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Date and Time of the Query: 2019-08-19 T16:41:41 PDT
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For refcode 2000ApJ...538...98R:
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2000ApJ...538...98R Probing the Dust Obscuration in Seyfert Galaxies Using Infrared Spectroscopy Joseph H. Rhee and James E. Larkin Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, CA 90095 Received 1999 September 21; accepted 2000 February 23 ABSTRACT We present near-infrared spectroscopy of four Seyfert 1 galaxies, one Seyfert 1.9 galaxy, and one Seyfert 2 galaxy, obtained using the Gemini infrared camera at the Lick Observatory 3 m Shane telescope. With the unique design of the Gemini camera, full J- and K-band spectra were taken simultaneously through the same slit. This produced a more accurate comparison of hydrogen recombination line fluxes than previous infrared studies. We have also used template galaxies to remove stellar features from the infrared spectra and produced more accurate measurements of the weak Br{gamma} feature. We concentrate on the velocity-resolved ratio of Pa{beta}/Br{gamma} and its implication for dust within the central active galactic nucleus (AGN). For our Seyfert 1s, the line ratios of Pa {beta}/Br{gamma} are not only comparable in both broad- and narrow-line regions but also consistent with case B recombination, confirming that the ratio Pa{beta}/Br{gamma} is less affected by collisional effects than optical lines and is a good indicator of dust extinction up to A_v_ ~ 10 in AGN. Using the same diagnostic the Seyfert 1.9 galaxy, NGC 2992, has an extinction of Av = 4.03 +/- 0.20 to the broad-line region while the narrow- line region is unobscured. Assuming that Seyfert 1.9 galaxy has the same broad-line region that Seyfert 1 galaxies have, we conclude that the obscuring dust is located between the broad-line regions and the narrow- line regions, consistent with the AGN unification model. The Seyfert 2 galaxy, NGC 5929, consistent with dust being present on larger scales, shows significant obscuration to the narrow-line region. These data are part of a larger program to measure many spectral properties of Seyfert galaxies. Subject headings: galaxies: active-galaxies: Seyfert-infrared: galaxies
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