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

Abstract

We present the first results of a pilot program to conduct an Atacama Large Millimeter Array (ALMA) band10 spectral line survey of the high-mass star-forming region NGC 6334I. The observations were taken in exceptional weather conditions (0.19 mm precipitable water) with typical system temperatures T sys <950K at ∼890GHz. A bright, bipolar north-south outflow is seen in HDO and CS emission, driven by the embedded massive protostar MM1B. This has allowed, for the first time, a direct comparison of the thermal water in this outflow to the location of water maser emission from prior 22GHz Very Large Array observations. The maser locations are shown to correspond to the sites along the outflow cavity walls, where high-velocity gas impacts the surrounding material. We also compare our new observations to prior Herschel Heterodyne Instrument for the Far-infrared (HIFI) spectral line survey data of this field, detecting an order of magnitude more spectral lines (695 versus 65) in the Atacama Large Millimeter/submillimeter Array (ALMA) data. We focus on the strong detections of the complex organic molecule glycolaldehyde (HC(O)CH 2 OH) in the ALMA data that is not detected in the heavily beamdiluted HIFI spectra. Finally, we stress the need for dedicated THz laboratory spectroscopy to support and exploit future high-frequency molecular line observations with ALMA.

ALMA Detection of Vibrationally Excited (vt = 1, 2) Acetic Acid toward NGC 6334I

“…The data have been analyzed with the Common Astronomy Software Applications (CASA) package (McMullin et al 2007). The relatively line-free continuum channels were selected with the techniques described in Brogan et al (2018) and used to subtract the continuum emission in the UV-plane. The Briggs weighting scheme and a Robust parameter of 0.5 for the Band 4 and 6 data and 0.0 for the Band 7 data were used in the TCLEAN task of CASA for imaging, which resulted in elliptical beam shapes.…”

“…As n H 2 ≫ n crit , it is reasonable to assume that these CH 3 COOH transitions are thermalized toward MM1. Following the convention of Turner (1991), we simulated the spectrum of CH 3 COOH in each state with the assumption that the transitions of CH 3 COOH are thermalized, as in McGuire et al (2018). Constant background continuum temperature (T bg ) is considered in each frequency range covered by the datasets.…”

“…The millimeter continuum emission maps have spatially resolved NGC 6334I into nine distinct sources, with most of the hot core molecular line emission originating from the two brightest continuum sources, MM1 and MM2 (Hunter et al 2006;Brogan et al 2016). MM1 is furthered characterized as a hot multi-core which comprises seven components and exhibits a high-velocity bipolar outflow (Brogan et al 2016(Brogan et al , 2018. NGC 6334I is complex not only in physical structure but also in chemical composition (Bøgelund et al 2018).…”

High-resolution millimeter-wave spectroscopy of CH2DCl: Paving the way for future astronomical observations of chloromethane isotopologues

“…The presence of chloromethane in environments other than our Solar system has been recently identified at a pre-planetary stage, thanks to the observation of CH 3 Cl emission towards the low-mass protostar IRAS 16293-2422 with the Atacama Large Millimeter/submillimeter Array (ALMA) [8]. In particular, this detection relied on the observation at submillimeter-wavelengths of some J = 13 ← 12 rotational transitions of the two stable chlorine isotopologues, CH 3 35 Cl and CH 3 37 Cl. The protostar IRAS 16293-2422 is also a rich source of interstellar deuterated species [9].…”

“…[14,15] and references therein). Extended line lists [16] and molecular database [17] are available for both the CH 3 35 Cl and CH 3 37 Cl species. Also the rare 13 C isotopologues have been spectroscopically characterized widely, from the millimeter-wave to the infrared domains (see, e.g., Refs.…”