Evolution of N/O ratios in galaxies from cosmological hydrodynamical simulations

Vincenzo, Fiorenzo; Kobayashi, Chiaki

Abstract

We study the redshift evolution of the gas-phase O/H and N/O abundances, both (i) for individual ISM regions within single spatially-resolved galaxies and (ii) when dealing with average abundances in the whole ISM of many unresolved galaxies. We make use of a cosmological hydrodynamical simulation including detailed chemical enrichment, which properly takes into account the variety of different stellar nucleosynthetic sources of O and N in galaxies. We identify $33$ galaxies in the simulation, lying within dark matter halos with virial mass in the range $10^{11}\le M_{\text{DM}} \le 10^{13}\,\text{M}_{\odot}$ and reconstruct how they evolved with redshift. For the local and global measurements, the observed increasing trend of N/O at high O/H can be explained, respectively, (i) as the consequence of metallicity gradients which have settled in the galaxy interstellar medium, where the innermost galactic regions have the highest O/H abundances and the highest N/O ratios, and (ii) as the consequence of an underlying average mass-metallicity relation that galaxies obey as they evolve across cosmic epochs, where -- at any redshift -- less massive galaxies have lower average O/H and N/O ratios than the more massive ones. We do not find a strong dependence on the environment. For both local and global relations, the predicted N/O--O/H relation is due to the mostly secondary origin of N in stars. We also predict that the O/H and N/O gradients in the galaxy interstellar medium gradually flatten as functions of redshift, with the average N/O ratios being strictly coupled with the galaxy star formation history. Because N production strongly depends on O abundances, we obtain a universal relation for the N/O--O/H abundance diagram whether we consider average abundances of many unresolved galaxies put together or many abundance measurements within a single spatially-resolved galaxy.

Citation

Vincenzo, F., & Kobayashi, C. (2018). Evolution of N/O ratios in galaxies from cosmological hydrodynamical simulations. Monthly notices of the Royal Astronomical Society, 478(1), 155–166. https://doi.org/10.1093/mnras/sty1047

• Journal Article Type: Article
• Acceptance Date: Apr 20, 2018
• Online Publication Date: Apr 26, 2018
• Publication Date: 2018-07
• Deposit Date: Mar 12, 2022
• Publicly Available Date: Mar 28, 2022
• Journal: Monthly notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 478
• Issue: 1
• Pages: 155–166
• DOI: https://doi.org/10.1093/mnras/sty1047
• Keywords: Astrophysics of Galaxies
• Public URL: https://hull-repository.worktribe.com/output/3946273