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.
Highlights
The Orion Kleinmann–Low nebula is the high-mass star-forming region closest to Earth (388 ± 5 pc, Kounkel et al 2017)
It is important to note that two main molecular components are associated with Orion-KL: the compact ridge, and the hot core
The latter region may have resulted from interaction of the surrounding gas with remnants of the explosive event, triggered by the close encounter of the sources I, n, and the BN object, which occurred in the region about 500–700 yr ago
Summary
The Orion Kleinmann–Low nebula (hereafter Orion–KL) is the high-mass star-forming region closest to Earth (388 ± 5 pc, Kounkel et al 2017). It is important to note that two main molecular components are associated with Orion-KL: the compact ridge, and the hot core The latter region may have resulted from interaction of the surrounding gas with remnants of the explosive event, triggered by the close encounter of the sources I, n, and the BN object, which occurred in the region about 500–700 yr ago (e.g., see Zapata et al 2011; Nissen et al 2012, and references therein). The detection of acetic acid in OrionKL has not yet been reported, a few transitions may be present in the IRAM 30 m survey by Tercero et al (2011) This species is known to be present in low-mass and highmass star-forming regions (e.g., Remijan et al 2003; Shiao et al 2010; Jørgensen et al 2016).
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