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 '' x 1.1 '') imaging of acetic acid (CH3COOH) and gGg'-ethylene glycol (gGg'(CH2OH)(2)) toward the Orion Kleinmann-Low (Orion-KL) nebula. The observations were carried out at similar to 1.3 mm with ALMA during Cycle 2. A notable result is that the spatial distribution of the acetic acid and ethylene glycol emission di ff ers from that of the other O-bearing molecules within Orion-KL. 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 toward the BN object), the emission 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 CH3COOH:aGg' (CH2OH)(2) and CH3COOH:gGg' (CH2OH)(2) ratios di ff er from those measured toward the low-mass protostar IRAS 16293-2422 by more than one order of magnitude. Our best hypothesis to explain these findings is that CH3COOH, aGg' (CH2OH)(2), and gGg' (CH2OH)(2) are formed on the icy surface of grains and are then released into the gas-phase via co-desorption with water, by way of a bullet of matter ejected during the explosive event that occurred in the heart of the nebula about 500 - 700 yr ago.