The Green Bank Ammonia Survey: Dense Cores Under Pressure in Orion A

TL;DR

This study analyzes dense cores in Orion A using ammonia and dust data, revealing most are pressure confined rather than gravitationally bound, highlighting the importance of external pressure in core stability.

Contribution

It provides a comprehensive assessment of the virial states of dense cores, emphasizing the role of external pressure in core confinement within Orion A.

Findings

Most dense cores are not gravitationally bound.

External pressure from ambient cloud material is crucial for core confinement.

Dense cores are primarily pressure confined rather than self-gravitating.

Abstract

We use gas temperature and velocity dispersion data from the Green Bank Ammonia Survey and core masses and sizes from the James Clerk Maxwell Telescope Gould Belt Survey to estimate the virial states of dense cores within the Orion A molecular cloud. Surprisingly, we find that almost none of the dense cores are sufficiently massive to be bound when considering only the balance between self-gravity and the thermal and non-thermal motions present in the dense gas. Including the additional pressure binding imposed by the weight of the ambient molecular cloud material and additional smaller pressure terms, however, suggests that most of the dense cores are pressure confined.