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Register a new userThe role of mergers and gas accretion in black hole growth and galaxy evolution
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We use a semi-analytic galaxy formation model to study the co-evolution of supermassive black holes (SMBHs) with their host galaxies. Although the coalescence of SMBHs is not important, the quasar-mode accretion induced by mergers plays a dominant role in the growth of SMBHs. Mergers play a more important role in the growth of SMBH host galaxies than in the SMBH growth. It is the combined contribution from quasar mode accretion and mergers to the SMBH growth and the combined contribution from starburst and mergers to their host galaxy growth that determine the observed scaling relation between the SMBH masses and their host galaxy masses. We also find that mergers are more important in the growth of SMBH host galaxies compared to normal galaxies which share the same stellar mass range as the SMBH host galaxies.
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The co-evolution of supermassive black holes (SMBHs) with their host galaxies remains to be fully explored, especially at high redshift. While often understood as a consequence of self-regulation via AGN feedback, it may also be explained by alternative SMBH accretion models. Here, we expand on previous work by studying the growth of SMBHs with the help of a large suite of cosmological zoom-in simulations (textsc{small{MassiveFIRE}}) that are part of the Feedback in Realistic Environments (FIRE) project. The growth of SMBHs is modeled in post-processing with different accretion models, placements, and merger treatments, and validated by comparing to on-the-fly calculations. Scaling relations predicted by the gravitational torque driven accretion (GTDA) model agree with observations at low redshift emph{without} the need for AGN feedback, in contrast to models in which the accretion rate depends strongly on SMBH mass. At high redshift, we find deviations from the local scaling relations in line with previous results. In particular, SMBHs are under-massive, presumably due to stellar feedback, but start to grow efficiently once their host galaxies reach $M_* sim 10^{10} M_{odot}$. We analyze and explain these findings in the context of a simple analytic model. Finally, we show that the predicted scaling relations depend sensitively on the efficiency of SMBH merging. These findings highlight the relevance of understanding the evolution of SMBH-galaxy scaling relations to predict the rate of gravitational wave signals from SMBH mergers across cosmic history.
Supermassive black hole dynamics during galaxy mergers is crucial in determining the rate of black hole mergers and cosmic black hole growth. As simulations achieve higher resolution, it becomes important to assess whether the black hole dynamics is influenced by the treatment of the interstellar medium in different simulation codes. We here compare simulations of black hole growth in galaxy mergers with two codes: the Smoothed Particle Hydrodynamics code Gasoline, and the Adaptive Mesh Refinement code Ramses. We seek to identify predictions of these models that are robust despite differences in hydrodynamic methods and implementations of sub-grid physics. We find that the general behavior is consistent between codes. Black hole accretion is minimal while the galaxies are well-separated (and even as they fly-by within 10 kpc at first pericenter). At late stages, when the galaxies pass within a few kpc, tidal torques drive nuclear gas inflow that triggers bursts of black hole accretion accompanied by star formation. We also note quantitative discrepancies that are model-dependent: our Ramses simulations show less star formation and black hole growth, and a smoother gas distribution with larger clumps and filaments, than our Gasoline simulations. We attribute these differences primarily to the sub-grid models for black hole fueling and feedback and gas thermodynamics. The main conclusion is that differences exist quantitatively between codes, and this should be kept in mind when making comparisons with observations. However, reassuringly, both codes capture the same dynamical behaviors in terms of triggering of black hole accretion, star formation, and black hole dynamics.
We present a simple semi-numerical model designed to explore black hole growth and galaxy evolution. This method builds on a previous model for black hole accretion that uses a semi-numerical galaxy formation model and universal Eddington ratio distribution to describe the full AGN population by independently connecting galaxy and AGN growth to the evolution of the host dark matter halos. We fit observed X-ray luminosity functions up to a redshift of z ~ 4, as well as investigate the evolution of the Eddington ratio distributions. We find that the Eddington ratio distribution evolves with redshift such that the slope of the low-Eddington accretion rate distribution increases with cosmic time, consistent with the behavior predicted in hydrodynamical simulations for galaxies with different gas fractions. We also find that the evolution of our average Eddington ratio is correlated with observed star formation histories, supporting a picture in which black holes and galaxies evolve together in a global sense. We further confirm the impact of luminosity limits on observed galaxy and halo properties by applying selection criteria to our fiducial model and comparing to surveys across a wide range of redshifts.
Large extragalactic surveys allow us to trace, in a statistical sense, how supermassive black holes, their host galaxies, and their dark matter halos evolve together over cosmic time, and so explore the consequences of AGN feedback on galaxy evolution. Recent studies have found significant links between the accretion states of black holes and galaxy stellar populations, local environments, and obscuration by gas and dust. This article describes some recent results and shows how such studies may provide new constraints on models of the co-evolution of galaxies and their central SMBHs. Finally, I discuss observational prospects for the proposed Wide-Field X-ray Telescope mission.
The formation, accretion and growth of supermassive black holes in the early universe are investigated. The accretion rate ${dot M}$ is calculated using the Bondi accretion rate onto black holes. Starting with initial seed black holes with masses $M_{rm BH}sim 10^2-10^3M_{odot}$, the Bondi accretion rate can evolve into a supermassive black hole with masses $M_{rm BH}sim 10^9-10^{10}M_{odot}$ and with a young quasar lifetime $sim 10^5-10^6$ years by super-Eddington accretion.
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