Abundances of hydrogen sulfide in star-forming regions

Abstract

Interstellar hydrogen sulfide (H 2 S) and its isotopic variant H 2 34 S have been observed toward several star-forming regions via their li 0-loi transitions at 2 mm, using the FCRAO telescope. In sources where both isotopic species H 2 S and H 2 34 S were observed, column densities of ~10 16 cm-2 were measured. Column density lower limits of ~10 14 cm-2 for H 2 S were found for other sources, where only the main isotopic line was observed. The fractional abundances of H 2 S relative to molecular hydrogen appear to be enhanced by at least an order of magnitude relative to quiescent cloud values (~10-9) for many of the observed sources. Such enhancement toward star-forming clouds suggests that some process involving elevated temperature aids in producing this species; this could be gas-phase reactions, grain-related processes, or both. Subject headings: interstellar: molecules-nebulae: abundances-stars: formation I. INTRODUCTION Interstellar hydrogen sulfide (H 2 S) was first observed in the ISM via its 11 o I o i transition toward several GMCs by Thad-deus et al. (1972). The clouds where positive detections were made using the NR AO 36 foot (11 m) telescope included OMC-1, DR 21, DR 21(OH), W51, W3, W3(OH), NGC 2264, NGC 7358, and Sgr B2. Dickel, Dickel, and Wilson (1981) have also detected the li 0-loi ü ne °f H 2 S toward NGC 7538. Recently, Minh, Irvine, and Ziurys (1989, hereafter Paper I), and Minh et al (1990; Paper II) have carried out new observations of this transition toward cold dark clouds and toward OMC-1, using the FCRAO 14 m telescope. They find the fractional abundance of H 2 S relative to molecular hydrogen, /(H 2 S), to be ~10-9 toward the dark clouds and quiescent regions, with a significant abundance enhancement toward Orion(KL), where /(H 2 S) ~ 10" 6. The high H 2 S abundances in the active regions of Orion(KL), a factor of 1000 larger than those in quiescent clouds, strongly suggest that the increased H 2 S production is related to activities in star-formation regions and possibly to grain-related processes (Paper II). In order to obtain further data on this question, we observed H 2 S and H 2 34 S toward several other star-forming regions. In this paper we report the results of these measurements.