Galaxy formation in WMAP1 and WMAP7 cosmologies

TL;DR

This study compares galaxy formation predictions in WMAP1 and WMAP7 cosmologies by scaling simulations and applying semi-analytic models, finding minimal differences in galaxy properties up to redshift 3 due to compensating effects of cosmological parameters.

Contribution

It demonstrates that galaxy formation and clustering predictions are very similar in WMAP1 and WMAP7 cosmologies when scaled appropriately, highlighting the difficulty in distinguishing cosmologies through galaxy observations.

Findings

Galaxy properties are similar in both cosmologies up to redshift 3.

Structure formation occurs slightly later in WMAP7, affecting star formation peak.

Clustering of low-mass galaxies at z=0 is closer to observations in WMAP7.

Abstract

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