Detection of the simplest sugar, glycolaldehyde, in a solar-type protostar with ALMA

TL;DR

This study reports the first detection of glycolaldehyde, a simple sugar, around a solar-type protostar using ALMA, revealing insights into organic molecule formation in star-forming regions.

Contribution

First detection of multiple glycolaldehyde transitions in a solar-type protostar, providing new data on its abundance and formation pathways in early star formation environments.

Findings

Glycolaldehyde coexists with methyl formate, which is more abundant.

Detected infall signatures indicating chemical processes near the protostar.

Data supports UV photochemistry of methanol-CO ices as a formation pathway.

Abstract

Glycolaldehyde (HCOCH2OH) is the simplest sugar and an important intermediate in the path toward forming more complex biologically relevant molecules. In this paper we present the first detection of 13 transitions of glycolaldehyde around a solar-type young star, through Atacama Large Millimeter Array (ALMA) observations of the Class 0 protostellar binary IRAS 16293-2422 at 220 GHz (6 transitions) and 690 GHz (7 transitions). The glycolaldehyde lines have their origin in warm (200-300 K) gas close to the individual components of the binary. Glycolaldehyde co-exists with its isomer, methyl formate (HCOOCH3), which is a factor 10-15 more abundant toward the two sources. The data also show a tentative detection of ethylene glycol, the reduced alcohol of glycolaldehyde. In the 690 GHz data, the seven transitions predicted to have the highest optical depths based on modeling of the 220 GHz lines all show red-shifted absorption profiles toward one of the components in the binary (IRAS16293B) indicative of infall and emission at the systemic velocity offset from this by about 0.2" (25 AU). We discuss the constraints on the chemical formation of glycolaldehyde and other organic species - in particular, in the context of laboratory experiments of photochemistry of methanol-containing ices. The relative abundances appear to be consistent with UV photochemistry of a CH3OH-CO mixed ice that has undergone mild heating. The order of magnitude increase in line density in these early ALMA data illustrate its huge potential to reveal the full chemical complexity associated with the formation of solar system analogs.