The Abundance and Radial Distribution of Satellite Galaxies
  Using detailed mock galaxy redshift surveys (MGRSs) we investigate the abundance and radial distribution of satellite galaxies. The mock surveys are constructed using the conditional luminosity function (CLF), and are compared against data from the 2dFGRS. We use Monte Carlo Markov Chains to explore the full posterior distribution of the CLF parameter space, and show that the average relation between light and mass is tightly constrained. The radial number density distribution of satellite galaxies in the 2dFGRS reveals a pronounced absence of satellites at small projected separations from their host galaxies. This is (at least partially) due to the overlap and merging of galaxy images in the APM catalogue. Because of the resulting close-pair incompleteness we are unfortunately unable to put meaningful constraints on the radial distribution of satellite galaxies. Marginalizing over the full CLF parameter space, we show that in a LCDM concordance cosmology the observed abundances of host and satellite galaxies in the 2dFGRS indicate a power spectrum normalization of sigma_8=0.7. The same cosmology but with sigma_8=0.9 is unable to simultanously match the abundances of host and satellite galaxies. This confirms our previous conclusions based on the pairwise peculiar velocity dispersions and the group multipliticy function. 
Frank C. van den Bosch (ETH), Xiaohu Yang (Umass), H.J. Mo (Umass),   Peder Norberg (ETH)