Histograms of “good” parameters for the central pixel of our FTS maps ([0,0] in Fig. 8; [RA, Dec] = [05^h39^m37^s, − 69°46′13′′]). To derive these histograms, the threshold of χ²≤ minimum χ² + 4.7 is applied to the calculated χ² distribution. Along with the log value of the best-fit parameter, the standard deviation of the χ² distribution measured in log space are shown in blue in the top right corner of each plot. The corresponding blue line of each histogram represents the best-fit parameter. Finally, the number in black in the T_k plot is the ratio of the number of “good” models to the total number of RADEX models in our study. See Sect. 4.2 for details.