Nuclear obscuration and scattering in Seyfert 2 galaxies

Gu, Qiusheng; Maiolino, R.; Dultzin‐Hacyan, D.

doi:10.1051/0004-6361:20000302

Cited by 32 publications

(44 citation statements)

References 29 publications

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“…This confirms the finding by several authors -also based on X-ray spectra -that non-HBLR and HBLR samples exhibit similar column densities and obscuration (e.g. Alexander 2001;Gu et al 2001;Tran 2003).…”

Section: Intrinsically Weak or Obscured Nucleisupporting

confidence: 91%

“…There is no doubt that dust lanes may obscure not only the nucleus but also the scattering mirror necessary for the detection of a HBLR. Hence, only under favourable circumstances one may expect detectable scattered light at all from a hidden AGN (Miller & Goodrich 1990;Heisler et al 1997;Gu et al 2001). The AGN-typical emission line [OIII] λ5007 Å (henceforth denoted [OIII]) has an average equivalent width which is higher for HBLRs than for non-HBLRs, indicating a stronger AGN/host contrast in HBLRs (Lumsden et al 2001;Moran 2007).…”

Section: Introductionmentioning

confidence: 99%

“…The AGN-typical emission line [OIII] λ5007 Å (henceforth denoted [OIII]) has an average equivalent width which is higher for HBLRs than for non-HBLRs, indicating a stronger AGN/host contrast in HBLRs (Lumsden et al 2001;Moran 2007). Generally, it is a challenge for spectropolarimetric observations to discern the few percent BLR signature of a relatively faint AGN against a luminous host galaxy (Alexander 2001;Gu et al 2001;Lumsden & Alexander 2001;Lumsden et al 2001). Although still half of the most nearby Sy2s resisted HBLR detection even with Keck spectropolarimetry, such sensitive observations are revealing broad lines in sources, which were previously classified as non-HBLRs using smaller telescopes.…”

Section: Introductionmentioning

confidence: 99%

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VISIR / VLT mid-infrared imaging of Seyfert nuclei: nuclear dust emission and the Seyfert-2 dichotomy

Haas

Siebenmorgen

Pantin

et al. 2007

A&A

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Aims. Half of the Seyfert-2 galaxies escaped detection of broad lines in their polarised spectra observed so far. Some authors have suspected that these non-HBLRs contain real Sy2 nuclei without intrinsic broad line region hidden behind a dust torus. If this were true, then their nuclear structure would fundamentally differ from that of Sy2s with polarised broad lines: in particular, they would not be explained by orientation-based AGN unification. Further arguments for two physically different Sy2 populations have been derived from the warm and cool IRAS F25/F60 ratios. These ratios, however, refer to the entire host galaxies and are unsuitable to conclusively establish the absence of a nuclear dust torus. Instead, a study of the Seyfert-2 dichotomy should be performed on the basis of nuclear properties only. Here we present the first comparison between [OIII] λ5007 Å and mid-infrared imaging at matching spatial resolution. The aim is to check whether the nuclear dust emission scales with AGN luminosity as traced by [OIII]. Methods. During the scientific verification phase of the VISIR instrument at the ESO Very Large Telescope we observed 16 Sy1 and Sy2 nuclei at 11.25 µm with 0. 35 spatial resolution (FWHM). We supplement our observations with high-resolution 10-12 µm literature data of 58 Seyfert galaxies, for which spectroscopic or spectropolarimetric information and far-infrared data are available. Results. Twelve of the 15 detected sources are unresolved and three sources show a dominant unresolved core surrounded by some faint knots in an area smaller than 1-2 radius. Our VISIR photometry agrees to better than 15% with published data obtained at 1. 5-5 spatial resolution. Exploring the Seyfert-2 dichotomy we find that the distributions of nuclear mid-infrared / [OIII] luminosity ratios are indistinguishable for Sy1s and Sy2s with and without detected polarised broad lines and irrespective of having warm or cool IRAS F25/F60 ratios. We find no evidence for the existence of a population of real Sy2s with a deficit of nuclear dust emission. Our results suggest 1) that all Seyfert nuclei possess the same physical structure including the putative dust torus and 2) that the cool IRAS colours are caused by a low contrast of AGN to host galaxy. Then the Seyfert-2 dichotomy is explained in part by unification of nonHBLRs with narrow-line Sy1s and to a larger rate by observational biases caused by a low AGN/host contrast and/or an unfavourable scattering geometry.

