VLASS tidal disruption events with optical flares II: discovery of two TDEs with intermediate width Balmer emission lines and connections to the ambiguous extreme coronal line emitters

TL;DR

This study analyzes two radio-selected tidal disruption events with unique intermediate-width emission lines, revealing their properties, host galaxy types, and possible connections to extreme coronal line emitters, advancing understanding of TDE diversity.

Contribution

It provides a detailed multiwavelength analysis of two TDEs with unprecedented emission lines, linking them to extreme coronal line emitters and exploring their outflow and shock properties.

Findings

Both TDEs are hosted by low star formation, green valley galaxies.

They exhibit intermediate-width Balmer and Helium emission lines.

One event shows coronal line emission, suggesting shock or outflow interactions.

Abstract

The multiwavelength properties of radio-emitting tidal disruption events (TDEs) are poorly understood. In a previous paper, we presented the first sample of radio-selected, optically-detected TDEs, which included two events (VT J1008 and VT J2012) associated with late-time (${\sim}2$ years post-optical flare) intermediate with emission lines that are largely unprecedented from TDEs. In this paper, we investigate these two events in detail. The multiwavelength properties of these events are otherwise consistent with optically-selected TDEs. They are hosted by green valley, E+A/Balmer dominated galaxies with low star formation rates and black holes masses $M_{\rm BH}\approx 10^{5-6}\,M_\odot$. The optical flare shapes are fully consistent with those of optically-selected TDEs, although they are slightly faint and cool at peak. The radio emission from both events is consistent with wide-angle, non-relativistic outflows with $L_R({\rm GHz}) \sim 10^{38}$ erg s$^{-1}$. Balmer and Helium emission lines are detected from both events with full-width-half-maxima ${\sim}700$ km s$^{-1}$ and asymmetric line profiles. VT J1008 additionally shows coronal line emission with a similar width. The lines from VT J2012 are redshifted by ${\sim}700$ km s$^{-1}$ relative to the host galaxy. We show that these events share many characteristics in common with the ambiguous class of extreme coronal line emitters. We argue that the lines are likely associated with a radiative shock or dense, photoionized clumps of outflowing gas in the circumnuclear medium.