scholarly journals The distribution of dark galaxies and spin bias

2020 ◽  
Vol 498 (1) ◽  
pp. L93-L97
Author(s):  
Raul Jimenez ◽  
Alan F Heavens
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Number Density ◽  
Expected Number ◽  
Mass Distributions ◽  
Spin Parameter ◽  
Luminous Galaxies

ABSTRACT In the light of the discovery of numerous (almost) dark galaxies from the ALFALFA and LITTLE THINGS surveys, we revisit the predictions of the existence of dark galaxies, based on the Toomre stability of rapidly spinning gas discs. We have updated the predictions for Λ-cold dark matter with parameters given by the Planck18 collaboration, computing the expected number densities of dark objects, and their spin parameter and mass distributions. Comparing with the data is more challenging, but where the spins are more reliably determined, the spins are close to the threshold for discs to be stable according to the Toomre criterion, where the expected number density is highest, and reinforces the concept that there is a bias in the formation of luminous galaxies based on the spin of their parent halo.

scholarly journals N-Body Results on Dark Matter

1987 ◽  
Vol 117 ◽  
pp. 263-278
Author(s):  
Simon D. M. White
Keyword(s):  
Dark Matter ◽  
Mass Distribution ◽  
Cold Dark Matter ◽  
Density Fluctuations ◽  
Major Difficulty ◽  
Mass Distributions ◽  
Galaxy Distribution ◽  
Galaxy Halos ◽  
Flat Rotation Curves ◽  
The Universe

The structure of the dominant “dark” component of the Universe may evolve primarily under the influence of gravity. A number of models for the evolution of the Universe make specific predictions for the statistical properties of density fluctuations at early times. N-body simulations can follow the nonlinear development of such fluctuations to the present day. A major difficulty arises because we cannot observe the present mass distribution directly. Recent N-body work has concentrated on models dominated by weakly interacting free elementary particles. Neutrino-dominated but otherwise conventional cosmologies pass rapidly from a smooth distribution to one dominated by lumps with masses greater than those of any known object. Cosmologies dominated by “cold dark matter” produce mass distributions which fit the observed galaxy distribution (i) if Ω = 0.1–0.2 and galaxies follow the mass distribution, or (ii) if Ω = 1, HO< 50 km/s/Mpc and galaxies form preferentially in high density regions. In the latter case, clumps form with flat rotation curves with about the amplitude and abundance expected for galaxy halos.

scholarly journals Voronoi volume function: a new probe of cosmology and galaxy evolution

2020 ◽  
Vol 495 (3) ◽  
pp. 3233-3251 ◽  
Author(s):  
Aseem Paranjape ◽  
Shadab Alam
Keyword(s):  
Dark Matter ◽  
Galaxy Evolution ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Voronoi Tessellation ◽  
Small Scale ◽  
Summary Statistics ◽  
Number Density ◽  
Volume Function ◽  
Space Effects

ABSTRACT We study the Voronoi volume function (VVF) – the distribution of cell volumes (or inverse local number density) in the Voronoi tessellation of any set of cosmological tracers (galaxies/haloes). We show that the shape of the VVF of biased tracers responds sensitively to physical properties such as halo mass, large-scale environment, substructure, and redshift-space effects, making this a hitherto unexplored probe of both primordial cosmology and galaxy evolution. Using convenient summary statistics – the width, median, and a low percentile of the VVF as functions of average tracer number density – we explore these effects for tracer populations in a suite of N-body simulations of a range of dark matter models. Our summary statistics sensitively probe primordial features such as small-scale oscillations in the initial matter power spectrum (as arise in models involving collisional effects in the dark sector), while being largely insensitive to a truncation of initial power (as in warm dark matter models). For vanilla cold dark matter (CDM) cosmologies, the summary statistics display strong evolution and redshift-space effects, and are also sensitive to cosmological parameter values for realistic tracer samples. Comparing the VVF of galaxies in the Galaxies & Mass Assembly (GAMA) survey with that of abundance-matched CDM (sub)haloes tentatively reveals environmental effects in GAMA beyond halo mass (modulo unmodelled satellite properties). Our exploratory analysis thus paves the way for using the VVF as a new probe of galaxy evolution physics as well as the nature of dark matter and dark energy.

scholarly journals Quantifying the power spectrum of small-scale structure in semi-analytic galaxies

2019 ◽  
Vol 488 (4) ◽  
pp. 5085-5092 ◽  
Author(s):  
Sean Brennan ◽  
Andrew J Benson ◽  
Francis-Yan Cyr-Racine ◽  
Charles R Keeton ◽  
Leonidas A Moustakas ◽  
...  
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
Scale Structure ◽  
Small Scale ◽  
Small Scale Structure ◽  
Mass Distributions ◽  
Theoretical Predictions ◽  
Spectrum Distribution

