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Paper: Seyfert 2 Galaxies Uncovered with Keck Spectropolarimetry
Volume: 343, Astronomical Polarimetry: Current Status and Future Directions
Page: 505
Authors: Kay, L.E.; Moran, E.C.; Barth, A.J.; Filippenko, A.V.; Magalhaes, A.M.M.
Abstract: We have surveyed the multiwavelength (radio–to–X-ray) properties of a large, distance-limited sample of the nearest classical Seyfert 2 galaxies to assess the universality of the unified Seyfert model and the contribution of type 2 AGNs to the cosmic X-ray background. Our survey combines published radio and mid-infrared data with our own optical spectropolarimetric observations from the Keck observatory and hard X-ray spectra from the ASCA satellite. Over 40% of the objects in our sample exhibit polarized broad emission lines, indicating that they are hidden type 1 nuclei. A composite X-ray spectrum of the galaxies that appear to lack hidden broad-line regions reveals that such objects are nonetheless heavily obscured sources. Comparisons of the radio luminosities, mid-IR colors, and X-ray properties of the galaxies in our unbiased sample point to the luminosity contrast between the nucleus and the host galaxy bulge as the principal factor governing the detectability of polarized broad lines in Seyfert 2s. Thus, the preponderance of evidence suggests that most nearby Seyfert 2 nuclei are indeed obscured type 1 objects, in accordance with the unified Seyfert model. Combining a composite X-ray spectrum for the entire sample with the measured evolution of the AGN X-ray luminosity function, we conclude that type 2 AGNs must account for the majority of the intensity of the 2-10 keV X-ray background and its flat spectral slope.
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