N/O Abundance Ratios: Milky Way and DLAs

Abstract

It has been recently shown in Chiappini et al. [2] that models of chemical evolution computed with the Meynet & Maeder [4] yields for the whole range of masses, predict a slower increase of N with respect to what is obtained with other sets of stellar yields, thus leading to important implications for the interpretation of the DLAs abundance data. Thanks to the slower increase of N in time, the DLAs abundance patterns can be reproduced by “bursting models” and in this framework, the “low N/O” (≃ −2.2 dex) and “high N/O” (≃ −1.6 dex) groups of DLAs could be explained as systems which show differences in their star formation histories rather than an age difference (see [2] references therein). In fact, we were able to obtain models that show both a low log(N/O) and a [O/Fe]∼0.2-0.3 dex during almost all their evolution, in agreement to what is observed in some DLAs. Alternative interpretations (see [2] for a discussion) of the “low N/O” DLAs suggested in the literature imply a high overabundance of α-elements in disagreement with observations. DLAs could also be identified with outer regions of spiral galaxies but in this case DLAs with low log(N/O) would be quite young systems (younger than ∼150 Myr) and no discontinuity in the log(N/O) vs. log(O/H) diagram would be expected [2].