Disentangling Stellar Mass and Environmental Effects on eROSITA AGN Activity using multi-wavelength data from GAMA, WISE, GALEX, and DESI Legacy Survey

Abstract

We use a stellar-mass complete sample of $\sim 36,000$ galaxies from GAMA/eFEDS to test whether AGN activity depends on environment independent of stellar mass. To isolate this effect, we introduce ${\delta }_{\mathrm{rank}}$, a novel local overdensity metric defined within narrow stellar mass bins. Our main result is that X-ray-selected AGNs show a clear environmental trend, the AGN fraction rises from $\sim 4\%$ in low-density regions to $\sim 6\%$ in high-density regions, with a sharp transition at ${\delta }_{\mathrm{rank}}\sim 0.4$. This environmental dependence is absent for WISE-selected and broad-line AGN, and Eddington ratios show no variation across environments. We also found that for galaxies with $\mathrm{SFR}>15M_{\odot }{\mathrm{yr}}^{-1}$, X-ray AGN fraction is approximately 5%, 60% and 20% in low, mid and high ${\delta }_{\mathrm{rank}}$ galaxies. We show that relationship between AGN fraction and SFR varies dramatically with both environment and selection method. We conclude that environment on scales of $\sim 5h^{-1}\mathrm{Mpc}$ regulates X-ray AGN triggering efficiency.