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A. Nava, R.B.C. Henry (U. of Oklahoma), J.X. Prochaska (Lick Obs./UCSC)
The portion of the stellar mass spectrum primarily responsible for nitrogen production in the universe has not been firmly established. To study the problem, we have rederived the N and O abundances for a carefully selected sample of 72 low metallicity [12+log(O/H)\le8.1] blue compact galaxies using published emission line strengths. In calculating the abundances we have paid particular attention to the determination of the associated abundance uncertainties. When the resulting values are plotted in the N/O-O/H plane, two distinct object groups emerge. The largest group comprises the well-known N/O plateau, where log(N/O) values exhibit a Gaussian distribution, and we employ a chi-square analysis to test the significance of the spread. A second, separate, smaller group consists of high N/O objects which fall above the plateau. Detailed chemical evolution models which properly account for the time delay in N release are employed in order to speculate about the origins of these two groups as well as the probable stellar synthesis site for nitrogen in the early universe. We gratefully acknowledge support from NSF grant AST-0307118 for this research.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.