Radex radiative transfer calculations on the excitation of ¹⁵NH₃. a) The modeled line ratios (red lines) and (blue lines) as a function of n_H2 and T_kin. The solid red and blue lines represent the calculated and line ratios which are labeled. The dashed lines represent observed line ratios and their upper and lower limits. b) The derived likelihood as a function of n_H2 and T_kin. Only metastable para–¹⁵NH₃ transitions are included in the modeling. The likelihood scale is indicated by the color bar. The contours represent the likelihoods 0.6, and 0.8. c) Same as Fig. 8a, but the solid red lines represent the line ratios of . d) Same as Fig. 8b, but the non-metastable transitions are also included in the modeling. e) Same as Fig. 8a, but the solid red and blue lines represent the line ratios of and . f) Same as Fig. 8d, but for ortho–¹⁵NH₃ transitions.