Stellar and black hole assembly inz< 0.3 infrared-luminous mergers: intermittent starbursts versus super-Eddington accretion

Abstract

We study stellar and black hole mass assembly in a sample of 42 infrared-luminous galaxy mergers at z < 0.3 by combining results from radiative transfer modelling with archival measures of molecular gas and black hole mass. The ratios of stellar mass, molecular gas mass, and black hole mass to each other are consistent with those of massive gas-rich galaxies at z < 0.3. The advanced mergers may show increased black hole mass to stellar mass ratios, consistent with the transition from AGN to ellipticals and implying substantial black hole mass growth over the course of the merger. Star formation rates are enhanced relative to the local main sequence, by factors of ∼100 in the starburst and ∼1.8 in the host, respectively. The starburst star formation rates appear distinct to star formation in the main sequence at all redshifts up to at least z ∼ 5. Starbursts may prefer late-stage mergers, but are observed at any merger stage. We do not find evidence that the starbursts in these low-redshift systems substantially increase the total stellar mass, with a soft upper limit on the stellar mass increase from starburst activity of about a factor of two. In contrast, 12 objects show evidence for super-Eddington accretion, associated with late-stage mergers, suggesting that many AGN in infrared-luminous mergers go through a super-Eddington phase. The super-Eddington phase may increase black hole mass by up to an order of magnitude at an accretion efficiency of $42\pm 33{{\ \rm per\ cent}}$ over a period of 44 ± 22 Myr. Our results imply that super-Eddington accretion is an important black hole growth channel in infrared-luminous galaxies at all redshifts.

A Preferential Growth Channel for Supermassive Black Holes in Elliptical Galaxies at z ≲ 2

“…A "major" merger with a gas-rich galaxy might suffice, if the encounter parameters strongly favored dissipation of angular momentum in the molecular gas so it could funnel to the nucleus. This is in some senses plausible: it has recently been shown that gas-rich major mergers can lead to the central SMBH growing by ∼1 dex, with the stellar mass increasing more modestly (Farrah et al 2022). Such an event would, however, lead to rapid gas accretion in a relatively short burst, resulting in an AGN.…”

The Wind Dynamics of Super-Eddington Sources in FRADO

“…A very recent radiative hydrodynamical simulation [13] found the super-Eddington phase as early stages when the bulge forms and the black hole seed is fed by a massive gaseous disk. The super-Eddington accretion phase was also recently detected in 12 objects within a sample of 42 infrared-luminous galaxy mergers where the super-Eddington accretion is claimed to be an important channel for the black hole growth in infrared-luminous galaxies at all redshifts [14]. In general, super-Eddington sources populate the extreme right tail of the Quasar Main Sequence in the optical plane showing the highest ratio of the Fe II pseudo-continuum to Hβ equivalent width and the narrowest emission lines [4,15], and the 26 sources selected as extreme in this plane show the mean Eddington ratio of 21 [16].…”

The opaque heart of the galaxy IC 860: Analogous protostellar, kinematics, morphology, and chemistry

“…IC 860's SMBH is predicted to be under massive, where the total enclosed mass of gas, dust, stars, and the SMBH is of order of the SMBH mass predicted by the M SMBH − σ relationship (M SMBH ∼ 10 7 M ; Aalto et al 2019;McConnell & Ma 2013;Davis et al 2019). Less massive SMBHs also more commonly accrete at super-Eddington levels (Shirakata et al 2019;Farrah et al 2022). Furthermore, IC 860's Paα luminosity is under luminous for normal star formation (Alonso-Herrero et al 2006).…”