ALMA Detection of Interstellar Methoxymethanol (CH₃OCH₂OH)

Abstract

We report the detection of interstellar methoxymethanol (CH 3 OCH 2 OH) in ALMA Bands 6 and 7 toward the MM1 core in the high-mass star-forming region NGC 6334I at ∼0.1 -1 spatial resolution. A column density of 4(2)×1018 cm −2at T ex = 200 K is derived toward MM1, ∼34 times less abundant than methanol (CH 3 OH), and significantly higher than predicted by astrochemical models. Probable formation and destruction pathways are discussed, primarily through the reaction of the CH 3 OH photodissociation products, the methoxy (CH 3 O) and hydroxymethyl (CH 2 OH) radicals. Finally, we comment on the implications of these mechanisms on gas-phase vs grain-surface routes operative in the region, and the possibility of electron-induced dissociation of CH 3 OH rather than photodissociation.

First Results of an ALMA Band 10 Spectral Line Survey of NGC 6334I: Detections of Glycolaldehyde (HC(O)CH2OH) and a New Compact Bipolar Outflow in HDO and CS

“…Self-calibration was performed on the continuum and applied to the spectral line data after subtracting the continuum in the UV plane. The details of the complementary band7 data used in this Letter are described in McGuire et al (2017), while the band4 data are described in the Appendix.…”

“…The location is ∼400au west of the brightest continuum peak, MM1B. This location was chosen for its proximity to the dense molecular gas while being far enough from the bright continuum that the majority of the molecular lines are not driven into absorption due to the high continuum brightness temperature (McGuire et al 2017).…”

“…As a few examples, Belloche et al (2014) reported the first detection of a branched carbon-chain molecule in the ISM, isopropyl cyanide (C H CN 3 7 ), in band3 observations of Sgr B2. Later, McGuire et al (2017) detected methoxymethanol (CH 3 OCH 2 OH) in surprisingly high abundance toward NGC 6334I in bands 6and7 observations, while Fayolle et al (2017) identified methyl chloride (CH 3 Cl) for the first time using band7 observations of IRAS 16293-2422. These observations, among many others, demonstrate the power of ALMA for studies of our molecular universe in the 1-3mm wavelength range.…”

“…Second, it has previously been targeted by single-dish observations in overlapping frequency ranges by Zernickel et al (2012) using the Heterodyne Instrument for the Far-Infrared (HIFI; de Graauw et al 2010) on the Herschel Space Observatory (Pilbratt et al 2010). Third, it displays a complex spatial structure consisting of a substantial number of embedded sources and outflows, and several chemically distinct regions separated by only ∼2000 au (∼1 5; Brogan et al 2016;McGuire et al 2017;Bøgelund et al 2018; Figure 1). …”

“…NGC 6334I was chosen as the target for three reasons. First, it is an exceptionally molecular line-rich source (McGuire et al 2017) with a relatively small heliocentric distance of 1.3kpc (Chibueze et al 2014;Reid et al 2014). Second, it has previously been targeted by single-dish observations in overlapping frequency ranges by Zernickel et al (2012) using the Heterodyne Instrument for the Far-Infrared (HIFI; de Graauw et al 2010) on the Herschel Space Observatory (Pilbratt et al 2010).…”