Changing Ionization Conditions in SDSS Galaxies with AGN as a Function of Environment from Pairs to Clusters

TL;DR

This study investigates how active galactic nuclei (AGN) activity varies with environment, from galaxy pairs to clusters, using SDSS data and emission-line diagnostics to understand the impact of interactions and environment on AGN fueling.

Contribution

It introduces a refined, continuous measure of AGN activity and disentangles environmental effects on AGN using emission-line ratios, revealing how interactions and cluster conditions influence AGN activity.

Findings

Galaxy interactions enhance AGN activity.

Cluster environments suppress AGN activity despite galaxy pairs.

Gas dynamics models explain environmental influence on AGN fueling.

Abstract

We study how AGN activity changes across environments from galaxy pairs to clusters using $143\, 843$ galaxies with $z<0.2$ from the Sloan Digital Sky Survey (SDSS). Using a refined technique, we apply a continuous measure of AGN activity, characteristic of the ionization state of the narrow-line emitting gas. Changes in key emission-line ratios ([NII]$\lambda6548$/H$\alpha$, [OIII]$\lambda5007$/H$\beta$) between different samples allow us to disentangle different environmental effects while removing contamination. We confirm that galaxy interactions enhance AGN activity. However, conditions in the central regions of clusters are inhospitable for AGN activity even if galaxies are in pairs. These results can be explained through models of gas dynamics in which pair interactions stimulate the transfer of gas to the nucleus and clusters suppress gas availability for accretion onto the central black hole.