The Effect of Intrinsic UV Absorbers on the Ionizing Continuum and Narrow Emission Line Ratios in Seyfert Galaxies

Abstract

We explore the effects of UV absorbing material on the shape of the EUV continuum radiation emitted by the active galactic nucleus, and on the relative strengths of emission lines, formed in the narrow line regions of Seyfert galaxies, excited by this continuum. Within a sample of Seyfert 1.5 galaxies, objects with flatter soft X-ray slopes tend to have lower values of He II 4686/H-beta, which implies a correlation between the observed spectral energy distribution of the ionizing continuum and the narrow emission line strengths. Objects with the flattest soft X-ray continua tend to possess high column density UV absorption and it is plausible that the differences in narrow emission line ratios among these galaxies are an indication of the effects of absorbing material internal to the narrow line region, rather than intrinsic differences in continuum shape. We have generated a set of photoionization models to examine the effect of a range of UV absorbers on the ionizing continuum and, hence, the resulting conditions in a typical narrow line cloud. Our results indicate that a low ionization UV absorber with large covering factor will indeed produce the combination of narrow line ratios and soft X-ray spectral characteristics observed in several Seyfert 1.5 galaxies. Our results also suggest that low ionization UV absorption may be more common than currently believed.

35 pages, Latex, includes 5 figures (encapsulated postscript), 3 additional tables in Latex, to appear in the Astrophysical Journal

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• Ultraviolet Diagnostics for the Emission Line Gas in Active Galaxies
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• Heavy and Complex X-ray Absorption Towards the Nucleus of Markarian 6
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• Far-UV Observations of NGC 4151 during the ORFEUS-SPAS II Mission

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• STIS Longslit Spectroscopy of the Narrow-Line Region of NGC 4151. II. Physical Conditions along Position Angle 221 Degress
• A new cosmological distance measure using AGN X-ray variability
• Interrogating Seyferts with NebulaBayes: Spatially probing the narrow-line region radiation fields and chemical abundances
• A Survey of Intrinsic Absorption in Active Galaxies using the Far Ultraviolet Spectroscopic Explorer
• STIS Echelle Observations of the Intrinsic UV Absorption in the Seyfert 1 Galaxy NGC 3783
• The Narrow Line Region of Narrow-Line Seyfert 1 Galaxies
• Probing the Ionizing Continuum of Narrow-Line Seyfert 1 Galaxies. I.Observational Results
• The Cosmic Baryon Fraction and the Extragalactic Ionizing Background
• On the Relationship Between the Optical Emission-Line and X-ray Luminosities in Seyfert 1 Galaxies
• Space Telescope and Optical Reverberation Mapping Project. XIII. An Atlas of UV and X-ray Spectroscopic Signatures of theDisk Wind in NGC 5548