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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 N II 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 starburst galaxies does not have a lower mass cutoff as high as 10 Mₛun_, but does not rule out that the IMF could be truncated below 1-3 Mₛun_. The scatter in N/O at constant O/H is larger than the estimated uncertainties at approximately the 2 σ level. If it is real, it is suggested that the scatter could arise from differences in the time accrued since each galaxy experienced its last major star-formation episode. Two suggested tests for this hypothesis are measurement of nitrogen abundances in galaxies, such as VII Zw 403, having O/H smaller than 0. 1 times solar, and dating of open star clusters in nearby irregular galaxies for which N/O has been measured.
D. R. Garnett (Thu,) studied this question.