Cosmological evolution of the Nitrogen abundance

TL;DR

This study models the cosmic evolution of nitrogen abundance in the interstellar medium, reconciling theoretical predictions with observations and identifying key stellar sources and galaxy properties influencing nitrogen levels.

Contribution

It provides a detailed chemical evolution model that explains nitrogen abundance trends and dispersion in DLAs, highlighting the roles of intermediate-mass stars and galaxy environment.

Findings

Nitrogen mainly originates from intermediate-mass stars.

Low N/H systems may be dominated by massive stars.

Dispersion in nitrogen abundance is due to galaxy mass and location effects.

Abstract

The abundance of nitrogen in the interstellar medium is a powerful probe of star for- mation processes over cosmological timescales. 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 DLAs at redshift 2 - 3. We study the evolution of nitrogen with a detailed chemical evolution model and find good agreement with observations, including the relative abundances of N/O and N/Si ratios. 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 production might possibly be dominated by massive stars. This last result could be strengthened if stellar rotation which is important at low metallicity can produce significant amounts of nitrogen. Moreover, these systems likely reside in host galaxies with stellar masses below 10**8.5 solar mass. 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: differ- ence in the masses of the DLA host galaxies, and difference in the their position inside the galaxy.