Morphologies in a Cluster of Extremely Red Galaxies with Old Stellar Populations at z=1.34

Abstract

We have identified a clustering of red galaxies from deep optical/IR images obtained as part of the Institute for Astronomy Deep Survey. Photometric spectral-energy distributions indicate that most of these galaxies comprise nearly pure old stellar populations at a redshift near 1.4, and Keck spectroscopy of the three brightest red galaxies confirm this interpretation and give redshifts ranging from 1.335 to 1.338. Four of the galaxies are close together on the sky and less than 30" from an R=13.5 star, and we have obtained deep adaptive-optics imaging of this group. Detailed analysis and modeling of the surface-brightness profiles of these galaxies shows that two are normal ellipticals, one is an S0, and one appears to be an essentially pure disk of old stars, with no significant bulge. All four are highly relaxed, symmetric systems. While the old, bulgeless disk galaxy represents a type that is rare at the present epoch, the other three galaxies have structural parameters that are essentially indistinguishable from those of present-day galaxies and differ only in the age of their stellar populations.