The Ks-band luminosity and stellar mass functions of galaxies in z∼1 clusters

We present the near-infrared (K-s-band) luminosity function of galaxies in two z similar to 1 cluster candidates, 3C 336 and Q1335+28. A third cluster, 3C 289, was observed but found to be contaminated by a foreground system. Our wide-field imaging data reach to K-s = 20.5 (5sigma), corresponding to similar to M* + 2.7 with respect to passive evolution. The near-infrared luminosity traces the stellar mass of a galaxy due to its small sensitivity to the recent star formation history. Thus the luminosity function can be transformed to the stellar mass function of galaxies using the J - K-s colours with only a small correction (factor less than or similar to 2) for the effects of ongoing star formation. The derived stellar mass function spans a wide range in mass from similar to3 x 10(11) M-. down to similar to6 x 10(9) M-. (set by the magnitude limit). The form of the mass function is very similar to lower-redshift counterparts such as that from 2MASS/LCRS clusters (given by Balogh et al.) and the z = 0.31 clusters (given by Barger et al.). This indicates little evolution of galaxy masses from z = I to the present day. Combined with colour data suggesting that star formation is completed early (z much greater than 1) in the cluster core, it seems that the galaxy formation processes (both star formation and mass assembly) are strongly accelerated in dense environments and have been largely completed by z = 1. We investigate whether the epoch of mass assembly of massive cluster galaxies is earlier than that predicted by the semi-analytic hierarchical galaxy formation models. These models predict the increase of characteristic mass by more than a factor of similar to3 between z = 1 and the present day. This seems incompatible with our data.