Constraining the abundances of complex organics in the inner regions of solar-type protostars

TL;DR

This study uses high-resolution interferometric observations to measure complex organic molecules in low-mass protostars, revealing that their abundances are similar to high-mass hot cores and highlighting gaps in astrochemical models.

Contribution

First multi-line detections of several COMs in low-mass protostars at high resolution, providing accurate abundance measurements and challenging existing astrochemical models.

Findings

COMs abundances are comparable across a wide range of protostellar luminosities.

High-resolution data refine source size and column density estimates.

Current models underpredict key COMs like methyl formate.

Abstract

The high abundances of Complex Organic Molecules (COMs) with respect to methanol, the most abundant COM, detected towards low-mass protostars, tend to be underpredicted by astrochemical models. This discrepancy might come from the large beam of the single-dish telescopes, encompassing several components of the studied protostar, commonly used to detect COMs. To address this issue, we have carried out multi-line observations of methanol and several COMs towards the two low-mass protostars NGC1333-IRAS2A and -IRAS4A with the Plateau de Bure interferometer at an angular resolution of 2 arcsec, resulting in the first multi-line detection of the O-bearing species glycolaldehyde and ethanol and of the N-bearing species ethyl cyanide towards low-mass protostars other than IRAS 16293. The high number of detected transitions from COMs (more than 40 methanol transitions for instance) allowed us to accurately derive the source size of their emission and the COMs column densities. The COMs abundances with respect to methanol derived towards IRAS2A and IRAS4A are slightly, but not substantitally, lower than those derived from previous single-dish observations. The COMs abundance ratios do not vary significantly with the protostellar luminosity, over five orders of magnitude, implying that low-mass hot corinos are quite chemically rich as high-mass hot cores. Astrochemical models still underpredict the abundances of key COMs, such as methyl formate or di-methyl ether, suggesting that our understanding of their formation remains incomplete.