Spectroscopic Study of Star-forming Galaxies in Filaments and the Field
  at $z\sim$0.5: Evidence for Environmental Dependence of Electron Density
  We study the physical properties of a spectroscopic sample of 28 star-forming
galaxies in a large filamentary structure in the COSMOS field at $z\sim$0.53,
with spectroscopic data taken with the Keck/DEIMOS spectrograph, and compare
them with a control sample of 30 field galaxies. We spectroscopically confirm
the presence of a large galaxy filament ($\sim$ 8 Mpc), along which five
confirmed X-ray groups exist. We show that within the uncertainties, the
ionization parameter, equivalent width (EW), EW versus specific star-formation
rate (sSFR) relation, EW versus stellar mass relation, line-of-sight velocity
dispersion, dynamical mass, and stellar-to-dynamical mass ratio are similar for
filament and field star-forming galaxies. However, we show that on average,
filament star-forming galaxies are more metal-enriched ($\sim$ 0.1$-$0.15 dex),
possibly due to the inflow of the already enriched intrafilamentary gas into
filament galaxies. Moreover, we show that electron densities are significantly
lower (a factor of $\sim$17) in filament star-forming systems compared to those
in the field, possibly because of a longer star-formation timescale for
filament star-forming galaxies. Our results highlight the potential
pre-processing role of galaxy filaments and intermediate-density environments
on the evolution of galaxies, which has been highly underestimated.
