Stellar mass-excitation fraction relation. Excitation types are based on mid-infrared colour diagnostics (mIRdds) representing central apertures (median size ∼3.12 kpc for the HRS). Section 2.1 details the HRS environmental classification. Stellar masses are binned from low to high (left to right): log (M_*/M_⊙), M1 ≤ 8.5, 8.5 < M2 ≤ 9.0, 9.0 < M3 ≤ 9.5, 9.5 < M4 ≤ 10.0, 10.0 < M5 ≤ 10.5, and 10.5 < M6. Top: Field and H I-normal galaxies. Middle: Virgo cluster members (VCMs) and H I-deficient galaxies. Bottom: Objects undergoing RPS in nearby clusters. Total galaxy counts are shown in the panel titles. Each panel lists excitation-type counts per mass bin (from left to right), with total counts and respective fractions shown on the rightmost side. The x axis labels indicate galaxy counts per stellar mass bin (top). Random uncertainties, indicated by vertical bars, are expressed as the ratio of the square root of each excitation-type count to the total. See also Tables 2, D.1, and D.2.