Cosmic distributions of stellar tidal disruptions by massive black holes at galactic centers

TL;DR

This paper models the cosmic rates and distributions of stellar tidal disruptions by massive black holes at galactic centers, highlighting the effects of galaxy shape and black hole mass on disruption rates across cosmic time.

Contribution

It provides a comprehensive analysis of how galaxy triaxiality and realistic galaxy distributions influence stellar disruption rates and their evolution with redshift.

Findings

Triaxial galaxy shapes significantly increase stellar disruption rates.

Disruption rates depend on black hole mass and galaxy brightness profiles.

Most TDEs at z=0 occur in galaxies with mass less than 10^{11} solar masses.

Abstract

Stars can be consumed (either tidally disrupted or swallowed whole) by massive black holes (MBHs) at galactic centers when they move into the vicinity of the MBHs. In this study, we investigate the rates of stellar consumption by central MBHs and their cosmic distributions, including the effects of triaxial galaxy shapes in enhancing the reservoir of low-angular-momentum stars and incorporating realistic galaxy distributions. We find that the enhancement in the stellar consumption rates due to triaxial galaxy shapes can be significant, by a factor of ~3 for MBH mass $M_{\rm BH}\sim10^5$-$10^6$Msun and up to more than one order of magnitude for $M_{\rm BH}\gtrsim10^8$Msun. Only for $M_{\rm BH}\lesssim10^7$Msun are the stellar consumption rates significantly higher in galaxies with steeper inner surface brightness profiles. The average (per galaxy) stellar consumption rates correlate with central MBH masses positively for $M_{\rm BH}\gtrsim10^7$Msun and negatively for $M_{\rm BH}\lesssim10^7$Msun. The volumetric stellar tidal disruption rates are ~$3\times10^{-5}$/yr/Mpc$^3$ for MBHs in the mass range of $10^5$-$10^8$Msun at z=0; and the volumetric stellar consumption rates by MBHs with higher masses are ~$10^{-6}$/yr/Mpc$^3$, which can be the stellar tidal disruption rate if the high-mass BHs are extremely spinning Kerr BHs or the rate of being swallowed if those BHs are Schwarzschild ones. The volumetric stellar consumption rates decrease with increasing redshift, and the decrease is relatively mild for $M_{\rm BH}\sim10^5$-$10^7$Msun and stronger for higher $M_{\rm BH}$. Most of the stellar tidal disruption events (TDEs) at z=0 occur in galaxies with mass $M_{\rm gal}\lesssim10^{11}$Msun, and about 1%-2% of the TDEs can occur in high-mass galaxies with $M_{\rm gal}\gtrsim10^{11}$Msun.