The complexity of Orion: an ALMA view. II. gGg'-Ethylene Glycol and Acetic Acid

Abstract

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.

arXiv commentAccepted for publication in Astronomy and Astrophysics, section 1. Letters to the Editor

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• The ALMA-PILS survey: Complex nitriles towards IRAS 16293--2422
• Chemical segregation of complex organic O-bearing species in Orion KL
• ALMA observations of the young protostellar system Barnard 1b: signatures of an incipient hot corino in B1b-S
• First Hot Corino detected around an Isolated Intermediate-Mass Protostar: Cep\,E-mm
• An Expanded Gas-Grain Model for Interstellar Glycine
• Shocking Sgr B2(N1) with its own outflow: A new perspective on segregation between O- and N-bearing molecules
• The complexity of Orion: an ALMA view III. The explosion impact
• The Explosion in Orion-KL as Seen by Mosaicking the Magnetic Field with ALMA
• ALMA Observations of Ethyl Formate toward Orion KL
• Observational evidence for rotational desorption of Complex Molecules by radiative torques from Orion BN/KL
• Mapping physical parameters in Orion KL at high spatial resolution