The evidence for anisotropy of the ionizing continuum of NGC 4151

Details The evidence for anisotropy of the ionizing continuum of NGC 4151 The evidence for anisotropy of the ionizing continuum of NGC 4151

Oct 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...278...29s&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 278, no. 1, p. 29-35

Astronomy and Astrophysics

Astrophysics

23

Anisotropy, Astronomical Models, Emission Spectra, Line Spectra, Photoionization, Seyfert Galaxies, Active Galactic Nuclei, Black Body Radiation, Chemical Analysis, Space Density

Scientific paper

The emission-line ratios from the very-narrow line region (VNLR) of NGC 4151 measured by Penston et al. (1990) are employed to find constraints for the shape and strength of the photoionizing continuum. Two fundamentally different types of models provide successful fits: (a) a single-component model based on ionization bounded clouds with constant density requires a strong bump in the ionizing continuum that can be represented by a 230,000 K-black body. This solution calls nearly inevitably for an anisotropic emission of the nuclear continuum; (b) multi-component models of two to three types of matter bounded clouds with different densities. Solutions are found that are consistent with an intrinsically isotropic continuum and an essentially ionization bounded total emission line region. Unfortunately, the ignorance of the structure of the VNLR precludes an assessment, which of the different solutions is closer to reality. However, we show that single-component photoionization models overestimate the strength of the necessary input continuum and, hence, emphasize anisotropy if significant density inhomogeneities occur at the same radial distance from the ionizing source.

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