Infrared Spectroscopy of NGC 1068: Probing the Obscured Ionizing AGN Continuum

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Abstract
The ISO-SWS 2.5-45 μm infrared spectroscopic observations of the nucleus of the Seyfert 2 galaxy NGC 1068 (see companion paper) are combined with a compilation of UV to IR narrow emission line data to determine the spectral energy distribution (SED) of the obscured extreme-UV continuum that photoionizes the narrow-line-emitting gas in the active galactic nucleus. We search a large grid of gas-cloud models and SEDs for the combination that best reproduces the observed line fluxes and narrow-line region (NLR) geometry. Our best-fit model reproduces the observed line fluxes to better than a factor of 2 on average and is in general agreement with the observed NLR geometry. It has two gas components that are consistent with a clumpy distribution of dense outflowing gas in the center and a more extended distribution of less dense and more clumpy gas farther out that has no net outflow. The best-fit SED has a deep trough at ~4 rydbergs, which is consistent with an intrinsic Big Blue Bump that is partially absorbed by ~6 × 1019 cm-2 of neutral hydrogen interior to the NLR.
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