Large-scale environmental dependence of the abundance ratio of nitrogen to oxygen in blue, star-forming galaxies fainter than L*

TL;DR

This study investigates how the large-scale cosmic environment influences the chemical evolution of faint, star-forming galaxies by comparing nitrogen-to-oxygen ratios in void and denser regions, revealing environmental effects on galaxy chemistry.

Contribution

It provides the first large-scale comparison of N/O ratios in dwarf galaxies across different cosmic environments using SDSS data, highlighting environmental impact on chemical evolution.

Findings

Void dwarf galaxies have slightly lower N/O ratios than denser region dwarfs.

Environmental dependence affects chemical evolution, with shifts observed across different luminosity bins.

Large-scale environment may influence galaxy evolution through mechanisms like star formation delay and dark matter halo differences.

Abstract

We examine how the cosmic environment affects the chemical evolution of galaxies in the Universe by comparing the N/O ratio of dwarf galaxies in voids with dwarf galaxies in more dense regions. Ratios of the forbidden [O III] and [S II] transitions provide estimates of a region's electron temperature and number density. We estimate the abundances of oxygen and nitrogen using these temperature and density estimates and the emission line fluxes [O II] 3727, [O III] 4959, 5007, and [N II] 6548, 6584 with the direct Te method. Using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, we are able to estimate the N/O ratio in 42 void dwarf galaxies and 89 dwarf galaxies in more dense regions. The N/O ratio for void dwarfs (Mr > -17) is slightly lower (12%) than for dwarf galaxies in denser regions. We also estimate the nitrogen and oxygen abundances of 2050 void galaxies and 3883 galaxies in more dense regions with Mr > -20. These somewhat brighter galaxies (but still fainter than L*) also display similar minor shifts in the N/O ratio. The shifts in the average and median element abundance values in all absolute magnitude bins studied are in the same direction, suggesting that the large-scale environment may influence the chemical evolution of galaxies. We discuss possible causes of such a large-scale environmental dependence of the chemical evolution of galaxies, including retarded star formation and a higher dark matter halo mass to stellar mass ratio in void galaxies.