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| Paper: |
Near Infrared Spectroscopy as a Probe of Dust Obscuration in Seyfert Galaxies |
| Volume: |
290, Active Galactic Nuclei: from Central Engine to Host Galaxy |
| Page: |
243 |
| Authors: |
Rhee, J. H.; Larkin, J. E. |
| Abstract: |
We report new near-infrared spectroscopy of Seyfert galaxies using the Gemini twin channel near-infrared camera on the Shane 3m telescope at Lick Observatory. We directly test the standard AGN model by measuring extinctions to both broad and narrow line regions for different Seyfert classes using the Pa Beta and Br gamma emission lines. With the unique design of the Gemini camera, full J and K spectra were taken simultaneously through the same slit greatly reducing systematic errors in the line ratio measurement that can be introduced by seeing variation and slit positioning. We find that for our sample of Seyfert 1s, the line ratios of PaB/Brg are not only comparable in both broad and narrow line regions but also are consistent with case B recombination indicating little or no extinction. Seyfert 2 galaxies, however, show substantial reddening to the narrow line regions. Historically, studies have found dust extinction in the narrow line regions of both Seyfert 1s and Seyfert 2s. We compare our results with recent optical data from the literature and find significant support for our findings. Several possible scenarios are discussed to explain this apparent difference of narrow line ratios between Seyfert 1s and Seyfert 2s, which represent modifications to the unified model. We also analyzed CO band-head absorption features to look for evidence of recent star formation activity. The CO band-head, especially in Seyfert 1s, show heavy contamination from nonstellar radiation, which is correlated with an H-K nuclear color index. After correcting for this effect, we confirm that the evidence of recent star formation in Seyfert 2's, as indicated by the CO spectral index, is weak. Finally we will discuss our plans to utilize the Keck Telescope to observe spatially resolved IR spectra of Seyfert 2's to attempt to localize the obscuring material. |
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