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)  ×  1011 cm−2, N(HCCS) = (6.8 ± 0.6)  ×  1011 cm−2, N(H2CCS) = (7.8 ± 0.8)  ×  1011 cm−2, N(H2CCCS) = (3.7 ± 0.4) × 1011 cm−2, N(C4S) = (3.8 ± 0.4) × 1010 cm−2, and N(C5S) = (5.0 ± 1.0) × 1010 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.