Dark Matter Substructure and Dwarf Galactic Satellites

Abstract

A decade ago cosmological simulations of increasingly higher resolution were used to demonstrate that virialized regions of Cold Dark Matter (CDM) halos are filled with a multitude of dense, gravitationally-bound clumps. These dark matter subhalos are central regions of halos that survived strong gravitational tidal forces and dynamical friction during the hierarchical sequence of merging and accretion via which the CDM halos form. Comparisons with observations revealed that there is a glaring discrepancy between abundance of subhalos and luminous satellites of the Milky Way and Andromeda as a function of their circular velocity or bound mass within a fixed aperture. This large discrepancy, which became known as the "substructure" or the "missing satellites" problem, begs for an explanation. In this paper I review the progress made during the last several years both in quantifying the problem and in exploring possible scenarios in which it could be accommodated and explained in the context of galaxy formation in the framework of the CDM paradigm of structure formation. In particular, I show that the observed luminosity function, radial distribution, and the remarkable similarity of the inner density profiles of luminous satellites can be understood within hierarchical CDM framework using a simple model in which efficiency of star formation monotonically decreases with decreasing virial mass satellites had before their accretion without any actual sharp galaxy formation threshold. 1

A unified model for the spatial and mass distribution of subhaloes

“…In this case, planting galaxies following the host halo profile is the correct choice. Such a selection effect has already been noted by Nagai & Kravtsov (2005) and Kravtsov (2010). Conroy, Wechsler & Kravtsov (2006) and Chen et al (2006) showed that populating subhaloes according to their infall properties provides a better match to the observed spatial distribution or clustering of galaxies, although they only studied surviving subhaloes (i.e.…”

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

“…Moore et al (1999) argue that the number of dark matter subhalos is 10 − 100 times larger than the number of satellites observed around the Milky Way (Kravtsov 2010). The so-called "missing satellite problem" has been revisited in a somewhat quantitative context (Boylan-Kolchin et al 2011;Lovell et al 2012;Boylan-Kolchin et al 2012).…”

Control of galactic scale star formation by gravitational instability or midplane pressure?

“…Including that in cosmological models seems to be one way forward to understanding the evolution of galaxies over cosmic time (Kravtsov 2010). Varying global efficiency of star formation is a natural consequence of gravitational instability in galaxies with varying properties.…”

“…Rather than H 2 formation being the gate to star formation, perhaps large scale gravitational collapse leads to both H 2 formation, and, not much later, to star formation. Indeed, simulations of H 2 formation in a self-gravitating, magnetized, periodic, turbulent box show that (Glover & Mac Low 2007, 2010) the density enhancements produced by supersonic turbulence can lead to substantial molecular fractions within a few million years. The fraction of molecular hydrogen in these simulations shows a clear dependence on the density of the gas in the box.…”