From dwarf spheroidals to cD galaxies: simulating the galaxy population in a ΛCDM cosmology

Abstract

We have updated and extended our semi-analytic galaxy formation modelling capabilities and applied them simultaneously to the stored halo/subhalo merger trees of the Millennium and Millennium-II Simulations (MS and MS-II, respectively). These differ by a factor of 125 in mass resolution, allowing explicit testing of resolution effects on predicted galaxy properties. We have revised the treatment of the transition between the rapid infall and cooling flow regimes of gas accretion, of the sizes of bulges, and of gaseous and stellar discs, of supernova feedback, of the transition between central and satellite status as galaxies fall into larger systems, and of gas and star stripping, once they become satellites. Plausible values of efficiency and scaling parameters yield an excellent fit not only to the observed abundance of low-redshift galaxies over five orders of magnitude in stellar mass and 9 mag in luminosity, but also to the observed abundance of Milky Way satellites. This suggests that reionization effects may not be needed to solve the 'missing-satellite' problem, except, perhaps, for the faintest objects. The same model matches the observed large-scale clustering of galaxies as a function of stellar mass and colour. The fit remains excellent down to ∼30 kpc for massive galaxies. For M * < 6 × 10 10 M , however, the model overpredicts clustering at scales below ∼1 Mpc, suggesting that the assumed fluctuation amplitude, σ 8 = 0.9, is too high. The observed difference in clustering between active and passive galaxies is matched quite well for all masses. Galaxy distributions within rich clusters agree between the simulations and match those observed, but only if galaxies without dark matter subhaloes (so-called orphans) are included. Even at MS-II resolution, schemes which assign galaxies only to resolved dark matter subhaloes cannot match observed clusters. Our model predicts a larger passive fraction among low-mass galaxies than is observed, as well as an overabundance of ∼10 10 M galaxies beyond z ∼ 0.6. (The abundance of ∼10 11 M galaxies is matched out to z ∼ 3.) These discrepancies appear to reflect deficiencies in the way star formation rates are modelled.

Star formation sustained by gas accretion

“…As in the case of Dayal et al (2013), the deviations from the stationary state are set by the galaxy age. Yates et al (2012) use the semi-analytical model L-Galaxies by Guo et al (2011) to explain the FMR. Thousands of individual galaxies are taken from purely dark-matter cosmological numerical simulations.…”

“…In addition to gas accretion, galaxies also grow through mergers (e.g, Guo et al 2011;Kormendy 2013). Simulations suggest that direct accretion from the cosmic web dominates mergers by about an order of magnitude (e.g., Wang et al 2011;L'Huillier et al 2012;Combes 2013;van de Voort et al 2011).…”

The influence of the environmental history on quenching star formation in a Λ cold dark matter universe

“…Some progress has been made by adopting a more gradual stripping of the hot gas associated with infalling galaxies (e.g. Font et al 2008;Weinmann et al 2010;Guo et al 2011). The improved models are, however, still inconsistent with observations (e.g.…”

“…The effect of environmental processes has been theoretically studied by using semi-empirical models (Wetzel et al 2012), numerical simulations (see De Lucia 2011 for a review) and semi-analytic models (De Lucia & Blaizot 2007;Font et al 2008;Kimm et al 2009;Weinmann et al 2010;Guo et al 2011). Most of the currently used galaxy formation models do not explicitly include environmental processes beyond the virial radius of haloes.…”

“…We take advantage of publicly available galaxy merger trees, obtained by applying the semianalytic model of Guo et al (2011) to the large cosmological dark matter Millennium simulation. The merger trees are analysed in order to study the history of the environment that galaxies have experienced during their life time, as a function of environmental density, stellar mass and galaxy type.…”