Using detailed mock galaxy redshift surveys ( MGRSs ) we investigate the abundance and radial distribution of satellite galaxies .
The mock surveys are constructed using large numerical simulations and the conditional luminosity function ( CLF ) , and are compared against data from the Two Degree Field Galaxy Redshift Survey ( 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 and in excellent agreement with our previous models and with that of Vale & Ostriker .
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 ; the data are consistent with a radial number density distribution that follows that of the dark matter particles , but we can not rule out alternatives with a constant number density core .
Marginalizing over the full CLF parameter space , we show that in a \Lambda CDM concordance cosmology the observed abundances of host and satellite galaxies in the 2dFGRS indicate a power spectrum normalization of \sigma _ { 8 } \simeq 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 .