THE ASSEMBLY OF SUPERMASSIVE BLACK HOLES AT HIGH REDSHIFTS
- Department of Astronomy, Columbia University, 550 W120th Street, New York, NY 10027 (United States)
The supermassive black holes (SMBHs) massive enough ({approx}> few x10{sup 9} M {sub sun}) to power the bright redshift z {approx} 6 quasars observed in the Sloan Digital Sky Survey (SDSS) are thought to have assembled by mergers and/or gas accretion from less massive 'seed' BHs. If the seeds are the {approx}10{sup 2} M {sub sun} remnant BHs from the first generation of stars, they must be in place well before redshift z = 6, and must avoid being ejected from their parent protogalaxies by the large (several x10{sup 2} km s{sup -1}) kicks they suffer from gravitational-radiation-induced recoil during mergers with other BHs. We simulate the SMBH mass function at redshift z > 6 using dark matter halo merger trees, coupled with a prescription for the halo occupation fraction, accretion histories, and radial recoil trajectories of the growing BHs. Our purpose is (1) to map out plausible scenarios for successful assembly of the z {approx} 6 quasar BHs by exploring a wide region of parameter space, and (2) to predict the rate of low-frequency gravitational wave events detectable by the Laser Interferometer Space Antenna (LISA) for each such scenario. Our main findings are as follows: (1) {approx}100 M {sub sun} seed BHs can grow into the SDSS quasar BHs without super-Eddington accretion, but only if they form in minihalos at z {approx}> 30 and subsequently accrete {approx}>60% of the time; (2) the scenarios with optimistic assumptions required to explain the SDSS quasar BHs overproduce the mass density in lower mass (few x10{sup 5} M {sub sun} {approx}< M {sub bh}{approx}< few x 10{sup 7} M {sub sun}) BHs by a factor of 10{sup 2}-10{sup 3}, unless seeds stop forming, or accrete at a severely diminished rates or duty cycles (e.g., due to feedback), at z {approx}< 20-30. We also present several successful assembly models and their LISA detection rates, including a 'maximal' model that gives the highest rate ({approx}30 yr{sup -1} at z = 6) without overproducing the total SMBH density.
- OSTI ID:
- 21300660
- Journal Information:
- Astrophysical Journal, Vol. 696, Issue 2; Other Information: DOI: 10.1088/0004-637X/696/2/1798; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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