### arXiv:2005.10818 [astro-ph.HE]AbstractReferencesReviewsResources

#### Dynamical evolution of cosmic supermassive binary black holes and their gravitational wave radiation

Yunfeng Chen, Qingjuan Yu, Youjun Lu

Published 2020-05-21Version 1

We investigate the evolution of supermassive binary black holes (BBHs) in galaxies with realistic property distributions and the gravitational wave (GW) radiation from the cosmic population of these BBHs. We incorporate a comprehensive treatment of the BBH dynamical interactions with their environments by including the effects of galaxy triaxial shapes and inner stellar distributions, and generate a large number of BBH evolution tracks. By combining these BBH evolution tracks, galaxy mass functions, galaxy merger rates, and supermassive black hole-host galaxy relations into our model, we obtain the statistical distributions of surviving BBHs, BBH coalescence rates, the strength of their GW radiation, and the stochastic GW background contributed by the cosmic BBH population. About ~1%-3% (or ~10%) of supermassive BHs at nearby galactic centers are expected to be binaries with mass ratio >1/ (or >1/100). The characteristic strain amplitude of the GW background at frequency 1/yr are estimated to be ~$2.0^{+1.4}_{-0.8}\times 10^{-16}$, and its upper bound of the results obtained with the different BH--host galaxy relations can be up to $5.4\times 10^{-16}$, which wait to be tested by future experiments (e.g., SKA, FAST, ngVLA). The turnover frequency of the GW background spectrum is at ~0.25nHz. The uncertainties to the above estimates and prospects for detecting individual sources are also discussed. The application of the cosmic BBH population to the LISA band provides a lower limit to the detection rate of BBHs by LISA, ~0.9/yr.

**Comments:**43 pages, 22 figures, accepted for publication in the Astrophysical Journal