J = 2−1 (opacity corrected) and J = 32 (no opacity corrections) ³⁴S/³⁶S and ³²S/³⁶S isotope ratios (see Eqs. (18) and (19)) plotted as functions of the distance from the Galactic center. Top: Filled black circles and filled black triangle present the ³⁴S/³⁶S ratios in the J = 2−1 and J = 3−2 transitions derived from C³⁴S/C³⁶S in this work with detections of C³⁶S, respectively. The open gray circles and open gray triangles present the ³⁴S/³⁶S ratios in the J = 2−1 and J = 3−2 transitions derived from C³⁴S/C³⁶S in this work with tentative detections of C³⁶S, respectively. The blue diamonds show the ³⁴S/³⁶S ratios in Mauersberger et al. (1996). The red symbol ⊙ indicates the ³⁴S/³⁶S isotope ratio in the Solar System. The resulting first-order polynomial fit to the ³⁴S/³⁶S ratios in Mauersberger et al. (1996) and this work, excluding the values from tentative detections, is plotted as a black solid line, with the green shaded area showing the 1 σ interval of the fit. Bottom: ³²S/³⁶S ratios obtained from ³⁴S/³⁶S ratios combined with the ³²S/³⁴S ratios derived in this work. The filled black circles and filled black triangle present the values in the J = 2−1 and J = 3−2 transitions from this work with detections of C³⁶S, respectively. The open gray circles and open gray triangles present ratios in the J = 2−1 and J = 3−2 transitions from this work with tentative detections of C³⁶S, respectively. The ³²S/³⁶S ratios derived with ³⁴S/³⁶S values from Mauersberger et al. (1996) are plotted as blue diamonds. The red symbol ⊙ indicates the ³²S/³⁶S isotope ratio in the Solar System. The ³²S/³⁶S gradient, excluding tentative detections, is plotted as a black solid line, with the pink shaded area showing the 1 σ interval of the fit. The red crosses visualize results from the GCE model of Kobayashi et al. (2011, 2020, see Sect. 4.9).