We have explored prevailing modes of galaxy growth for redshifts z ~ 6-14, comparing substantially overdense and normal regions of the universe, using high-resolution zoom-in cosmological simulations. Such rare overdense regions have been projected t
o host high-z quasars. We demonstrate that galaxies in such environments grow predominantly by a smooth accretion from cosmological filaments which dominates the mass input from major, intermediate and minor mergers. We find that by z ~6, the accumulated galaxy mass fraction from mergers falls short by a factor of 10 of the cumulative accretion mass for galaxies in the overdense regions, and by a factor of 5 in the normal environments. Moreover, the rate of the stellar mass input from mergers also lies below that of an in-situ star formation (SF) rate. The fraction of stellar masses in galaxies contributed by mergers in overdense regions is ~12%, and ~33% in the normal regions, at these redshifts. Our median SF rates for ~few X 10^9 Mo galaxies agrees well with the recently estimated rates for z ~ 7 galaxies from Spitzers SURF-UP survey. Finally, we find that the main difference between the normal and overdense regions lies in the amplified growth of massive galaxies in massive dark matter halos. This leads to the formation of >= 10^{10} Mo galaxies due to the ~100-fold increase in mass during the above time period. Such galaxies are basically absent in the normal regions at these redshifts.
The temperature profile of hot gas in galaxies and galaxy clusters is largely determined by the depth of the total gravitational potential and thereby by the dark matter (DM) distribution. We use high-resolution hydrodynamical simulations of galaxy f
ormation to derive a surprisingly simple relation between the gas temperature and DM properties. We show that this relation holds not just for galaxy clusters but also for equilibrated and relaxed galaxies at radii beyond the central stellar-dominated region of typically a few kpc. It is then clarified how a measurement of the temperature and density of the hot gas component can lead to an indirect measurement of the DM velocity anisotropy in galaxies. We also study the temperature relation for galaxy clusters in the presence of self-regulated, recurrent active galactic nuclei (AGN), and demonstrate that this temperature relation even holds outside the inner region of 30 kpc in clusters with an active AGN.
We study the central dark matter (DM) cusp evolution in cosmological galactic halos. Models with and without baryons (baryons+DM, hereafter BDM model, and pure DM, PDM model, respectively) are advanced from identical initial conditions. The DM cusp p
roperties are contrasted by a direct comparison of pure DM and baryonic models. We find a divergent evolution between the PDM and BDM models within the inner ~10 kpc region. The PDM model forms a R^{-1} cusp as expected, while the DM in the BDM model forms a larger isothermal cusp R^{-2} instead. The isothermal cusp is stable until z~1 when it gradually levels off. This leveling proceeds from inside out and the final density slope is shallower than -1 within the central 3 kpc (i.e., expected size of the R^{-1} cusp), tending to a flat core within ~2 kpc. This effect cannot be explained by a finite resolution of our code which produces only a 5% difference between the gravitationally softened force and the exact Newtonian force of point masses at 1 kpc from the center. Neither is it related to the energy feedback from stellar evolution or angular momentum transfer from the bar. Instead it can be associated with the action of DM+baryon subhalos heating up the cusp region via dynamical friction and forcing the DM in the cusp to flow out and to `cool down. The process described here is not limited to low z and can be efficient at intermediate and even high z.
We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyze the matter distribution and cosmic velocity flows in the Local Universe on the basis of the PSCz galaxy survey. The prime objective of this study is the production o
f optimal resolution three-dimensional maps fully volume-covering of the volume-weighted velocity and density fields throughout the nearby Universe, out to a distance of 150 Mpc/h. Based on the Voronoi and Delaunay tessellation defined by the spatial galaxy sample, DTFE involves the estimate of density values on the basis of the volume of the related Delaunay tetrahedra and the subsequent use of theDelaunay tessellation as natural multidimensional (linear) interpolation grid for the corresponding density and velocity fields throughout the sample volume. The linearized model of the spatial galaxy distribution and the corresponding peculiar velocities of the PSCz galaxy sample, produced by Brachini et al. (1999), forms the input sample for the DTFE study. The DTFE maps reproduce the high-density supercluster regions in optimal detail, both their internal structure as well as their elongated or flattened shape. The corresponding velocity flows trace the bulk and shear flows marking the region extending from the Pisces-Perseus supercluster, via the Local superclusters, towards the Hydra-Centaurus and the Shapley concentration. The most outstanding and unique feature of the DTFE maps is the sharply defined radial outflow regions in and around underdense voids, marking the dynamical importance of voids in the Local Universe. The maximum expansion rate of voids defines a sharp cutoff in the DTFE velocity divergence pdf. We found that on the basis of this cutoff DTFE manages to consistently reproduce the value of O_m ~ 0.35 underlying the linearized velocity dataset.
