Variability of the coronal line region in NGC 4151

Hermine Landt, Martin J. Ward, Katrien C. Steenbrugge, Gary J. Ferland

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


We present the first extensive study of the coronal line variability in an active galaxy. Our data set for the nearby source NGC 4151 consists of six epochs of quasi-simultaneous optical and near-infrared spectroscopy spanning a period of about 8 yr and five epochs of X-ray spectroscopy overlapping in time with it. None of the coronal lines showed the variability behaviour observed for the broad emission lines and hot dust emission. In general, the coronal lines varied only weakly, if at all. Using the optical [Fe VII] and X-ray OVII emission lines we estimate that the coronal line gas has a relatively low density of ne ~ 103 cm-3 and a relatively high ionization parameter of logU ~ 1. The resultant distance of the coronal line gas from the ionizing source is about two light years, which puts this region well beyond the hot inner face of the obscuring dusty torus. The high ionization parameter implies that the coronal line region is an independent entity rather than part of a continuous gas distribution connecting the broad and narrow emission line regions. We present tentative evidence for the X-ray heated wind scenario of Pier & Voit. We find that the increased ionizing radiation that heats the dusty torus also increases the cooling efficiency of the coronal line gas, most likely due to a stronger adiabatic expansion.

Original languageEnglish
Pages (from-to)3795-3805
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Mar 21 2015

Bibliographical note

Publisher Copyright:
© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


  • Galaxies: Seyfert
  • Infrared: galaxies
  • Quasars: emission lines
  • Quasars: individual: NGC 4151
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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