The weak imprint of environment on the stellar populations of galaxies
  We investigate the environmental dependence of the stellar populations of
galaxies in SDSS DR7. Echoing earlier works, we find that satellites are both
more metal-rich (<0.1 dex) and older (<2 Gyr) than centrals of the same stellar
mass. However, after separating star-forming, green valley and passive
galaxies, we find that the true environmental dependence of both stellar
metallicity (<0.03 dex) and age (<0.5 Gyr) is in fact much weaker. We show that
the strong environmental effects found when galaxies are not differentiated
result from a combination of selection effects brought about by the
environmental dependence of the quenched fraction of galaxies, and thus we
strongly advocate for the separation of star-forming, green valley and passive
galaxies when the environmental dependence of galaxy properties are
investigated. We also study further environmental trends separately for both
central and satellite galaxies. We find that star-forming galaxies show no
environmental effects, neither for centrals nor for satellites. In contrast,
the stellar metallicities of passive and green valley satellites increase
weakly (< 0.05 dex and < 0.08 dex, respectively) with increasing halo mass,
increasing local overdensity and decreasing projected distance from their
central; this effect is interpreted in terms of moderate environmental
starvation (`strangulation') contributing to the quenching of satellite
galaxies. Finally, we find a unique feature in the stellar mass--stellar
metallicity relation for passive centrals, where galaxies in more massive
haloes have larger stellar mass (~0.1 dex) at constant stellar metallicity;
this effect is interpreted in terms of dry merging of passive central galaxies
and/or progenitor bias.
