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