The Faint and Extremely Red K-band Selected Galaxy Population in the DEEP2/Palomar Fields

TL;DR

This study analyzes faint, red K-band selected galaxies in the DEEP2/Palomar fields, revealing their redshift distribution, stellar masses, and morphological properties, and assesses their implications for galaxy formation models.

Contribution

It provides new insights into the redshift, mass, and morphology of K-selected galaxies, especially extremely red objects, and evaluates galaxy formation scenarios.

Findings

Most K<17 galaxies are at z<1.5

38.3% of K>19 systems are at z>1.5

EROs are predominantly early-type and peculiar galaxies

Abstract

We present in this paper an analysis of the faint and red near-infrared selected galaxy population found in near-infrared imaging from the Palomar Observatory Wide-Field Infrared Survey. This survey covers 1.53 deg^2 to 5-sigma detection limits of K_vega = 20.5-21 and J_vega = 22.5, and overlaps with the DEEP2 spectroscopic redshift survey. We discuss the details of this NIR survey, including our J and K band counts. We show that the K-band galaxy population has a redshift distribution that varies with K-magnitude, with most K < 17 galaxies at z < 1.5 and a significant fraction (38.3+/-0.3%) of K > 19 systems at z > 1.5. We further investigate the stellar masses and morphological properties of K-selected galaxies, particularly extremely red objects, as defined by (R-K) > 5.3 and (I-K) > 4. One of our conclusions is that the ERO selection is a good method for picking out galaxies at z > 1.2, and within our magnitude limits, the most massive galaxies at these redshifts. The ERO limit finds 75% of all M_* > 10^{11} M_0 galaxies at z ~ 1.5 down to K_vega = 19.7. We further find that the morphological break-down of K < 19.7 EROs is dominated by early-types (57+/-3%) and peculiars (34+/-3%). However, about a fourth of the early-types are distorted ellipticals, and within CAS parameter space these bridge the early-type and peculiar population, suggesting a morphological evolutionary sequence. We also investigate the use of a (I-K) > 4 selection to locate EROs, finding that it selects galaxies at slightly higher average redshifts (<z> = 1.43+/-0.32) than the (R-K) > 5.3 limit with <z> = 1.28+/-0.23. Finally, by using the redshift distribution of K < 20 selected galaxies, and the properties of our EROs, we are able to rule out all monolithic collapse models for the formation of massive galaxies.