Sulfur Isotopes Toward the Extended Envelope of Sagittarius B2 in the Galactic Center

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, (OCS)-S-34, (OCS)-C-13, and (OCS)-S-33 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 S-32/S-34 ratio of 17.1 +/- 0.9 was derived with OCS and (OCS)-S-34 lines, while a S-34/S-33 ratio of 6.8 +/- 1.9 was derived directly from the integrated intensity ratio of (OCS)-S-34 and (OCS)-S-33. With independent and accurate measurements of the S-32/S-34 ratio, our results confirm the termination of the decreasing trend of S-32/S-34 ratios toward the Galactic Center, suggesting a drop in the production of massive stars at the Galactic Center.