DR 21 South Filament: a Parsec-sized Dense Gas Accretion Flow onto the DR 21 Massive Young Cluster

TL;DR

This study characterizes the DR 21 South filament as a large, coherent molecular structure with ongoing accretion feeding a massive young cluster, revealing its physical properties and early evolutionary stage.

Contribution

It provides detailed measurements of the filament's physical parameters and demonstrates an accretion flow feeding the DR 21 cluster, highlighting its early evolutionary status.

Findings

Mass transfer rate of 1.1 x 10^-3 M_sun/yr

Identification of star-forming sites with temperature excesses

Evidence of accretion flow feeding the cluster

Abstract

DR21 south filament (DR21SF) is a unique component of the giant network of filamentary molecular clouds in the north region of Cygnus X complex. Unlike the highly fragmented and star-forming active environment it resides, DR21SF exhibits a coherent profile in the column density map with very few star formation signposts, even though the previously reported linear density of the filament is an order of magnitude higher than the thermal stable threshold. We derive the size (3.6~pc by 0.13~pc), temperature (10 to 15~K), and mass (1048~\textit{M$_\odot$}) of DR21SF from Shanghai 65 m TianMa Radio Telescope (TMRT) observations of NH$_3$ (1, 1) and (2, 2) inversion lines in conjunction with the column density map from our previous work. Star-forming sites are identified along the filament where gas temperature excesses. We find clear gradients in radial velocity and intrinsic line-width along the spine of the filament. The gradients can be well interpreted with a scenario of an accretion flow feeding DR 21 at a mass transfer rate of $1.1 \times 10^{-3}$~\textit{M$_\odot$} yr$^{-1}$. Based on the analysis of its kinematic temperature, intrinsic line-width and mass distribution, we conclude that DR21SF is in an overall trans-critical status, which indicates an early evolutionary stage.