AGN-Host Connection at 0.5 < z < 2.5: A rapid evolution of AGN fraction in red galaxies during the last 10 Gyr

TL;DR

This study investigates how the fraction and accretion rates of moderate-luminosity AGNs depend on host galaxy color at 0.5<z<2.5, revealing rapid evolution in red galaxies and high AGN activity in green galaxies at high redshift.

Contribution

It provides new insights into the color-dependent evolution of AGN activity and accretion rates in galaxies over the last 10 billion years.

Findings

Red galaxies have the lowest AGN fraction (~5%) at z~1 but show rapid increase to ~24% at z~2.

Green galaxies exhibit the highest AGN fraction, exceeding 50% at z~2 for M* > 10^{10.6} M_sun.

The probability of hosting an AGN follows a universal Eddington ratio distribution with different evolution patterns for each host color.

Abstract

We explore the dependence of the incidence of moderate-luminosity ($L_{X} = 10^{41.9-43.7}$ erg s$^{-1}$) AGNs and the distribution of their accretion rates on host color at 0.5 < z < 2.5, using deep X-ray data in GOODS fields. We use extinction-corrected rest-frame U-V colors to divide both AGN hosts and non-AGN galaxies into red sequence (quiescent), green valley (transition), and blue cloud (star-forming) populations. We find that both the AGN fraction at fixed stellar mass and its evolution with redshift are dependent on host colors. Most notably, red galaxies have the lowest AGN fraction (~5\%) at z~1 yet with most rapid redshift evolution, increasing by a factor of 5 (~24\%) at z~2. Green galaxies exhibit the highest AGN fraction across all redshifts, which is most pronounced at z~2 with more than half of them hosting an AGN at $M_{*} > 10^{10.6} M_{\odot}$. Together with the high AGN fraction in red galaxies at z~2, this indicates that X-ray AGNs could be important in both transforming blue galaxies into red ones and subsequently maintaining their quiescence at high redshift. Furthermore, consistent with low-redshift studies, we find that the probability of hosting an AGN in the total galaxy population can be characterized by a universal Eddington ratio ($p(\lambda_{Edd}) \sim \lambda_{Edd}^{-0.4}$) and a moderate redshift evolution. Yet consistent with their different AGN fractions, different populations appear to also have different $p(\lambda_{Edd})$ with red galaxies exhibiting more rapid redshift evolution than green and blue ones. Evidence for a steeper power law of $p(\lambda_{Edd})$ in red galaxies is also presented, though larger samples are needed to confirm. These results suggest that the AGN accretion or the growth of supermassive black holes is related to their host properties, and may also influence their hosts in a different mode dependent on the host color.