Driving the Growth of the Earliest Supermassive Black Holes with Major Mergers of Host Galaxies

Abstract

The formation mechanism of supermassive black holes (SMBHs) in general, and of $\sim 10^9{\mathrm{M}}_{\odot }$ SMBHs observed as luminous quasars at redshifts $z>6$ in particular, remains an open fundamental question. The presence of such massive BHs at such early times, when the Universe was less than a billion years old, implies that they grew via either super-Eddington accretion, or nearly uninterrupted gas accretion near the Eddington limit; the latter, at first glance, is at odds with empirical trends at lower redshifts, where quasar episodes associated with rapid BH growth are rare and brief. In this work, I examine whether and to what extent the growth of the $z>6$ quasar SMBHs can be explained within the standard quasar paradigm, in which major mergers of host galaxies trigger episodes of rapid gas accretion below or near the Eddington limit. Using a suite of Monte Carlo merger tree simulations of the assembly histories of the likely hosts of the $z>6$ quasars, I investigate (i) their growth and major merger rates out to $z\sim 40$, and (ii) how long the feeding episodes induced by host mergers must last in order to explain the observed $z>6$ quasar population without super-Eddington accretion. The halo major merger rate scales roughly as $\propto (1+z{)}^{5/2}$, with quasar hosts typically experiencing $>10$ major mergers between $15>z>6$ ($\approx 650\mathrm{Myr}$), compared to $\sim 1$ for typical massive galaxies at $3>z>0$ ($\approx 11\mathrm{Gyr}$). An example of a viable sub-Eddington SMBH growth model is one where a host merger triggers feeding for a duration comparable to the halo dynamical time. These findings suggest that the growth mechanisms of the earliest quasar SMBHs need not have been drastically different from their counterparts at lower redshifts.

24 pages, 5 figures, invited submission to a focus issue on galactic centers in Classical and Quantum Gravity

References in corpus (35)

• A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: I. Galaxy Mergers & Quasar Activity
• A luminous quasar at a redshift of z = 7.085
• Formation of Supermassive Black Holes by Direct Collapse in Pregalactic Halos
• Observational constraints on Cosmic Reionization
• The Illustris simulation: the evolving population of black holes across cosmic time
• Large Merger Recoils and Spin Flips From Generic Black-Hole Binaries
• Supermassive black hole formation during the assembly of pre-galactic discs
• The bulk of the black hole growth since z~1 occurs in a secular universe: No major merger-AGN connection
• Clustering of High Redshift ($z\ge 2.9$) Quasars from the Sloan Digital Sky Survey
• The halo mass function from the dark ages through the present day
• A synthesis model for AGN evolution: supermassive black holes growth and feedback modes
• Formation of z ~ 6 quasars from hierarchical galaxy mergers
• Accretion onto the First Stellar Mass Black Holes
• Evidence for Quasar Activity Triggered by Galaxy Mergers in HST Observations of Dust-reddened Quasars
• Fluctuations in the High-Redshift Lyman-Werner Background: Close Halo Pairs as the Origin of Supermassive Black Holes
• Super-Critical Growth of Massive Black Holes from Stellar-Mass Seeds
• The First Galaxies: Assembly, Cooling and the Onset of Turbulence
• Getting a kick out of numerical relativity
• Growth and activity of black holes in galaxy mergers with varying mass ratios
• Quasars at z=6: the survival of the fittest
• Rapid growth of seed black holes in the early universe by supra-exponential accretion
• Quasars Are Not Light-Bulbs: Testing Models of Quasar Lifetimes with the Observed Eddington Ratio Distribution
• Resolving the Formation of Protogalaxies. I. Virialization
• Black-Hole Mass and Growth Rate at High Redshift
• The metallicity of the most distant quasars
• Merger Rates of Dark-Matter Haloes
• Supermassive Black Holes in the Hierarchical Universe: A General Framework and Observational Tests
• Constraints on the correlation between QSO luminosity and host halo mass from high-redshift quasar clustering
• Hot Accretion With Conduction: Spontaneous Thermal Outflows
• The merger fraction of active and inactive galaxies in the local Universe through an improved non-parametric classification
• A No-Go Theorem for Direct Collapse Black Holes Without a Strong Ultraviolet Background
• Cosmological Evolution of the Duty Cycle of Quasars
• Global Compton heating and cooling in hot accretion flows
• Close companions to two high-redshift quasars
• Radiation from early black holes - I: effects on the neutral inter-galactic medium

Cited by in corpus (7)

• Quasar UV luminosity function evolution up to z=8
• Looking for Population III stars with He II line intensity mapping
• The mass assembly of high-redshift black holes
• Limits on luminosity and mass accretion rate of a radiation pressure dominated accretion disc
• SMBH growth parameters in the early Universe of Millennium and Millennium-II simulations
• Massive black holes in high-redshift Lyman Break Galaxies
• An Estimate of the Impact of Reionization on Supermassive Black Hole Growth