AT 2018dyk: tidal disruption event or active galactic nucleus? Follow-up observations of an extreme coronal line emitter with the Dark Energy Spectroscopic Instrument

TL;DR

This study confirms AT 2018dyk as a tidal disruption event occurring in a gas-rich environment, using follow-up spectroscopy and host galaxy analysis, and explores its MIR properties and relation to coronal line emitters.

Contribution

The paper provides new spectroscopic and host galaxy evidence supporting the classification of AT 2018dyk as a TDE, and analyzes its MIR characteristics in relation to coronal line emitters.

Findings

AT 2018dyk is confirmed as a TDE in a gas-rich environment.

MIR properties of TDEs show a continuum linked to environmental density.

Larger MIR outbursts correlate with redder MIR peaks.

Abstract

We present fresh insights into the nature of the tidal disruption event (TDE) candidate AT 2018dyk. AT 2018dyk has sparked a debate in the literature around its classification as either a bona-fide TDE or as an active galactic nucleus (AGN) turn-on state change. A new follow-up spectrum taken with the Dark Energy Spectroscopic Instrument, in combination with host-galaxy analysis using archival SDSS-MaNGA data, supports the identification of AT 2018dyk as a TDE. Specifically, we classify this object as a TDE that occurred within a gas-rich environment, which was responsible for both its mid-infrared (MIR) outburst and development of Fe coronal emission lines. Comparison with the known sample of TDE-linked extreme coronal line emitters (TDE-ECLEs) and other TDEs displaying coronal emission lines (CrL-TDEs) reveals similar characteristics and shared properties. For example, the MIR properties of both groups appear to form a continuum with links to the content and density of the material in their local environments. This includes evidence for a MIR colour-luminosity relationship in TDEs occurring within such gas-rich environments, with those with larger MIR outbursts also exhibiting redder peaks.