First Results of an ALMA Band 10 Spectral Line Survey of NGC 6334I: Detections of Glycolaldehyde (HC(O)CH$_2$OH) and a New Compact Bipolar Outflow in HDO and CS

TL;DR

This paper reports initial ALMA Band 10 spectral line survey results of NGC 6334I, revealing a bipolar outflow, glycolaldehyde detection, and emphasizing the need for THz laboratory spectroscopy for future high-frequency molecular studies.

Contribution

First ALMA Band 10 survey of NGC 6334I, detecting glycolaldehyde and a new bipolar outflow, with comparisons to previous data and highlighting the importance of laboratory spectroscopy.

Findings

Detection of glycolaldehyde (HC(O)CH2OH) in ALMA data

Identification of a bipolar outflow in HDO and CS

Significant increase in spectral lines compared to Herschel HIFI

Abstract

We present the first results of a pilot program to conduct an 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 $T_{\rm{sys}}$ $<$950 K at $\sim$890 GHz. A bright, bipolar north-south outflow is seen in HDO and CS emission, driven by the embedded massive protostar MM1B. This has allowed, for the first time, a direct comparison of the thermal water in this outflow to the location of water maser emission from prior 22 GHz VLA observations. The maser locations are shown to correspond to the sites along the outflow cavity walls where high velocity gas impacts the surrounding material. We also compare our new observations to prior Herschel HIFI spectral line survey data of this field, detecting an order of magnitude more spectral lines (695 vs 65) in the ALMA data. We focus on the strong detections of the complex organic molecule glycolaldehyde (HC(O)CH$_2$OH) in the ALMA data that is not detected in the heavily beam-diluted HIFI spectra. Finally, we stress the need for dedicated THz laboratory spectroscopy to support and exploit future high-frequency molecular line observations with ALMA.