NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-20 T05:47:30 PDT
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For refcode 2016A&A...586A..28B:
Retrieve 29 NED objects in this reference.
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2016A&A...586A..28B On the relation of optical obscuration and X-ray absorption in Seyfert galaxies Burtscher, L.; Davies, R. I.; Gracia-Carpio, J.; Koss, M. J.; Lin, M.-Y.; Lutz, D.; Nandra, P.; Netzer, H.; Orban de Xivry, G.; Ricci, C.; Rosario, D. J.; Veilleux, S.; Contursi, A.; Genzel, R.; Schnorr-Muller, A.; Sternberg, A.; Sturm, E.; Tacconi, L. J. Abstract. The optical classification of a Seyfert galaxy and whether it is considered X-ray absorbed are often used interchangeably. There are many borderline cases, however, and also numerous examples where the optical and X-ray classifications appear to be in disagreement. In this article we revisit the relation between optical obscuration and X-ray absorption in active galactic nuclei (AGNs). We make use of our "dust colour" method to derive the optical obscuration A_V_, and consistently estimated X-ray absorbing columns using 0.3-150 keV spectral energy distributions. We also take into account the variable nature of the neutral gas column N_H_ and derive the Seyfert subclasses of all our objects in a consistent way. We show in a sample of 25 local, hard-X-ray detected Seyfert galaxies (log L_X_/ (erg / s) ~ 41.5-43.5) that there can actually be a good agreement between optical and X-ray classification. If Seyfert types 1.8 and 1.9 are considered unobscured, the threshold between X-ray unabsorbed and absorbed should be chosen at a column N_H_ = 10^22.3^ cm^-2^ to be consistent with the optical classification. We find that N_H_ is related to A_V_ and that the N_H_/A_V_ ratio is approximately Galactic or higher in all sources, as indicated previously. However, in several objects we also see that deviations from the Galactic ratio are only due to a variable X-ray column, showing that (1) deviations from the Galactic N_H_/A_V_ can be simply explained by dust-free neutral gas within the broad-line region in some sources; that (2) the dust properties in AGNs can be similar to Galactic dust and that (3) the dust colour method is a robust way to estimate the optical extinction towards the sublimation radius in all but the most obscured AGNs. Key words: galaxies: active, galaxies: nuclei, galaxies: Seyfert, dust, extinction
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