Complex Molecules in the L1157 Molecular Outflow

TL;DR

This study reports the first detection of complex organic molecules in a low-mass protostellar outflow, suggesting grain surface formation and ejection by shocks as key processes in such environments.

Contribution

It provides new evidence of complex molecule presence in low-mass star outflows and highlights the efficiency of grain surface chemistry in these regions.

Findings

Detection of complex molecules like HCOOCH3, CH3CN, HCOOH, and C2H5OH in L1157 outflow.

Complex molecules likely formed on grain surfaces before shock ejection.

Similar abundance ratios to hot cores and galactic center clouds.

Abstract

We report the detection of complex organic molecules in the young protostellar outflow L1157. We identify lines from HCOOCH3, CH3CN, HCOOH and C2H5OH at the position of the B1 shock in the blueshifted lobe, making it the first time that complex species have been detected towards a molecular outflow powered by a young low-mass protostar. The time scales associated with the warm outflow gas (< 2,000 yr) are too short for the complex molecules to have formed in the gas phase after the shock-induced sputtering of the grain mantles. It is more likely that the complex species formed in the surface of grains and were then ejected from the grain mantles by the shock. The formation of complex molecules in the grains of low-mass star forming regions must be relatively efficient, and our results show the importance of considering the impact of outflows when studying complex molecules around protostars. The relative abundance with respect to methanol of most of the detected complex molecules is similar to that of hot cores and molecular clouds in the galactic center region, which suggests that the mantle composition of the dust in the L1157 dark cloud is similar to dust in those regions.