The abundance of nitrogen in the interstellar medium is a powerful probe of star formation processes over cosmological time-scales. Since nitrogen can be produced both in massive and intermediate-mass stars with metallicity-dependent yields, its evolution is challenging to model, as evidenced by the differences between theoretical predictions and observations. In this work, we attempt to identify the sources of these discrepancies using a cosmic evolution model. To further complicate matters, there is considerable dispersion in the abundances from observations of damped Lya absorbers (DLAs) at z ~ 2-3. We study the evolution of nitrogen with a detailed cosmic chemical evolution model and find good agreement with these observations, including the relative abundances of (N/O) and (N/Si).We find that the principal contribution of nitrogen comes from intermediate-mass stars, with the exception of systems with the lowest N/H, where nitrogen productionmight possibly be dominated by massive stars. This last result could be strengthened if stellar rotationwhich is important at lowmetallicity can produce significant amounts of nitrogen. Moreover, these systems likely reside in host galaxies with stellar masses below 108.5M⊙. We also study the origin of the observed dispersion in nitrogen abundances using the cosmological hydrodynamical simulations Horizon-AGN. We conclude that this dispersion can originate from two effects: difference in the masses of the DLA host galaxies, and difference in their position inside the galaxy.
Bibliographical noteFunding Information:
We thank warmly Georges Meynet for very fruitful discussions. This work is made in the ILP LABEX (under reference ANR-10-LABX-63) supported by French state funds managed by the ANR within the Investissements d’Avenir programme under reference ANR-11-IDEX-0004-02. The work of KAO was supported in part by DOE grant DE–SC0011842 at the University of Minnesota. TK is supported by the National Research Foundation of Korea to the Center for Galaxy Evolution Research (No. 2017R1A5A1070354).
© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science