Maps of the optical depths of the a) ¹³CO (J = 1–0) and b) C¹⁸O (J = 1–0) emission lines, and maps of the column densities of c) ¹³CO and d) C¹⁸O molecules. The optical depths and column densities are estimated on the assumption that the excitation temperatures of the ¹³CO and C¹⁸O (J = 1–0) lines are equal to the peak temperatures of the ¹²CO (J = 1–0) emission in T_MB and are calculated for pixels with intensities above the 8σ noise levels.