The Dynamics of the Envelope Surrounding the Protostar HH 211-mm

TL;DR

This study investigates the structure and dynamics of the dense gas envelope around the protostar HH 211-mm, revealing its elongated shape, rotational motion, partial collapse, internal heating, and interaction with outflows, using VLA ammonia observations.

Contribution

It provides detailed insights into the envelope's geometry, rotation, collapse region, heating, and outflow interactions around a Class 0 protostar, based on high-resolution ammonia data.

Findings

Envelope is elongated and rotates along its major axis.

Gas within 0.005 pc shows signs of collapse.

Envelope is mainly internally heated by the protostar.

Abstract

We present a study of the structure and dynamics of the dense gas surrounding the HH 211-mm source, using VLA observations of the ammonia (1,1) and (2,2) inversion transitions. We find the envelope around this Class 0 source has an elongated geometry, extending about 104 AU in the direction perpendicular to the well-known HH 211 jet, and exhibits a velocity distribution consistent with rotation along the major axis. Our VLA observations indicate that the envelope is mostly in virial equilibrium. However, comparing our data with results from previous studies it appears that the gas within approximately 0.005 pc of the central protostar is undergoing dynamical collapse. The size of this collapsing radius may constrain the amount of mass that can eventually infall into the forming star. We also find that the envelope is mostly internally heated, most probably by radiation from the central protostar. In addition, we detect evidence of outflow-envelope interaction in the ammonia data. These include a velocity gradient in the dense gas along the outflow axis and significant line broadening that is spatially correlated with the jet and it might be the result of outflow-induced turbulence in the envelope.