scholarly journals Formation of dwarf galaxies and small-scale problems of CDM

2006 ◽  
Vol 2 (S235) ◽  
pp. 385-388
Author(s):  
Oleg Y. Gnedin
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Galactic Halo ◽  
Dwarf Galaxies ◽  
Small Scale ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Gas Cooling ◽  
Low Efficiency ◽  
The Universe

AbstractThe concordance cosmological model based on cold dark matter makes definitive predictions for the growth of galaxies in the Universe, which are being actively studied using numerical simulations. These predictions appear to contradict the observations of dwarf galaxies. Dwarf dark matter halos are more numerous and have steeper central density profiles than the observed galaxies. The first of these small-scale problems, the “missing satellites problem”, can be resolved by accounting for the low efficiency of gas cooling and star formation in dwarf halos. A newly-discovered class of HyperVelocity Stars will soon allow us to test another generic prediction of CDM models, the triaxial shapes of dark matter halos. Measuring the proper motions of HVS will probe the gravitational potential out to 100 kpc and will constrain the axis ratios and the orientation of the Galactic halo.

scholarly journals The Cusp–Core Problem in Gas-Poor Dwarf Spheroidal Galaxies

Galaxies ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 5
Author(s):  
Pierre Boldrini
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Small Scale ◽  
Density Profiles ◽  
True Nature ◽  
Dwarf Spheroidal Galaxies ◽  
Stellar Feedback ◽  
Second Category ◽  
Core Problem

This review deals with the inconsistency of inner dark matter density profiles in dwarf galaxies, known as the cusp–core problem. In particular, we aim to focus on gas-poor dwarf galaxies. One of the most promising solutions to this cold dark matter small-scale issue is the stellar feedback, but it seems to be only designed for gas-rich dwarfs. However, in the regime of classical dwarfs, this core mechanism becomes negligible. Therefore, it is required to find solutions without invoking these baryonic processes as dark matter cores tend to persist even for these dwarfs, which are rather dark-matter-dominated. Here, we have presented two categories of solutions. One consists of creating dark matter cores from cusps within cold dark matter by altering the dark matter potential via perturbers. The second category gathers solutions that depict the natural emergence of dark matter cores in alternative theories. Given the wide variety of solutions, it becomes necessary to identify which mechanism dominates in the central region of galaxies by finding observational signatures left by them in order to highlight the true nature of dark matter.

scholarly journals Structure of Dark Matter Halo

1999 ◽  
Vol 183 ◽  
pp. 155-155
Author(s):  
Toshiyuki Fukushige ◽  
Junichiro Makino
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Temperature Inversion ◽  
Dark Matter Halo ◽  
Temperature Structure ◽  
Galactic Halos ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Order Of Magnitude ◽  
Special Purpose Computer

We performed N-body simulation on special-purpose computer, GRAPE-4, to investigate the structure of dark matter halos (Fukushige, T. and Makino, J. 1997, ApJL, 477, L9). Universal profile proposed by Navarro, Frenk, and White (1996, ApJ, 462, 563), which has cusp with density profiles ρ ∝r−1in density profile, cannot be reproduced in the standard Cold Dark Matter (CDM) picture of hierarchical clustering. Previous claims to the contrary were based on simulations with relatively few particles, and substantial softening. We performed simulations with particle numbers an order of magnitude higher, and essentially no softening, and found that typical central density profiles are clearly steeper than ρ ∝r−1, as shown in Figure 1. In addition, we confirm the presence of a temperature inversion in the inner 5 kpc of massive galactic halos, and give a natural explanation for formation of the temperature structure.

scholarly journals DARK MATTER AXIONS

2010 ◽  
Vol 25 (02n03) ◽  
pp. 554-563 ◽  
Author(s):  
P. SIKIVIE
Keyword(s):  
Dark Matter ◽  
Particle Physics ◽  
Cold Dark Matter ◽  
Einstein Condensate ◽  
Dark Matter Halos ◽  
Linear Regime ◽  
Bose Einstein Condensate ◽  
Invisible Axion ◽  
Bose Einstein ◽  
The Universe

The hypothesis of an 'invisible' axion was made by Misha Shifman and others, approximately thirty years ago. It has turned out to be an unusually fruitful idea, crossing boundaries between particle physics, astrophysics and cosmology. An axion with mass of order 10-5 eV (with large uncertainties) is one of the leading candidates for the dark matter of the universe. It was found recently that dark matter axions thermalize and form a Bose-Einstein condensate (BEC). Because they form a BEC, axions differ from ordinary cold dark matter (CDM) in the non-linear regime of structure formation and upon entering the horizon. Axion BEC provides a mechanism for the production of net overall rotation in dark matter halos, and for the alignment of cosmic microwave anisotropy multipoles. Because there is evidence for these phenomena, unexplained with ordinary CDM, an argument can be made that the dark matter is axions.

scholarly journals The coherent motion of Cen A dwarf satellite galaxies remains a challenge for ΛCDM cosmology