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Section: Intrinsically Weak or Obscured Nucleisupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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VISIR / VLT mid-infrared imaging of Seyfert nuclei: nuclear dust emission and the Seyfert-2 dichotomy

Haas

Siebenmorgen

Pantin

et al. 2007

A&A

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“…Based on a smaller sample, Alexander (2001) argued that the absorbing column density N H of HBLR and non-HBLR S2 galaxies do not show any significant difference. Gu et al (2001), on the other hand, suggested that HBLR S2 galaxies may have on average smaller N H than non-HBLR S2 galaxies, using data available for a heterogeneous sample of HBLR S2 galaxies. For our larger and more complete sample, we show in Figure large uncertainties and thus may not reflect the true nature of the obscuration in S2 galaxies.…”

Section: Observations and Resultsmentioning

confidence: 99%

Hidden Broad-Line Seyfert 2 Galaxies in the C[CLC]f[/CLC]A and 12 μ[CLC]m[/CLC] Samples

Tran

2001

The Astrophysical Journal

177

230

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We report the results of a spectropolarimetric survey of the CfA and 12 mm samples of Seyfert 2 (S2) galaxies. Polarized (hidden) broad-line regions (HBLRs) are confirmed in a number of galaxies, and several new cases (F02581Ϫ1136, MCG Ϫ3-58-7, NGC 5995, NGC 6552, NGC 7682) are reported. The 12 mm S2 galaxy sample shows a significantly higher incidence of HBLRs (50%) than its CfA counterpart (30%), suggesting that the latter may be incomplete in hidden active galactic nuclei. Compared to the non-HBLR S2 galaxies, the HBLR S2 galaxies display distinctly higher radio power relative to their far-infrared output and hotter dust temperature as indicated by the color. However, the level of obscuration is indistinguishable between the two types of S2 f /f 25 60 galaxies. These results strongly support the existence of two intrinsically different populations of S2 galaxies: one harboring an energetic, hidden S1 nucleus with a broad-line region and the other a "pure" S2 galaxy, with a weak or absent S1 nucleus and a strong, perhaps dominating starburst component. Thus, the simple purely orientation-based unification model is not applicable to all Seyfert galaxies.

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“…Furthermore, there are also studies that separate Type I from Type II objects (e.g. Hunt et al 1997;Maiolino et al 1997;Gu et al 2001), implying that recent star formation is only present in Type II objects (see also Coldwell et al 2009). Based on the number and proximity of close ( 60-100 h −1 kpc) neighbours, around different types of active (Sy1, Sy2 and BIRG) galaxies (e.g.…”

Section: Discussionmentioning

confidence: 99%

Activity of the Seyfert galaxy neighbours

Koulouridis

Plionis

Chavushyan

et al. 2013

A&A

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We present a follow-up study of a series of papers concerning the role of close interactions as a possible triggering mechanism of AGN activity. We have already studied the close (≤100 h −1 kpc) and the large-scale (≤1 h −1 Mpc) environment of a local sample of Sy1, Sy2, and bright IRAS galaxies (BIRG) and of their respective control samples. The results led us to the conclusion that a close encounter appears capable of activating a sequence where an absorption line galaxy (ALG) galaxy first becomes a starburst, then a Sy2, and finally a Sy1. Here we investigate the activity of neighbouring galaxies of different types of AGN, since both galaxies of an interacting pair should be affected. To this end we present the optical spectroscopy and X-ray imaging of 30 neighbouring galaxies around two local (z 0.034) samples of 10 Sy1 and 13 Sy2 galaxies. Although this is a pilot study of a small sample, various interesting trends have been discovered that imply physical mechanisms that may lead to different Seyfert types. Based on the optical spectroscopy, we find that more than 70% of all neighbouring galaxies exhibit star forming and/or nuclear activity (namely recent star formation and/or AGN), while an additional X-ray analysis showed that this percentage might be significantly higher. Furthermore, we find a statistically significant correlation, at a 99.9% level, between the value of the neighbour's [OIII]/Hβ ratio and the activity type of the central active galaxy, i.e. the neighbours of Sy2 galaxies are systematically more ionized than the neighbours of Sy1s. This result, in combination with trends found using the Equivalent Width of the Hα emission line and the stellar population synthesis code STARLIGHT, indicate differences in the stellar mass, metallicity, and star formation history between the samples. Our results point towards a link between close galaxy interactions and activity and also provide more clues regarding the possible evolutionary sequence inferred by our previous studies.

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Nuclear obscuration and scattering in Seyfert 2 galaxies

Cited by 32 publications

References 29 publications

VISIR / VLT mid-infrared imaging of Seyfert nuclei: nuclear dust emission and the Seyfert-2 dichotomy

VISIR / VLT mid-infrared imaging of Seyfert nuclei: nuclear dust emission and the Seyfert-2 dichotomy

Hidden Broad-Line Seyfert 2 Galaxies in the C[CLC]f[/CLC]A and 12 μ[CLC]m[/CLC] Samples

Activity of the Seyfert galaxy neighbours

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