The Gas-Phase Metallicity of Central and Satellite Galaxies in the SDSS

TL;DR

This study investigates how environment influences the gas-phase metallicities of star-forming galaxies, revealing that satellites generally have higher metallicities than centrals of similar mass, due to environmental effects like strangulation and ram-pressure stripping.

Contribution

It provides a detailed analysis of environmental impacts on galaxy metallicity, highlighting mechanisms beyond stellar mass stripping that shape gas-phase metallicity differences.

Findings

Satellites have higher gas-phase metallicities than centrals at fixed stellar mass.

Gas-phase metallicity of satellites increases with halo mass, especially for low-mass galaxies.

Environmental effects such as strangulation and ram-pressure stripping likely cause observed metallicity differences.

Abstract

We exploit the SDSS galaxy groups catalogue of Yang et al. to study how the gas-phase metallicities of star-forming galaxies depend on environment. We find that satellite and central galaxies follow a qualitatively similar stellar mass (M_*) - gas-phase metallicity relation. Satellites, though, have higher gas-phase metallicities than equally massive centrals, and this difference increases with decreasing M_*. We also find that the gas-phase metallicity of satellites increases with halo mass at fixed stellar mass. This increment is more pronounced for less massive galaxies. We also show that low mass satellite galaxies have higher gas-phase metallicities than central galaxies of the same stellar metallicity. This difference becomes negligible for more massive galaxies of roughly solar metallicity. We demonstrate that the observed differences in gas-phase metallicity between centrals and satellites at fixed M_* are not a consequence of stellar mass stripping (advocated by Pasquali et al. in order to explain similar differences but in stellar metallicity), nor to the past star formation history of these galaxies as quantified by their surface mass density or gas mass fraction. Rather, we argue that these trends probably originate from a combination of three environmental effects: (i) strangulation, which prevents satellite galaxies from accreting new, low metallicity gas which would otherwise dilute their ISM, (ii) ram-pressure stripping of the outer gas disk, thereby inhibiting radial inflows of low-metallicity gas, and (iii) external pressure provided by the hot gas of the host halo which prevents metal-enriched outflows from escaping the galaxies. [abridged]