An H2CO 6cm Maser Pinpointing a Possible Circumstellar Torus in IRAS18566+0408

TL;DR

This study uses multi-wavelength radio and infrared observations to identify a torus structure and ionized jet in IRAS18566+0408, revealing the location of H2CO maser emission and challenging previous excitation models.

Contribution

It provides the first detailed imaging of a potential circumstellar torus associated with H2CO maser emission in a massive star-forming region.

Findings

H2CO 6cm maser coincides with the center of a torus-like structure.

The ionized jet is aligned with 4.5um excess emission.

The maser excitation is not due to radiative pumping by radio continuum.

Abstract

We report observations of 6cm, 3.6cm, 1.3cm, and 7mm radio continuum, conducted with the Very Large Array towards IRAS18566+0408, one of the few sources known to harbor H2CO 6cm maser emission. Our observations reveal that the emission is dominated by an ionized jet at cm wavelengths. Spitzer/IRAC images from GLIMPSE support this interpretation, given the presence of 4.5um excess emission at approximately the same orientation as the cm continuum. The 7mm emission is dominated by thermal dust from a flattened structure almost perpendicular to the ionized jet, thus, the 7mm emission appears to trace a torus associated with a young massive stellar object. The H2CO 6cm maser is coincident with the center of the torus-like structure. Our observations rule out radiative pumping via radio continuum as the excitation mechanism for the H2CO 6cm maser in IRAS18566+0408.