a) Radial plots centered on the southwest portion of “The Brick”. The top panel shows the ratio p - H₂CO S_ν(3_2,1−2_2,0) /S_ν(3_0,3−2_0,2) as a function of aperture size, starting from a single pixel. The derived temperature using Fig. 6 is shown on the right axis; temperatures ≳150 K should be regarded as lower limits. The bottom panel shows the line width σ = FWHM/ 2.35 as a function of aperture size. b) The same as a) but for a region centered on G1.23-0.08, a local peak in the p - H₂CO3_0,3−2_0,2 emission. In this case, the ratio p - H₂CO S_ν(3_2,1−2_2,0) /S_ν(3_0,3−2_0,2) is lower at the center and increases toward larger radii.