to off-diagonal NSI parameters at the level of ɛ ˜ {O} (0.05 - 0.5). We also identify two degeneracies among standard and non-standard parameters, which could be partially resolved by combining T2HK and DUNE data.

  4. Non-Standard Interactions in propagation at the Deep Underground Neutrino Experiment

    DOE PAGESBeta

    Coloma, Pilar

    2016-03-03

    Here, we study the sensitivity of current and future long-baseline neutrino oscillation experiments to the effects of dimension six operators affecting neutrino propagation through Earth, commonly referred to as Non-Standard Interactions (NSI). All relevant parameters entering the oscillation probabilities (standard and non-standard) are considered at once, in order to take into account possible cancellations and degeneracies between them. We find that the Deep Underground Neutrino Experiment will significantly improve over current constraints for most NSI parameters. Most notably, it will be able to rule out the so-called LMA-dark solution, still compatible with current oscillation data, and will be sensitive to off-diagonal NSI parameters at the level of ε ~more » $$ \\mathcal{O} $$ (0.05 – 0.5). We also identify two degeneracies among standard and non-standard parameters, which could be partially resolved by combining T2HK and DUNE data.« less

  5. HOBBY-EBERLY TELESCOPE OBSERVATIONS OF THE DARK HALO IN NGC 821

    SciTech Connect

    Forestell, Amy D.; Gebhardt, Karl E-mail: gebhardt@astro.as.utexas.ed

    2010-06-10

    We present stellar line-of-sight velocity distributions (LOSVDs) of elliptical galaxy NGC 821 obtained to approximately 100'' (over two effective radii) with long-slit spectroscopy from the Hobby-Eberly Telescope. Our measured stellar LOSVDs are larger than the planetary nebulae measurements at similar radii. We fit axisymmetric orbit-superposition models with a range of dark halo density profiles, including two-dimensional kinematics at smaller radii from SAURON data. Within our assumptions, the best-fitted model gives a total enclosed mass of 2.0 x 10{sup 11} M {sub sun} within 100'', with an accuracy of 2%; this mass is equally divided between halo and stars. At 1 R{sub e} , the best-fitted dark matter halo accounts for 13% of the total mass in the galaxy. This dark halo is inconsistent with previous claims of little to no dark matter halo in this galaxy from planetary nebula measurements. We find that a power-law dark halo with a slope 0.1 is the best-fitted model; both the no dark halo and Navarro-Frenk-White models are worse fits at a greater than 99% confidence level. NGC 821 does not appear to have the expected dark halo density profile. The internal moments of the stellar velocity distribution show that the model with no dark halo is radially anisotropic at small radii and tangentially isotropic at large radii, while the best-fitted halo models are slightly radially anisotropic at all radii. We test the potential effects of model smoothing and find that there are no effects on our results within the errors. Finally, we run models using the planetary nebula kinematics and assuming our best-fitted halos and find that the planetary nebulae require radial orbits throughout the galaxy.

  6. Near Ballistic Halo-to-Halo Transfers between Planetary Moons

    NASA Astrophysics Data System (ADS)

    Lantoine, Gregory; Russell, Ryan P.

    2011-07-01

    Intermoon transfers are important components of planetary tour missions. However, these transfers are challenging to design due in part to the chaotic environment created by the multi-body dynamics. The specific objective of this work is to develop a systematic methodology to find fuel optimal, near ballistic Halo-to-Halo trajectories between planetary moons, and we achieve this goal by combining dynamical systems theory with a variety of nonlinear programming techniques. The spacecraft is constrained to start at a Halo orbit of a moon and end at another Halo orbit of a second moon. Our approach overcomes the obstacles of the chaotic dynamics by combining multiple "resonant-hopping" gravity assists with manifolds that control the low-energy transport near the Halo orbits of the moons. To help construct good initial guesses, contours of semimajor axes that can be reached by falling off a Halo orbit are presented. An empirical relationship is then derived to find quickly the boundary conditions on the Halo orbits that lead to ballistic capture and escape trajectories, and connect to desired resonances. The overall optimization procedure is broken into four parts of increasing fidelity: creation of the initial guess from unstable resonant orbits and manifolds, decomposition and optimization of the trajectory into two independent ideal three-body portions, end-to-end refinement in a patched three-body model, and transition to an ephemeris model using a continuation method. Each step is based on a robust multiple shooting approach to reduce the sensitivities associated with the close approach trajectories. Numerical results of an intermoon transfer in the Jovian system are presented. In an ephemeris model, using only 55 m/s and 205 days, a spacecraft can transfer between a Halo orbit of Ganymede and a Halo orbit of Europa.

