On the Effects of Local Environment on Active Galactic Nucleus (AGN) in the Horizon Run 5 Simulation

TL;DR

This study uses the Horizon Run 5 simulation to analyze how local galaxy environment and intrinsic properties influence AGN activity, highlighting the dominant role of nearest neighbor environment at small scales.

Contribution

It demonstrates that the nearest neighbor environment significantly impacts AGN properties and cold gas content, providing new insights into environmental effects on AGN activity.

Findings

Nearest neighbor environment dominates AGN luminosity and gas content.

Cold gas availability is crucial for triggering AGN activity.

Small-scale environment effects become dominant at less than half the neighbor's virial radius.

Abstract

We use the Horizon Run 5 cosmological simulation to study the effect of galaxy intrinsic properties and the local environment on AGNs characterized by their threshold of the accretion rate. We select galaxies in the stellar mass range $10^{9.5} \le M^{}{*}/M^{}{\odot} \le 10^{10.5}$ in the snapshot at redshift $z$=0.625. Among various intrinsic properties, we find that the star formation rate of the host galaxy is most correlated to the AGN activity. To quantify the environment, we use background galaxy number density (large-scale environment) and distance and morphological type of the nearest neighbors (small-scale environment), and study their relative effects on the AGN properties. We find that, compared to the background density, the nearest neighbor environment is the dominant quantity determining the bolometric luminosity, star formation rate, and kinematic properties of AGNs and better dictates the gas mass of the host galaxy. We show that the cold gas content in the host galaxies is crucial in triggering AGN activity. However, when the nearest neighbor environment effects start to act at the neighbor distance of less than about half the virial radius of the neighbor, the neighbor environmental effects are the most dominant factor for quasar activity.