Mapping the nuclear environments of extreme coronal line emitting galaxies

Abstract Extreme coronal line emitters (ECLEs) are a rare class of galactic nuclei exhibiting unusually strong high-ionisation forbidden emission lines, and several ECLEs have been linked to tidal disruption events (TDEs). In this work, we compile and analyse optical spectra of 33 ECLEs, dividing them into variable, TDE-linked sources and non-variable, AGN-linked systems. Using multi-epoch spectroscopy from the Sloan Digital Sky Survey, Dark Energy Spectroscopic Instrument, and other facilities, we investigate the evolution of the emission line spectra and measure emission line profiles. Many variable ECLEs have changing spectra in which the highest-ionisation lines (e.g., [Fe x]–[Fe xiv]) appear and fade first, followed by [Fe vii], accompanied by brightening of [O iii]. These changes may reflect a softening ionising continuum, the outward propagation of the ionisation front following the TDE flare, or both. Assuming virial motion, we translate line widths into characteristic radial distances, reconstructing the spatial distribution of line-emitting gas. Coronal lines are generally emitted at radii intermediate between the broad line region and the low-ionisation narrow line region. This ionisation stratification is seen in many sources, with similar incidence in variable and non-variable ECLEs, suggesting no apparent difference in circumnuclear gas distributions between active and quiescent nuclei. We find positive correlations between gas distance and black hole mass for both [O iii] and [Fe vii]: the log(Distance)-log(Mass) relations have slopes 0.63 ± 0.08 and 0.69 ± 0.12, respectively, broadly consistent with a Mass0.5 dependence and with characteristic radii set primarily by photoionisation.

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Journal
Monthly Notices of the Royal Astronomical Society
Published
2026-09-04
DOI
https://doi.org/10.1093/mnras/stag1681
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
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article

Mapping the nuclear environments of extreme coronal line emitting galaxies

Daniel Kynoch, Or Graur, G. Gutierrez, H. Zou et al.
Monthly Notices of the Royal Astronomical Society
Galaxies: Formation, Evolution, Phenomena
article

Mapping the nuclear environments of extreme coronal line emitting galaxies

Daniel Kynoch, Or Graur, G. Gutierrez, H. Zou, J. E. Forero-Romero, S. Ahlen, D. Schlegel, S. Panda, F. Prada, J. Silber, R. Zhou, D. Bianchi, L. Le Guillou, A. Meisner, B. A. Weaver, E. Sanchez, W. J. Percival, D. Sprayberry, S. Gontcho A Gontcho, J. Moustakas, T. Claybaugh, S. Juneau, P. Doel, D. Brooks, R. Joyce, M. Landriau, G. Rossi, J. A. Olmos Aguilar, Peter Clark, R. Miquel, A. de la Macorra, G. Tarlé, I. Pérez-Ràfols
article en

Abstract

Abstract Extreme coronal line emitters (ECLEs) are a rare class of galactic nuclei exhibiting unusually strong high-ionisation forbidden emission lines, and several ECLEs have been linked to tidal disruption events (TDEs). In this work, we compile and analyse optical spectra of 33 ECLEs, dividing them into variable, TDE-linked sources and non-variable, AGN-linked systems. Using multi-epoch spectroscopy from the Sloan Digital Sky Survey, Dark Energy Spectroscopic Instrument, and other facilities, we investigate the evolution of the emission line spectra and measure emission line profiles. Many variable ECLEs have changing spectra in which the highest-ionisation lines (e.g., [Fe x]–[Fe xiv]) appear and fade first, followed by [Fe vii], accompanied by brightening of [O iii]. These changes may reflect a softening ionising continuum, the outward propagation of the ionisation front following the TDE flare, or both. Assuming virial motion, we translate line widths into characteristic radial distances, reconstructing the spatial distribution of line-emitting gas. Coronal lines are generally emitted at radii intermediate between the broad line region and the low-ionisation narrow line region. This ionisation stratification is seen in many sources, with similar incidence in variable and non-variable ECLEs, suggesting no apparent difference in circumnuclear gas distributions between active and quiescent nuclei. We find positive correlations between gas distance and black hole mass for both [O iii] and [Fe vii]: the log(Distance)-log(Mass) relations have slopes 0.63 ± 0.08 and 0.69 ± 0.12, respectively, broadly consistent with a Mass0.5 dependence and with characteristic radii set primarily by photoionisation.

Monthly Notices of the Royal Astronomical Society
Boston University (US), Institució Catalana de Recerca i Estudis Avançats (ES), Universidad Complutense de Madrid (ES), Centre National de la Recherche Scientifique (FR), Fermi National Accelerator Laboratory (US), American Museum of Natural History (US), Lawrence Berkeley National Laboratory (US), University of Waterloo (CA), State Street (United States) (US), Universidad de Los Andes (CO), Perimeter Institute (CA), Institute for High Energy Physics (ES), University of Milan (IT), University of Michigan (US), Brera Astronomical Observatory (IT), Sejong University (KR), Sorbonne Université (FR), Laboratoire de Physique Nucléaire et de Hautes Énergies (FR), Gemini South Observatory (CL), Institut National de Physique Nucléaire et de Physique des Particules (FR), Community Science and Data Center (US), Istituto Nazionale di Fisica Nucleare, Sezione di Milano (IT), NSF NOIRLab (US), Universidad de Los Andes (BO), Instituto de Astrofísica de Andalucía (ES), National Astronomical Observatories (CN), University of Southampton (GB), University College London (GB), University of Virginia (US), University of Portsmouth (GB), Universidad Nacional Autónoma de México (MX), Siena College (US), Universitat Politècnica de Catalunya (ES)
National Science Foundation, U.S. Department of Energy, Alfred P. Sloan Foundation, Gordon and Betty Moore Foundation, Carnegie Institution of Washington, New Mexico State University, Ministerio de Ciencia, Innovación y Universidades, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Office of Science, Science and Technology Facilities Council, Agencia Estatal de Investigación, Division of Astronomical Sciences
Openalex Percentile: Top 46%
Galaxies: Formation, Evolution, Phenomena
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