http://arxiv.org/abs/1806.08385
In this paper, 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 use this model to 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) between stars and IMBHs. This is done for both main-sequence (MS) and white dwarf (WD) stars, and we compare their relative rates as a function of cosmic time for different assumed time-averaged stellar mass functions. We find that, for many host galaxies, the integrated TDE rate for the entire GC population can exceed the corresponding rates in a given galactic nucleus due to an SMBH and that 50% and 90% of the TDEs reside in GCs within a maximum radius of $\sim 2-4$ kpc and $\sim 5-15$ kpc, respectively, 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-centre TDEs as predicted here may already have been observed. We further find that the TDE rates in elliptical and spiral galaxies are similar to within $10\%$. MS TDE rates are more common than WD TDE rates by a factor 30 (100) at $z\leq 0.5$ ($z=2$). 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 $\approx 0.5-3$ Gpc$^{-3}$ yr$^{-1}$, which becomes as high as $\approx 100$ Gpc$^{-3}$ yr$^{-1}$ near the peak of GC formation at $z=3$. Advanced ET combined with LIGO, VIRGO, KAGRA and \textit{LISA} will be able to observe the top-end and bottom-end of the IMBH population, respectively.
G. Fragione, N. Leigh, I. Ginsburg, et. al.
Mon, 25 Jun 18
5/54
Comments: 12 pages, 11 figures, 1 table, submitted to ApJ
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