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N. R. Collins, S. B. Kraemer (CUA), D. M. Crenshaw (GSU)
We used the photoionization model code CLOUDY and {\emph Hubble Space Telescope} Space Telescope Imaging Spectrograph (HST/STIS) spectroscopy to study the physical conditions in the Markarian~3 narrow-line region (NLR) gas and to infer the nature of the ionizing continuum. The position angle of the low-resolution long-slit aperture was 71\degr east of north, coincident with the elongated reverse-``S'' shaped feature of the NLR. We modelled 11 emission line sources in 7 contiguous regions spanning central 2\arcsec of the NLR. Most of the calculated line ratios match the dereddened observed ratios within the a factor of two. The NLR gas is photoionized by an absorbed broken power-law continuum. A heterogeneous distribution of dusty and dust-free gas at a range of three different ionization states comprises the modelled NLR gas. We find that the NLR gas component with the lowest ionization state must lie at a greater distance from the active nucleus (along the same line-of-sight) than the other components. This is required to match the high observed fluxes from low critical density emission lines ([\ion{O}{2}]\lambda~3727 and [\ion{N}{2}]\lambda~6584) produced by low ionization potential ionic species. We also find that the lowest ionization state component on a given line-of-sight is illuminated by a more highly absorbed continuum than the remaining components. Furthermore, the amount of continuum absorption to the low ionization state components varies from one region to another along the slit. We infer the distribution of the absorbing gas from this variation.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.