Abstract In the cold dark matter (CDM) picture of structure formation, galaxy mass distributions are predicted to have a considerable amount of structure on small scales. Strong gravitational lensing has proven to be a useful tool for studying this small-scale structure. Much of the attention has been given to detecting individual dark matter subhaloes through lens modelling, but recent work has suggested that the full population of subhaloes could be probed using a power spectrum analysis. In this paper, we quantify the power spectrum of small-scale structure in simulated galaxies, with the goal of understanding theoretical predictions and setting the stage for using measurements of the power spectrum to test dark matter models. We use a sample of simulated galaxies generated from the galacticus semi-analytic model to determine the power spectrum distribution first in the CDM paradigm and then in a warm dark matter scenario. We find that a measurement of the slope and amplitude of the power spectrum on galaxy strong lensing scales (k ∼ 1 kpc−1) could be used to distinguish between CDM and alternate dark matter models, especially if the most massive subhaloes can be directly detected via gravitational imaging.

scholarly journals Dwarf Galaxies as Cosmological Probes

2018 ◽  
Vol 14 (S344) ◽  
pp. 455-463
Author(s):  
Julio F. Navarro
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Dark Matter Halos ◽  
Too Big To Fail ◽  
Sharp Minimum ◽  
Luminous Galaxies ◽  
Small Scales ◽  
Low Mass

AbstractThe Lambda Cold Dark Matter (LCDM) paradigm makes specific predictions for the abundance, structure, substructure and clustering of dark matter halos, the sites of galaxy formation. These predictions can be directly tested, in the low-mass halo regime, by dark matter-dominated dwarf galaxies. A number of potential challenges to LCDM have been identified when confronting the expected properties of dwarfs with observation. I review our understanding of a few of these issues, including the “missing satellites” and the “too-big-to-fail” problems, and argue that neither poses an insurmountable challenge to LCDM. Solving these problems requires that most dwarf galaxies inhabit halos of similar mass, and that there is a relatively sharp minimum halo mass threshold to form luminous galaxies. These predictions are eminently falsifiable. In particular, LCDM predicts a large number of “dark” low-mass halos, some of which should have retained enough primordial gas to be detectable in deep 21 cm or Hα surveys. Detecting this predicted population of “mini-halos” would be a major discovery and a resounding success for LCDM on small scales.

scholarly journals Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

2014 ◽  
Vol 10 (S311) ◽  
pp. 72-77
Author(s):  
John Kormendy ◽  
K. C. Freeman
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Scaling Laws ◽  
Large Population ◽  
Elliptical Galaxies ◽  
Dark Matter Halos ◽  
Fundamental Plane ◽  
Dwarf Spheroidal Galaxies ◽  
Visible Matter ◽  
Luminous Galaxies

AbstractDark 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 Vcirc ~ 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 Vcirc ≲ 42 ± 4 km s−1, in agreement with Vcirc 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.

scholarly journals Kinematics of Milky Way Satellites: Mass Estimates, Rotation Limits, and Proper Motions

2010 ◽  
Vol 2010 ◽  
pp. 1-11 ◽  
Author(s):  
Louis E. Strigari
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Dark Matter Halo ◽  
Data Sets ◽  
Proper Motions ◽  
Kinematic Data ◽  
Velocity Anisotropy ◽  
Mass Distributions ◽  
Wide Range

In the past several years kinematic data sets from Milky Way satellite galaxies have greatly improved, furthering the evidence that these systems are the most dark matter dominated objects known. This paper discusses a maximum likelihood formalism that extracts important quantities from these kinematic data sets, including the amplitude of a rotational signal, proper motions, and the mass distributions. Using a simple model for galaxy rotation it is shown that the expected error on the amplitude of a rotational signal is∼0.5 kms−1with∼103stars from either classical or ultra-faint satellites. As an example Sculptor is analyzed for the presence of a rotational signal; no significant detection of rotation is found, with a 90% c.l. upper limit of∼2 kms−1. A criterion for model selection is presented that determines the parameters required to describe the dark matter halo density profiles and the stellar velocity anisotropy. Applied to four data sets with a wide range of velocities, models with variable velocity anisotropy are preferred relative to those with constant velocity anisotropy, and that central dark matter profiles both less cuspy and more cuspy than Lambda-Cold Dark Matter-based fits are equally acceptable.

scholarly journals Void Formation: Does the Void-in-Cloud Process Matter?

