Abstract
Abstract For over 60 yr, the scientific community has studied actively growing central supermassive black holes (active galactic nuclei, AGNs), but fundamental questions on their genesis remain unanswered. Numerical simulations and theoretical arguments show that black hole growth occurs during short-lived periods (∼107–108 yr) of powerful accretion. Major mergers are commonly invoked as the most likely dissipative process to trigger the rapid fueling of AGNs. If the AGN–merger paradigm is true, we expect galaxy mergers to coincide with black hole accretion during a heavily obscured AGN phase (N H > 1023 cm−2). Starting from one of the largest samples of obscured AGNs at 0.5 < z < 3.1, we select 40 nonstarbursting lower-luminosity obscured AGNs. We then construct a one-to-one matched redshift and near-IR magnitude-matched nonstarbursting inactive galaxy control sample. Combining deep color Hubble Space Telescope imaging and a novel method of human classification, we test the merger–AGN paradigm prediction that heavily obscured AGNs are strongly associated with galaxies undergoing a major merger. On the total sample of 80 galaxies, we estimate each individual classifier’s accuracy at identifying merging galaxies/postmerging systems and isolated galaxies. We calculate the probability of each galaxy being in either a major merger or an isolated system, given the accuracy of the human classifiers and the individual classifications of each galaxy. We do not find statistically significant evidence that obscured AGNs at cosmic noon are predominantly found in systems with evidence of significant merging/postmerging features.
Highlights
Super-massive blackholes (SMBHs) are essentially in every massive galaxy, and when they are actively accreting matter, known as active galactic nuclei (AGN), they can potentially inject energy into the gas and expel it and/or prevent it from cooling and collapsing into stars(e.g. Bower et al 2006; Croton et al 2006; Heckman & Best 2014)
If the AGN-merger paradigm is true, we expect galaxy mergers to coincide with black hole accretion during a heavily obscured AGN phase (NH > 1023 cm−2)
We calculate the probability of each galaxy being in either a major merger or isolated system, given the accuracy of the human classifiers and the individual classifications of each galaxy
Summary
Super-massive blackholes (SMBHs) are essentially in every massive galaxy, and when they are actively accreting matter, known as active galactic nuclei (AGN), they can potentially inject energy into the gas and expel it and/or prevent it from cooling and collapsing into stars(e.g. Bower et al 2006; Croton et al 2006; Heckman & Best 2014). Matter must lose almost all (∼99.9%) of its angular momentum in order to accrete onto the SMBH, studying dissipative processes such as mergers, tidal interactions, stellar bars and disk instabilities is central to understanding the details of AGN fueling. Despite distinct differences between dissipative processes, neither observational nor theoretical studies converge on a dominant mechanism for funneling matter onto the central SMBH (Jogee 2006). Galaxy mergers with comparable mass ratios (≥ 1 : 4 defined as major mergers) are one of the most popular mechanisms invoked, yet the observational consensus is mixed. If the AGN-merger paradigm is true, we can expect a heavily obscured accretion AGN phase to coincide with galaxy coalescence (Sanders & Mirabel 1996; Cattaneo et al 2005; Hopkins et al 2008). If a major-merger triggers most AGN, AGN behind large neutral hydrogen column densities (NH > 1023 cm−2) should exist in association with the most spectacular phases of mergers
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