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. 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.

  17. 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.

  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

    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

  8. 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.

  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

    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.

  13. 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.

  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 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.

  20. 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.

  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. 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.

  10. 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.

  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. 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.

  16. 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.

  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. 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.

  20. 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.

  1. 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.

  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. 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.

  5. 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.

  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. 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.

  13. 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.

  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. 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.

  7. 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.

  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. 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.

  8. 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.

  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.

    2016-04-01

    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.

  17. 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.

  18. 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.

  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. 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.

  13. 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.

  14. 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.

  15. 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.

  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. 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.

  18. 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.

  19. 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.

  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. 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.

  4. 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.

  5. 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.

  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. 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.

  4. 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.

  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. 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.

  15. 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.

  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. 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.

  20. 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.

  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

    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.

  4. 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.

  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.