Probing the dust obscuration in Seyfert galaxies using infrared spectroscopy

We present near-infrared spectroscopy of four Seyfert 1 galaxies, one Seyfe rt 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 hydroge n recombination line fluxes than previous infrared studies. We have also us ed template galaxies to remove stellar features from the infrared spectra a nd produced more accurate measurements of the weak Br gamma feature. We con centrate on the velocity-resolved ratio of Pa beta/Br gamma and its implica tion for dust within the central active galactic nucleus (AGN). For our Sey fert Is, the line ratios of Pa beta/Br gamma are not only comparable in bot h broad- and narrow-line regions but also consistent with case B recombinat ion, confirming that the ratio Pa beta/Br gamma is less affected by collisi onal effects than optical lines and is a good indicator of dust extinction up to A(v) similar to 10 in AGN. Using the same diagnostic the Seyfert 1.9 galaxy, NGC 2992, has an extinction of A(v) = 4.03 +/- 0.20 to the broad-li ne 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. Th e 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 Seyfer t galaxies.