Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976apj...203...66s&link_type=abstract
Astrophysical Journal, vol. 203, Jan. 1, 1976, pt. 1, p. 66-71.
Astronomy and Astrophysics
Astrophysics
116
Abundance, H Beta Line, Metallic Stars, Spiral Galaxies, Stellar Mass, Temperature Gradients, Galactic Nuclei, H Ii Regions, Helium, Hot Stars, Line Spectra, Star Distribution, Stellar Spectra
Scientific paper
The equivalent width of the H-beta emission from H II regions in spiral galaxies increases with distance from the nucleus. This equivalent width gradient is interpreted in terms of a radial gradient in the temperature of the hottest exciting stars. A numerical value is inferred for the temperature gradient from the intermediate to outermost spiral arms of M101. There is also a radial decrease in the metal abundance (Z) across M101, and the temperature gradient is consistent with the prediction that the upper mass limit for star formation should be smaller in regions of high Z. It is noted that, even in the absence of changes in the upper mass limit, a temperature gradient is expected because metal-rich stars of a given mass have smaller effective temperatures. It is clear that the presence of a temperature gradient may lead to several important systematic changes in the interpretation of gradients in the properties of H II regions across galaxies. A temperature gradient reduces the Z gradient that is inferred from emission-line ratios and may help to explain why forbidden O II emission is strong in the innermost regions where forbidden O III emission is weak. It may also partly camouflage a helium-abundance gradient.
Shields Gregory A.
Tinsley Beatrice M.
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