Herschel Hi-GAL imaging of massive young stellar objects

TL;DR

This study uses Herschel Hi-GAL data to analyze the envelope density distribution of massive young stellar objects, revealing partial resolution at 70μm and suggesting the need for more complex models to accurately describe their circumstellar matter.

Contribution

It demonstrates the partial resolution of MYSOs at 70μm with Herschel data and highlights the limitations of spherical models, advocating for 2D axisymmetric modeling.

Findings

MYSOs are partially resolved at 70μm.

Best-fit density profile has an index of ~0.5, shallower than expected.

Spherical models may not fully capture bipolar outflow cavity effects.

Abstract

We used Herschel Hi-GAL survey data to determine whether massive young stellar objects (MYSOs) are resolved at 70$\mu$m and to study their envelope density distribution. Our analysis of three relatively isolated sources in the l=30{\deg} and l=59{\deg} Galactic fields show that the objects are partially resolved at 70$\mu$m. The Herschel Hi-GAL survey data have a high scan velocity which makes unresolved and partially resolved sources appear elongated in the 70$\mu$m images. We analysed the two scan directions separately and examine the intensity profile perpendicular to the scan direction. Spherically symmetric radiative transfer models with a power law density distribution were used to study the circumstellar matter distribution. Single dish sub-mm data were also included to study how different spatial information affects the fitted density distribution. The density distribution which best fits both the 70$\mu$m intensity profile and SED has an average index of ~0.5. This index is shallower than expected and is probably due to the dust emission from bipolar outflow cavity walls not accounted for in the spherical models. We conclude that 2D axisymmetric models and Herschel images at low scan speeds are needed to better constrain the matter distribution around MYSOs.