Spectrophotometric observations of ionized hydrogen regions in nearby spiral and irregular galaxies.
Abstract
A program of direct photography and spectrophotometry has been carried out on H ii regions in a selection of nearby spiral and irregular galaxies. Abundance analyses for H ii regions in MiOl and M33 show a strong radial gradient in the O!H ratio, decreasing by approximately a factor of 10 across the galaxy disks. The Ne/O and S/O abundance ratios are constant. The derived nitrogen abundances, coupled with the line ratios for other H ii regions, indicate a weak gradient in the ratio of N!O, decreasing by about a factor of 4 from the nuclear regions outward. No large helium abundance differences are observed, although the most oxygen-poor regions may show marginally significant helium deficiencies. Excitation differences among the H ii regions of Sbc-Scd-Irr galaxies can best be understood in terms of an abundance sequence which progresses from higher to lower heavy-element enrichment as one progresses from the earlier to later type galaxies. Subject headings: abundances, nebular - galaxies - nebulae
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 1975
- DOI:
- 10.1086/153727
- Bibcode:
- 1975ApJ...199..591S
- Keywords:
-
- Astronomical Photometry;
- Galactic Structure;
- Hydrogen Clouds;
- Interstellar Gas;
- Ionized Gases;
- Spiral Galaxies;
- Abundance;
- Heavy Elements;
- Line Spectra;
- Radial Velocity;
- Spectrophotometry;
- Astrophysics