M/LB and Color Evolution for a Deep Sample of M Cluster Galaxies at z ~ 1: The Formation Epoch and the Tilt of the Fundamental Plane

We have measured velocity dispersions ( Delta *s) for a sample of 36 galaxies with J < 21.2 or Mr < --20.6 mag in MS 1054-03, a massive cluster of galaxies at z = 0.83. Our data are of uniformly high quality down to our selection limit, our 16 hr exposures typically yielding errors of only Delta *d( Delta *s) ~ 10% for L* and fainter galaxies. By combining our measurements with data from the literature, we have 53 cluster galaxies with measured dispersions, and HST/ACS-derived sizes, colors and surface brightness. This sample is complete for the typical L galaxy at z ~ 1, unlike most previous z ~ 1 cluster samples which are complete only for the massive cluster members (>1011 M ). We find no evidence for a change in the tilt of the fundamental plane (FP). Nor do we find evidence for evolution in the slope of the color- Delta *s relation and M/LB - Delta *s relations; measuring evolution at a fixed Delta *s should minimize the impact of structural evolution found in other work. The M/LB at fixed Delta *s evolves by Delta *Dlog10 M/LB = --0.50 ? 0.03 between z = 0.83 and z = 0.02 or dlog10 M/LB = --0.60 ? 0.04 dz, and we find Delta *D(U -- V) z = --0.24 ? 0.02 mag at fixed Delta *s in the rest frame, matching the expected evolution in M/LB within 2.25 standard deviations. The implied formation redshift from both the color and M/LB evolution is z = 2.0 ? 0.2 ? 0.3(sys), during the epoch in which the cosmic star formation activity peaked, with the systematic uncertainty showing the dependence of z on the assumptions we make about the stellar populations. The lack of evolution in either the tilt of the FP or in the M/L- Delta *s and color- Delta *s relations imply that the formation epoch depends weakly on mass, ranging from z = 2.3+1.3 --0.3 at Delta *s = 300 km s-1 to z = 1.7+0.3 --0.2 at Delta *s = 160 km s-1 and implies that the initial mass function similarly varies slowly with galaxy mass.