Antifreeze in the hot core of Orion - First detection of ethylene glycol in Orion-KL

TL;DR

This study reports the first detection of ethylene glycol in Orion-KL using ALMA, revealing its specific spatial distribution and physical conditions, and highlighting its significance in understanding interstellar and cometary chemistry.

Contribution

First detection of ethylene glycol in Orion-KL with high-resolution ALMA data, providing detailed spatial and physical characterization of this complex organic molecule in a hot core.

Findings

Detected ethylene glycol's aGg' conformer in Orion-KL

Derived a rotational temperature of 145 K and a column density of 4.6×10^{15} cm^{-2}

Found a different spatial distribution compared to other O-bearing species

Abstract

Comparison of their chemical compositions shows, to first order, a good agreement between the cometary and interstellar abundances. However, a complex O-bearing organic molecule, ethylene glycol (CH$_{2}$OH)$_{2}$, seems to depart from this correlation because it was not easily detected in the interstellar medium although it proved to be rather abundant with respect to other O-bearing species in comet Hale-Bopp. Ethylene glycol thus appears, together with the related molecules glycolaldehyde CH$_{2}$OHCHO and ethanol CH$_{3}$CH$_{2}$OH, as a key species in the comparison of interstellar and cometary ices as well as in any discussion on the formation of cometary matter. We focus here on the analysis of ethylene glycol in the nearest and best studied hot core-like region, Orion-KL. We use ALMA interferometric data because high spatial resolution observations allow us to reduce the line confusion problem with respect to single-dish observations since different molecules are expected to exhibit different spatial distributions. Furthermore, a large spectral bandwidth is needed because many individual transitions are required to securely detect large organic molecules. Confusion and continuum subtraction are major issues and have been handled with care. We have detected the aGg' conformer of ethylene glycol in Orion-KL. The emission is compact and peaks towards the Hot Core close to the main continuum peak, about 2" to the south-west; this distribution is notably different from other O-bearing species. Assuming optically thin lines and local thermodynamic equilibrium, we derive a rotational temperature of 145 K and a column density of 4.6 10$^{15}$ cm$^{-2}$. The limit on the column density of the gGg' conformer is five times lower.