Variability of the Coronal Line Region in NGC 4151

Authors

Hermine Landt, Durham University, UK
Martin J. Ward, Durham University, UK
Katrien C. Steenbrugge, Universidad Católica del Norte, Chile
Gary J. Ferland, University of KentuckyFollow

Abstract

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 O vii emission lines we estimate that the coronal line gas has a relatively low density of n_e ∼ 10³ cm⁻³ and a relatively high ionization parameter of log U ∼ 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.

Document Type

Article

Publication Date

6-1-2015

Notes/Citation Information

Published in Monthly Notices of the Royal Astronomical Society, v. 449, no. 4, p. 3795-3805.

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

Digital Object Identifier (DOI)

http://dx.doi.org/10.1093/mnras/stv062

Funding Information

HL is supported by a European Union COFUND/Durham Junior Research Fellowship (under EU grant agreement number 267209). KCS thanks the astronomy group at Durham University for its hospitality during a collaborative visit supported by a Santander Mobility Grant. GJF acknowledges support by NSF (1108928, 1109061, and 1412155), NASA (10-ATP10-0053, 10-ADAP10-0073, NNX12AH73G, and ATP13-0153), and STScI (HST-AR-13245, GO-12560, HST-GO-12309, GO-13310.002-A, and HST-AR-13914), and to the Leverhulme Trust for support via the award of a Visiting Professorship at Queen's University Belfast (VP1-2012-025).

Repository Citation

Landt, Hermine; Ward, Martin J.; Steenbrugge, Katrien C.; and Ferland, Gary J., "Variability of the Coronal Line Region in NGC 4151" (2015). Physics and Astronomy Faculty Publications. 274.
https://uknowledge.uky.edu/physastron_facpub/274