Wandering intermediate-mass black holes and off-nuclear tidal disruption events from early star clusters

Abstract

Off-nuclear tidal disruption events (TDEs) reveal evidence for massive black holes outside galactic centers, but the origins of this wandering population remain uncertain. We investigate wandering intermediate-mass black holes (IMBHs) formed through runaway stellar collisions in dense, high-redshift star clusters and predict their TDE signatures across cosmic time. Our semi-analytic model samples clusters associated with low-mass subhalos at $7<z<20$ and uses merger trees from the IllustrisTNG TNG50 simulation to follow the assembly of 15 elliptical galaxies with stellar masses of $10^9-10^{11}{M}_{\odot }$. We compare two models for high-redshift cluster formation: a maximal model taken from a high-resolution simulation and a conservative model calibrated from local cluster relations. Off-nuclear TDEs produced through this mechanism occur in bursts within 10-100 Myr of IMBH formation as the loss-cone surrounding the black hole is depleted. We estimate the rate of off-nuclear TDEs expected across time per galaxy, and characterize these events as typically occurring between $10-10^3$ kpc from their host galaxy centers. Event rates increase with galaxy mass; in the maximal model, the progenitors of the most massive galaxies reach peak off-nuclear TDE rates of approximately $5\times 10^{-4}-4\times 10^{-2}{\mathrm{yr}}^{-1}$ per galaxy at $7\lesssim z\lesssim 13$. This work provides a framework for constraining the early population of star clusters that form IMBHs through runaway collapse via their contribution to the rate of off-nuclear TDEs in the high redshift Universe.

27 pages, 11 figures