A Low-mass Cold and Quiescent Core Population in a Massive Star Protocluster

TL;DR

This study identifies and characterizes a population of low-mass, cold, and quiescent pre-stellar core candidates in a massive star-forming region, revealing their physical properties and potential for future star formation.

Contribution

First detection and detailed analysis of low-mass pre-stellar cores in a massive star-forming environment using high-resolution ALMA data.

Findings

17 low-mass starless core candidates identified

9 cores are gravitationally bound as pre-stellar candidates

Cores show low turbulence, high NH$_{2}$D$ and NH$_{3}$ deuterium fractionation

Abstract

Pre-stellar cores represent the initial conditions of star formation. Although these initial conditions in nearby low-mass star-forming regions have been investigated in detail, such initial conditions remain vastly unexplored for massive star-forming regions. We report the detection of a cluster of low-mass starless and pre-stellar core candidates in a massive star protocluster forming cloud, NGC6334S. With the ALMA observations at a $\sim$0.02 pc spatial resolution, we identified 17 low-mass starless core candidates that do not show any evidence of protostellar activity. These candidates present small velocity dispersions, high fractional abundances of NH$_{2}$D, high NH$_{3}$ deuterium fractionations, and are completely dark in the infrared wavelengths from 3.6 up to 70~$\mu$m. Turbulence is significantly dissipated and the gas kinematics are dominated by thermal motions toward these candidates. Nine out of the 17 cores are gravitationally bound, and therefore are identified as pre-stellar core candidates. The embedded cores of NGC6334S show a wide diversity in masses and evolutionary stages.