ChandraObservations of Candidate “True” Seyfert 2 Nuclei

The Unification Model for active galactic nuclei posits that Seyfert 2s areintrinsically like Seyfert 1s, but that their broad-line regions (BLRs) arehidden from our view. A Seyfert 2 nucleus that truly lacked a BLR, instead ofsimply having it hidden, would be a so-called "true" Seyfert 2. No object hasas yet been conclusively proven to be one. We present a detailed analysis offour of the best "true" Seyfert 2 candidates discovered to date: IC 3639, NGC3982, NGC 5283, and NGC 5427. None of the four has a broad H-alpha emissionline, either in direct or polarized light. All four have rich, high-excitationspectra, blue continua, and Hubble Space Telescope (HST) images showing them tobe unresolved sources with no host-galaxy obscuration. To check for possibleobscuration on scales smaller than that resolvable by HST, we obtained X-rayobservations using the Chandra X-ray Observatory. All four objects showevidence of obscuration and therefore could have hidden BLRs. The picture thatemerges is of moderate to high, but not necessarily Compton-thick, obscurationof the nucleus, with extra-nuclear soft emission extended on thehundreds-of-parsecs scale that may originate in the narrow-line region. Sincethe extended soft emission compensates, in part, for the nuclear soft emissionlost to absorption, both absorption and luminosity are likely to be severelyunderestimated unless the X-ray spectrum is of sufficient quality todistinguish the two components. This is of special concern where the source istoo faint to produce a large number of counts, or where the source is too faraway to resolve the extended soft X-ray emitting region.Comment: 26 pages, 12 figures, submitted to Ap