Galaxy formation in WMAP1 and WMAP7 cosmologies

Abstract

Using the technique of Angulo & White (2010) we scale the Millennium and\nMillennium-II simulations of structure growth in a LCDM universe from the\ncosmological parameters with which they were carried out (based on first-year\nresults from the Wilkinson Microwave Anisotropy Probe, WMAP1) to parameters\nconsistent with the seven-year WMAP data (WMAP7). We implement semi-analytic\ngalaxy formation modelling on both simulations in both cosmologies to\ninvestigate how the formation, evolution and clustering of galaxies are\npredicted to vary with cosmological parameters. The increased matter density\nOmega_m and decreased linear fluctuation amplitude sigma8 in WMAP7 have\ncompensating effects, so that the abundance and clustering of dark halos are\npredicted to be very similar to those in WMAP1 for z <= 3. As a result, local\ngalaxy properties can be reproduced equally well in the two cosmologies by\nslightly altering galaxy formation parameters. The evolution of the galaxy\npopulations is then also similar. In WMAP7, structure forms slightly later.\nThis shifts the peak in cosmic star formation rate to lower redshift, resulting\nin slightly bluer galaxies at z=0. Nevertheless, the model still predicts more\npassive low-mass galaxies than are observed. For rp< 1Mpc, the z=0 clustering\nof low-mass galaxies is weaker for WMAP7 than for WMAP1 and closer to that\nobserved, but the two cosmologies give very similar results for more massive\ngalaxies and on large scales. At z>1 galaxies are predicted to be more strongly\nclustered for WMAP7. Differences in galaxy properties, including, clustering,\nin these two cosmologies are rather small up to redshift 3. Given that there\nare still considerable residual uncertainties in galaxy formation models, it is\nvery difficult to distinguish WMAP1 from WMAP7 through observations of galaxy\nproperties or their evolution.\n