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Free keywords:
ACTIVE GALACTIC NUCLEI; DIGITAL SKY SURVEY; ENHANCED STAR-FORMATION;
GALAXY PAIRS; ILLUSTRISTNG SIMULATIONS; INTERACTING GALAXIES;
BLACK-HOLES; LUMINOSITY FUNCTION; INFRARED GALAXIES; FORMING GALAXIESAstronomy & Astrophysics; methods: statistical; techniques: image processing; galaxies: evolution;
galaxies: interactions; galaxies: peculiar;
Abstract:
Major mergers between galaxies are predicted to fuel their central supermassive black holes (SMBHs), particularly after coalescence. However, determining the prevalence of active galactic nuclei (AGNs) in mergers remains a challenge, because AGN diagnostics are sensitive to details of the central structure (e.g. nuclear gas clouds, geometry, and orientation of a dusty torus) that are partly decoupled from SMBH accretion. X-rays, expected to be ubiquitous among accreting systems, are detectable through non-Compton-thick screens of obscuring material, and thus offer the potential for a more complete assessment of AGNs in mergers. But extant statistical X-ray studies of AGNs in mergers have been limited by either sparse, heterogeneous, or shallow on-sky coverage. We use new X-ray observations from the first SRG/eROSITA all-sky data release to characterize the incidence, luminosity, and observability of AGNs in mergers. Combining machine learning and visual classification, we identify 923 post-mergers in Dark Energy Camera Legacy Survey (DECaLS) imaging and select 4565 interacting galaxy pairs (with separations <120 kpc and mass ratios within 1:10) from the Sloan Digital Sky Survey. We find that galaxies with X-ray AGNs are 2.0 +/- 0.24 times as likely to be identified as post-mergers compared to non-AGN controls, and that post-mergers are 1.8 +/- 0.1 times as likely to host an X-ray AGN as non-interacting controls. A multiwavelength census of X-ray, optical, and mid-IR-selected AGNs suggests a picture wherein the underlying AGN fraction increases during pair-phase interactions, that galaxy pairs within similar to 20 kpc become heavily obscured, and that the obscuration often clears post-coalescence.
