Sulfur-bearing molecules in a sample of early star-forming cores

Abstract

The sulfur content in dense molecular regions of the interstellar medium is highly depleted in comparison to diffuse clouds. The reason of this phenomenon is unclear, thus it is necessary to carry out observational studies of sulfur-bearing species towards dense regions, mainly at early evolutive stages to uncover the early sulfur chemistry. Using data from the Atacama Large Millimeter Array (ALMA) data archive, we investigated a sample of 37 dense cores embedded in the most massive infrared-quiet molecular clumps from the ATLASGAL survey. Lines of 34SO, SO2, NS, SO, SO+, and H2CS were analyzed and column densities of each molecular species were obtained. From the continuum emission, and two CH3OH lines, the 37 cores were characterized in density and temperature, and the corresponding H2 column densities were derived. The abundances of such sulfur-bearing species were derived and studied. We find that the abundances of the analyzed species increase with the growth of the gas temperature, suggesting that the chemistry involved in the formation of each of the analyzed molecule may have a similar dependence with Tk in the range 20 to 100 K. We find that the comparisons among abundances are, in general, highly correlated. Given that such correlation decreases in more evolved sources, we suggest that the sulfur-bearing species here analyzed should have a similar chemical origin. From the measured line widths we point out that molecules with oxygen content (34SO, SO2, SO, and SO+) may be associated with warmer and more turbulent gas than the other ones. H2CS and NS are associated with more quiescent gas, probably in the external envelopes of the cores. This work gives quantitative information about abundances that could be useful in chemical models pointing to explain the sulfur chemistry in the interstellar medium.