  7. Reducing sample variance: halo biasing, non-linearity and stochasticity

    NASA Astrophysics Data System (ADS)

    Gil-Marín, Héctor; Wagner, Christian; Verde, Licia; Jimenez, Raul; Heavens, Alan F.

    2010-09-01

    Comparing clustering of differently biased tracers of the dark matter distribution offers the opportunity to reduce the sample or cosmic variance error in the measurement of certain cosmological parameters. We develop a formalism that includes bias non-linearities and stochasticity. Our formalism is general enough that it can be used to optimize survey design and tracers selection and optimally split (or combine) tracers to minimize the error on the cosmologically interesting quantities. Our approach generalizes the one presented by McDonald & Seljak of circumventing sample variance in the measurement of f ≡ d lnD/d lna. We analyse how the bias, the noise, the non-linearity and stochasticity affect the measurements of Df and explore in which signal-to-noise regime it is significantly advantageous to split a galaxy sample in two differently biased tracers. We use N-body simulations to find realistic values for the parameters describing the bias properties of dark matter haloes of different masses and their number density. We find that, even if dark matter haloes could be used as tracers and selected in an idealized way, for realistic haloes, the sample variance limit can be reduced only by up to a factor σ2tr/σ1tr ~= 0.6. This would still correspond to the gain from a three times larger survey volume if the two tracers were not to be split. Before any practical application one should bear in mind that these findings apply to dark matter haloes as tracers, while realistic surveys would select galaxies: the galaxy-host halo relation is likely to introduce extra stochasticity, which may reduce the gain further.

  8. Do Not Forget the Forest for the Trees: The Stellar-mass Halo-mass Relation in Different Environments

    NASA Astrophysics Data System (ADS)

    Tonnesen, Stephanie; Cen, Renyue

    2015-10-01

    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 assembly 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 1011 and 1012.9 M⊙. 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.

  9. Universality of galactic surface densities within one dark halo scale-length.

    PubMed

    Gentile, Gianfranco; Famaey, Benoit; Zhao, HongSheng; Salucci, Paolo

    2009-10-01

    It was recently discovered that the mean dark matter surface density within one dark halo scale-length (the radius within which the volume density profile of dark matter remains approximately flat) is constant across a wide range of galaxies. This scaling relation holds for galaxies spanning a luminosity range of 14 magnitudes and the whole Hubble sequence. Here we report that the luminous matter surface density is also constant within one scale-length of the dark halo. This means that the gravitational acceleration generated by the luminous component in galaxies is always the same at this radius. Although the total luminous-to-dark matter ratio is not constant, within one halo scale-length it is constant. Our finding can be interpreted as a close correlation between the enclosed surface densities of luminous and dark matter in galaxies. PMID:19794488

  10. Clumpy cold dark matter

    NASA Technical Reports Server (NTRS)

    Silk, Joseph; Stebbins, Albert

    1993-01-01

    A study is conducted of cold dark matter (CDM) models in which clumpiness will inhere, using cosmic strings and textures suited to galaxy formation. CDM clumps of 10 million solar mass/cu pc density are generated at about z(eq) redshift, with a sizable fraction surviving. Observable implications encompass dark matter cores in globular clusters and in galactic nuclei. Results from terrestrial dark matter detection experiments may be affected by clumpiness in the Galactic halo.

  11. Kinematically Detected Halo Streams

    NASA Astrophysics Data System (ADS)

    Smith, Martin C.

