The Space Density and Colors of Massive Galaxies at 2 < z < 3: The Predominance of Distant Red Galaxies

Abstract

Using the deep multiwavelength MUSYC, GOODS, and FIRES surveys we construct a stellar mass-limited sample of galaxies at 2 1011 M☉ distributed over four independent fields with a total area of almost 400 arcmin2. The mean number density of massive galaxies in this redshift range ρ(M > 1011 M☉) = (2.2 ± 0.6) × 10-4 h Mpc-3. We present values and 25th and 75th percentiles for the distributions of observed RAB magnitudes, observed J - Ks colors, and rest-frame ultraviolet continuum slopes, M/LV ratios, and U - V colors. The galaxies show a large range in all these properties. The median galaxy is faint in the observer's optical (RAB = 25.9), red in the observed near-IR (J - Ks = 2.48), has a rest-frame UV spectrum that is relatively flat in Fλ (β = -0.4), and rest-frame optical colors resembling those of nearby spiral galaxies (U - V = 0.62). We determine which galaxies would be selected as Lyman break galaxies (LBGs) or distant red galaxies (DRGs, having J - Ks > 2.3) in this mass-limited sample. By number DRGs make up 69% of the sample, and LBGs 20%, with a small amount of overlap. By mass DRGs make up 77%, and LBGs 17%. Neither technique provides a representative sample of massive galaxies at 2 < z < 3 as they only sample the extremes of the population. As we show here, multiwavelength surveys with high-quality photometry are essential for an unbiased census of massive galaxies in the early universe. The main uncertainty in this analysis is our reliance on photometric redshifts; confirmation of the results presented here requires extensive near-infrared spectroscopy of optically faint samples.