Aarhus Universitets segl

New center article - Yuan Chen

New paper on the observation of COMs in hot cores

O-COM ratios wrt CH3OH
Column density ratios of six O-COMs with respect to methanol versus bolometric luminosity. From left to right, top to bottom is dimethyl ether (DME, CH3OCH3), methyl formate (MF, CH3OCHO), ethanol (C2H5OH), acetaldehyde (CH3CHO), glycolaldehyde (GA, CH2OHCHO), and ethylene glycol (EG, (CH2OH)2). The red points show the CoCCoA data of 14 high-mass sources derived in this work, and the blue ones show the literature data of five low-mass sources: IRAS 16293-2242 A & B (Manigand et al. 2020; Jørgensen et al. 2018), S68N, B1c, and B1-bS (van Gelder et al. 2020). Upper limits are denoted by downward triangles instead of circles. The data points of NGC 6334-38 and NGC 6334-43 are denoted by leftward triangles due to their upper limits on luminosity. The solid line in gray corresponds to the mean column density ratio of each species, and the shaded area in gray shows the standard deviation weighted by the uncertainty on log scales. The mean and standard deviation are calculated from both the high-mass sources and the low-mass ones. The dashed and dotted lines in black correspond to the modeled COM ratios at the end of the cold collapse stage (stage 1) and the warm-up stage (stage 2) in G22, respectively.

Title: CoCCoA: Complex Chemistry in hot Cores with ALMA. Selected oxygen-bearing species


Summary: Complex organic molecules (COMs) have been observed to be abundant in the gas phase toward protostars, while statistical studies on oxygen-bearing COMs (O-COMs) in high-mass protostars using ALMA are still lacking. With the recent CoCCoA survey, we are able to determine the column density ratios of six O-COMs with respect to methanol (CH3OH) in a sample of 14 high-mass protostellar sources to investigate their formation history through ice and/or gas-phase chemistry. The selected O-COMs are CH3CHO, C2H5OH, CH3OCH3, CH3OCHO, CH2OHCHO, and (CH2OH)2. We compare their ratios wrt CH3OH in high-mass CoCCoA sources with those in 5 low-mass protostars available from the literature, along with the results from experiments and simulations. We find that the O-COM ratios are interestingly on the same level in both the high- and low-mass samples, which suggests that these species are mainly formed in similar environments during star formation, probably in ice mantles on dust grains during early pre-stellar stages. Current simulations and experiments can reproduce most observational trends with a few exceptions, and hypotheses exist to explain the differences between observations and simulations/experiments.