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 < z < 3. The sample comprises 294 galaxies with M > 10 11 M ⊙ distributed over four independent fields with a total area of almost 400 arcmin 2 . The mean number density of massive galaxies in this redshift range p(M > 10 11 M ⊙ ) = (2.2 ± 0.6) × 10 -4 h 70 3 Mpc -3 . We present median values and 25th and 75th percentiles for the distributions of observed R AB magnitudes, observed J - K s colors, and rest-frame ultraviolet continuum slopes, M/L V 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 (R AB = 25.9), red in the observed near-IR (J - K s = 2.48), has a rest-frame UV spectrum that is relatively flat in F λ (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 - K s > 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. © 2006. The American Astronomical Society. All rights reserved.