The Rise of Massive Red Galaxies: the color-magnitude and color-stellar mass diagrams for z < ~2 from the MUltiwavelength Survey by Yale-Chile (MUSYC)
Abstract
We present the color-magnitude and color-stellar mass diagrams for galaxies with zphot < ~2, based on a K < 22 (AB) catalog of the Extended Chandra Deep Field South (ECDFS) from the MUltiwavelength Survey by Yale-Chile (MUSYC). Our main sample of 7840 galaxies contains 1297 M* > 1011 MSol galaxies in the range 0.2 < zphot < 1.8. We show empirically that this catalog is approximately complete for M* > 1011 MSol galaxies for zphot < 1.8. For this mass-limited sample, we show that the locus of the red sequence color-stellar mass relation evolves as Del(u-r) ~ (-0.44+/-0.02) zphot for zphot < ~1.2. For zphot > ~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 < zphot <1.8, the comoving number density of M* > 1011 MSol galaxies is ~50% of the local value, with a red fraction of ~33%. Making a parametric fit to the observed evolution, we find ntot(z) ~ (1+zphot)(-0.52+/-0.12(+/-0.20)). We find stronger evolution in the red fraction: fred(z) ~ (1+zphot)(-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>>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 MSol were already in place at z ~ 2.