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For refcode 1994A&A...291...18M:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1994A&A...291...18M A [Si VI] (1.962 micron) coronal line survey of galactic nuclei A. Marconi, A.F.M. Moorwood, M. Salvali, and E. Oliva Dipartimento di Astronomia e Scienza dello Spazio, Universita di Firenze, Largo E. Fermi 5,1-50125 Firenze, Italy European Southern Observatory, Karl Schwarzschild Str. 2, D-85748 Garching bei Munchen, Germany Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5,1-50125 Firenze, Italy Received 31 January 19941 Accepted 3 May 1994 Abstract. We present the results of a (Si VI]{lambda}1.962 emission line survey of active, starburst and IRAS luminous galaxies. The line was only detected in known Seyfert type 1 and 2 nuclei confirming previous suggestions that [Si VI] is related to Seyfert activity. By modelling the formation of [Si VI] and (Fe VII]{lambda}6087 we find further strong evidence that these lines arise in gas photoionized by the active nucleus although collisional ionization e.g. by shock fronts may be important in some galaxies exhibiting (Fe VII]>>[Si VI). Our failure to detect [Si VI] in the IRAS ultraluminous galaxies does not exclude the possible presence of obscured AGN's, particularly as some of the known Seyferts were also not detected. Molecular hydrogen lines (a by-product of our spectra) are common in all galaxy types including several IRAS ultraluminous galaxies whose H_2_ equivalent widths (W_{lambda}_ < 20 A) are `normal' and much lower than the extreme value (W_{lambda}_ ~ 70 A) found in NGC 6240 and NGC 1275. `Bare' Seyferts have W_{lambda}_(H_2_)< 1 A and a factor ~> 10 lower than starbursts, and we do not confirm previous claims of H_2_ line emission in the quasar 3C 273. Although the ratio of H_2_ to [Si VI] emission varies over a wide range it does not appear to provide a useful indicator of activity type or to impose constraints on the H_2_ excitation mechanism. Key words: line: formation - galaxies: active - galaxies: nuclei - galaxies: Seyfert - infrared: galaxies
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