Top: dust scaling relations from the Herschel Reference Survey (Cortese et al. 2012); the specific dust mass M_dust/M_⋆ as a function of the stellar mass surface density μ_⋆ (left) and NUV-r colour (right). NUV-r serves as an inverse tracer of the sSFR. Red are Herschel detected galaxies, green are upper limits for the undetected ones. The blue dots represent the macro-regions of M 31 and the cyan dot indicates the position of the galaxy itself. The thick black line is the HRS mean trend. The vertical solid line indicates our division between late-type and early-type galaxies. The dashed vertical lines indicate the bluest early-type galaxy and the reddest late-type galaxy, respectively. Bottom: same scaling relations, but now represented in a density plot using single pixel regions from M 31. Yellow points indicate a higher density of points, red a lower density. The black line is the HRS mean trend, the green line is the M 31 mean trend.