Imaging spectrophotometry of ionized gas in NGC 1068. II - Global ionization of the inner disk

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Galactic Nuclei, Galactic Structure, Gas Ionization, Ionized Gases, Seyfert Galaxies, Spectrophotometry, Balmer Series, Fabry-Perot Interferometers, H Alpha Line, Interferometry, Spectral Line Width, Galaxies: Individual (Ngc 1068) Galaxies: Nuclei Galaxies: Seyfert Galaxies: Structure Interferometry Spectrophotometry

Scientific paper

Spectrophotometric observations with the Hawaii Imaging Fabry-Perot Interferometer (HIFI) of the Hα and [N II] λλ6548, 6584 lines has detected a diffuse ionized medium (DIM) pervading the inner ˜10 kpc diameter disk of the nearby, luminous Seyfert galaxy NGC 1068. The physics and dynamics of this energetic gas are distinct from the population of adjacent disk H II regions which have line intensity ratios [N II] λ6584/Hα < 0.5, equivalent widths of Hα 15-100 Å, and [N II] λ6584 line widths 100 km s-1 FWHM. The DIM exhibits broader lines (150-250 km s-1 FWHM) than the H II regions which suggests an exponential scale height of at least ˜400 pc, compared with ˜50 pc for the cold neutral phase. The DIM is characterized by strong [N II] λ6584 emission (3.0 × 1041 ergs s-1) when compared to Hα (1.2 × 1041 ergs s-1), with [N II] λ6584/Hα ˜ 1 throughout and reaching 2-3 NE and SW along the radio axis. Because the chemical abundances throughout the inner disk are known to be approximately solar and we have corrected for Balmer absorption by the underlying stellar population, the extent of the high [N II] λ6584/Hα gas and, for a filling factor φ, the associated cooling time (≍ 2 × 105φ0.5 yr) indicate substantial excitation of the DIM. We discuss heating by the Seyfert nucleus and the extended starburst region because these regions share the bolometric luminosity.

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