    Clues to the origins and evolution of our Galaxy can be found in the kinematics of stars around us. Remnants of accreted satellite galaxies produce over-densities in velocity-space, which can remain coherent for much longer than spatial over-densities. This chapter reviews a number of studies that have hunted for these accretion relics, both in the nearby solar-neighborhood and the more-distant stellar halo. Many observational surveys have driven this field forwards, from early work with the Hipparcos mission, to contemporary surveys like RAVE and SDSS. This active field continues to flourish, providing many new discoveries, and will be revolutionized as the Gaia mission delivers precise proper motions for a billion stars in our Galaxy.

  12. On the (non-)universality of halo density profiles

    NASA Astrophysics Data System (ADS)

    Diemer, Benedikt

    We present a systematic study of the density profiles of dark matter halos in LambdaCDM cosmologies, focusing on the question whether these profiles are "universal", i.e., whether they follow the same functional form regardless of halo mass, redshift, cosmology, and other parameters. The inner profiles (r [special character omitted] R vir) can be described as a function of only mass and concentration, and we thus begin by investigating whether there is a universal, cosmology-independent relation between those two parameters. We propose a model in which concentration is a function only of a halo's peak height and the local slope of the matter power spectrum. This model matches the concentrations in LambdaCDM and scale-free simulations, correctly extrapolates over 16 orders of magnitude in halo mass, and differs significantly from all previously proposed models at high masses and redshifts. We find that the outer profiles (r [special character omitted] Rvir) are remarkably universal across redshifts when radii are rescaled by R200m, whereas the inner profiles are most universal in units of R200c, highlighting that universality depends upon the definition of the halo boundary. Furthermore, we discover that the profiles exhibit significant deviations from the supposedly universal analytic formulae previously suggested in the literature, such as the NFW and Einasto forms. In particular, the logarithmic slope of the profiles of massive or rapidly accreting halos steepens more sharply than predicted around r ≈ R200m, where the steepness increases with increasing peak height or mass accretion rate. We propose a new, accurate fitting formula that takes these dependencies into account. Finally, we demonstrate that the profile steepening corresponds to the caustic at the apocenter of infalling matter on its first orbit. We call the location of the caustic the splashback radius, Rsp, and propose this radius as a new, physically motivated definition of the halo boundary. We

  13. Evidence for core-halo decoupling in halo systems

    SciTech Connect

    Aguilera, E. F.; Kolata, J. J.; Acosta, L.

    2010-01-15

    Evidence is presented showing that for the {sup 6}He+{sup 209}Bi system, the reaction cross sections can be entirely accounted for by interactions of the halo state of {sup 6}He plus reactions that occur with the {sup 4}He core. These and similar conclusions about core-halo decoupling reported earlier for {sup 8}B+{sup 58}Ni are further supported by proving that no such decoupling occurs for reactions with {sup 17}O, whose valence neutron is rather weakly bound but does not form a halo. The preceding conclusions are based on comparisons with purely experimental data, using a quite reasonable scaling. Thus such a decoupling seems to stand out as a characteristic feature of true halo systems.

  14. Modern Standard Arabic vs. Non-Standard Arabic: Where Do Arab Students of EFL Transfer From?

    ERIC Educational Resources Information Center

    Mahmoud, Abdulmoneim

    2000-01-01

    Focuses on the learning of English as a foreign language (EFL) by Arabic-speaking secondary school students. To see which variety students transferred from, they were asked to translate into English two versions of a short Arabic text: one Modern Standard Arabic (MSA), and the other non-standard Arabic (NSA). Results indicate the importance of…

  15. Non-Standard Italian Dialect Heritage Speakers' Acquisition of Clitic Placement in Standard Italian

    ERIC Educational Resources Information Center

    Chan, Lionel

    2014-01-01

    This dissertation examines the acquisition of object clitic placement in Standard Italian by heritage speakers (HSs) of non-standard Italian dialects. It compares two different groups of Standard Italian learners--Northern Italian dialect HSs and Southern Italian dialect HSs--whose heritage dialects contrast with each other in clitic word order.…

  16. Educational Failure or Success: Aboriginal Children's Non-Standard English Utterances

    ERIC Educational Resources Information Center

    Dixon, Sally

    2013-01-01

    Within the Australian education system, Aboriginal students' use of non-standard English features is often viewed simplistically as evidence of non-attainment of literacy and oral-English milestones. One reason for this is the widespread use of assessment tools which fail to differentiate between native-English speakers and students who are…