In order to investigate the structure and dynamics of the recently discovered massive (M_* > 10^11 M_sun) compact z~2 galaxies, cosmological hydrodynamical/N-body simulations of a proto-cluster region have been undertaken. At z=2, the highest resolut
ion simulation contains ~5800 resolved galaxies, of which 509, 27 and 5 have M_* > 10^10 M_sun, > 10^11 M_sun and > 4x10^11 M_sun, respectively. Effective radii and characteristic stellar densities have been determined for all galaxies. At z=2, for the definitely well resolved mass range of M_* > 10^11 Msun, the mass-size relation is consistent with observational findings for the most compact z~2 galaxies. The very high velocity dispersion recently measured for a compact z~2 galaxy (~510 km/s; van Dokkum et al 2009) can be matched at about the 1-sigma level, although a somewhat larger mass than the estimated M_* ~ 2 x 10^11 M_sun is indicated. For the above mass range, the galaxies have an average axial ratio <b/a> = 0.64 +/- 0.02 with a dispersion of 0.1, an average rotation to 1D velocity dispersion ratio <v/sigma> = 0.46 +/- 0.06 with a dispersion of 0.3, and a maximum value of v/sigma ~ 1.1. Rotation and velocity anisotropy both contribute in flattening the compact galaxies. Some of the observed compact galaxies appear flatter than any of the simulated galaxies. Finally, it is found that the massive compact galaxies are strongly baryon dominated in their inner parts, with typical dark matter mass fractions of order only 20% inside of r=2R_eff.
A numerical code for solving various Lyman alpha (Lya) radiative transfer (RT) problems is presented. The code is suitable for an arbitrary, three-dimensional distribution of Lya emissivity, gas temperature, density, and velocity field. Capable of ha
ndling Lya RT in an adaptively refined grid-based structure, it enables detailed investigation of the effects of clumpiness of the interstellar (or intergalactic) medium. The code is tested against various geometrically and physically idealized configurations for which analytical solutions exist, and subsequently applied to three Lyman-break galaxies, extracted from high-resolution cosmological simulations at redshift z = 3.6. Proper treatment of the Lya scattering reveals a diversity of surface brightness (SB) and line profiles. Specifically, for a given galaxy the maximum observed SB can vary by an order of magnitude, and the total flux by a factor of 3 - 6, depending on the viewing angle. This may provide an explanation for differences in observed properties of high-redshift galaxies, and in particular a possible physical link between Lyman-break galaxies and regular Lya emitters.
To assess the effect of baryonic ``pinching of galaxy cluster dark matter (DM) haloes, cosmological (LCDM) TreeSPH simulations of the formation and evolution of two galaxy clusters have been performed, with and without baryons included. The simulat
ions with baryons invoke star formation, chemical evolution with non-instantaneous recycling, metallicity dependent radiative cooling, strong star-burst, driven galactic super-winds and the effects of a meta-galactic UV field, including simplified radiative transfer. The two clusters have T_X~3 and 6 keV, respectively, and, at z~0, both host a prominent, central cD galaxy. Comparing the simulations without and with baryons, it is found for the latter that the inner DM density profiles, r<50-100 kpc, steepen considerably: Delta(alpha)~0.5-0.6, where -alpha is the logarithmic DM density gradient. This is mainly due to the central stellar cDs becoming very massive, as a consequence of the onset of late time cooling flows and related star formation. Once these spurious cooling flows have been corrected for, and the cluster gravitational potentials dynamically adjusted, much smaller pinching effects are found: Delta(alpha)~0.1. Including the effects of baryonic pinching, central slopes of alpha~1.0 and 1.2 are found for the DM in the two clusters, interestingly close to recent observational findings. For the simulations with baryons, the inner density profile of DM+ICM gas combined is found to be only very marginally steeper than that of the DM, Delta(alpha)<0.05. However, the total matter inner density profiles are found to be Delta(alpha)~0.5 steeper than the inner profiles in the dark matter only simulations.
We compute the escape of ionizing radiation from galaxies in the redshift interval z=4-10, i.e., during and after the epoch of reionization, using a high-resolution set of galaxies, formed in fully cosmological simulations. The simulations invoke ear
ly, energetic feedback, and the galaxies evolve into a realistic population at z=0. Our galaxies cover nearly four orders of magnitude in masses (10^{7.8}-10^{11.5}msun) and more than five orders in star formation rates (10^{-3.5}-10^{1.7}msunyr^{-1}), and we include an approximate treatment of dust absorption. We show that the source-averaged Lyman-limit escape fraction at z=10.4 is close to 80% declining monotonically with time as more massive objects build up at lower redshifts. Although the amount of dust absorption is uncertain to 1-1.5 dex, it is tightly correlated with metallicity; we find that dust is unlikely to significantly impact the observed UV output. These results support reionization by stellar radiation from low-luminosity dwarf galaxies and are also compatible with Lyman continuum observations and theoretical predictions at zsim3-4.
Ongoing accretion onto galactic disks has been recently theorized to progress via the unstable cooling of the baryonic halo into condensed clouds. These clouds have been identified as analogous to the High-Velocity Clouds (HVCs) observed in HI in our
Galaxy. Here we compare the distribution of HVCs observed around our own Galaxy and extra-planar gas around the Andromeda galaxy to these possible HVC analogs in a simulation of galaxy formation that naturally generates these condensed clouds. We find a very good correspondence between these observations and the simulation, in terms of number, angular size, velocity distribution, overall flux and flux distribution of the clouds. We show that condensed cloud accretion only accounts for ~ 0.2 M_solar / year of the current overall Galactic accretion in the simulations. We also find that the simulated halo clouds accelerate and become more massive as they fall toward the disk. The parameter space of the simulated clouds is consistent with all of the observed HVC complexes that have distance constraints, except the Magellanic Stream which is known to have a different origin. We also find that nearly half of these simulated halo clouds would be indistinguishable from lower-velocity gas and that this effect is strongest further from the disk of the galaxy, thus indicating a possible missing population of HVCs. These results indicate that the majority of HVCs are consistent with being infalling, condensed clouds that are a remnant of Galaxy formation.
