All lines of a) H₂CO, b) H₂C¹⁷O, and c) H₂C¹⁸O with the best fit LTE model overplotted in blue. Synthetic spectra in red indicate optical depth beginning to play a significant role i.e., τ > 0.6. Numbers in top right corner with red boxes indicate lines used to fit the column density. We note that the two optically thick lines of H₂CO are the ones with a significant amount of extended emission (covered in van der Wiel, in prep.). The number in parenthesis is the estimated optical depth. Lines in figure b panels 5 and 8 have stronger H₂¹³CO lines blended (see panels 9 and 11 in Fig. B.2).