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In the history of astronomy, major advances in our understanding of the Universe frequently arise from dramatic improvements in our ability to accurately measure astronomical quantities. Aided by rapid progress in information technology, current sky surveys are changing the way we view and study the Universe. Next-generation surveys will maintain this(More)
We present results of a convergence study in which we compare the density profiles of CDM dark matter halos simulated with varying mass and force resolution. We show that although increasing the mass and force resolution allows one to probe deeper into the inner halo regions, the halo profiles converge at scales larger than the " effective " spatial(More)
We discuss how measurements of the absorption of gamma-rays from GeV to TeV energies via pair production on the extragalactic background light (EBL) can probe important issues in galaxy formation. Semi-analytic models (SAMs) of galaxy formation, based on the flat LCDM hierarchical structure formation scenario, are used to make predictions of the EBL from(More)
The Milky Way has at least twenty-three known satellite galaxies that shine with luminosities ranging from about a thousand to a billion times that of the Sun. Half of these galaxies were discovered in the past few years in the Sloan Digital Sky Survey, and they are among the least luminous galaxies in the known Universe. A determination of the mass of(More)
I present an analysis of the density shapes of dark matter halos in ΛCDM and ΛWDM cosmologies. The main results are derived from a statistical sample of galaxy-mass halos drawn from a high resolution ΛCDM N-body simulation. Halo shapes show significant trends with mass and redshift: low-mass halos are rounder than high mass halos, and, for a fixed mass,(More)
The violent hierarchical nature of the Λ-Cold Dark Matter cosmology poses serious difficulties for the formation of disk galaxies. To help resolve these issues, we describe a new, merger-driven scenario for the cosmological formation of disk galaxies at high redshifts that supplements the standard model based on dissipational collapse. In this picture,(More)
We propose a new explanation for the origin of angular momentum in galaxies and their dark halos, in which the halos obtain their spin through the cumulative acquisition of angular momentum from satellite accretion. In our model, the build-up of angular momentum is a random walk process associated with the mass assembly history of the halo's major(More)
We present a Chandra study of mass profiles in 7 elliptical galaxies, of which 3 have galaxy-scale and 4 group-scale halos. These represent the best available data for nearby objects with comparable X-ray luminosities. We measure ∼flat mass-to-light (M/L) profiles within an optical half-light radius (R eff), rising by an order of magnitude at ∼10R eff ,(More)
We study the formation of fifty-three galaxy cluster-size dark matter halos (M = 10 14.0−14.76 M ⊙) formed within a pair of cosmological ΛCDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host ∼ 0.1L * galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters(More)