MOIRCS deep survey. I: DRG number counts

Abstract

We used very deep near-infrared imaging data taken with the Multi-Object InfraRed Camera and Spectrograph (MOIRCS) on the Subaru Telescope to investigate the number counts of Distant Red Galaxies (DRGs). We observed a 4′ × 7′ field in the Great Observatories Origins Deep Survey-North (GOODS-N), and our data reached J = 24.6 and K = 23.2 (5σ, Vega magnitude). The surface density of DRGs selected by J - K > 2.3 is 2.35 ±0.31 arcmin-2 at K < 22 and 3.54 ±0.38arcmin -2 at K < 23, respectively. These values are consistent with those in the GOODS-South and FIRES. Our deep and wide data suggest that the number counts of DRGs turn over at K ∼ 22, and the surface density of the faint DRGs with K > 22 is smaller than that expected from the number counts at the brighter magnitude. The result indicates that while there are many bright galaxies at 2 < z < 4 with the relatively old stellar population and/or heavy dust extinction, the number of faint galaxies with a similar red color is relatively small. Different behavior patterns of the number counts of the DRGs and bluer galaxies with 2 < zphot < 4 at K > 22 suggest that the mass-dependent color distribution, where most of the low-mass galaxies are blue, while more massive galaxies tend to have redder colors, had already been established at that epoch. © 2006. Astronomical Society of Japan.