Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990apj...363..142g&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 363, Nov. 1, 1990, p. 142-153. Research supported by the Robert A. Welch Fo
Astronomy and Astrophysics
Astrophysics
190
Dwarf Galaxies, H Ii Regions, Irregular Galaxies, Nitrogen, Abundance, Astronomical Models, Emission Spectra, Interstellar Extinction, Star Clusters, Star Formation
Scientific paper
A study of nitrogen in giant H II regions located within low-abundance irregular galaxies is presented. Both observations and theoretical models are used to examine variations in the abundance of nitrogen relative to oxygen in these galaxies. Analysis of these and previously published observations suggests that the use of low spectral resolution is the main contributing factor in reported discrepancies in nitrogen abundances. Photoionization models, combined with the limited existing data on N(2+), suggest that, in nebulae having low abundances and/or ionizing stars hotter than 40,000 K, the N(+)/O(+) ratio is an accurate estimator of N/O. The detection of forbidden N II line in the extreme metal-poor galaxy I Zw 18 confirms that N/O does not exhibit a systematic variation with O/H in irregular galaxies, while the relatively high N/O suggests that the IMF in dwarf star-burst galaxies does not have a lower mass cutoff as high as 10 solar masses, but does not rule out that the IMF could be truncated below 1-3 solar mass.
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