On the Origin of Nitrogen in Low-Metallicity Galaxies

Abstract.

Recently a remarkably small scatter in the N/O ratios for the HII regions in low-metallicity blue compact galaxies (BCG) has been found. It lead to the conclusion that N is produced by massive stars. Conversely, the N/Si ratios in damped Ly$\alpha$ absorbers (DLA) show a large scatter. This provides support for the time-delay model of nitrogen production in intermediate-mass stars, nitrogen production in massive stars being not required.

Here it has been tested whether these observational data are compatible with each other and with the existing ideas on the chemical evolution of galaxies. We find that it is possible to reconcile the constancy of N/O ratios in low-metallicity BCGs and the scatter of N/Si ratios in DLAs under the assumptions that a significant part of nitrogen is produced by intermediate-mass stars, and previous star formation events are responsible for measured heavy element abundances of HII regions in BCGs.