The complexity of Orion: an ALMA view. II. gGg'-Ethylene Glycol and
  Acetic Acid
  We report the first detection and high angular resolution (1.8" $\times$
1.1") imaging of acetic acid (CH$_3$COOH) and gGg$^{\prime}$--ethylene glycol
(gGg$^{\prime}$(CH$_2$OH)$_2$) towards the Orion Kleinmann--Low nebula. The
observations were carried out at $\sim$1.3mm with ALMA during the Cycle~2. A
notable result is that the spatial distribution of the acetic acid and ethylene
glycol emission differs from that of the other O-bearing molecules within
Orion-KL. Indeed, while the typical emission of O-bearing species harbors a
morphology associated with a "V-shape" linking the Hot Core region to the
Compact Ridge (with an extension towards the BN object), that of acetic acid
and ethylene glycol mainly peaks at about 2" southwest from the hot core region
(near sources I and n). We find that the measured
CH$_3$COOH:aGg$^{\prime}$(CH$_2$OH)$_2$ and
CH$_3$COOH:gGg$^{\prime}$(CH$_2$OH)$_2$ ratios differ from the ones measured
towards the low-mass protostar IRAS 16293--2422 by more than one order of
magnitude. Our best hypothesis to explain these findings is that CH$_3$COOH,
aGg$^{\prime}$(CH$_2$OH)$_2$ and gGg$^{\prime}$(CH$_2$OH)$_2$ are formed on the
icy-surface of grains and then released into the gas-phase, via co-desorption
with water, due to a bullet of matter ejected during the explosive event that
occurred in the heart of the Nebula about 500-700 years ago.
