Investigating Galaxy Quenching with the SDSS: Stellar Metallicities as a Tracer of Quenching Mechanisms

Peng et al. (2015, Nature, 521, 192) analysed stellar metallicities of 26,000 SDSS galaxies and found that galaxies with stellar masses below 10¹¹ solar masses are primarily quenched due to the halting of the supply of cold gas (strangulation). We take this analysis further by making use of the much larger spectroscopic sample of galaxies in SDSS DR7, analysing the stellar metallicities of 70,000 local galaxies. We compare the observed stellar metallicity difference between star-forming and passive galaxies with the predictions of simple models for galaxy evolution to put constraints on the possible quenching mechanisms and timescales. We find that the observed stellar metallicity differences are well reproduced by closed-box models, indicating that local galaxies quench primarily through strangulation over a mass-independent timescale of 2 Gyr. We also investigate the dependence of galaxy quenching on environment, in terms of both the central/satellite dichotomy and the local overdensity. We find that there is no strong dependence of the stellar metallicity difference on the overdensity, even over an overdensity range of 2 dex.  This result further suggests that the environment cannot be solely responsible for galaxy strangulation.