Environment and Gas Fraction in Type-2 AGN versus Non-AGN Galaxies
Jyoti Yadav, Jong-Hak Woo, Ashraf Ayubinia
TL;DR
This study compares environment and gas content between type-2 AGN hosts and non-AGN galaxies using SDSS DR7 data (z≤0.3) with gas masses inferred from NUV−r colors and SFRs from IR luminosity. It finds that large-scale and local environments (quantified by P, F, T and nearest-neighbor metrics) exert minimal differential influence on AGN versus non-AGN populations, while AGN activity—especially strong outflows—connects to lower global gas fractions at fixed stellar mass and SFR, and to higher gas fractions in strong-outflow systems with elevated SFR and younger ages, suggesting delayed AGN feedback. The results imply AGN feedback regulates the cold gas reservoir and star formation more strongly than the environment, though strong outflows may initially coincide with gas-rich, star-forming hosts. The authors emphasize the need for direct molecular-gas measurements (e.g., CO) to refine the gas content estimates and to clarify the spatial distribution and timescales of AGN-driven gas depletion. Overall, the work underscores the role of internal AGN processes in shaping gas reservoirs and galaxy evolution, with environment playing a secondary role in this context.
Abstract
We investigate the environmental parameters and gas fraction (f$_{gas}$) properties of type~2 AGN and non-AGN galaxies, utilizing a large sample of galaxies from SDSS DR7 with z $\le$ 0.3. We find that the environment affects type~2 AGN and non-AGN galaxies in similar ways and does not impact the strength of AGN-driven outflows. The f$_{gas}$ of type~2 AGN and non-AGN host galaxies show no variation between group and isolated environments, suggesting that host galaxy gas content is largely independent of large-scale environment. We find that type~2 AGN host galaxies possess systematically lower f$_{gas}$ than their non-AGN counterparts when matched in stellar mass and star formation rate (SFR). This suggests that AGN activity plays a significant role in regulating the molecular gas reservoir and, consequently, the star formation processes within galaxies. We find that Type~2 AGNs exhibiting strong outflows are associated with higher gas fractions, higher star-formation rates, and younger stellar populations than those with weak or no outflows. This may indicate either concurrent star formation in gas-rich systems hosting powerful outflows, or a time delay between AGN activity and its effect on star formation consistent with a delayed AGN feedback scenario.