The growth of massive black holes in galaxy merger simulations with feedback by radiation pressure

Abstract

We study the growth of massive black holes (BHs) in galaxies using smoothed particle hydrodynamic simulations of major galaxy mergers with new implementations of BH accretion and feedback. The effect of BH accretion on gas in its host galaxy is modelled by depositing momentum at the rate of ∼τL/c into the ambient gas, where L is the luminosity produced by accretion on to the BH and τ is the wavelength‐averaged optical depth of the galactic nucleus to the AGN’s radiation (a free parameter of our model). The accretion rate on to the BH is relatively independent of our subgrid accretion model and is instead determined by the BH’s dynamical impact on its host galaxy: BH accretion is thus self‐regulated rather than ‘supply limited’. We show that the final BH mass and total stellar mass formed during a merger are more robust predictions of the simulations than the time dependence of the star formation rate or BH accretion rate. In particular, the latter depend on the assumed interstellar medium physics, which determines when and where the gas fragments to form star clusters; this in turn affects the fuel available for further star formation and BH growth. Simulations over a factor of ∼30 in galaxy mass are consistent with the observed MBH–σ relation for a mean optical depth of τ∼ 25. This requires that most BH growth occur when the galactic nucleus is optically thick to far‐infrared radiation, consistent with the hypothesized connection between ultraluminous infrared galaxies and quasars. We find tentative evidence for a shallower MBH–σ relation in the lowest‐mass galaxies, σ≲ 100 km s−1. Our results demonstrate that feedback‐regulated BH growth and consistency with the observed MBH–σ relation do not require that BH feedback terminate star formation in massive galaxies or unbind large quantities of cold gas.

ALMA Observations Show Major Mergers Among the Host Galaxies of Fast-growing, High-redshift, Supermassive Black Holes

“…However, most simulations of major mergers suggest that the SMBH would produce a luminous quasar, with high L L Edd , at the final coalescence phase, and not in the first passage phase. These same simulations also suggest that the first passage enhances SFR in the interacting hosts, to levels comparable to those found in the later,final coalescence phase (see, e.g., Blecha et al 2011;DeBuhr et al 2011;Sijacki et al 2011;Van Wassenhove et al 2012, but also Volonteri et al 2015and Gabor et al 2016 , for both high-and low-SFR quasar hostsand among systems with and without an interacting companion.…”

“…All this supports a general idea that both processes (SF and AGNs) are fed by a common reservoir of cold gas that collapses, forms stars, and (eventually) reaches the central region of the host galaxyto be accreted by the SMBH. M 1000 yr 1 in some simulations; see, e.g., Blecha et al 2011;DeBuhr et al 2011;Sijacki et al 2011;Capelo et al 2015;Volonteri et al 2015;Gabor et al 2016). Observationally, however, the relevance of mergers to fast SMBH growth, and indeed to the co-evolutionary framework,…”

NIHAO – XXII. Introducing black hole formation, accretion, and feedback into the NIHAO simulation suite

“…Tremmel et al (2017) modify the Bondi-Hoyle-Lyttleton parametrization to take the angular momentum of the gas into account. Debuhr et al (2011Debuhr et al ( , 2012 calculate the black hole accretion rate based on the viscous evolution of an accretion disc that surrounds the black hole. Hopkins & Quataert (2011) and the FIRE simulations (Anglés-Alcázar et al 2017) calculate the black hole accretion rate based on angular momentum and gravitational torques around the black hole.…”

ALMA INVESTIGATION OF VIBRATIONALLY EXCITED HCN/HCO+/HNC EMISSION LINES IN THE AGN-HOSTING ULTRALUMINOUS INFRARED GALAXY IRAS 20551−4250

“…Numerical simulations of such gas-rich galaxy mergers not only suggest that many stars form rapidly in dust-/gas-obscured regions, but also suggest that SMBHs have high-mass accretion rates and become luminous AGNs, deeply buried in the nuclear dust/gas, making such gas-rich galaxy mergers luminous in the infrared (Hopkins et al 2006). It is essential to evaluate the importance of buried AGNs in dust-/gas-rich infrared luminous galaxy mergers by separating them from the surrounding starbursts if we are to observationally understand the physical processes that occur during this key epoch in the co-evolution of stars and SMBHs (Hopkins et al 2005;Debuhr et al 2011). However, unlike optically selected AGNs, where a central mass-accreting SMBH is surrounded by toroidally shaped dust/gas (the socalled dusty molecular torus) and the AGNʼs radiation can photo-ionize gas clouds along the torus axis above a torus scale height (Antonucci & Millar 1985), deeply buried AGNs are optically elusive and their detection requires observations at wavelengths of low dust extinction.…”