Merger Driven or Internal Evolution? A New Morphological Study of Tidal Disruption Event Host Galaxies

TL;DR

This study investigates the morphological features of TDE host galaxies, finding that bars and rings, rather than recent mergers, are more common and may drive the conditions leading to tidal disruption events.

Contribution

It introduces a new morphological analysis using deep survey data and machine learning to challenge the merger hypothesis, highlighting bar-driven evolution in TDE hosts.

Findings

TDE hosts are ~16% more centrally concentrated than controls.

No evidence of recent mergers in TDE hosts from morphology or machine learning.

TDE hosts are 1.5 to 2.5 times more likely to have bars or rings.

Abstract

Host galaxies of tidal disruption events (TDEs) show enhanced central stellar concentration and are preferentially found in post-starburst and green valley populations. This connection has led to the proposal that TDE host galaxies likely have gone through recent mergers. We conduct a new morphological study of 14 TDE host galaxies, using the r-band images from Sloan Digital Sky Survey (SDSS), Dark Energy Camera Legacy Survey (DECaLS), and Ultraviolet Near-Infrared Optical Northern Survey (UNIONS), with the images from the latter two surveys having much higher depth and resolution than SDSS. We examine galaxy structures using conventional methods and also apply diagnostics of merger activity from machine learning models. Consistent with previous studies, our results show that TDE host galaxies are ~16% more centrally concentrated when compared to non-TDE-host controls. However, surprisingly, TDE hosts lack any indication of recent merger activity from both morphological analysis and our machine learning merger classifier. Instead, our results reveal that TDE host galaxies are approximately 1.5 to 2.5 times more likely to have bar-like or ring-like structures than their controls. This enhancement is even more prominent for TDEs in the green valley, with the factor reaching almost 3. Based on these results, we propose that bar-driven secular evolution, instead of merger, likely dominates the recent evolution of TDE hosts found in the green valley, which can simultaneously explain their distinctive nuclear properties and enhanced TDE rates.