The Fundamental Plane at z = 1.27: First Calibration of the Mass Scale of Red Galaxies at Redshifts z > 1

Abstract

We present results on the fundamental plane of early-type galaxies in the cluster RDCS J0848+4453 at z=1.27. Internal velocity dispersions of three K-selected early-type galaxies are determined from deep Keck spectra, using absorption lines in the rest-frame wavelength range 3400-4000 Å. Structural parameters are determined from Hubble Space Telescope NICMOS images. The galaxies show substantial offsets from the fundamental plane of the nearby Coma Cluster, as expected from passive evolution of their stellar populations. The offsets from the fundamental plane can be expressed as offsets in mass-to-light (M/L) ratio. The M/L ratios of the two most massive galaxies are consistent with an extrapolation of results obtained for clusters at 0.02 3 and R-K>5, and our results show that it is hazardous to use simple models for converting luminosity to mass for these objects. The work presented here, and previous mass measurements at lower redshift, can be considered first steps to empirically disentangle luminosity and mass evolution at the high-mass end of the galaxy population, lifting an important degeneracy in the interpretation of evolution of the luminosity function.