All ETG 3.6 μm surface brightness profiles (fixed isophotal parameters, Δr = 2″; see Sect. 3.2), normalized by effective radius. Left panel: profiles color-coded by total stellar mass, while the right panel shows profiles color-coded by morphological T-type. Surface brightness is converted to mass surface density in the right panel as well, for convenience. Data quality at very low surface brightness is poor, and hence all profiles are truncated at μ_3.6, AB = 27.5.