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L. E. Kay (Barnard College, Columbia University), E. C. Moran (Wesleyan University), A. J. Barth (U. C. Irvine), A. V. Filippenko (U. C. Berkeley), A. M. Magalhaes (IAGUSP)
An important but unresolved question regarding unification models of Seyfert galaxies is whether all type 2 Seyferts are obscured Seyfert 1s. The answer is relevant not only for an improvement of our classification scheme, but also for establishing whether heavily obscured AGNs are capable of producing the majority of the cosmic X-ray background radiation. To address these issues we have conducted a spectropolarimetric survey of nearby Seyfert 2s using the distance-limited sample of Ulvestad and Wilson (1989), which represents a reasonably complete, unbiased set of classical Seyfert 2s. Except for two very southern objects observed with the CTIO 4m, our observations were obtained with the Keck 10m telescope. Five of the 31 galaxies in this sample were known to possess hidden BLRs prior to the start of our survey. We identified additional hidden BLRs with spectropolarimetry at Lick (NGC 788), at CTIO (NGC 424), and at Keck (NGC 591, NGC 2273, NGC 3081, NGC 4507, NGC 5347 and NGC 5929). Thus, we find that at least 13/31, or 42%, of nearby classical Seyfert 2s have polarized broad emission lines, indicating that they are obscured primarily by material located a few parsecs from the nucleus, rather than by large-scale foreground dust lanes. Seyfert 2s without polarized broad lines tend to be less luminous objects and their spectra tend to be more diluted by unpolarized host-galaxy starlight, which may explain why polarized optical emission from them has not yet been detected. We predict that longer observations with Keck, or with the next largest telescope, would reveal HBLRs in more of the objects in our sample.
Support from the Mellon Foundation and Barnard College (LEK) is acknowledged.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.