Tidal Disruption Events and Gravitational Waves from Intermediate-mass Black Holes in Evolving Globular Clusters across Space and Time

Abstract

Abstract We present a semi-analytic model for self-consistently evolving a population of globular clusters (GCs) in a given host galaxy across cosmic time. We compute the fraction of GCs still hosting intermediate-mass black holes (IMBHs) at a given redshift in early and late -type galaxies of different masses and sizes, and the corresponding rate of tidal disruption events (TDEs), both main-sequence (MS) and white dwarf (WD) stars. We find that the integrated TDE rate for the entire GC population can exceed the corresponding rate in a given galactic nucleus and that ∼90% of the TDEs reside in GCs within a maximum radius of ∼2–15 kpc from the host galaxy’s center. This suggests that observational efforts designed to identify TDEs should not confine themselves to galactic nuclei alone, but should also consider the outer galactic halo where massive old GCs hosting IMBHs would reside. Indeed, such off-center TDEs as predicted here may already have been observed. MS TDE rates are more common than WD TDE rates by a factor of 30 (100) at z ≤ 0.5 (z = 2). We also calculate the rate of IMBH-SBH mergers across cosmic time, finding that the typical IMRI rate at low redshift is of the order of ∼0.5–3 Gpc−3 yr−1, which becomes as high as ∼100 Gpc−3 yr−1 near the peak of GC formation. Advanced LIGO, combined with VIRGO, KAGRA, the Einstein Telescope, and LISA will be able to observe the bottom end and top end of the IMBH population.