Modelling carbon chain and complex organic molecules in the DR21(OH) clump

¹ Department of Physics and Astronomy, University of Calgary, Calgary, Canada
² Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France
³ Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Mumbai 400005, India

^★ Corresponding author: pamela.freeman@ucalgary.ca

Received: 19 November 2024
Accepted: 14 April 2025

Abstract

Context. Star-forming regions host a large and evolving suite of molecular species. Molecular transition lines, particularly of complex molecules, can reveal the physical and dynamical environment of star formation.

Aims. We aim to study the large-scale structure and environment of high-mass star formation through single-dish observations of CH₃CCH, CH₃OH, and H₂CO.

Methods. We conducted a wide-band spectral survey with the Institut de radioastronomie millimétrique 30 m telescope and the 100 m Green Bank Telescope towards the high-mass star-forming region DR21(OH)/N44. We used a multi-component local thermodynamic equilibrium (LTE) model to determine the large-scale physical environment near DR21(OH) and the surrounding dense clumps. We followed up with a radiative transfer code for CH₃OH to look at non-LTE behaviour. We then used a gas-grain chemical model to understand the formation routes of these molecules in their observed environments.

Results. We disentangled multiple components of DR21(OH) in each of the three molecules. We find both a warm and cold component towards both the dusty condensations MM1 and MM2, and a fifth broad, outflow component. We also find warm and cold components towards other dense clumps in our maps: N40, N36, N41, N38, and N48. We find that thermal mechanisms are adequate to produce the observed abundances of H₂CO and CH₃CCH while non-thermal mechanisms are needed to produce CH₃OH. We determine that the production routes of these species are dominated by grain chemistry.

Conclusions. Through a combination of wide-band mapping observations, LTE and non-LTE model analysis, and chemical modelling, the chemical and physical environments of star-forming regions are revealed. This method allows us to disentangle the different velocity and temperature components within our clump-scale beam, a scale that encompasses both the star-forming core and its parent cloud.