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

TL;DR

This paper reports the first detection of several sulfur-bearing molecules in the starless core TMC-1, providing new insights into sulfur chemistry in cold interstellar environments and highlighting the need for improved chemical models.

Contribution

First detection of NCS, HCCS, H2CCS, H2CCCS, C4S, and C5S in space, expanding knowledge of sulfur chemistry in cold clouds.

Findings

Detected multiple sulfur-bearing molecules in TMC-1.

Derived column densities and abundance ratios for the molecules.

Compared observations with chemical models, revealing discrepancies.

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.