Counting the Unseen II: Tidal Disruption Event Rates in Nearby Galaxies with REPTiDE

TL;DR

This paper introduces REPTiDE, a Python tool for calculating TDE rates in galaxies, and applies it to a sample of nearby galaxies to analyze TDE rate distributions and black hole growth.

Contribution

The paper presents a new software package, REPTiDE, for predicting TDE rates, and applies it to real galaxy data to study TDE rate variations and black hole growth.

Findings

TDE rates range from 10^{-7.7} to 10^{-2.9} per year per galaxy.

Peak TDE rates occur at galaxy mass ~10^{9.5} M_sun and black hole mass ~10^{6.5} M_sun.

Lower mass black holes gain a higher fraction of their mass through TDEs.

Abstract

Tidal disruption events (TDEs) are a class of transients that occur when a star is destroyed by the tides of a massive black hole (MBH). Their rates encode valuable MBH demographic information, but this can only be extracted if accurate TDE rate predictions are available for comparisons with observed rates. In this work, we present a new, observer-friendly Python package called REPTiDE, which implements a standard loss cone model for computing TDE rates given a stellar density distribution and an MBH mass. We apply this software to a representative sample of 91 nearby galaxies over a wide range of stellar masses with high-resolution nuclear density measurements from arXiv:2407.10911. We measure per-galaxy TDE rates ranging between 10$^{-7.7}$ and 10$^{-2.9}$ per year and find that the sample-averaged rates agree well with observations. We find a turnover in the TDE rate as a function of both galaxy stellar mass and black hole mass, with the peak rates being observed in galaxies at a galaxy mass of $10^{9.5}$ M$_\odot$ and a black hole mass of $10^{6.5}$ M$_\odot$. Despite the lower TDE rates inferred for intermediate-mass black holes, we find that they have gained a higher fraction of their mass through TDEs when compared to higher mass black holes. This growth of lower mass black holes through TDEs can enable us to place interesting constraints on their spins; we find maximum spins of $a_\bullet \approx 0.9$ for black holes with masses below $\sim10^{5.5}$ M$_\odot$.