³⁴S/³³S and ³²S/³³S isotope ratios (for the latter, see Eqs. (12) and (13)) plotted as functions of the distance from the Galactic center. Top: ³⁴S/³³S ratios derived from C³⁴S/C³³S in the J = 2−1 and J = 3−2 transitions plotted as black and green dots, respectively. The red solid and the two dashed lines show the average value and its standard deviation, 4.35 ± 0.44, of ³⁴S/³³S with corrections of optical depth toward our sample in the J = 2−1 transition. The yellow solid and the two dashed lines show the average value and its standard deviation, 3.49 ± 0.26, of ³⁴S/³³S toward our sample in the J = 3−2 transition. The red symbol ⊙ indicates the ³⁴S/³³S isotope ratio in the Solar System. Bottom: Black and green dots show the ³²S/³³S ratios in the J = 2−1 and J = 3−2 transitions, respectively. The red symbol ⊙ indicates the ³²S/³³S value in the Solar System. The resulting first-order polynomial fits to the ³²S/³³S ratios in the J = 2−1 and J = 3−2 transitions in this work are plotted as red and green solid lines, respectively, with the pink and yellow shaded area showing the 1 σ standard deviations. The red crosses are the results from the GCE model of Kobayashi et al. (2011, 2020, see also Sect. 4.9).