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Constraints on the broad-line region properties and extinction in local Seyferts

Schnorr-Mueller, A and Davies, RI and Korista, KT and Burtscher, L and Rosario, D and Storchi-Bergmann, T and Contursi, A and Genzel, R and Gracia-Carpio, J and Hicks, EKS and Janssen, A and Koss, M and Lin, M-Y and Lutz, D and Maciejewski, W and Muller-Sanchez, F and de Xivry, GO and Riffel, R and Riffel, RA and Schartmann, M and Sternberg, A and Sturm, E and Tacconi, L and Veilleux, S and Ulrich, OA (2016) Constraints on the broad-line region properties and extinction in local Seyferts. Monthly Notices of the Royal Astronomical Society, 462 (4). pp. 3570-3590. ISSN 0035-8711

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Abstract

We use high-spectral resolution (R > 8000) data covering 3800–13 000 Å to study the physical conditions of the broad-line region (BLR) of nine nearby Seyfert 1 galaxies. Up to six broad H i lines are present in each spectrum. A comparison – for the first time using simultaneous optical to near-infrared observations – to photoionization calculations with our devised simple scheme yields the extinction to the BLR at the same time as determining the density and photon flux, and hence distance from the nucleus, of the emitting gas. This points to a typical density for the H i emitting gas of 1011 cm−3 and shows that a significant amount of this gas lies at regions near the dust sublimation radius, consistent with theoretical predictions. We also confirm that in many objects, the line ratios are far from case B, the best-fitting intrinsic broad-line Hα/H β ratios being in the range 2.5–6.6 as derived with our photoionization modelling scheme. The extinction to the BLR, based on independent estimates from H i and He ii lines, is AV ≤ 3 for Seyfert 1–1.5s, while Seyfert 1.8–1.9s have AV in the range 4–8. A comparison of the extinction towards the BLR and narrow-line region (NLR) indicates that the structure obscuring the BLR exists on scales smaller than the NLR. This could be the dusty torus, but dusty nuclear spirals or filaments could also be responsible. The ratios between the X-ray absorbing column NH and the extinction to the BLR are consistent with the Galactic gas-to-dust ratio if NH variations are considered.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 06 Dec 2016 10:47
Last Modified: 10 Sep 2017 06:17
DOI or Identification number: 10.1093/mnras/stw1865
URI: http://researchonline.ljmu.ac.uk/id/eprint/5026

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