Modelling galaxy stellar mass evolution from z ∼ 0.8 to today

We apply the empirical method built for redshift z = 0 in the previous work of Wang et al. to a higher redshift, to link galaxy stellar mass directly with its hosting dark matter halo mass at a redshift of around 0.8. The M(stars)-M(infall) relation of the galaxy stellar mass M(stars) and the host halo mass M(infall) is constrained by fitting both the stellar mass function and the correlation functions at different stellar mass intervals of Visible Multiobject Spectrograph-Very Large Telescope Deep Survey (VVDS) observations, where M(infall) is the mass of the hosting halo at the time when the galaxy was last the central galaxy. We find that for low-mass haloes, the residing central galaxies at high redshift are less massive than those at low redshift. For high-mass haloes, central galaxies in these haloes at high redshift are somewhat more massive than the galaxies at low redshift. Satellite galaxies are less massive at earlier times, for any given mass of hosting halo. Fitting both Sloan Digital Sky Survey (SDSS) and VVDS observations simultaneously, we also propose a unified model of the M(stars)-M(infall) relation, which describes the evolution of central galaxy mass as a function of time. The stellar mass of a satellite galaxy is determined by the M(stars)-M(infall) relation of central galaxies at the time when the galaxy is accreted and becomes a subcomponent of a larger group. With these models, we study the amount of galaxy stellar mass increase from z similar to 0.8 to the present day through galaxy mergers and star formation. Low-mass galaxies (< 3 x 1010 h-1 M(circle dot)) gain their stellar masses from z similar to 0.8 to z = 0 mainly through star formation. For galaxies of higher mass, we find that the increase of stellar mass solely through mergers from z = 0.8 can make massive galaxies a factor similar to 2 larger than observed at z = 0, unless the satellite stellar mass is scattered to intracluster stars by gravitational tidal stripping or to the extended halo around the central galaxy, which is not counted in local observations. We can also predict stellar mass functions for redshifts up to z similar to 3, and the results are consistent with the latest observations. In future, more precise observational data will allow us better to constrain our model.