Letter to the Editor

Chemical segregation of complex organic O-bearing species in Orion KL^⋆

¹ Observatorio Astronómico Nacional (OAN-IGN), Calle Alfonso XII, 3, 28014 Madrid, Spain
e-mail: b.tercero@oan.es
² Instituto de Física Fundamental (IFF-CSIC), Calle Serrano 123, 28006 Madrid, Spain
e-mail: s.cuadrado@csic.es
³ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
e-mail: jose.cernicharo@csic.es

Received: 12 October 2018
Accepted: 15 November 2018

Abstract

We investigate the chemical segregation of complex O-bearing species (including the largest and most complex ones detected to date in space) towards Orion KL, the closest high-mass star-forming region. The molecular line images obtained using the ALMA science verification data reveal a clear segregation of chemically related species depending on their different functional groups. We map the emission of ¹³CH₃OH, HCOOCH₃, CH₃OCH₃, CH₂OCH₂, CH₃COOCH₃, HCOOCH₂CH₃, CH₃CH₂OCH₃, HCOOH, OHCH₂CH₂OH, CH₃COOH, CH₃CH₂OH, CH₃OCH₂OH, OHCH₂CHO, and CH₃COCH₃ with ∼1.5″ angular resolution and provide molecular abundances of these species toward different gas components of this region. We disentangle the emission of these species in the different Orion components by carefully selecting lines free of blending and opacity effects. Possible effects in the molecular spatial distribution due to residual blendings and different excitation conditions are also addressed. We find that while species containing the C−O−C group, i.e. an ether group, exhibit their peak emission and higher abundance towards the compact ridge, the hot core south is the component where species containing a hydroxyl group (−OH) bound to a carbon atom (C−O−H) present their emission peak and higher abundance. This finding allows us to propose methoxy (CH₃O−) and hydroxymethyl (−CH₂OH) radicals as the major drivers of the chemistry in the compact ridge and the hot core south, respectively, as well as different evolutionary stages and prevailing physical processes in the different Orion components.