Carbon-Chain Chemistry vs. Complex-Organic-Molecule Chemistry in Envelopes around Three Low-Mass Young Stellar Objects in the Perseus Region

TL;DR

This study uses ALMA data to compare carbon-chain and complex-organic-molecule chemistry in three low-mass young stellar objects, revealing differences in molecular distributions and supporting the role of warm carbon chain chemistry in molecule formation.

Contribution

It provides the first detailed comparison of HC$_{3}$N and CH$_{3}$OH distributions and abundances in these objects, confirming the WCCC mechanism's role at specific temperatures.

Findings

HC$_{3}$N detected in all sources with similar sizes (~3000 au).

CH$_{3}$OH detected only in IRAS 03245, with a smaller emission region (~1760 au).

Observed CH$_{3}$OH/HC$_{3}$N ratios match models at 30-35 K, supporting WCCC formation.

Abstract

We have analyzed ALMA Cycle 5 data in Band 4 toward three low-mass young stellar objects (YSOs), IRAS 03235+3004 (hereafter IRAS 03235), IRAS 03245+3002 (IRAS 03245), and IRAS 03271+3013 (IRAS 03271), in the Perseus region. The HC$_{3}$N ($J=16-15$; $E_{\rm {up}}/k = 59.4$ K) line has been detected in all of the target sources, while four CH$_{3}$OH lines ($E_{\rm {up}}/k = 15.4-36.3$ K) have been detected only in IRAS 03245. Sizes of the HC$_{3}$N distributions ($\sim 2930-3230$ au) in IRAS 03235 and IRAS 03245 are similar to those of the carbon-chain species in the warm carbon chain chemistry (WCCC) source L1527. The size of the CH$_{3}$OH emission in IRAS 03245 is $\sim 1760$ au, which is slightly smaller than that of HC$_{3}$N in this source. We compare the CH$_{3}$OH/HC$_{3}$N abundance ratios observed in these sources with predictions of chemical models. We confirm that the observed ratio in IRAS 03245 agrees with the modeled values at temperatures around 30--35 K, which supports the HC$_{3}$N formation by the WCCC mechanism. In this temperature range, CH$_{3}$OH does not thermally desorb from dust grains. Non-thermal desorption mechanisms or gas-phase formation of CH$_{3}$OH seem to work efficiently around IRAS 03245. The fact that IRAS 03245 has the highest bolometric luminosity among the target sources seems to support these mechanisms, in particular the non-thermal desorption mechanisms.