A (Si VI) (1.92 micrometer) coronal line survey of galactic nuclei

Details A (Si VI) (1.92 micrometer) coronal line survey of galactic nuclei A (Si VI) (1.92 micrometer) coronal line survey of galactic nuclei

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...291...18m&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 291, no. 1, p. 18-28

Astronomy and Astrophysics

Astrophysics

39

Active Galactic Nuclei, Emission Spectra, Near Infrared Radiation, Seyfert Galaxies, Silicon, Starburst Galaxies, Hydrogen, Iron, Opacity, Photoionization, Stellar Luminosity

Scientific paper

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 modeling the formation of (Si VI) and (Fe VIII) 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) much greater than (Si VI). Our failure to detect (Si VI) in the IRAS ultraluminous galaxies does not exclude the possible presence of obscured Active Galactic Nuclei (AGNs), 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 (Wlambda less that 20 A) are 'normal'and much lower than the extreme value (Wlambda approximately = 70 A) found in NGC 6240 and NGC 1275. 'Bare' Seyferts have Wlambda(H2) less than 1 A and a factor greater than or approximately 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 (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 He excitation mechanism.

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