Unabsorbed Seyfert 2 galaxies

By F. Panessa, L. Bassani. 2002

155 citations recorded by the source corpus.

We present a sample of 17 type 2 Seyfert galaxies which have an X-ray column density lower than 10 22 cm 2 .T he Compton thin nature of these sources is strongly suggested by isotropic indicators. We estimate the fraction of these sources to be in the range of 10%-30% of the population of type 2 Seyfert galaxies. Furthermore, this fraction appears to increase progressively at lower luminosities. The simple formulation of the Unified Model for Seyfert galaxies is not applicable in such sources since the pc-scale molecular torus is not likely to be responsible for the low column density observed; instead the absorption observed is likely to originate at larger scales. According to this hypothesis, in these objects the broad line regions are covered by some dusty obscuring material. In particular, this could occur in objects with dust lanes, patches or HII regions. However, we cannot rule out that in the lowest luminosity sources the BLR is weak, absent or has faded away. This last scenario is consistent with the predictions of some recent theoretical models for low luminosity AGNs.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b9be0a96bcfe68c8cc236391bfce865698357853

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In Astronomy and Astrophysics

1. D. M. Alexander
2. R. Hickox
3. P. Hopkins
4. W. N. Brandt
5. H. Netzer
6. L. Hernquist
7. Luis C. Ho
8. Mara Salvato

In Instrumentation

1. D. M. Alexander
2. R. Hickox
3. P. Hopkins
4. H. Netzer
5. L. Hernquist
6. Mara Salvato
7. A. Koekemoer
8. D. Lutz

Citations in the corpus

• On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies ! (2006, methodology): “To do so, we have taken advantage of some powerful diagnostic tools like the flux diagnostic diagrams (Bassani et al. 1999; Panessa & Bassani 2002).”
• The HELLAS2XMM Survey. VII. The Hard X-Ray Luminosity Function of AGNs up to z = 4: More Absorbed AGNs at Low Luminosities and High Redshifts (2005, background): “The analysis of this issue is beyond the scope of this paper (see Panessa & Bassani 2002; Page et al. 2003; Steffen et al. 2003; Ueda et al. 2003; Brusa et al. 2003; Perola et al. 2004; Barger et al. 2005 for similar results and discussions; see also x 4.6).”
• Revisiting the Unified Model of Active Galactic Nuclei (2015, background): “In the local Universe, such objects represent about 30% of all type-II objects (Panessa & Bassani 2002, Tran 2003, Shi et al. 2010, Brightman & Nandra 2011b, Marinucci et al. 2012, Merloni et al. 2014).”
• X-ray spectral survey with XMM-Newton of a complete sample of nearby Seyfert galaxies (2005, background): “Another way of evaluating the true amount of absorption is through flux diagnostic diagrams (e.g., Bassani et al. 1999, Panessa & Bassani 2002, Panessa 2004, Guainazzi et al. 2005).”
• Active galactic nuclei: what’s in a name? (2017, background): “…between absorption indicators for a small subset of the AGN population (e.g. X-ray unabsorbed type 2 AGN and X-ray absorbed type 1 AGN; e.g. Panessa and Bassani 2002; Bianchi et al. 2012) also provide interesting insight into the overall universality of the basic unified model (see Netzer…”
• Nuclear Activity in Nearby Galaxies (2008, background): “Others, however, are too faint for spectral analysis, and for these, their status as Compton-thick sources was based on the observed ratio of 2−10 keV flux to [O III] λ5007 flux (Bassani et al. 1999; Panessa & Bassani 2002).”
• The incidence of obscuration in active galactic nuclei (2013, background): “These might well include so-called true type-2 AGN (Panessa & Bassani 2002; Brightman & Nandra 2008; Bianchi et al. 2012a), i.e. accreting black holes without a hidden broad-line region.”
• The subarcsecond mid-infrared view of local active galactic nuclei – II. The mid-infrared–X-ray correlation (2015, background): “The idea of so-called true type II AGN is based observationally on the absence of broad emission lines in polarized light (but see Antonucci 2012) and the absence of significant X-ray absorption in many type II AGN (Ptak et al. 1996; Pappa et al. 2001; Panessa & Bassani 2002).”
• Evolution of broad-line emission from active galactic nuclei (2013, background): “…in low-luminosity AGNs by infrared observations (van der Wolk et al. 2010; Trump et al. 2011), and the existence of “true type 2” AGNs—unobscured sources that lack broad-line emission—has been established in studies by Tran (2001, 2003), Panessa & Bassani (2002), and Laor (2003), among others.”