2024PASJ...76...46L

Isotopic ratios are good tools for probing stellar nucleosynthesis and chemical evolution. We perform high-sensitivity mapping observations of the J = 7-6 rotational transitions of OCS, OC³⁴S, O¹³CS, and OC³³S toward the Galactic Center giant molecular cloud Sagittarius B2 with the IRAM 30 m telescope. Positions with optically thin and uncontaminated lines are chosen to determine the sulfur isotope ratios. A ³²S/³⁴S ratio of 17.1 ± 0.9 was derived with OCS and OC³⁴S lines, while a ³⁴S/³³S ratio of 6.8 ± 1.9 was derived directly from the integrated intensity ratio of OC³⁴S and OC³³S. With independent and accurate measurements of the ³²S/³⁴S ratio, our results confirm the termination of the decreasing trend of ³²S/³⁴S ratios toward the Galactic Center, suggesting a drop in the production of massive stars at the Galactic Center.