Poster Title: History of Mass Assembly of Galaxies in z~1 Clusters.
Abstract: Authors: Tadayuki Kodama (National Astronomical Observatory in Japan), Richard Bower (Univ of Durham)
We present the near-infrared (Ks-band) luminosity function of galaxies in two z~1 cluster candidates, 3C336 and Q1335+28. A third cluster, 3C289, was observed but found to be contaminated by a foreground system. Our wide field imaging data reach to Ks=20.5 (5sigma), corresponding to ~M*+2.7 with respect to the 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 colours with only a small correction (factor < 2) for the effects of on-going star formation. The derived stellar mass function spans a wide range in mass from ~3 x 10^{11} Msun down to ~6 x 10^{9} Msun (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 (Balogh et al. 2001) and the z=0.31 clusters (Barger et al. 1998). This indicates little evolution of galaxy masses from z=1 to the present-day. Combined with colour data that suggest star formation is completed early (z>>1) in the cluster core, it seems that the galaxy formation processes (both star formation and mass assembly) are strongly accerelated in dense environments and has 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 factor 3 between z=1 and the present day. This seems incompatible with our data.
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