The galactic halo in mixed dark matter cosmologies

The cold dark matter (CDM) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. We review the current observational and theoretical status of these "small-scale controversies." Cosmological simulations that incorporate only gravity and collisionless CDM predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: Recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the Milky Way do not host visible galaxies. However, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. Alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. Gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with CDM predictions. These observational approaches will get more powerful over the next few years.dark matter | cosmology | galaxy formation T he cold dark matter (CDM) hypothesis-that dark matter consists of a weakly interacting particle whose velocity dispersion in the early universe was too small to erase structure on a galactic or subgalactic scale-emerged in the early 1980s and quickly became a central element of the theory of cosmic structure formation. Influential early papers include Peebles' calculation of cosmic microwave background (CMB) anisotropies and the matter power spectrum (1), discussions of galaxy formation with particle dark matter by Bond et al. (2) and Blumenthal et al. (3,4), and Davis et al.'s (5) numerical simulations of galaxy clustering. By the mid-1990s, the simplest CDM model with scale-invariant primordial fluctuations and a critical matter density of ðΩ m = 1Þ had run afoul of multiple lines of observational evidence, including the shape of the galaxy power spectrum, estimates of the mean matter density from galaxy clusters and galaxy motions, the age of the universe inferred from estimates of the Hubble constant, and the amplitude of matter clustering extrapolated forward from the fluctuations measured in the CMB. Many variants on "canonical" CDM were proposed to address these challenges, and by the turn of the century, the combination of supernova evidence for cosmic acceleration and CMB evidence for ...

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“…There have been numerous numerical simulations of structure formation with WDM (recent examples include refs. [58][59][60][61][62][63].…”

Section: Solutions In Dark Matter Physics?mentioning

confidence: 99%

Cold dark matter: Controversies on small scales

Weinberg

Bullock

Governato

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

421

346

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“…The distribution of satellites (faint companions) around isolated primary galaxies provides important information about galaxy formation, as well as a critical test of the ΛCDM model on small scales (Einasto & Einasto 1987;Choi et al 2007;Agustsson & Brainerd 2010;Ferrero et al 2012;Anderhalden et al 2013;Bozek et al 2013). This explains the growing interest in studying the satellite distribution (Prada et al 2003;Sales & Lambas 2005;Guo et al 2012), and in exploring the link between galaxy properties and the satellite population (Park et al 2007;Guo et al 2011;Karachentseva et al 2011;Edman et al 2012;Wang & White 2012;González et al 2013;Cen 2014).…”

Section: Introductionmentioning

confidence: 99%

Effects of the environment on galaxies in the Catalogue of Isolated Galaxies: physical satellites and large scale structure

Argudo-Fernández

Verley

Bergond

et al. 2014

A&A

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Context. We present a study of the 3D environment for a sample of 386 galaxies in the Catalogue of Isolated Galaxies (CIG, Karachentseva 1973) using the Ninth Data Release of the Sloan Digital Sky Survey (SDSS-DR9). Aims. We aim to identify and quantify the effects of the satellite distribution around a sample of galaxies in the CIG, as well as the effects of the large-scale structure (LSS). Methods. To recover the physically bound galaxies we first focused on the satellites that are within the escape speed of each CIG galaxy. We also propose a more conservative method using the stacked Gaussian distribution of the velocity difference of the neighbours. The tidal strengths affecting the primary galaxy were estimated to quantify the effects of the local and LSS environments. We also defined the projected number density parameter at the fifth nearest neighbour to characterise the LSS around the CIG galaxies. Results. Out of the 386 CIG galaxies considered in this study, at least 340 (88% of the sample) have no physically linked satellite. Following the more conservative Gaussian distribution of physical satellites around the CIG galaxies leads to upper limits. Out of the 386 CIG galaxies, 327 (85% of the sample) have no physical companion within a projected distance of 0.3 Mpc. The CIG galaxies are distributed following the LSS of the local Universe, although presenting a large heterogeneity in their degree of connection with it. When present around a CIG galaxy, the effect of physically bound galaxies largely dominates (typically by more than 90%) the tidal strengths generated by the LSS. Conclusions. The CIG samples a variety of environments, from galaxies with physical satellites to galaxies without neighbours within 3 Mpc. A clear segregation appears between early-type CIG galaxies with companions and isolated late-type CIG galaxies. Isolated galaxies are in general bluer, with probably younger stellar populations and very high star formation compared with older, redder CIG galaxies with companions. Reciprocally, the satellites are redder and with an older stellar populations around massive early-type CIG galaxies, while they have a younger stellar content around massive late-type CIG galaxies. This suggests that the CIG is composed of a heterogeneous population of galaxies, sampling from old to more recent, dynamical systems of galaxies. CIG galaxies with companions might have a mild tendency (0.3−0.4 dex) to be more massive, and may indicate a higher frequency of having suffered a merger in the past.

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“…The most important fact is that the entropy per comoving volume is conserved, so that sa 3 is constant, where s is the entropy density, and a is the scale factor. The effective number N eff follows from ρ r (T γ 0 ) = (π 2 /15)(1 + (7/8)(4/11) 4/3 N eff ) T 4 γ 0 and is given by Kolb and Turner [125], Steigman [140], Anchordoqui and Goldberg [141], Steigman et al [142], Anderhalden et al [143,145], Anchordoqui et al [144], and Weinberg [146] …”

Section: Dark Radiationmentioning

confidence: 99%

Multicomponent Dark Matter in Radiative Seesaw Models

2017

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We discuss radiative seesaw models, in which an exact Z 2 × Z ′ 2 symmetry is imposed. Due to the exact Z 2 × Z ′ 2 symmetry, neutrino masses are generated at a two-loop level and at least two extra stable electrically neutral particles are predicted. We consider two models: one has a multi-component dark matter system and the other one has a dark radiation in addition to a dark matter. In the multi-component dark matter system, non-standard dark matter annihilation processes exist. We find that they play important roles in determining the relic abundance and also responsible for the monochromatic neutrino lines resulting from the dark matter annihilation process. In the model with the dark radiation, the structure of the Yukawa coupling is considerably constrained and gives an interesting relationship among cosmology, lepton flavor violating decay of the charged leptons and the decay of the inert Higgs bosons.

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The galactic halo in mixed dark matter cosmologies

Cited by 61 publications

References 77 publications

Cold dark matter: Controversies on small scales

Cold dark matter: Controversies on small scales

Effects of the environment on galaxies in the Catalogue of Isolated Galaxies: physical satellites and large scale structure

Multicomponent Dark Matter in Radiative Seesaw Models

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