On the Origin of Nitrogen in Damped Ly - α Systems 3 3

Abstract. Recent measurements of nitrogen and alpha elements in over 20 damped Ly-α systems (DLA) are compared with similar measurements for numerous emission line objects and stars. It is found that the DLA distribution in the N/α-α/H plane is bimodal, where most sample DLAs fall along the N/α plateau defined at low Z by dwarf irregulars, while a small group possesses N/α values roughly 0.7 dex less than those on the plateau at similar α/H values. We demonstrate with chemical evolution models that a top-heavy or truncated IMF can account for the low N in this second group.