Surface density maps of DC873756: Gas (left, traced by [CII]), obscured FIR SFR (center, traced by the 158 μm rest-frame continuum), and unobscured UV SFR (right, traced by the F814W observer-frame continuum). The black contours are the (3+2k) σ levels (k ≥ 0) of the gas surface density. The thicker solid and dashed lines, respectively, are used to highlight the 5σΣ_gas limit and the border between the low- and high-density regions used in our analysis (see Sect. 3). The ALMA synthesized beam size is shown in the lower left corner. The unobscured SFR surface density map based on HST data is convolved by a Gaussian kernel to match the ALMA resolution.