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