Speaker
Description
We investigate the environmental dependence of active galactic nucleus (AGN) activity using a stellar mass-complete sample of 36,000 galaxies from the Galaxy and Mass Assembly (GAMA) survey overlapping with the eROSITA Final Equatorial Depth Survey (eFEDS) field. By combining
X-ray observations from eROSITA, optical and infrared photometry from Legacy Survey and WISE, UV data from GALEX, and DESI DR1 spectroscopy, we perform comprehensive spectral energy distribution (SED) fitting with CIGALE to derive stellar masses and star formation rates (SFRs).
We identify AGN through three independent methods: X-ray maximum-likelihood flux threshold of log(FML /erg cm−2 s−1 ) > −14.05 in the 0.5–2 keV band (corresponding to 90% completeness) , WISE color selection, and broad-line emission. To isolate environmental effects from the well-known stellar mass dependence of AGN fraction, we introduce a novel δrank parameter that ranks galaxies by local overdensity within narrow stellar mass bins. We find that X-ray selected AGN exhibit a significant environmental dependence, with the AGN fraction increasing from ∼4.5% in low-density regions to ∼6.5% in high-density environments (transition at δrank ∼ 0.4), independent of galaxy color. This trend is absent in WISE-selected and broad-line AGN. In high-density regions (δrank > 0.5), the AGN fraction rises sharply with SFR, reaching ∼25% for SFR > 15 M⊙ yr−1 in X-ray selected samples. Remarkably, we find no significant difference in Eddington ratios across environments. Our results suggest that environment modulates AGN triggering efficiency in star-forming galaxies without affecting the accretion physics, with density scales of 2–5 Mpc/h being most relevant for this process.