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Are AGN broad emission lines formed by discrete clouds? Analysis of Keck high-resolution spectroscopy of NGC 4151

Arav, Nahum and Barlow, Tom A. and Laor, Ari and Sargent, Wallace L. W. and Blandford, Roger D. (1998) Are AGN broad emission lines formed by discrete clouds? Analysis of Keck high-resolution spectroscopy of NGC 4151. Monthly Notices of the Royal Astronomical Society, 297 (4). pp. 990-998. ISSN 0035-8711. https://resolver.caltech.edu/CaltechAUTHORS:20180418-153910700

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Abstract

We search for a direct signature of discrete ‘clouds’ in the broad-line region (BLR) of the Seyfert galaxy NGC 4151. For this purpose we apply cross-correlation (CC) analysis to a high-resolution Keck spectrum of the galaxy. No such signature is found in the data. In order for cloud models to be compatible with this result, there must be at least ∼3×10^7 emitting clouds in the BLR, where the limit is based on simulation of a homogeneous cloud population. More realistic distributions increase the lower limit to above 10^8. These numbers are an order-of-magnitude improvement on our previous limit from Mrk 335, where the improvement comes from higher signal-to-noise ratio (S/N), broader lines and refined simulations. Combined with the predicted upper limit for the number of emitting clouds in NGC 4151 (10^6–10^7), the derived lower limit puts a strong constraint on the cloud scenario in the BLR of this object. Similar constraints can be placed on models where the emission originates in streams and sheets. Thus, this investigation suggests that the broad emission lines (BELs) in NGC 4151, and by extension in all AGNs, are not made of an ensemble of discrete independent emitters.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1046/j.1365-8711.1998.297004990.xDOIArticle
ORCID:
AuthorORCID
Blandford, Roger D.0000-0002-1854-5506
Additional Information:© 1998 RAS. We thank S. Vogt for leading the construction of the HIRES spectrograph and Michael Rauch for assisting with the observations. NA and RDB acknowledge support form NSF grants 92-23370 and 95-29170. AL acknowledges support from the E. and J. Bishop research fund, and from the Milton and Lillian Edwards academic lectureship fund.
Group:TAPIR
Funders:
Funding AgencyGrant Number
NSFAST 92-23370
NSFAST 95-29170
Subject Keywords:galaxies: active, galaxies: individual: NGC 4151, quasars: emission lines, galaxies: Seyfert
Issue or Number:4
Record Number:CaltechAUTHORS:20180418-153910700
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180418-153910700
Official Citation:Nahum Arav, Tom A. Barlow, Ari Laor, Wallace L. W. Sargent, Roger D. Blandford; Are AGN broad emission lines formed by discrete clouds? Analysis of Keck high-resolution spectroscopy of NGC 4151, Monthly Notices of the Royal Astronomical Society, Volume 297, Issue 4, 11 July 1998, Pages 990–998, https://doi.org/10.1046/j.1365-8711.1998.297004990.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85954
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:19 Apr 2018 17:38
Last Modified:03 Oct 2019 19:37

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