Hierarchical Cold Dark Matter (CDM) models predict that Milky Way sized halos contain several hundred dense low-mass dark matter satellites (the substructure), an order of magnitude more than the number of observed satellites in the Local Group. If the CDM paradigm is correct, this prediction implies that the Milky Way and Andromeda are filled with numerous dark halos. To understand why these h...

Rotation curves place important constraints on the radial mass distribution of dark matter halos, ρ(r). At large radii, rotation curves tend to become asymptotically flat. For ρ(r) ∝ r, this implies α ≈ −2, which persists as far out as can be measured. At small radii, the data strongly prefer dark matter halos with constant density cores (α ≈ 0) over the cuspy halos (α ≤ −1) predicted by cosmol...

Aims. We revisit the study of the mass functions and the bias of dark matter halos. Methods. Focusing on the limit of rare massive halos, we point out that exact analytical results can be obtained for the large-mass tail of the halo mass function. This is most easily seen from a steepest-descent approach, that becomes asymptotically exact for rare events. We also revisit the traditional derivat...

We present a new method for calculating the merger history of matter halos in hierarchical clustering cosmologies. The linear density field is smoothed on a range of scales, these are then ordered in decreasing density and a merger tree constructed. The method is similar in many respects to the block model of Cole & Kaiser but has a number of advantages: (i) it retains information about the spa...

We present results of combined N-body and three-dimensional reionization calculations to determine the relationship between reionization history and local environment in a volume 1 Gpc h−1 across and a resolution of about 1 Mpc. We resolve the formation of about 2× 106 halos of mass greater than ∼ 10M⊙ at z = 0, allowing us to determine the relationship between halo mass and reionization epoch ...

In the standard paradigm, satellite galaxies are believed to be associated with the population of dark matter subhalos. The assumption usually made is that the relationship between satellite galaxies and sub-halos is similar to that between central galaxies and host halos. In this paper, we use the conditional stellar mass functions of satellite galaxies obtained from a large galaxy group catal...

The balance of evidence indicates that individual galaxies and groups or clusters of galaxies are embedded in enormous distributions of cold, weakly interacting dark matter. These dark matter “halos” provide the scaffolding for all luminous structures in the universe, and their properties comprise an essential part of the current cosmological model. I review the internal properties of dark matt...

We use a suite of high-resolution N-body simulations to study the properties, abundance and clustering of high mass halos at high redshift, including their mass assembly histories and mergers. We find that the analytic form which best fits the abundance of halos depends sensitively on the assumed definition of halo mass, with common definitions of halo mass differing by a factor of two for thes...

The first-generation stars in the ΛCDM universe are considered to have formed in dark halos with total masses in the range ∼ 10−10M⊙ at z ∼ 20−50. These stars expected to be very massive and in some cases they end their lives as the first supernovae (SNe). We explore the problem of whether star formation in low mass dark halos (6 10M⊙) was triggered or suppressed by the SN feedback from neighbo...

Using a high-resolution cosmologicalN -body simulation, we identify the ejected population of subhalos, which are halos at redshift z = 0 but were once contained in more massive ‘host’ halos at high redshifts. The fraction of the ejected subhalos in the total halo population of the same mass ranges from 9% to 4% for halo masses from ∼ 10 to ∼ 10 hM⊙. Most of the ejected subhalos are distributed...