# The Dependence of AGN Activity on Environment in SDSS

## TL;DR

This study investigates how active galactic nucleus (AGN) activity relates to galaxy environment in SDSS, finding that internal processes mainly trigger AGN, with minimal influence from external environmental factors.

## Contribution

It introduces a new way to define AGN fraction based on star-forming galaxies, revealing a weaker dependence on environment than previous definitions.

## Key findings

- AGN fraction shows little dependence on environment when defined relative to star-forming galaxies.
- Passive galaxy fraction strongly depends on environment, affecting previous AGN-environment correlation results.
- Internal secular processes are the main drivers of AGN activity, external environment plays a minor role.

## Abstract

Environment is one of the key external drivers of the galaxies, while active galactic nucleus (AGN) is one of the key internal drivers. Both of them play fundamental roles in regulating the formation and evolution of galaxies. We explore the interrelationship between environment and AGN in SDSS. At a given stellar mass, the specific star formation rate distribution of the AGN host galaxies remains unchanged with over-density, with the peak of the distribution around the Green Valley. We show that, at a given stellar mass, the AGN fraction that has been commonly used in previous studies (defined as the number of AGNs relative to all galaxies including passive and star forming ones) does decrease with increasing over-density for satellites. This is largely due to the fact that the fraction of passive galaxies strongly depends on environment. In order to investigate the intrinsic correlation between AGN and environment, especially under the assumption that AGN feedback is responsible for star formation quenching, the AGN fraction should be defined as the number of AGNs relative to the star-forming galaxies only. With the new definition, we find little dependence of AGN fraction on over-density, central/satellite, and group halo mass. There is only marginal evidence that AGN may prefer denser regions, which is possibly due to more frequent interaction of galaxies or higher merger rate in groups. Our results support the scenario that internal secular evolution is the predominant mechanism of triggering AGN activity, while external environment related processes only play a minor role.