The complexity of Orion: an ALMA view

II. gGg′-ethylene glycol and acetic acid

¹ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5 Firenze 50125 Italy
e-mail: cfavre@arcetri.astro.it
² LERMA, UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l’Observatoire, 75014 Paris, France
³ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁴ Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109, USA
⁵ Dpto. Ciencias Integradas, Unidad GIFMAN-UHU Asociada al CSIC, Universidad de Huelva, 21071 Huelva, Spain
⁶ Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada, Granada, Spain
⁷ Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS, UMR 7583, Université de Paris-Est et Paris Diderot, 61, Av. du Général de Gaulle, 94010 Créteil Cedex, France
⁸ Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA
⁹ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA

Received: 7 June 2017
Accepted: 5 July 2017

Abstract

We report the first detection and high angular resolution (1.8″× 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 ~1.3 mm with ALMA during 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. 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 differ 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.