Carbon Chains and Methanol toward Embedded Protostars

TL;DR

This study investigates the relationship between carbon chains and saturated complex organic molecules in early star formation, revealing their coexistence and potential formation pathways through observational data.

Contribution

It provides new observational evidence linking carbon chain and COM molecules in embedded protostars, suggesting a formation pathway involving CH4 ice desorption.

Findings

Positive correlation between CH3OH and C4H abundances.

C4H/CH3OH ratio correlates with ice abundance ratios.

Supports carbon chain formation via CH4 ice desorption.

Abstract

Large interstellar organic molecules are potential precursors of prebiotic molecules. Their formation pathways and chemical relationships with one another and simpler molecules are therefore of great interest. In this paper, we address the relationship between two classes of large organic molecules, carbon chains and saturated complex organic molecules (COMs), at the early stages of star formation through observations of C4H and CH3OH. We surveyed these molecules with the IRAM 30m telescope toward 16 deeply embedded low-mass protostars selected from the Spitzer c2d ice survey. We find that CH3OH and C4H are positively correlated indicating that these two classes of molecules can coexist during the embedded protostellar stage. The C4H/CH3OH gas abundance ratio tentatively correlates with the CH4/CH3OH ice abundance ratio in the same lines of sight. This relationship supports a scenario where carbon chain formation in protostellar envelopes begins with CH4 ice desorption.