Clustering and physical properties of AGN and Star-Forming Galaxies at fixed stellar mass: does assembly bias have a role in AGN activity?

TL;DR

This study compares the clustering and physical properties of AGN and star-forming galaxies at fixed stellar mass, finding that differences in properties are likely due to galaxy evolution rather than environment, suggesting stochastic AGN activity.

Contribution

It provides evidence that AGN activity is influenced by galaxy assembly history rather than environmental factors, challenging previous assumptions.

Findings

No significant difference in clustering strength between AGN and SFG.

Significant differences in colour, SFR, D4000, and morphology after matching stellar mass.

Differences are consistent across different environmental densities.

Abstract

We analyze a volume-limited sample from the Sloan Digital Sky Survey (SDSS) to compare the spatial clustering and physical properties of active galactic nuclei (AGN) and star-forming galaxies (SFG) at fixed stellar mass. We find no statistically significant difference in clustering strength or local density between AGN and SFG. However, after matching their stellar mass distributions, we detect statistically significant differences (at a confidence level $>99.99\%$) in colour, star formation rate (SFR), $4000\r{A}$ break measurements (D$4000$), and morphology. These differences persist across both low- and high-density environments, suggesting that AGN are not driven by environmental factors. The development of favourable conditions for AGN activity within a galaxy may depend on the diverse evolutionary histories of galaxies. Our results imply that AGN activity may arise stochastically, modulated by the complex assembly history of galaxies.