Early results in the search for extreme coronal line emitters with the Dark Energy Spectroscopic Instrument

TL;DR

This paper reports early findings from DESI's EDR, identifying three TDE-linked ECLEs and over 200 AGNs with coronal lines, demonstrating DESI's capability to discover nuclear transients and estimating their occurrence rate.

Contribution

The study introduces a new search method for ECLEs using DESI data, successfully identifying TDE-linked ECLEs and estimating their galaxy-normalized rate, with a custom Python tool for the search.

Findings

Identified three TDE-linked ECLEs in DESI EDR.

Estimated TDE-linked ECLE rate of approximately 5×10^{-6} galaxy^{-1} yr^{-1}.

Discovered over 200 AGNs with coronal emission lines.

Abstract

Here we present the results of our search through the Early Data Release (EDR) of the Dark Energy Spectroscopic Instrument (DESI) for extreme coronal line emitters (ECLEs) - a rare classification of galaxies displaying strong, high-ionization iron coronal emission lines within their spectra. With the requirement of a strong X-ray continuum to generate the coronal emission, ECLEs have been linked to both active galactic nuclei (AGNs) and tidal disruption events (TDEs). We focus our search on identifying TDE-linked ECLEs. We identify three such objects within the EDR sample, highlighting DESI's effectiveness for discovering new nuclear transients, and determine a galaxy-normalized TDE-linked ECLE rate of $R_\mathrm{G}=5~^{+5}_{-3}\times10^{-6}~\mathrm{galaxy}^{-1}~\mathrm{yr}^{-1}$ at a median redshift of z = 0.2 - broadly consistent with previous works. Additionally, we also identify more than 200 AGNs displaying coronal emission lines, which serve as the primary astrophysical contaminants in searches for TDE-related events. We also include an outline of the custom python code developed for this search.