Hybridisation coefficients of W4 with either FUV (, panels a, b, and c) or Hα (, panels d and e) as a function of sSFR (left), L_Hα/L_W1 (middle), and L_FUV/L_W1 (right). These coefficients are calibrated to match the SFR obtained from Balmer-decrement-corrected Hα for individual 15″ (∼kpc scale) regions (grey dots). Red hexagons and shaded areas show the median trends and scatter. Median relations are fitted with a broken power law (Eq. (7)), and the best-fit model is shown as a dashed blue line. The scatter σ of the data with respect to the best fit is presented in the bottom right corner. Values of and from the literature are shown as dashed black horizontal lines. Our data for kpc scale regions agree well with the literature values at high sSFR, but show a systematic deviation for lower sSFR, which is captured well by the power-law model.