Star formation rate surface density, computed based on the extinction–corrected Hα line, the rest-frame UV luminosity, the dust luminosity, and the sum of UV- and dust-based SFR, in the PJ308–21 system (see Sect. 4.10 for details). The green, blue, and red contours map the quasar host galaxy, the western companion, and the eastern companion respectively. Dashed gray lines mark the loci of constant depletion times.