X-Ray Emitting Active Galactic Nuclei from z = 0.6-1.3 in the Intermediate and High-Density Environments of the ORELSE Survey

TL;DR

This study investigates AGN activity in high-density environments at redshifts 0.6-1.3, finding that major mergers likely trigger luminous AGNs in specific regions, while other mechanisms dominate elsewhere.

Contribution

It provides new insights into the environmental dependence of AGN triggering mechanisms, highlighting the role of major mergers in specific LSSs at intermediate redshifts.

Findings

AGN in certain LSSs are more luminous and merger-driven.

No significant relation between AGN activity and location within LSSs.

Major mergers likely trigger luminous AGNs in specific environments.

Abstract

We studied AGN activity in twelve LSSs in the ORELSE survey, at 0.65<z<1.28, using a combination of Chandra observations, optical and NIR imaging and spectroscopy. We located a total of 61 AGNs across our sample that were successfully matched to optical counterparts in the LSSs. Seeking to study AGN triggering mechanisms, we examined the spatial distribution of the AGNs and their average spectral properties. We found that AGN populations across our sample had less time since the last starburst than the overall galaxy populations. We did not find any relation between AGN activity and location within the LSSs, suggesting triggering mechanisms which depend on global environment are at most sub-dominant. To focus on differences between our AGNs, we grouped them into four sub-samples based on the spectral properties of their parents LSSs. We found one of the sub-samples, SG0023 & SC1604, stood out from the others: AGNs in this sample were disproportionately luminous, their average time since the last starburst event was the smallest, despite the fact that this was not true of the overall galaxy population in those LSSs, and both the AGNs and the overall galaxy population had the largest fraction of close kinematic pairs, which indicates a higher rate of galaxy mergers and interactions. These results suggest that major mergers are driving AGN activity in SG0023 & SC1604, while other processes are likely triggering less luminous AGNs in the rest of our sample. Additionally, minor mergers are unlikely to play a significant role, since the same conditions that lead to more major mergers should should also lead to more minor mergers, which is not observed in SG0023 & SC1604.