Environmental influences on dark matter haloes and consequences for the galaxies within them
ABSTRACT We use large N-body simulations of dissipationless gravitational clustering in cold dark matter (CDM) cosmologies to study whether the properties of dark matter haloes are affected by their environment. We look for correlations between the masses, formation redshifts, concentrations, shapes and spins of haloes and the overdensity of their local environment. We also look for correlations of these quantities with the local tidal field. Our conclusion is extremely simple. Only the mass distribution varies as a function of environment. This variation is well described by a simple analytic formula based on the conditional Press--Schechter theory. We find no significant dependence of any other halo property on environment. Our results do not depend on our choice of cosmology. According to current hierarchical models, the structure and evolutionary history of a galaxy are fully determined by the structure and evolutionary history of the dark halo in which it is embedded. If these models are correct, clustering variations between galaxies of differing morphological types, luminosities, colours and surface brightnesses must all arise because the halo mass function is skewed towards high-mass objects in overdense regions of the Universe and towards low-mass objects in underdense regions.
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ABSTRACT: Using semi-analytic models of galaxy formation, we investigate galaxy properties such as the Tully-Fisher relation, the B and K-band luminosity functions, cold gas contents, sizes, metallicities, and colours, and compare our results with observations of local galaxies. We investigate several different recipes for star formation and supernova feedback, including choices that are similar to the treatment in Kauffmann, White & Guiderdoni (1993) and Cole et al. (1994) as well as some new recipes. We obtain good agreement with all of the key local observations mentioned above. In particular, in our best models, we simultaneously produce good agreement with both the observed B and K-band luminosity functions and the I-band Tully-Fisher relation. Improved cooling and supernova feedback modelling, inclusion of dust extinction, and an improved Press-Schechter model all contribute to this success. We present results for several variants of the CDM family of cosmologies, and find that models with values of $\Omega_0 \simeq 0.3$--0.5 give the best agreement with observations. Comment: 26 pages, LaTeX, MNRAS format, 23 inlined postscript figures. Accepted for publication in MNRAS. Revised version contains substantial changes including improved models. High resolution figures, original version, and summary of changes may be found at http://www.fiz.huji.ac.il/~rachels/papers/sp.htmlMonthly Notices of the Royal Astronomical Society 02/1998; 310. DOI:10.1046/j.1365-8711.1999.03032.x · 5.23 Impact Factor
Article: Formation of Disc Galaxies[Show abstract] [Hide abstract]
ABSTRACT: We investigate the influence of the cooling epoch on the formation of galaxies in a cold dark matter dominated universe. Isolated haloes, with circular speeds typical of spiral galaxies, have been selected from a low resolution numerical simulation for re-simulation at higher resolution with dark matter and gas components. The initial conditions are evolved with two smoothed particle hydrodynamics codes, TREESPH and GRAPESPH. In previous SPH simulations, strong outward transport of angular momentum has led to the formation of disc-like systems with much smaller angular momenta than observed in real disc galaxies. Here we investigate whether this problem can be circumvented if feedback processes prevent disc formation until late epochs. The results of varying the cooling epoch for each of five different haloes are analysed. When cooling and star formation occur at early times, stellar discs are destroyed during merger events and we observe similar catastrophic transport of angular momentum as seen in previous work. With cooling suppressed until z=1, discs can form by the present day with angular momenta comparable to those of observed disc galaxies. We conclude that feedback processes, which prevent gas from collapsing until late epochs, are an essential ingredient in disc galaxy formation.Monthly Notices of the Royal Astronomical Society 03/1998; DOI:10.1046/j.1365-8711.1998.t01-1-01931.x · 5.23 Impact Factor
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ABSTRACT: We suggest that the bulge-to-disc ratios of spiral galaxies are primarily determined by the angular momenta of their host haloes predicted in current hierarchical clustering models for structure formation. Gas with low specific angular momentum becomes self-gravitating and presumably forms stars before it can settle into a rotationally supported disc. We assume this part of the gas in a dark halo to form a bulge, while the rest is assumed to settle into a rotationally supported disc. With these assumptions the predicted bulge-to-disc ratios in mass and in size, and other correlations between the bulge and disc components can match current observational results. This model predicts the existence of a population of low-surface-brightness galaxies which are bulgeless. The model also predicts that the bulge component has many properties in common with the disc component, because both form through similar processes. In particular, many bulges should be supported (at least partially) by rotation.