1994A&A...291...18M

We present the results of a [SiVI]λ1.962 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 [SiVI] is related to Seyfert activity. By modelling the formation of [SiVI] and [FeVII]λ6087 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 [FeVII]≫[SiVI]. Our failure to detect [SiVI] 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 H₂ equivalent widths (W_λ<20A) are "normal" and much lower than the extreme value (W_λ≃70 A) found in NGC6240 and NGC1275. "Bare" Seyferts have W_λ(H₂)<1 A and a factor >10 lower than starbursts, and we do not confirm previous claims of H₂ line emission in the quasar 3C273. Although the ratio of H₂ to [SiVI] emission varies over a wide range it does not appear to provide a useful indicator of activity type or to impose constraints on the H₂ excitation mechanism.