Mid-Infrared Outbursts in Nearby Galaxies: Nuclear Obscuration and Connections to Hidden Tidal Disruption Events and Changing-Look Active Galactic Nuclei

TL;DR

This study investigates mid-infrared outbursts in nearby galaxies, finding they are mostly due to obscured, highly variable active galactic nuclei rather than hidden tidal disruption events, based on analysis of galaxy properties and dust obscuration.

Contribution

It demonstrates that mid-infrared outbursts are primarily caused by obscured, variable AGN, challenging the idea they are mainly tidal disruption events, through analysis of galaxy properties and dust content.

Findings

Nuclear obscuration does not correlate with host galaxy type or stellar properties.

Mid-infrared outburst hosts are more centrally concentrated and have higher Sersic indices.

Most mid-infrared outbursts are consistent with obscured, variable AGN rather than tidal disruption events.

Abstract

We study the properties of galaxies hosting mid-infrared outbursts in the context of a catalog of five hundred thousand galaxies from the Sloan Digital Sky Survey. We find that nuclear obscuration, as inferred by the surrounding dust mass, does not correlate with host galaxy type, stellar properties (e.g. total mass and mean age), or with the extinction of the host galaxy as estimated by the Balmer decrement. This implies that nuclear obscuration may not be able to explain any over-representation of tidal disruption events in particular host galaxies. We identify a region in the galaxy catalog parameter space that contains all unobscured tidal disruption events but only harbors $\lesssim $ 11\% of the mid-infrared outburst hosts. We find that mid-infrared outburst hosts appear more centrally concentrated and have higher galaxy S\'ersic indices than galaxies hosting active galactic nuclei (AGN) selected using the BPT classification. We thus conclude that the majority of mid-infrared outbursts are not hidden tidal disruption events but are instead consistent with being obscured AGN that are highly variable, such as changing-look AGN.