Key points are not available for this paper at this time.
We suggest that recent observations of the N/O abundance ratio in external galaxies can be understood if nitrogen is a primary nucleosynthesis product, manufactured principally in stars of 1–2.5 M⊙. The N/O ratio of a galaxy then becomes an indicator of the time that has elapsed since the bulk of star formation occurred, or in other words the nominal ‘age’ of the galaxy.
Edmunds et al. (Wed,) studied this question.