The Post-Starburst Evolution of Tidal Disruption Event Host Galaxies

TL;DR

This study investigates the recent star formation histories of galaxies hosting tidal disruption events (TDEs), revealing that TDEs occur in post-starburst galaxies with specific merger and stellar concentration characteristics, but not primarily due to starburst mass.

Contribution

It provides detailed constraints on the star formation histories and merger scenarios of TDE host galaxies, highlighting factors influencing TDE rates beyond starburst mass.

Findings

TDE hosts experienced recent short starbursts ending 10-1000 Myr ago.

The starburst mass fraction is insufficient to explain TDE rate boosts.

Host galaxies have stellar masses between 10^9.4 and 10^10.3 solar masses.

Abstract

We constrain the recent star formation histories of the host galaxies of eight optical/UV-detected tidal disruption events (TDEs). Six hosts had quick starbursts of <200 Myr duration that ended 10 to 1000 Myr ago, indicating that TDEs arise at different times in their host's post-starburst evolution. If the disrupted star formed in the burst or before, the post-burst age constrains its mass, generally excluding O, most B, and highly massive A stars. If the starburst arose from a galaxy merger, the time since the starburst began limits the coalescence timescale and thus the merger mass ratio to more equal than 12:1 in most hosts. This uncommon ratio, if also that of the central supermassive black hole (SMBH) binary, disfavors the scenario in which the TDE rate is boosted by the binary but is insensitive to its mass ratio. The stellar mass fraction created in the burst is 0.5-10% for most hosts, not enough to explain the observed 30-200x boost in TDE rates, suggesting that the host's core stellar concentration is more important. TDE hosts have stellar masses 10^9.4 - 10^10.3 Msun, consistent with the SDSS volume-corrected, quiescent Balmer-strong comparison sample and implying SMBH masses of 10^5.5 - 10^7.5 Msun. Subtracting the host absorption line spectrum, we uncover emission lines; at least five hosts have ionization sources inconsistent with star formation that instead may be related to circumnuclear gas, merger shocks, or post-AGB stars.