Properties of galaxy groups in the Sloan Digital Sky Survey -- I. The dependence of colour, star formation and morphology on halo mass

Using a large galaxy group catalogue constructed from the Sloan Digital Sky Survey Data Release 2, we investigate the correlation between various galaxy properties and halo mass. We split the population of galaxies in early-types, late-types and intermediate-types, based on their colour and specific star formation rate. At fixed luminosity, the late- (early-)type fraction of galaxies increases (decreases) with decreasing halo mass. Most importantly, this mass dependence is smooth and persists over the entire mass range probed, without any break or feature at any mass-scale. We argue that the previous claim of a characteristic feature on galaxy group scales is an artefact of the environment estimators used. At…