Galaxy Environments in the UKIDSS Ultra Deep Survey (UDS)

TL;DR

This study analyzes galaxy environments up to redshift 2 using UKIDSS UDS data, revealing correlations between galaxy color, luminosity, and local density, and demonstrating robustness against redshift uncertainties.

Contribution

It extends previous galaxy environment studies to higher redshifts with infrared data, showing strong color-environment correlations and the impact of luminosity on galaxy surroundings.

Findings

Red/passive galaxies are in denser environments than blue/star-forming ones up to z~1.5.

Galaxy luminosity correlates with environment on small scales at z~1.

Results are robust despite photometric redshift uncertainties.

Abstract

We present a study of galaxy environments to z~2, based on a sample of over 33,000 K-band selected galaxies detected in the UKIDSS Ultra Deep Survey (UDS). The combination of infrared depth and area in the UDS allows us to extend previous studies of galaxy environment to z>1 without the strong biases associated with optical galaxy selection. We study the environments of galaxies divided by rest frame (U-B) colours, in addition to `passive' and `star-forming' subsets based on template fitting. We find that galaxy colour is strongly correlated with galaxy overdensity on small scales (<1Mpc diameter), with red/passive galaxies residing in significantly denser environments than blue/star-forming galaxies to z~1.5. On smaller scales (<0.5Mpc diameter) we also find a relationship between galaxy luminosity and environment, with the most luminous blue galaxies at z~1 inhabiting environments comparable to red, passive systems at the same redshift. Monte Carlo simulations demonstrate that these conclusions are robust to the uncertainties introduced by photometric redshift errors.