Long-term follow-up observations of extreme coronal line emitting galaxies

Peter Clark, Or Graur, Joseph Callow, Jessica Aguilar, Steven Ahlen, Joseph P. Anderson, Edo Berger, Thomas Brink, David Brooks, Ting-Wan Chen, Todd Claybaugh, Axel de la Macorra, Peter Doel, Alexei Filippenko, Jamie Forero-Romero, Sebastian Gomez, Mariusz Gromadzki, Klaus Honscheid, Cosimo Inserra, Theodore KisnerMartin Landriau, Lydia Makrygianni, Marc Manera, Aaron Meisner, Ramon Miquel, John Moustakas, Tomás E. Müller-Bravo, Matt Nicholl, Jundan Nie, Francesca Onori, Antonella Palmese, Claire Poppett, Thomas Reynolds, Mehdi Rezaie, Graziano Rossi, Eusebio Sanchez, Michael Schubnell, Gregory Tarlé, Benjamin A. Weaver, Thomas Wevers, David R. Young, WeiKang Zheng, Zhimin Zhou

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Abstract

We present new spectroscopic and photometric follow-up observations of the known sample of extreme coronal line emitting galaxies (ECLEs) identified in the Sloan Digital Sky Survey (SDSS). With these new data, observations of the ECLE sample now span a period of two decades following their initial SDSS detections. We confirm the nonrecurrence of the iron coronal line signatures in five of the seven objects, further supporting their identification as the transient light echoes of tidal disruption events (TDEs). Photometric observations of these objects in optical bands show little overall evolution. In contrast, mid-infrared (MIR) observations show ongoing long-term declines. The remaining two objects had been classified as active galactic nuclei (AGN) with unusually strong coronal lines rather than being TDE related, given the persistence of the coronal lines in earlier follow-up spectra. We confirm this classification, with our spectra continuing to show the presence of strong, unchanged coronal-line features and AGN-like MIR colours and behaviour. We have constructed spectral templates of both subtypes of ECLE to aid in distinguishing the likely origin of newly discovered ECLEs. We highlight the need for higher cadence, and more rapid, follow-up observations of such objects to better constrain their properties and evolution. We also discuss the relationships between ECLEs, TDEs, and other identified transients having significant MIR variability.
Original languageEnglish
Pages (from-to)7076-7102
JournalMonthly Notices of the Royal Astronomical Society
Volume528
Issue number4
Early online date26 Feb 2024
DOIs
Publication statusPublished - 1 Mar 2024

Keywords

  • astro-ph.HE
  • galaxies: active
  • transients: tidal disruption events
  • UKRI
  • STFC
  • ST/S000550/1
  • ST/W001225/1
  • ST/T000198/1
  • ST/S006109/1

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