The satellite luminosity functions of galaxies in Sloan Digital Sky Survey

We study the luminosity function of satellite galaxies around isolated primaries using the Sloan Digital Sky Survey (SDSS) spectroscopic and photometric galaxy samples. We select isolated primaries from the spectroscopic sample and search for potential satellites in the much deeper photometric sample. For primaries of similar luminosity to the Milky Way and M31, we are able to stack as many as similar to 20 000 galaxy systems to obtain robust statistical results. We derive the satellite luminosity function extending almost 8 mag fainter than the primary galaxy. We also determine how the satellite luminosity function varies with the luminosity, colour and concentration of the primary. We find that, in the mean, isolated primaries of comparable luminosity to the Milky Way and M31 contain about a factor of 2 fewer satellites brighter than M-V = -14 than the average of the Milky Way and M31.