2021 ◽  
Vol 645 ◽  
pp. L5
Author(s):  
Oliver Müller ◽  
Marcel S. Pawlowski ◽  
Federico Lelli ◽  
Katja Fahrion ◽  
Marina Rejkuba ◽  
...  
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Similar Case ◽  
Dwarf Galaxies ◽  
Elliptical Galaxy ◽  
Satellite System ◽  
Coherent Motion ◽  
Small Scale ◽  
Planar Structures ◽  
Scale Challenges

The plane-of-satellites problem is one of the most severe small-scale challenges for the standard Λ cold dark matter (ΛCDM) cosmological model: Several dwarf galaxies around the Milky Way and Andromeda co-orbit in thin, planar structures. A similar case has been identified around the nearby elliptical galaxy Centaurus A (Cen A). In this Letter, we study the satellite system of Cen A, adding twelve new galaxies with line-of-sight velocities from VLT/MUSE observations. We find that 21 out of 28 dwarf galaxies with measured velocities share a coherent motion. Similarly, flattened and coherently moving structures are found only in 0.2% of Cen A analogs in the Illustris-TNG100 cosmological simulation, independently of whether we use its dark-matter-only or hydrodynamical run. These analogs are not co-orbiting, and they arise only by chance projection, thus they are short-lived structures in such simulations. Our findings indicate that the observed co-rotating planes of satellites are a persistent challenge for ΛCDM, which is largely independent from baryon physics.

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 To β or not to β: can higher order Jeans analysis break the mass–anisotropy degeneracy in simulated dwarfs?

2020 ◽  
Vol 498 (1) ◽  
pp. 144-163
Author(s):  
A Genina ◽  
J I Read ◽  
C S Frenk ◽  
S Cole ◽  
A Benítez-Llambay ◽  
...  
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Local Environment ◽  
Higher Order ◽  
Analysis Method ◽  
Density Profiles ◽  
Velocity Anisotropy ◽  
Density Distributions ◽  
Mass Profiles

ABSTRACT We test a non-parametric higher order Jeans analysis method, GravSphere, on 32 simulated dwarf galaxies comparable to classical Local Group dwarfs like Fornax. The galaxies are selected from A Project Of Simulating The Local Environment (APOSTLE) suite of cosmological hydrodynamics simulations with cold dark matter (CDM) and self-interacting dark matter (SIDM) models, allowing us to investigate cusps and cores in density distributions. We find that, for CDM dwarfs, the recovered enclosed mass profiles have a bias of no more than 10 per cent, with a 50 per cent scatter in the inner regions and a 20 per cent scatter near the half-light radius, consistent with standard mass estimators. The density profiles are also recovered with a bias of no more than 10 per cent and a scatter of 30 per cent in the inner regions. For SIDM dwarfs, the mass and density profiles are recovered within our 95 per cent confidence intervals but are biased towards cuspy dark matter distributions. This is mainly due to a lack of sufficient constraints from the data. We explore the sources of scatter in the accuracy of the recovered profiles and suggest a χ2 statistic to separate successful models from biased ones. Finally, we show that the uncertainties on the mass profiles obtained with GravSphere are smaller than those for comparable Jeans methods and that they can be further improved if stronger priors, motivated by cosmological simulations, are placed on the velocity anisotropy. We conclude that GravSphere is a promising Jeans-based approach for modelling dark matter distributions in dwarf galaxies.

scholarly journals The True Surface Mass density of Cold Dark Matter Halos

2007 ◽  
Vol 3 (S244) ◽  
pp. 358-359
Author(s):  
Janne Holopainen ◽  
E. Zackrisson ◽  
A. Knebe ◽  
P. Nurmi ◽  
P. Heinämaki ◽  
...  
Keyword(s):  
Dark Matter ◽  
Analytical Model ◽  
Light Propagation ◽  
Cold Dark Matter ◽  
Mass Density ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Surface Mass ◽  
Symmetric Density ◽  
Surface Mass Density

AbstractThe cold dark matter (CDM) scenario generically predicts the existence of triaxial dark matter halos which contain notable amounts of substructure. However, analytical halo models with smooth, spherically symmetric density profiles are routinely adopted in the modelling of light propagation effects through such objects. In this paper, we report the biases introduced by this procedure by comparing the surface mass densities of actual N-body halos against the widely used analytical model suggested by Navarro, Frenk and White (1996) (NFW). We conduct our analysis in the redshift range of 0.0 − 1.5.In cluster sized halos, we find that triaxiality can cause scatter in the surface mass density of the halos up to σ+= +60% and σ−= −70%, where the 1-σ limits are relative to the analytical NFW model given value. Subhalos can increase this scatter to σ+= +70% and σ−= −80%. In galaxy sized halos, the triaxial scatter can be as high as σ+= +80% and σ−= −70%, and with subhalos the values can change to σ+= +40% and σ−= −80%.We have developed an analytical model for the surface mass density scatter as a function of distance to the halo centre, halo redshift and halo mass. The analytical description enables one to investigate the reliability of results obtained with simplified halo models. Additionally, it provides the means to add simulated surface density scatter to analytical density profiles. We have tested our model on the calculation of microlensing optical depths for MACHOs in CDM halos.

