TDE Hosts are Green and Centrally Concentrated: Signatures of a Post-Merger System

TL;DR

This study analyzes the properties of galaxies hosting TDEs, revealing they are predominantly compact, green valley galaxies with high central concentration, possibly due to post-merger enhancements in star density.

Contribution

It provides the first detailed analysis of TDE host galaxy properties using a representative sample, highlighting the role of galaxy color and concentration in TDE occurrence.

Findings

TDE hosts are mainly compact green valley galaxies.

E+A galaxies are overrepresented among TDE hosts.

The overrepresentation is explained by galaxy mass, color, and concentration.

Abstract

We study the properties of the galaxies hosting the first 19 tidal disruption events (TDEs) detected with the Zwicky Transient Facility (ZTF) within the context of a carefully constructed, representative host galaxy sample. We find that the ZTF sample of TDE hosts is dominated by compact "green valley" galaxies. After we restrict the comparison sample to galaxies with a similar concentration, as measured by Sersic index, we find this green valley over representation is even larger. That is, concentrated red sequence galaxies are not producing TDEs at elevated levels. We present host galaxy spectra which show that E+A galaxies are overrepresented in the ZTF sample by a factor of $\approx$22, which is lower than previous TDE host galaxy studies have found. We find that this overrepresentation can be fully accounted for when taking into account the masses, colors, and S\'ersic indices of the ZTF TDE hosts. The combination of both green colors and high S\'ersic index of the typical TDE host galaxy could be explained if the TDE rate is temporarily enhanced following a merger that leads to a higher central concentration of stars.