Intermediate-mass hot cores at 500 AU: disks or outflows?

TL;DR

This study uses high-resolution observations to identify hot cores in two intermediate-mass star-forming regions, revealing that complex molecules trace protostellar disks rather than envelopes, with implications for understanding star formation processes.

Contribution

It provides the first evidence that complex organic molecules in intermediate-mass hot cores primarily trace protostellar disks at ~500 AU scales.

Findings

Complex molecules are detected at ~500 AU scales in both regions.

Most complex molecules trace protostellar disks rather than envelopes.

Velocity gradients indicate disk rotation and dynamic masses over 4 solar masses.

Abstract

Observations with the Plateau de Bure Interferometer in the most extended configuration toward two intermediate-mass star-forming regions, IRAS22198+6336 and AFGL5142, reveal the presence of several complex organic molecules at ~500 AU scales, confirming the presence of hot cores in both regions. The hot cores are not rich in CN-bearing molecules, as often seen in massive hot cores, and are mainly traced by CH3CH2OH, (CH2OH)2, CH3COCH3, and CH3OH, with additionally CH3CHO, CH3OD and HCOOD for IRAS22198+6336, and C6H, and O13CS for AFGL5142. The emission of complex molecules is resolved down to sizes of ~300 and ~600 AU, for IRAS22198+6336 and AFGL5142, respectively, and most likely is tracing protostellar disks rather than flattened envelopes or toroids as usually found. This is specially clear for the case of IRAS22198+6336, where we detect a velocity gradient for all the mapped molecules perpendicular to the most chemically rich outflow of the region, yielding a dynamic mass >4 Msun. As for AFGL5142, the hot core emission is resolved into two elongated cores separated 1800 AU. A detailed comparison of the complex molecule peaks to the new CO(2-1) data and H2O maser data from literature suggests that also for AFGL5142 the complex molecules are mainly associated with disks, except for a faint and extended molecular emission found to the west, which is possibly produced in the interface between one of the outflows and the dense surrounding gas.