Sulfur isotopes toward the extended envelope of Sagittarius B2 in the Galactic Center

Abstract

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.