Investigating the Complex Velocity Structures within Dense Molecular Cloud Cores with GBT-Argus

TL;DR

This study uses high-resolution spectral observations of dense molecular cloud cores to investigate their internal gas dynamics, revealing complex velocity structures and challenging traditional assumptions about core rotation and angular momentum transport.

Contribution

First high-spectral resolution N$_2$H$^+$ observations of dense cores at core scales, revealing complex velocity structures and questioning the rotation interpretation.

Findings

Velocity gradients align with angular momentum-size power law.

Gas structures suggest turbulence or convergent flows, not rotation.

Star-forming disks sometimes perpendicular to velocity gradients.

Abstract

We present the first results of high-spectral resolution (0.023 km/s) N$_2$H$^+$ observations of dense gas dynamics at core scales (~0.01 pc) using the recently commissioned Argus instrument on the Green Bank Telescope (GBT). While the fitted linear velocity gradients across the cores measured in our targets nicely agree with the well-known power-law correlation between the specific angular momentum and core size, it is unclear if the observed gradients represent core-scale rotation. In addition, our Argus data reveal detailed and intriguing gas structures in position-velocity (PV) space for all 5 targets studied in this project, which could suggest that the velocity gradients previously observed in many dense cores actually originate from large-scale turbulence or convergent flow compression instead of rigid-body rotation. We also note that there are targets in this study with their star-forming disks nearly perpendicular to the local velocity gradients, which, assuming the velocity gradient represents the direction of rotation, is opposite to what is described by the classical theory of star formation. This provides important insight on the transport of angular momentum within star-forming cores, which is a critical topic on studying protostellar disk formation.