Environment of $1\le z \le 2$ obscured and unobscured AGNs in the Extended Chandra Deep Field South

TL;DR

This study compares the environments of obscured and unobscured AGNs at redshifts 1 to 2, finding that obscured AGNs are in denser regions, challenging simple unified models and suggesting galaxy interactions influence obscuration.

Contribution

It provides observational evidence that AGN obscuration occurs at galactic scales, indicating the need to extend unified models beyond local torus orientation.

Findings

Obscured AGNs are optically fainter, indicating dust extinction.

Obscured AGNs are in denser environments than unobscured ones.

Galaxy interactions may play a role in AGN obscuration.

Abstract

In unified models, different types of active galaxy nuclei correspond to a single class of objects, where their observed differences are solely due to the different orientations of the obscuring material around the central inner regions. Recent studies also show that this obscuring material can even extend at galactic scales due to debris and/or mergers. In standard unified models the different AGN types are expected to show similar galaxy environments. We aim to investigate properties and environment of obscured and unobscured AGNs selected from the MUSYC survey, in order to test the unified model and evolutionary scenarios. The sample of AGNs was selected from images obtained with the IRAC Camera, based on their MIR colors. We selected two samples of AGNs with redshifts in the range $1\le z \le 2$ and $M_v\leq -$21: obscured and unobscured AGNs by means of a simple optical-MIR color cut criterion. We find that obscured AGNs are intrinsically optically faint in the R band, suggesting that luminous IR-selected AGNs have a significant dust extinction. From a cross-correlation with several X-ray surveys, we find that the majority of the AGNs have X-ray luminosities similar to those found in Seyfert-like galaxies. Neighbouring galaxies located close to ($\sim$200 kpc) obscured AGNs tend to have redder colors, compared to the local environment of unobscured AGNs. Results obtained from a KS test show that the two color distributions are different at $\sim$95% confidence level. We find that obscured AGNs are located in denser local galaxy environments compared to the unobscured AGN sample. Our results suggest that AGN obscuration can occur at galactic scales, possibly due to galaxy interactions or mergers, and that the simple unified model based solely on the local torus orientation may not be sufficient to explain all the observations.