Luminosity evolution of early-type galaxies to z=0.83:: constraints on formation epoch and Ω

We present deep Keck telescope spectroscopy of eight galaxies in the luminous X-ray cluster MS 1054-03 at z = 0.83, The data are combined with imaging observations from the Hubble Space Telescope (HST). The spectroscopic data are used to measure the internal kinematics of the galaxies, and the HST data are used to measure their structural parameters. Six galaxies have early-type spectra, and two have "E + A" spectra. The galaxies with early-type spectra define a tight fundamental plane (FP) relation. The evolution of the mass-to-light ratio is derived from the FP. The M/L ratio evolves as Delta log M/L-B proportional to -0.40z (Omega(m) = 0.3, Omega(Lambda) = 0). The observed evolution of the MIL ratio provides a combined constraint on the formation redshift of the stars, the initial mass function (IMF), and cosmological parameters. For a Salpeter IMF (x = 2.35), we find that z(form) > 2.8 and Omega(m) < 0.86 with 95% confidence. The constraint on the formation redshift is weaker if Omega(Lambda) > 0: z(form) > 1.7 if Omega(m) = 0.3 and Omega(Lambda) = 0.7. At present, the limiting factor in constraining z(form) and Omega from the observed luminosity evolution of early-type galaxies is the poor understanding of the IMF We find that if Omega(m) = 1, the IMF must be significantly steerer than the Salpeter IMF (x > 2.6).