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Spectroscopic Study of Star-forming Galaxies in Filaments and the Field at z ~ 0.5: Evidence for Environmental Dependence of Electron Density

B. Darvish, B. Mobasher, D. Sobral, S. Hemmati, H. Nayyeri, I. Shivaei

Abstract
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 ̃ 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 (̃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 (̃0.1-0.15 dex), possibly owing to the inflow of the already-enriched intrafilamentary gas into filament galaxies. Moreover, we show that electron densities are significantly lower (a factor of ̃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.

Keywords
galaxies: abundances, galaxies: evolution, galaxies: fundamental parameters, galaxies: starburst, large-scale structure of universe

The Astrophysical Journal
Volume 814, Number 84
2015 November

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Fundação para a Ciência e a Tecnologia
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