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

We present results on the Fundamental Plane (FP) of early-type galaxies inthe cluster RDCS J0848+4453 at z=1.27. Internal velocity dispersions of threeK-selected early-type galaxies are determined from deep Keck spectra.Structural parameters are determined from HST NICMOS images. The galaxies showsubstantial offsets from the FP of the nearby Coma cluster, as expected frompassive evolution of their stellar populations. The offsets from the FP can beexpressed as offsets in M/L ratio. The M/L ratios of the two most massivegalaxies are consistent with an extrapolation of results obtained atz=0.02-0.83. The evolution of early-type galaxies with masses >10^11 M_sun iswell described by ln M/L(B) = (-1.06 +- 0.09) z, corresponding to passiveevolution of -1.50 +- 0.13 mag at z=1.3. Ignoring selection effects, the bestfitting stellar formation redshift is z*=2.6, corresponding to a luminosityweighted age at the epoch of observation of ~2 Gyr. The M/L ratios of these twogalaxies are also in excellent agreement with predictions from models thatinclude progenitor bias. The third galaxy is a factor ~10 less massive than theother two, shows strong Balmer absorption lines in its spectrum, and is offsetfrom the Coma Fundamental Plane by 2.9 mag in rest-frame B. Despite their largerange in M/L ratios, all three galaxies fall in the ``Extremely Red Object''(ERO) class with I-H>3 and R-K>5, and our results show that it is hazardous touse simple models for converting luminosity to mass for these objects.Measurements of M/L ratios at high redshift can be considered first steps toempirically disentangle luminosity and mass evolution at the high mass end ofthe galaxy population, lifting an important degeneracy in the interpretation ofevolution of the luminosity function. [SHORTENED]Comment: Accepted for publication in the Astrophysical Journa