scholarly journals Probing the nature of dark matter with accreted globular cluster streams

2020 ◽  
Vol 501 (1) ◽  
pp. 179-200 ◽  
Author(s):  
Khyati Malhan ◽  
Monica Valluri ◽  
Katherine Freese
Keyword(s):  
Dark Matter ◽  
Globular Cluster ◽  
Particle Physics ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Density Profiles ◽  
Parallel Structures ◽  
Stellar Streams ◽  
Future Data ◽  
Low Mass

ABSTRACT The steepness of the central density profiles of dark matter (DM) in low-mass galaxy haloes (e.g. dwarf galaxies) is a powerful probe of the nature of DM. We propose a novel scheme to probe the inner profiles of galaxy subhaloes using stellar streams. We show that the present-day morphological and dynamical properties of accreted globular cluster (GC) streams – those produced from tidal stripping of GCs that initially evolved within satellite galaxies and later merged with the Milky Way (MW) – are sensitive to the central DM density profile and mass of their parent satellites. GCs that accrete within cuspy cold dark matter (CDM) subhaloes produce streams that are physically wider and dynamically hotter than streams that accrete inside cored subhaloes. A first comparison of MW streams ‘GD-1’ and ‘Jhelum’ (likely of accreted GC origin) with our simulations indicates a preference for cored subhaloes. If these results hold up in future data, the implication is that either the DM cusps were erased by baryonic feedback, or their subhaloes naturally possessed cored density profiles implying particle physics models beyond CDM. Moreover, accreted GC streams are highly structured and exhibit complex morphological features (e.g. parallel structures and ‘spurs’). This implies that the accretion scenario can naturally explain the recently observed peculiarities in some of the MW streams. We also propose a novel mechanism for forming ‘gaps’ in stellar streams when the remnant of the parent subhalo (which hosted the GC) later passes through the GC stream. This encounter can last a longer time (and have more of an impact) than the random encounters with DM subhaloes previously considered, because the GC stream and its parent subhalo are on similar orbits with small relative velocities. Current and future surveys of the MW halo will uncover numerous faint stellar streams and provide the data needed to substantiate our preliminary tests with this new probe of DM.

scholarly journals The Structure of Cold Dark Matter Halos

1996 ◽  
Vol 171 ◽  
pp. 255-258 ◽  
Author(s):  
Julio F. Navarro
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Large Range ◽  
Disk Galaxies ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Halo Structure ◽  
Disk Rotation ◽  
Disk Mass ◽  
The Masses

High resolution N-body simulations show that the density profiles of dark matter halos formed in the standard CDM cosmogony can be fit accurately by scaling a simple “universal” profile. Regardless of their mass, halos are nearly isothermal over a large range in radius, but significantly shallower than r–2 near the center and steeper than r–2 in the outer regions. The characteristic overdensity of a halo correlates strongly with halo mass in a manner consistent with the mass dependence of the epoch of halo formation. Matching the shape of the rotation curves of disk galaxies with this halo structure requires (i) disk mass-to-light ratios to increase systematically with luminosity, (ii) halo circular velocities to be systematically lower than the disk rotation speed, and (iii) that the masses of halos surrounding bright galaxies depend only weakly on galaxy luminosity. This offers an attractive explanation for the puzzling lack of correlation between luminosity and dynamics in observed samples of binary galaxies and of satellite companions of bright spiral galaxies, suggesting that the structure of dark matter halos surrounding bright spirals is similar to that of cold dark matter halos.

scholarly journals An excess of small-scale gravitational lenses observed in galaxy clusters

Science ◽  
2020 ◽  
Vol 369 (6509) ◽  
pp. 1347-1351 ◽  
Author(s):  
Massimo Meneghetti ◽  
Guido Davoli ◽  
Pietro Bergamini ◽  
Piero Rosati ◽  
Priyamvada Natarajan ◽  
...  
Keyword(s):  
Dark Matter ◽  
Galaxy Clusters ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
Small Scale ◽  
Gravitational Lenses ◽  
Strong Lensing ◽  
Luminous Matter ◽  
Order Of Magnitude ◽  
The Universe

Cold dark matter (CDM) constitutes most of the matter in the Universe. The interplay between dark and luminous matter in dense cosmic environments, such as galaxy clusters, is studied theoretically using cosmological simulations. Observations of gravitational lensing are used to characterize the properties of substructures—the small-scale distribution of dark matter—in clusters. We derive a metric, the probability of strong lensing events produced by dark-matter substructure, and compute it for 11 galaxy clusters. The observed cluster substructures are more efficient lenses than predicted by CDM simulations, by more than an order of magnitude. We suggest that systematic issues with simulations or incorrect assumptions about the properties of dark matter could explain our results.

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