We describe cosmological galaxy formation simulations with the adaptive mesh refinement code Enzo that incorporate a star formation prescription regulated by the local abundance of molecular hydrogen. We show that this H2-regulated prescription leads
to a suppression of star formation in low mass halos (M_h < ~10^10 M_sun) at z>4, alleviating some of the dwarf galaxy problems faced by theoretical galaxy formation models. H2 regulation modifies the efficiency of star formation of cold gas directly, rather than indirectly reducing the cold gas content with supernova feedback. We determine the local H2 abundance in our most refined grid cells (76 proper parsec in size at z=4) by applying the model of Krumholz, McKee, & Tumlinson, which is based on idealized 1D radiative transfer calculations of H2 formation-dissociation balance in ~100 pc atomic--molecular complexes. Our H2-regulated simulations are able to reproduce the empirical (albeit lower z) Kennicutt-Schmidt relation, including the low Sigma_gas cutoff due to the transition from atomic to molecular phase and the metallicity dependence thereof, without the use of an explicit density threshold in our star formation prescription. We compare the evolution of the luminosity function, stellar mass density, and star formation rate density from our simulations to recent observational determinations of the same at z=4-8 and find reasonable agreement between the two.
The unambiguous detection of Galactic dark matter annihilation would unravel one of the most outstanding puzzles in particle physics and cosmology. Recent observations have motivated models in which the annihilation rate is boosted by the Sommerfeld
effect, a non-perturbative enhancement arising from a long range attractive force. Here we apply the Sommerfeld correction to Via Lactea II, a high resolution N-body simulation of a Milky-Way-size galaxy, to investigate the phase-space structure of the Galactic halo. We show that the annihilation luminosity from kinematically cold substructure can be enhanced by orders of magnitude relative to previous calculations, leading to the prediction of gamma-ray fluxes from up to hundreds of dark clumps that should be detectable by the Fermi satellite.
During the final phases of inspiral, a massive black hole (MBH) binary experiences a recoil due to the asymmetric emission of gravitational waves. We use recent results from numerical relativity simulations together with models of the assembly and gr
owth of MBHs in hierarchical cosmologies, to study the dynamics, statistics, and observability of recoling MBHs. We find that, at redshift z<3, kicked non-rotating holes are typically found between 1 and 30 kpc from their galaxy centers, while rapidly rotating ones are typically between 10 and a few hundred kpc. A recoiling hole that carries an accretion disk may shine as an off-nuclear AGN while it moves away from the center of its host galaxy. We predict that, depending on the hole spin distribution and the duration of their active phase, a population of off-nuclear AGN may already be detectable at low and intermediate redshifts in present deep Hubble Space Telescope observations. The James Webb Space Telescope may discover tens of wandering AGN per square degree, most of them moving within their host halos on unbound trajectories.
