2009ApJ...694.1171T

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 Δ(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)^{–0.52±0.12(±0.20)}. We find stronger evolution in the red fraction: f_red(z) ∝ (1 + z_phot)^{–1.17±0.18(±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 {Gt} 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.