Spatially Offset Active Galactic Nuclei. II: Triggering in Galaxy Mergers

Abstract

Galaxy mergers are likely to play a role in triggering active galactic nuclei (AGN), but the conditions under which this process occurs are poorly understood. In Paper I, we constructed a sample of spatially offset X-ray AGN that represent galaxy mergers hosting a single AGN. In this paper, we use our offset AGN sample to constrain the parameters that affect AGN observability in galaxy mergers. We also construct dual AGN samples with similar selection properties for comparison. We find that the offset AGN fraction shows no evidence for a dependence on AGN luminosity, while the dual AGN fractions show stronger evidence for a positive dependence, suggesting that the merger events forming dual AGN are more efficient at instigating accretion onto supermassive black holes than those forming offset AGN. We also find that the offset and dual AGN fractions both have a negative dependence on nuclear separation and are similar in value at small physical scales. This dependence may become stronger when restricted to high AGN luminosities, though a larger sample is needed for confirmation. These results indicate that the probability of AGN triggering increases at later merger stages. This study is the first to systematically probe down to nuclear separations of <1 kpc (~0.8 kpc) and is consistent with predictions from simulations that AGN observability peaks in this regime. We also find that the offset AGN are not preferentially obscured compared to the parent AGN sample, suggesting that our selection may be targeting galaxy mergers with relatively dust-free nuclear regions.

14 pages, 6 figures, accepted for publication in The Astrophysical Journal

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• Dancing to ChaNGa: A Self-Consistent Prediction For Close SMBH Pair Formation Timescales Following Galaxy Mergers
• Wandering Supermassive Black Holes in Milky Way Mass Halos
• Massive BH Binaries as Periodically-Variable AGN
• Buried AGNs in Advanced Mergers:Mid-infrared color selection as a dual AGN finder
• Varstrometry for Off-nucleus and Dual sub-Kpc AGN (VODKA): Methodology and Initial Results with Gaia DR2
• Buried Black Hole Growth in IR-selected Mergers: New Results from Chandra
• UGC 4211: A Confirmed Dual Active Galactic Nucleus in the Local Universe at 230 pc Nuclear Separation
• A Catalog of 220 Offset and Dual AGNs: Increased AGN Activation in Major Mergers and Separations under 4 kpc
• A Second Look at 12 Candidate Dual AGNs using $\mathtt{BAYMAX}$
• A Bayesian Analysis of SDSS J0914+0853, a Low-Mass Dual AGN Candidate
• Gravitational Lenses as High-Resolution Telescopes
• A hidden active galactic nucleus powering bright [O III] nebulae in a protocluster at $z=4.5$ revealed by JWST
• A Census of WISE-selected Dual and Offset AGN Across the Sky: New Constraints on Merger-Driven Triggering of Obscured AGN
• Observational Constraints on Correlated Star Formation and Active Galactic Nuclei in Late-Stage Galaxy Mergers
• Spatially Offset Active Galactic Nuclei III: Discovery of Late-Stage Galaxy Mergers with The Hubble Space Telescope
• 2MASX J00423991+3017515: An offset active galactic nucleus in an interacting system
• Shocks and Spatially Offset Active Galactic Nuclei Produce Velocity Offsets in Emission Lines
• Hydrodynamical Simulations of the Triggering of Nuclear Activities by Minor Mergers of Galaxies
• Galaxies as High-Resolution Telescopes
• Host galaxy and nuclear properties of IR-selected AGNs with and without outflow signatures