Statistics of satellite galaxies around milky-way-like hosts

We calculate the probability that a Milky-Way (MW)-like halo in the standard cosmological model has the observed number of Magellanic Clouds (MCs). The statistics of the number of MCs in the lambda cold dark matter model are in good agreement with observations of a large sample of Sloan Digital Sky Survey (SDSS) galaxies. Under the subhalo abundance matching assumption of a relationship with small scatter between galaxy r-band luminosities and halo internal velocities v _max, we make detailed comparisons to similar measurements using SDSS Data Release7 data by Liu etal. Models and observational data give very similar probabilities for having zero, one, and two MC-like satellites. In both cases, MW luminosity hosts have just a 10% chance of hosting two satellites similar to the MCs. In addition, we present a prediction for the probability for a host galaxy to have N _sats satellite galaxies as a function of the magnitudes of both the host and satellite. This probability and its scaling with host properties is significantly different from that of mass-selected objects because of scatter in the mass-luminosity relation and because of variations in the star formation efficiency with halo mass.