Abstract

We present the color-magnitude and color-stellar mass diagrams for galaxies with z phot ? 2, based on a K (AB) < 22 catalog of the × ?° Extended Chandra Deep Field South from the MUltiwavelength Survey by Yale-Chile. Our main sample of 7840 galaxies contains 1297 M *>1011 M ? galaxies in the range 0.2 < z phot < 1.8. We show empirically that this catalog is approximately complete for M *>1011 M ? galaxies for z phot < 1.8. For this mass-limited sample, we show that the locus of the red sequence color-stellar mass relation evolves as ?(u - r) (-0.44 ± 0.02)z phot for z phot ? 1.2. For z phot ? 1.3, however, we are no longer able to reliably distinguish red and blue subpopulations from the observed color distribution; we show that this would require much deeper near-infrared data. At 1.5 < z phot < 1.8, the comoving number density of M *>1011 M ? galaxies is 50% of the local value, with a red fraction of 33%. Making a parametric fit to the observed evolution, we find n tot(z) (1 + z phot)-0.520.12(0.20). We find stronger evolution in the red fraction: f red(z) (1 + z phot) -1.170.18(0.21). Through a series of sensitivity analyses, we show that the most important sources of systematic error are (1) systematic differences in the analysis of the z ˜ 0 and z » 0 samples; (2) systematic effects associated with details of the photometric redshift calculation; and (3) uncertainties in the photometric calibration. With this in mind, we show that our results based on photometric redshifts are consistent with a completely independent analysis which does not require redshift information for individual galaxies. Our results suggest that, at most, 1/5 of local red sequence galaxies with M *>1011 M ? were already in place at z 2. © 2009 The American Astronomical Society.