摘要：Context.High-mass stars form in much richer environments than those associated with isolated low-mass stars, and once they reach a certain mass, produce ionised (HII) regions. The formation of these pockets of ionised gas are unique to the formation of high-mass stars (M> 8 M⊙), and present an excellent opportunity to study the final stages of accretion, which could include accretion through the HIIregion itself.Aim.This study of the dynamics of the gas on both sides of these ionisation boundaries in very young HIIregions aims to quantify the relationship between the HIIregions and their immediate environments.Methods.We present high-resolution (~0.5″) ALMA observations of nine HIIregions selected from the red MSX source survey with compact radio emission and bolometric luminosities greater than 104 L⊙. We focus on the initial presentation of the data, including initial results from the radio recombination line H29α, some complementary molecules, and the 256 GHz continuum emission.Results.Of the six (out of nine) regions with H29αdetections, two appear to have cometary morphologies with velocity gradients across them, and two appear more spherical with velocity gradients suggestive of infalling ionised gas. The remaining two were either observed at low resolution or had signals that were too weak to draw robust conclusions. We also present a description of the interactions between the ionised and molecular gas (as traced by CS (J = 5 − 4)), often (but not always) finding the HIIregion had cleared its immediate vicinity of molecules.Conclusions.Of our sample of nine, the observations of the two clusters expected to have the youngest HIIregions (from previous radio observations) are suggestive of having infalling motions in the H29αemission, which could be indicative of late stage accretion onto the stars despite the presence of an HIIregion.
关键词：Key wordsenstars: massivestars: formationHII regionsISM: kinematics and dynamicssubmillimetre: ISM
