TMC-1, the starless core sulfur factory: Discovery of NCS, HCCS, H2CCS, H2CCCS, and C4S and detection of C5S

Abstract

We report the detection of the sulfur-bearing species NCS, HCCS, H2CCS, H2CCCS, and C4S for the first time in space. These molecules were found towards TMC-1 through the observation of several lines for each species. We also report the detection of C5S for the first time in a cold cloud through the observation of five lines in the 31-50 GHz range. The derived column densities are N(NCS) = (7.8 +/- 0.6)e11 cm-2, N(HCCS) = (6.8 +/- 0.6)e11 cm-2, N(H2CCS) = (7.8 +/- 0.8)e11 cm-2, N(H2CCCS) = (3.7 +/- 0.4)e11 cm-2, N(C4S) = (3.8 +/- 0.4)e10 cm-2, and N(C5S) = (5.0 +/- 1.0)e10 cm-2. The observed abundance ratio between C3S and C4S is 340, that is to say a factor of approximately one hundred larger than the corresponding value for CCS and C3S. The observational results are compared with a state-of-the-art chemical model, which is only partially successful in reproducing the observed abundances. These detections underline the need to improve chemical networks dealing with S-bearing species.

Accepted for publication in A&A Letters

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