How accurate is our knowledge of the galaxy bias?

Abstract

Observations of the clustering of galaxies can provide useful information about the distribution of dark matter in the universe. In order to extract accurate cosmological parameters from galaxy surveys, it is important to understand how the distribution of galaxies is biased with respect to the matter distribution. The large-scale bias of galaxies can be quantified either by directly measuring the large-scale (λ ≳ 60 h -1 Mpc) power spectrum of galaxies or by modeling the halo occupation distribution of galaxies using their clustering on small scales (λ ≲ 30 h -1 Mpc). We compare the luminosity dependence of the galaxy bias (both the shape and the normalization) obtained by these methods and check for consistency. Our comparison reveals that the bias of galaxies obtained by the small-scale clustering measurements is systematically larger than that obtained from the large-scale power spectrum methods. We also find systematic discrepancies in the shape of the galaxy-bias-luminosity relation. We comment on the origin and possible consequences of these discrepancies which had remained unnoticed thus far. © 2011 The American Astronomical Society. All rights reserved.