Intermediate-mass black hole binary parameter estimation with next-generation ground-based detector networks

Astrophysical scenarios for the formation and evolution of intermediate-mass black holes (IMBHs) in the mass range ${10}^{2}{M}_{\ensuremath{\bigodot}}\ensuremath{\lesssim}M\ensuremath{\lesssim}{10}^{6}{M}_{\ensuremath{\bigodot}}$ remain uncertain, but future ground-based gravitational-wave (GW) interferometers will probe the lower end of the IMBH mass range. We study the detectability of IMBH binary mergers and the measurability of their parameters with next-generation ground-based detector networks consisting of various combinations of Cosmic Explorer (CE) and Einstein Telescope (ET) interferometers. We find that, for binaries with component masses ${m}_{1,2}\ensuremath{\sim}1000{M}_{\ensuremath{\bigodot}}$, an optimal 3-detector network can constrain the masses with errors $\ensuremath{\lesssim}0.1%$ ($\ensuremath{\lesssim}1%$) at $z=0.5$ ($z=2$), and the source redshift can be measured with percent-level accuracy or better at $z\ensuremath{\lesssim}2$. The redshift of lighter binaries (${m}_{1,2}\ensuremath{\lesssim}300{M}_{\ensuremath{\bigodot}}$) can still be measured with $\mathcal{O}(10)%$ accuracy even at $z=10$. Binaries with $z\ensuremath{\lesssim}0.5$ can be localized within $1\text{ }\text{ }{\mathrm{deg}}^{2}$ for ${m}_{1,2}\ensuremath{\lesssim}1000{M}_{\ensuremath{\bigodot}}$, and within $0.1\text{ }\text{ }{\mathrm{deg}}^{2}$ for comparable mass systems. The sky localization is good enough that it may be possible to cross-correlate GW searches with galaxy catalogs and to search for electromagnetic counterparts to IMBH mergers. We also point out that the low-frequency sensitivity of the detectors is crucial for IMBH detection and parameter estimation. It will be interesting to use our results in conjunction with population synthesis codes to constrain astrophysical IMBH formation models.