From voids to Coma: the prevalence of pre-processing in the local Universe

Abstract

We examine the effects of pre-processing across the Coma Supercluster, including 3505 galaxies over 500 sq deg, by quantifying the degree to which star-forming (SF) activity is quenched as a function of environment. We characterise environment using the complementary techniques of Voronoi Tessellation, to measure the density field, and the Minimal Spanning Tree, to define continuous structures, and so we measure SF activity as a function of local density and the type of environment (cluster, group, filament, and void), and quantify the degree to which environment contributes to quenching of SF activity. Our sample covers over two orders of magnitude in stellar mass (10^8.5 to 10^11 Msun), and consequently we trace the effects of environment on SF activity for dwarf and massive galaxies, distinguishing so-called "mass quenching" from "environment quenching". Environmentally-driven quenching of SF activity, measured relative to the void galaxies, occurs to progressively greater degrees in filaments, groups, and clusters, and this trend holds for dwarf and massive galaxies alike. A similar trend is found using g-r colours, but with a more significant disparity between galaxy mass bins driven by increased internal dust extinction in massive galaxies. The SFR distributions of massive SF galaxies have no significant environmental dependence, but the distributions for dwarf SF galaxies are found to be statistically distinct in most environments. Pre-processing plays a significant role at low redshift, as environmentally-driven galaxy evolution affects nearly half of the galaxies in the group environment, and a significant fraction of the galaxies in the more diffuse filaments. Our study underscores the need for sensitivity to dwarf galaxies to separate mass-driven from environmentally-driven effects, and the use of unbiased tracers of SF activity.