  We present an observational study of the stellar mass function of satellite
galaxies around central galaxies at 0.2<z<1.2. Using statistical background
subtraction of contaminating sources we derive satellite stellar mass
distributions in four bins of central galaxy mass in three redshift ranges. Our
results show that the stellar mass function of satellite galaxies increases
with central galaxy mass, and that the distribution of satellite masses at
fixed central mass is at most weakly dependent on redshift. We conclude that
the average mass distribution of galaxies in groups is remarkably universal
even out to z=1.2 and that it can be uniquely characterized by the group
central galaxy mass. This further suggests that as central galaxies grow in
stellar mass, they do so in tandem with the mass growth of their satellites.
Finally, we classify all galaxies as either star forming or quiescent, and
derive the mass functions of each subpopulation separately. We find that the
mass distribution of both star forming and quiescent satellites show minimal
redshift dependence at fixed central mass. However, while the fraction of
quiescent satellite galaxies increases rapidly with increasing central galaxy
mass, that of star forming satellites decreases.
