The DEEP2 Galaxy Redshift Survey: The Red Sequence AGN Fraction and its Environment and Redshift Dependence

TL;DR

This study investigates how the fraction of active galactic nuclei (AGN) on the red sequence depends on environment and redshift, revealing different behaviors at z~1 compared to local universe, with implications for galaxy evolution.

Contribution

It provides the first detailed analysis of environment dependence of red sequence AGN at z~1, comparing high-redshift and local populations to understand evolutionary trends.

Findings

High-redshift LINERs favor denser environments.

Seyferts and X-ray AGN show little environment dependence at z~1.

At z~0, AGN fraction declines with increasing density.

Abstract

We measure the dependence of the AGN fraction on local environment at z~1, using spectroscopic data taken from the DEEP2 Galaxy Redshift Survey, and Chandra X-ray data from the All-Wavelength Extended Groth Strip International Survey (AEGIS). To provide a clean sample of AGN we restrict our analysis to the red sequence population; this also reduces additional colour-environment correlations. We find evidence that high redshift LINERs in DEEP2 tend to favour higher density environments relative to the red population from which they are drawn. In contrast, Seyferts and X-ray selected AGN at z~1 show little (or no) environmental dependencies within the same underlying population. We compare these results with a sample of local AGN drawn from the SDSS. Contrary to the high redshift behaviour, we find that both LINERs and Seyferts in the SDSS show a slowly declining red sequence AGN fraction towards high density environments. Interestingly, at z~1 red sequence Seyferts and LINERs are approximately equally abundant. By z~0, however, the red Seyfert population has declined relative to the LINER population by over a factor of 7. We speculate on possible interpretations of our results.