Are AGN broad emission lines formed by discrete clouds? Analysis of Keck high-resolution spectroscopy of NGC 4151
Identifieur interne : 000632 ( Main/Exploration ); précédent : 000631; suivant : 000633Are AGN broad emission lines formed by discrete clouds? Analysis of Keck high-resolution spectroscopy of NGC 4151
Auteurs : Nahum Arav [États-Unis] ; Tom A. Barlow ; Ari Laor [Israël] ; Wallace L. W. Sargent ; Roger D. BlandfordSource :
- Monthly Notices of the Royal Astronomical Society [ 0035-8711 ] ; 1998-07-11.
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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 ∼3×107 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 108. 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 (106–107), 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.
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DOI: 10.1046/j.1365-8711.1998.297004990.x
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Analysis of Keck high-resolution spectroscopy of NGC 4151</title><author><name sortKey="Arav, Nahum" sort="Arav, Nahum" uniqKey="Arav N" first="Nahum" last="Arav">Nahum Arav</name><affiliation></affiliation><affiliation wicri:level="1"><country wicri:rule="url">États-Unis</country></affiliation></author><author><name sortKey="Barlow, Tom A" sort="Barlow, Tom A" uniqKey="Barlow T" first="Tom A." last="Barlow">Tom A. Barlow</name><affiliation><wicri:noCountry code="subField"></wicri:noCountry></affiliation></author><author><name sortKey="Laor, Ari" sort="Laor, Ari" uniqKey="Laor A" first="Ari" last="Laor">Ari Laor</name><affiliation wicri:level="1"><country xml:lang="fr">Israël</country><wicri:regionArea>Physics Department, Technion, Haifa 3200</wicri:regionArea><wicri:noRegion>Haifa 3200</wicri:noRegion></affiliation></author><author><name sortKey="Sargent, Wallace L W" sort="Sargent, Wallace L W" uniqKey="Sargent W" first="Wallace L. W." last="Sargent">Wallace L. W. 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Soc.</title><idno type="ISSN">0035-8711</idno><idno type="eISSN">1365-2966</idno><imprint><publisher>Blackwell Science Ltd</publisher><pubPlace>Oxford, UK</pubPlace><date type="published" when="1998-07-11">1998-07-11</date><biblScope unit="volume">297</biblScope><biblScope unit="issue">4</biblScope><biblScope unit="page" from="990">990</biblScope><biblScope unit="page" to="998">998</biblScope></imprint><idno type="ISSN">0035-8711</idno></series><idno type="istex">C847A61B2E5FDC8282F7B5934B408A066FE6A61B</idno><idno type="DOI">10.1046/j.1365-8711.1998.297004990.x</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0035-8711</idno></seriesStmt></fileDesc><profileDesc><textClass><keywords scheme="KwdEn" xml:lang="en"><term>galaxies: Seyfert.</term><term>galaxies: active</term><term>galaxies: individual: NGC 4151</term><term>quasars: emission lines</term></keywords></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">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 ∼3×107 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 108. 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 (106–107), 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.</div></front></TEI><affiliations><list><country><li>Israël</li><li>États-Unis</li></country></list><tree><noCountry><name sortKey="Barlow, Tom A" sort="Barlow, Tom A" uniqKey="Barlow T" first="Tom A." last="Barlow">Tom A. Barlow</name><name sortKey="Blandford, Roger D" sort="Blandford, Roger D" uniqKey="Blandford R" first="Roger D." last="Blandford">Roger D. Blandford</name><name sortKey="Sargent, Wallace L W" sort="Sargent, Wallace L W" uniqKey="Sargent W" first="Wallace L. W." last="Sargent">Wallace L. W. 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