Enhancement of the tidal disruption event rate in galaxies with a nuclear star cluster: from dwarfs to ellipticals

Abstract

We compute the tidal disruption event (TDE) rate around local massive black holes (MBHs) with masses as low as $2.5\times10^4 {\rm M}_\odot$, thus probing the dwarf regime for the first time. We select a sample of 37 galaxies for which we have the surface stellar density profile, a dynamical estimate of the mass of the MBH, and 6 of which, including our Milky Way, have a resolved nuclear star cluster (NSC). For the Milky Way, we find a total TDE rate of $\sim 10^{-4}{\rm yr}^{-1}$ when taking the NSC in account, and $\sim 10^{-7} {\rm yr}^{-1}$ otherwise. TDEs are mainly sourced from the NSC for light ($<3\times 10^{10}{\rm M}_\odot$) galaxies, with a rate of few $10^{-5}{\rm yr}^{-1}$, and an enhancement of up to 2 orders of magnitude compared to non-nucleated galaxies. We create a mock population of galaxies using different sets of scaling relations to explore trends with galaxy mass, taking into account the nucleated fraction of galaxies. Overall, we find a rate of few $10^{-5}{\rm yr}^{-1}$ which drops when galaxies are more massive than $10^{11}{\rm M}_\odot$ and contain MBHs swallowing stars whole and resulting in no observable TDE.