Dual AGN in the Horizon-AGN simulation and their link to galaxy and massive black hole mergers, with an excursus on multiple AGN

Abstract

The occurrence of dual active galactic nuclei (AGN) on scales of a few tens of kpc can be used to study merger-induced accretion on massive black holes (MBHs) and to derive clues on MBH mergers, using dual AGN as a parent population of precursors. We investigate the properties of dual AGN in the cosmological simulation Horizon-AGN. We create catalogs of dual AGN selected with distance and luminosity criteria, plus sub-catalogs where further mass cuts are applied. We divide the sample into dual AGN hosted in different galaxies, on the way to a merger, and into those hosted in one galaxy, after the galaxy merger has happened. We find that the relation between MBH and galaxy mass is similar to that of general AGN population and we compare the properties of dual AGN also with a control sample, discussing differences and similarities in masses and Eddington ratios. The typical mass ratio of galaxy mergers associated to dual AGN is 0.2, with mass loss in the smaller galaxy decreasing the mass ratio as the merger progresses. Between 30 and 80 per cent of dual AGN with separations between 4 and 30 kpc can be matched to an ensuing MBH merger. The dual AGN fraction increases with redshift and with separation threshold, although above 50 kpc the increase of multiple AGN limits that of duals. Multiple AGN are generally associated with massive haloes, and mass loss of satellites shapes the galaxy-halo relation.

New multiple AGN systems with subarcsec separation: Confirmation of candidates selected via the novel GMP method

“…There are three main possible explanations for a triple object: (1) a triple lensed system, that is, three images of the same object; (2) lensing of a dual AGN, in other words two distinct objects, one of which has two detected lensed images; and (3) a system of three different AGNs, a possibility predicted by current models (e.g., Ni et al 2022;Bhowmick et al 2020;Volonteri et al 2022) and previously observed in the local Universe (e.g., Pfeifle et al 2019;Foord et al 2021;Yadav et al 2021).…”

“…Given the long merging timescale (∼1 Gyr, e.g., Tremmel et al 2017), a population of dual or multiple SMBHs must exist in many galaxies (Volonteri et al 2003). SMBHs are expected to accrete material from the merging host galaxies, producing dual or multiple luminous active galactic nuclei (AGNs) in the same galaxy (Steinborn et al 2016;Rosas-Guevara et al 2019;Volonteri et al 2022). For example, Volonteri et al (2022) estimate that at z > 2 more than 1% of the bright AGNs (L bol > 10 43 erg s −1 ) are expected to have a companion within 10 kpc.…”

“…SMBHs are expected to accrete material from the merging host galaxies, producing dual or multiple luminous active galactic nuclei (AGNs) in the same galaxy (Steinborn et al 2016;Rosas-Guevara et al 2019;Volonteri et al 2022). For example, Volonteri et al (2022) estimate that at z > 2 more than 1% of the bright AGNs (L bol > 10 43 erg s −1 ) are expected to have a companion within 10 kpc. The discovery of dual AGNs at a kiloparsec-scale separation is therefore crucial to support the hierarchical formation model.…”

Varstrometry for Off-nucleus and Dual Subkiloparsec AGN (VODKA). SDSS J1608+2716: A Subarcsecond Quadruply Lensed Quasar at z = 2.575

“…Overall, only ∼0.1% of the triple systems at cosmic noon in ASTRID have L bol  10 45 erg s −1 for each member at r p < 40 kpc. Similarly, in the Horizon-AGN simulation, quadruple systems with each AGN brighter than L bol > 10 45 erg s −1 (like J1608) and separated by r p < 30 kpc only constitute ∼0.001% of the entire AGN population at z ∼ 2.5 (Volonteri et al 2022). The realistic probability of observing a luminous quadruple quasar system with r p  7 kpc (∼0 9) would be even lower.…”

Massive Black Hole Binaries from the TNG50-3 Simulation. II. Using Dual AGNs to Predict the Rate of Black Hole Mergers

“…The luminosity used in this work to describe both AGNs is the rest-frame bolometric luminosity, with no correction for extinction or host galaxy contamination. We characterize the dAGN luminosity as the sum of the two bolometric luminosities (similar to Volonteri et al 2022, and other works in the literature) to provide a scale for the luminosity of the system. 9 We defer a careful analysis of the spectral properties of the two AGNs, and strategies to best detect them, to future work.…”