Ethynyl (C2H) in massive star formation: Tracing the initial conditions?

TL;DR

This study investigates the presence and distribution of ethynyl (C2H) in massive star-forming regions, revealing its potential as a tracer for initial conditions in massive star formation through observations and modeling.

Contribution

It provides the first detailed observational and modeling analysis of C2H distribution across different evolutionary stages of massive star formation.

Findings

C2H is nearly ubiquitous across all studied stages.

High-resolution data show a shell-like C2H distribution around hot cores.

C2H abundance remains high in outer regions due to UV-driven dissociation of CO.

Abstract

APEX single-dish observations at sub-millimeter wavelengths toward a sample of massive star-forming regions reveal that C2H is almost omni-present toward all covered evolutionary stages from Infrared Dark Clouds via High-Mass Protostellar Objects to Ultracompact HII regions. High-resolution data from the Submillimeter Array toward one hot-core like High-Mass Protostellar Object show a shell-like distribution of C2H with a radius of ~9000AU around the central submm peak position. These observed features are well reproduced by a 1D cloud model with power-law density and temperature distributions and a gas-grain chemical network. The reactive C2H radical (ethynyl) is abundant from the onset of massive star formation, but later it is rapidly transformed to other molecules in the core center. In the outer cloud regions the abundance of C2H remains high due to constant replenishment of elemental carbon from CO being dissociated by the interstellar UV photons. We suggest that C2H may be a molecule well suited to study the initial conditions of massive star formation.