Seeds of Life in Space (SOLIS). X. Interstellar Complex Organic Molecules in the NGC 1333 IRAS 4A outflows

TL;DR

This study detects interstellar complex organic molecules in the NGC 1333 IRAS 4A outflows, revealing chemical diversity and supporting gas-phase formation pathways, thus advancing understanding of organic molecule formation in star-forming regions.

Contribution

First detection of iCOMs in NGC 1333 IRAS 4A outflows, showing chemical differentiation and supporting gas-phase formation models, expanding knowledge beyond the previously studied L1157 outflow.

Findings

Detection of methanol, acetaldehyde, formamide, and dimethyl ether in IRAS 4A outflows

Chemical differentiation indicates different outflow ages

GRAINOBLE+ model supports gas-phase formation of acetaldehyde

Abstract

Aims: A unique environment to study how interstellar Complex Organic Molecules (iCOMs) can be formed is the shocked gas along low-mass protostellar outflows, as the dust mantles composition is sputtered into the gas phase. The chemical richness in these environments has been so far studied only in the L1157 blue shifted outflow. Methods: To understand if the L1157-B1 case is unique, we imaged the NGC 1333 IRAS 4A outflows using the NOEMA (NOrthern Extended Millimeter Array) interferometer as part of the IRAM SOLIS (Seeds Of Life in Space) Large Program and compared the observations with the GRAINOBLE+ gas phase astrochemical model. Results: Several iCOMs were detected in the IRAS 4A outflows: methanol (CH$_3$OH), acetaldehyde (CH$_3$CHO), formamide (NH$_2$CHO) and dimethyl ether (CH$_3$OCH$_3$), all sampling upper excitation energy up to $\sim$30 K. We found a significant chemical differentiation between the IRAS 4A1 outflow, showing a richer molecular content, and the IRAS 4A2 one. The CH$_3$OH/CH$_3$CHO abundance ratio is lower by a factor $\sim$4 in the former; furthermore the ratio in both outflows is lower by a factor $\sim$10 with respect to hot corinos values. Conclusions: After L1157-B1, IRAS 4A outflow is now the second outflow to show an evident chemical complexity. Given that CH$_3$OH is a grain surface species, GRAINOBLE+ reproduced our observations assuming acetaldehyde formation in gas phase by the reaction of ethyl radical (CH$_3$CH$_2$) with atomic oxygen. Moreover, the chemical differentiation between the two outflows suggests that the IRAS 4A1 outflow is likely younger than the IRAS 4A2 one. Further investigation is needed to constrain the age of the outflow and observations of even younger shocks are necessary and future spectroscopic studies on CH$_3$CH$_2$ are needed to be able to observe this species and provide strong constraints on the CH$_3$CHO formation.