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Upholding the unified model for Active Galactic Nuclei: VLT/FORS2 spectropolarimetry of Seyfert 2 galaxies

Upholding the unified model for Active Galactic Nuclei: VLT/FORS2 spectropolarimetry of Seyfert 2 galaxies
Upholding the unified model for Active Galactic Nuclei: VLT/FORS2 spectropolarimetry of Seyfert 2 galaxies
The origin of the unification model for Active Galactic Nuclei (AGN) was the detection of broad hydrogen recombination lines in the optical polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden broad-line region (HBLR) of nearby Sy2s started, but polarized broad lines have only been detected in ?30–40% of the nearby Sy2s observed to date. Here we present new VLT/FORS2 optical spectropolarimetry of a sample of 15 Sy2s, including Compton-thin and Compton-thick sources. The sample includes six galaxies without previously published spectropolarimetry, some of them normally treated as non-hidden BLR (NHBLR) objects in the literature, four classified as NHBLR, and five as HBLR based on previous data. We report ?4? detections of a HBLR in 11 of these galaxies (73% of the sample) and a tentative detection in NGC 5793, which is Compton-thick according to the analysis of X-ray data performed here. Our results confirm that at least some NHBLRs are misclassified, bringing previous publications reporting differences between HBLR and NHBLR objects into question. We detect broad H? and H? components in polarized light for 10 targets, and just broad H? for NGC 5793 and NGC 6300, with line widths ranging between 2100 and 9600 km s?1. High bolometric luminosities and low column densities are associated with higher polarization degrees, but not necessarily with the detection of the scattered broad components.
0035-8711
1-18
Ramos Almeida, C.
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Martinez Gonzalez, M.J.
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Asensio Ramos, A.
dca27505-3a0a-4f84-a930-fcecf99e1ada
Acosta-Pulido, J.A.
d73ea5db-84f0-415e-ad48-a5484d5637bf
Hoenig, S.F.
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Alonso-Herrero, A.
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Tadhunter, C.N.
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Gonzalez-Martin, O.
dc84a0b8-4350-4053-b1d5-5d2d75142b61
Ramos Almeida, C.
5de8e01a-be52-4502-864b-f47ea0d6473c
Martinez Gonzalez, M.J.
bc5a2014-bb73-4b7f-ade1-7e612ef92121
Asensio Ramos, A.
dca27505-3a0a-4f84-a930-fcecf99e1ada
Acosta-Pulido, J.A.
d73ea5db-84f0-415e-ad48-a5484d5637bf
Hoenig, S.F.
be0bb8bc-bdac-4442-8edc-f735834f3917
Alonso-Herrero, A.
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Tadhunter, C.N.
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Gonzalez-Martin, O.
dc84a0b8-4350-4053-b1d5-5d2d75142b61

Ramos Almeida, C., Martinez Gonzalez, M.J., Asensio Ramos, A., Acosta-Pulido, J.A., Hoenig, S.F., Alonso-Herrero, A., Tadhunter, C.N. and Gonzalez-Martin, O. (2016) Upholding the unified model for Active Galactic Nuclei: VLT/FORS2 spectropolarimetry of Seyfert 2 galaxies. Monthly Notices of the Royal Astronomical Society, 1-18. (doi:10.1093/mnras/stw1388).

Record type: Article

Abstract

The origin of the unification model for Active Galactic Nuclei (AGN) was the detection of broad hydrogen recombination lines in the optical polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden broad-line region (HBLR) of nearby Sy2s started, but polarized broad lines have only been detected in ?30–40% of the nearby Sy2s observed to date. Here we present new VLT/FORS2 optical spectropolarimetry of a sample of 15 Sy2s, including Compton-thin and Compton-thick sources. The sample includes six galaxies without previously published spectropolarimetry, some of them normally treated as non-hidden BLR (NHBLR) objects in the literature, four classified as NHBLR, and five as HBLR based on previous data. We report ?4? detections of a HBLR in 11 of these galaxies (73% of the sample) and a tentative detection in NGC 5793, which is Compton-thick according to the analysis of X-ray data performed here. Our results confirm that at least some NHBLRs are misclassified, bringing previous publications reporting differences between HBLR and NHBLR objects into question. We detect broad H? and H? components in polarized light for 10 targets, and just broad H? for NGC 5793 and NGC 6300, with line widths ranging between 2100 and 9600 km s?1. High bolometric luminosities and low column densities are associated with higher polarization degrees, but not necessarily with the detection of the scattered broad components.

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Accepted/In Press date: 7 June 2016
e-pub ahead of print date: 9 June 2016
Organisations: Astronomy Group

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Local EPrints ID: 396963
URI: http://eprints.soton.ac.uk/id/eprint/396963
ISSN: 0035-8711
PURE UUID: 4f3a1b81-01bd-4342-9025-05b42fb5ac8e

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Date deposited: 17 Jun 2016 09:28
Last modified: 16 Dec 2019 19:52

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Contributors

Author: C. Ramos Almeida
Author: M.J. Martinez Gonzalez
Author: A. Asensio Ramos
Author: J.A. Acosta-Pulido
Author: S.F. Hoenig
Author: A. Alonso-Herrero
Author: C.N. Tadhunter
Author: O. Gonzalez-Martin

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