Large-scale Environmental Dependence of the Abundance Ratio of Nitrogen to Oxygen in Blue, Star-forming Galaxies Fainter than L*
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 that of dwarf galaxies in denser 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] λ 3727, [O III] λ λ 4959,5007, and [N II] λ λ 6548,6584 with the direct T e 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 denser regions. The N/O ratio for void dwarfs ({M}r> -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 denser regions with {M}r> -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 ratio of dark matter halo mass to stellar mass in void galaxies.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2017
- DOI:
- 10.3847/1538-4357/aa5e53
- arXiv:
- arXiv:1612.04908
- Bibcode:
- 2017ApJ...837...42D
- Keywords:
-
- galaxies: abundances;
- galaxies: active;
- galaxies: dwarf;
- galaxies: evolution;
- galaxies: ISM;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 17 pages, 14 figures, 2 tables, accepted for publication ApJ (01-2017)