The ALMA-QUARKS survey: Hot Molecular Cores are a long-standing phenomenon in the evolution of massive protostars

TL;DR

This study analyzes high-resolution ALMA data of protoclusters, revealing diverse hot molecular core structures and suggesting that hot cores are a long-standing, polymorphic phase in massive star formation, independent of feedback effects.

Contribution

It introduces a detailed classification of hot molecular fragments in protoclusters, highlighting their diversity and long-term presence during massive star formation.

Findings

125 Hot Molecular Fragments identified

Diverse morphologies of HMFs observed

Sequential star formation likely not driven by feedback

Abstract

We present an analysis of the QUARKS survey sample, focusing on protoclusters where Hot Molecular Cores (HMCs, traced by CH3CN(12--11)) and UC HII regions (traced by H30\alpha/H40\alpha) coexist. Using the high-resolution, high-sensitivity 1.3 mm data from the QUARKS survey, we identify 125 Hot Molecular Fragments (HMFs), which represent the substructures of HMCs at higher resolution. From line integrated intensity maps of CH3CN(12--11) and H30\alpha, we resolve the spatial distribution of HMFs and UC HII regions. By combining with observations of CO outflows and 1.3 mm continuum, we classify HMFs into four types: HMFs associated with jet-like outflow, with wide-angle outflow, with non-detectable outflow, and shell-like HMFs near UC HII regions. This diversity possibly indicates that the hot core could be polymorphic and long-standing phenomenon in the evolution of massive protostars. The separation between HMFs and H30\alpha/H40\alpha emission suggests that sequential high-mass star formation within young protoclusters is not likely related to feedback mechanisms.