Q-band Line Survey Observations toward a Carbon-chain-rich Clump in the Serpens South Region

TL;DR

This study conducted a comprehensive Q-band line survey of a carbon-chain-rich clump in Serpens South, revealing a chemically young, complex organic molecule-rich environment indicative of a pre-cluster stage without star formation.

Contribution

First detailed Q-band spectral survey of a Serpens South clump, identifying numerous molecules and revealing its chemical youth and pre-cluster status.

Findings

Detected ~180 lines from 52 molecules, including complex organics.

Found chemical features similar to both young and evolved prestellar cores.

Indicated the region is a pre-cluster clump with no current star formation.

Abstract

We have conducted Q-band (30 GHz $-$ 50 GHz) line survey observations toward a carbon-chain emission peak in the Serpens South cluster-forming region with the extended Q-band (eQ) receiver installed on the Nobeyama 45 m radio telescope. Approximately 180 lines have been detected including tentative detection, and these lines are attributed to 52 molecules including isotopologues. It has been found that this position is rich in carbon-chain species as much as Cyanopolyyne Peak in Taurus Molecular Cloud-1 (TMC-1 CP), suggesting chemical youth. Not only carbon-chain species, but several complex organic molecules (CH$_3$OH, CH$_3$CHO, HCCCHO, CH$_3$CN, and tentatively C$_2$H$_3$CN) have also been detected, which is similar to the chemical complexity found in evolved prestellar cores. The HDCS/H$_2$CS ratio has been derived to be $11.3 \pm 0.5$ %, and this value is similar to the prestellar core L1544. The chemically young features that are similar to the less-dense starless core TMC-1 CP ($10^4$ cm$^{-3}$ $-$ $10^5$ cm$^{-3}$) and chemically evolved characters which resemble the dense prestellar core L1544 ($\sim 10^6$ cm$^{-3}$) mean that the clump including the observed position is a pre-cluster clump without any current star formation activity.