Letter to the Editor

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

¹ Grupo de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain
e-mail: jose.cernicharo@csic.es
² Observatorio Astronómico Nacional (IGN), C/ Alfonso XII, 3, 28014 Madrid, Spain
³ Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain

Received: 23 February 2021
Accepted: 17 March 2021

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.