2019 ◽  
Author(s):  
Hei Yin Jowett Chan ◽  
Masashi Chiba ◽  
Tomoaki Ishiyama
Keyword(s):  
Dark Matter ◽  
Analytical Model ◽  
Cold Dark Matter ◽  
Void Formation ◽  
Critical Threshold ◽  
Number Density ◽  
The Press ◽  
Void Effect ◽  
Cloud Effect ◽  
Cloud Process

Abstract We investigate the basic properties of voids from high resolution, cosmological N-body simulations of Λ–dominated cold dark matter (ΛCDM) models, in order to compare with the analytical model of Sheth and van de Weygaert (SvdW) for void statistics. For the subsample of five dark matter simulations in the ΛCDM cosmology with box sizes ranging from 1000h−1Mpc to 8 h−1Mpc, we find that the standard void–in–cloud effect is too simplified to explain several properties of identified small voids in simulations. (i) The number density of voids is found to be larger than the prediction of the analytical model up to 2 orders of magnitude below 1h−1Mpc scales. The Press-Schechter model with the linear critical threshold of void δv = −2.71, or a naive power law, is found to provide an excellent agreement with the void size function, suggesting that the void-in-cloud effect does not suppress as much voids as predicted by the SvdW model. (ii) We then measured the density and velocity profiles of small voids, and find that they are mostly partially collapsing underdensities, instead of being completely crushed in the standard void–in–cloud scenario. (iii) Finally, we measure the void distributions in four different tidal environments, and find that the void–in-void effect alone can explain the correlation between distribution and environments, whereas the void–in–cloud effect is only weakly influencing the abundance of voids, even in filaments and clusters.

Dark matter as residual of topological changes

2016 ◽  
Vol 13 (03) ◽  
pp. 1650027
Author(s):  
Cécile Barbachoux ◽  
Joseph Kouneiher
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Particle Number ◽  
Particle Number Density ◽  
Number Density ◽  
Quantum Regime ◽  
Extended Group ◽  
The Universe ◽  
Spacetime Foam ◽  
Finite Particle

We investigate in this paper the possibilities that the observed cold dark matter density can be generated by decays of a heavy scalar field which dominate the universe at the quantum regime. Indeed, we present two approaches based on an extension of quantum field theory to the case when spacetime topology fluctuates (spacetime foam, at the quantum regime). In this extension the number of bosonic fields becomes a variable and the ground state is characterized by a finite particle number density. In the second approach it is the gauge-group parameters which became dynamical. This is tributary on the Centrally Extended Group and Cohomology.

Relic Densities for Kaluza–Klein Dark Matter

2003 ◽  
Vol 18 (24) ◽  
pp. 1705-1710 ◽  
Author(s):  
Debasish Majumdar
Keyword(s):  
Dark Matter ◽  
Boltzmann Equation ◽  
Extra Dimensions ◽  
Cold Dark Matter ◽  
Entropy Density ◽  
Number Density ◽  
Kaluza Klein ◽  
Freeze Out

We consider the lightest Kaluza–Klein particle in universal extra dimensions (UED) to be a possible candidate for cold dark matter (CDM). We compute the relic densities for such Kaluza–Klein dark matter. This is done by first solving Boltzmann equation numerically to obtain freeze-out temperature and the ratio of number density and entropy density, for different masses. The relic densities (Ωh2) are then computed to find their variation with CDM masses. These calculations are performed considering two coannihilation channels namely B1 B1 → e+e- and B1 B1 → qq.

scholarly journals Halo concentration strengthens dark matter constraints in galaxy-galaxy strong lensing analyses

2021 ◽  
Author(s):  
Nicola C Amorisco ◽  
James Nightingale ◽  
Qiuhan He ◽  
Aristeidis Amvrosiadis ◽  
Xiaoyue Cao ◽  
...  
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Large Population ◽  
Dark Matter Particle ◽  
Mass Function ◽  
Gravitational Lenses ◽  
High Concentration ◽  
Expected Number ◽  
Order Of Magnitude ◽  
Low Mass

Abstract A defining prediction of the cold dark matter (CDM) cosmological model is the existence of a very large population of low-mass haloes. This population is absent in models in which the dark matter particle is warm (WDM). These alternatives can, in principle, be distinguished observationally because halos along the line-of-sight can perturb galaxy-galaxy strong gravitational lenses. Furthermore, the WDM particle mass could be deduced because the cut-off in their halo mass function depends on the mass of the particle. We systematically explore the detectability of low-mass haloes in WDM models by simulating and fitting mock lensed images. Contrary to previous studies, we find that halos are harder to detect when they are either behind or in front of the lens. Furthermore, we find that the perturbing effect of haloes increases with their concentration: detectable haloes are systematically high-concentration haloes, and accounting for the scatter in the mass-concentration relation boosts the expected number of detections by as much as an order of magnitude. Haloes have lower concentration for lower particle masses and this further suppresses the number of detectable haloes beyond the reduction arising from the lower halo abundances alone. Taking these effects into account can make lensing constraints on the value of the mass function cut-off at least an order of magnitude more stringent than previously appreciated.

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