Forbidden S II H-alpha intensity ratios in faint, extended H II regions and the origin of the interstellar emission-line background

Details Forbidden S II H-alpha intensity ratios in faint, extended H II regions and the origin of the interstellar emission-line background Forbidden S II H-alpha intensity ratios in faint, extended H II regions and the origin of the interstellar emission-line background

Oct 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988apj...333..341r&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 333, Oct. 1, 1988, p. 341-352.

Astronomy and Astrophysics

Astrophysics

65

Emission Spectra, Fabry-Perot Spectrometers, Galaxies, H Alpha Line, H Ii Regions, Interstellar Matter, Lyman Alpha Radiation, Nebulae, O Stars, Photoionization

Scientific paper

The Wisconsin large-aperture Fabry-Perot spectrometer was used to measure forbidden S II 6716/H-alpha intensity ratios in very faint (emission measures as low as 5 cm to the -6th pc), extended (diameters as large as 260 pc) H II regions surrounding O and early B stars to investigate whether such regions can be the source of the interstellar emission-line background. H II regions with very dilute ionizing radiation fields were found to have higher forbidden S II/H-alpha intensity ratios than more compact regions. However, the forbidden S II/H-alpha ratios in the dilute H II regions are not as high as the ratios found in the interstellar emission-line background. The data sugggest that, if the interstellar background is produced by photoionized H II regions, then the regions have emission measures EM less than 1 cm to the -6th pc and are ionized by a Lyman continuum flux F less than 6 x 10 to the 5th photons/cm s. This places important constraints on the origin and nature of the warm, ionized gas in the diffuse interstellar medium.

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