LIGO/Virgo Sources from Merging Black Holes in Ultradwarf Galaxies

Journal Article · Thu Feb 06 00:00:00 EST 2020 · The Astrophysical Journal (Online)

DOI:https://doi.org/10.3847/1538-4357/ab5dad· OSTI ID:1561552

Conselice, Christopher J.  ^[1]; Bhatawdekar, Rachana ^[1]; Palmese, Antonella  ^[2]; Hartley, William G. ^[3]

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1. Univ. of Nottingham (United Kingdom)
2. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
3. Univ. College London (United Kingdom)

The origin of the black-hole: black-hole mergers discovered through gravitational waves with for example the LIGO/Virgo collaboration are a mystery. We investigate the idea that some of these black holes originate from the centers of extremely low-mass ultra-dwarf galaxies that have merged together in the distant past at $z>1$. Extrapolating the central black hole to stellar mass ratio suggests that the black holes in these mergers could arise from galaxies of masses $$\sim 10^{5} - 10^{6}$$ M$$_{\odot}\,$$. We investigate whether these galaxies merge enough, or too much, to be consistent with the observed GW rate of $$\sim 9.7-101$$ Gpc$$^{-3}$$ yr$$^{-1}$$ using the latest LIGO/Virgo results. We show that in the nearby universe the merger rate and number densities of ultra-dwarf galaxies are too low, by an order or magnitude, to produce these black hole mergers. However, by considering that the merger fraction, merger-time scales, and the number densities of low-mass galaxies all conspire at $z>1-1.5$ to increase the merger rate for these galaxies at higher redshifts we argue that it is possible that some of the observed GW events arise from BHs in the centers of low-mass galaxies. The major uncertainty in this calculation is the dynamical time-scales for black holes in low-mass galaxies. Our results however suggest a very long BH merger time-scale of 4-7 Gyr, consistent with an extended black hole merger history. Further simulations are needed to verify this possibility, however our theory can be tested by searching for host galaxies of gravitational wave events. Results from these searches would will put limits on dwarf galaxy mergers and/or the presence and formation mechanisms of black holes through PopIII stars in the lowest mass galaxies.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: AC02-07CH11359
• OSTI ID: 1561552
• Report Number(s): arXiv:1907.05361; FERMILAB-PUB-19-384-AE; oai:inspirehep.net:1743750
• Journal Information: The Astrophysical Journal (Online), Vol. 890, Issue 1; ISSN 1538-4357
• Publisher: Institute of Physics (IOP)
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS