Separating Accretion and Mergers in the Cosmic Growth of Black Holes with X-ray and Gravitational Wave Observations

Abstract

Black holes across a broad range of masses play a key role in the evolution of galaxies. The initial seeds of black holes formed at $z\sim 30$ and grew over cosmic time by gas accretion and mergers. Using observational data for quasars and theoretical models for the hierarchical assembly of dark matter halos, we study the relative importance of gas accretion and mergers for black hole growth, as a function of redshift ($0<z<10$) and black hole mass ($10^3{\mathrm{M}}_{\odot }<M_{\bullet }<10^{10}{\mathrm{M}}_{\odot }$). We find that (i) growth by accretion is dominant in a large fraction of the parameter space, especially at $M_{\bullet }>10^8{\mathrm{M}}_{\odot }$ and $z>6$; and (ii) growth by mergers is dominant at $M_{\bullet }<10^5{\mathrm{M}}_{\odot }$ and $z>5.5$, and at $M_{\bullet }>10^8{\mathrm{M}}_{\odot }$ and $z<2$. As the growth channel has direct implications for the black hole spin (with gas accretion leading to higher spin values), we test our model against $\sim 20$ robust spin measurements available thus far. As expected, the spin tends to decline toward the merger-dominated regime, thereby supporting our model. The next generation of X-ray and gravitational-wave observatories (e.g. Lynx, AXIS, Athena and LISA) will map out populations of black holes up to very high redshift ($z\sim 20)$, covering the parameter space investigated here in almost its entirety. Their data will be instrumental to providing a clear picture of how black holes grew across cosmic time.

Accepted for publication in The Astrophysical Journal. This is the final version of the manuscript. 12 pages, 5 figures

References in corpus (21)

• A Catalog of Quasar Properties from SDSS DR7
• An Observational Determination of the Bolometric Quasar Luminosity Function
• An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
• Supermassive black hole formation during the assembly of pre-galactic discs
• The Final SDSS High-Redshift Quasar Sample of 52 Quasars at z>5.7
• Formation of the first nuclear clusters and massive black holes at high redshift
• Generating Dark Matter Halo Merger Trees
• Super-Critical Growth of Massive Black Holes from Stellar-Mass Seeds
• Initial mass function of intermediate mass black hole seeds
• Remnant mass, spin, and recoil from spin aligned black-hole binaries
• Constraining the high redshift formation of black hole seeds in nuclear star clusters with gas inflows
• A survey of luminous high-redshift quasars with SDSS and WISE II. the bright end of the quasar luminosity function at z ~ 5
• Conditions for Optimal Growth of Black Hole Seeds
• Mass without radiation: heavily obscured AGN, the X-ray Background and the Black Hole Mass Density
• Exploring SMBH Assembly with Semi-analytic Modelling
• Quasar UV luminosity function evolution up to z=8
• Hyperaccreting black holes in galactic nuclei
• AGN and their host galaxies in the local Universe: two mass independent Eddington ratio distribution functions characterize black hole growth
• Feedback Limits to Maximum Seed Masses of Black Holes
• On the Absence of High-Redshift AGNs: Little Growth in the Supermassive Black Hole Population at High Redshifts
• Reality or Mirage? Observational Test and Implications for the Claimed Extremely Magnified Quasar at $z=6.3$

Cited by in corpus (26)

• Key Science Goals for the Next-Generation Event Horizon Telescope
• Mildly Super-Eddington Accretion Onto Slowly-Spinning Black Holes Explains the X-Ray Weakness of the Little Red Dots
• Origins and Demographics of Wandering Black Holes
• Two can play at that game: constraining the role of supernova and AGN feedback in dwarf galaxies with cosmological zoom-in simulations
• Gravitational-Wave Lunar Observatory for Cosmology
• Seeking the growth of the first black hole seeds with JWST
• The Search for the Farthest Quasar: Consequences for Black Hole Growth and Seed Models
• Formation of supermassive black hole seeds in nuclear star clusters via gas accretion and runaway collisions
• Are the Newly-Discovered $z\sim 13$ Drop-out Sources Starburst Galaxies or Quasars?
• Exploring the AGN Fraction of a Sample of JWST's Little Red Dots at $5<z<8$: Overmassive Black Holes Are Strongly Favored
• The Active Fraction of Massive Black Holes in Dwarf Galaxies
• Using Machine Learning to Link Black Hole Accretion Flows with Spatially Resolved Polarimetric Observables
• Effect of mass loss due to stellar winds on the formation of supermassive black hole seeds in dense nuclear star clusters
• Possible Connection between Dark Matter and Supermassive Black Holes
• Dynamics of Intermediate-Mass Black Holes Wandering in the Milky Way Galaxy Using the Illustris TNG50 Simulation
• Inception of a first quasar at cosmic dawn
• Probing the Merger Rates of Supermassive Black Holes and Galaxies with Gravitational Waves
• No black holes from light
• Quantum gravity phenomenology at the dawn of the multi-messenger era -- A review
• Orbital and Radiative Properties of Wandering Intermediate-Mass Black Holes in the ASTRID Simulation
• Observational Signatures of Massive Black Hole Progenitor Pathways: Could Leo I a Smoking Gun?
• X-ray AGN in Boötes: The lack of growth of the most massive black holes since z=4
• Over-massive Central Black Holes in the Cosmological Simulations ASTRID and Illustris TNG50
• Polarimetry of the potential binary supermassive black hole system in J1430+2303
• Astrophysics with the Laser Interferometer Space Antenna
• Properties of Ultralight Bosons from Spins of Heavy Quasars via Superradiance