Multi-wavelength Probes of Obscuration Towards the Narrow Line Region in Seyfert Galaxies (PREPRINT)
NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
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We present a study of reddening and absorption towards the Narrow Line Regions NLR in active galactic nuclei AGN selected from the Revised Shapley- Ames, 12 micrometers, and SwiftBurst Alert Telescope samples. For the sources in host galaxies with inclinations of ba 0.5, we find that mean ratio of O III 5007 from ground-based observations, and O IV 28.59 micrometers, from SpitzerInfrared Spectrograph observations, is a factor of 2 lower in Seyfert 2s than Seyfert 1s. The combination of low O IIIO IV and O III lambda-4363 lambda-5007 ratios in Seyfert 2s suggests more extinction of emission from the NLR than in Seyfert 1s. Similar column densities of dusty gas, NH several x 10exp 21squared centimeters, can account for the suppression of both O III lambda-5007 and O III lambda-4363, as compared to those observed in Seyfert 1s. Also, we find that the X-ray line O VII lambda-22.1 Angstroms is weaker in Seyfert 2s, consistent with absorption by the same gas that reddens the optical emission. Using a Hubble Space TelescopeSpace Telescope Imaging Spectrograph slitless spectrum of the Seyfert 1 galaxy NGC 4151, we estimate that only 30 of the O III lambda-5007 comes from within 30 pc of the central source, which is insufficient to account for the low O IIIO IV ratios in Seyfert 2s. If Seyfert 2 galaxies have similar intrinsic O III spatial profiles, the external dusty gas must extend further out along the NLR, perhaps in the form of nuclear dust spirals that have been associated with fueling flows towards the AGN.
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