The formation of high-mass stars and stellar clusters

Abstract

The earliest phase of high-mass star formation has remained a challenging topic. The distinguishing feature between competing theoretical models is the prediction for the high-mass prestellar cores. This thesis presents (sub)arcsecond-resolution interferometric observations in conjunction with synthetic observations at submillimeter wavelengths towards high-mass pre-/proto-stellar objects, for the purpose of characterising the physical and kinematic properties of the early stages of high-mass star formation.

Chapter two showcases deep ALMA 0.82 mm observations (θ ∼ 0.5′′) towards the high-mass prestellar core candidate G11.92-0.61 MM2. Extensive N2H+ (4-3) emission is detected around MM2, displaying complex spectra with multiple velocity components present. Gaussian decomposition and hierarchical clustering are performed to the N₂H⁺ data cube to investigate the kinematics of the N₂H⁺-emitting gas, which reveals a hierarchical system with filamentary substructures showing velocity gradients. The most dominant N₂H⁺ substructure probably traces the accretion flows towards MM2. A mass inflow rate of 2 ×10⁻⁴ ∼ 1.2 ×10⁻³ M⊙ yr⁻¹ is derived with the hypothesis of filamentary accretion flows.

Chapter three presents synthetic 1.3 mm dust continuum images of high-mass star-forming clumps generated with analytic prescriptions and radiative transfer modelling. 432 models with different combinations of stellar masses, separations of sources, and beam sizes are considered. This parametric study predicts that the low-mass objects with masses ≦ 1 M⊙ will not be detected if located ≦ 0.1 pc from a 50 M⊙ protostar in 0.5′′observations.

Chapter four summarises the SMA 1.3 mm observations towards the high-mass protostellar object G34.24+0.13MM. The 1′′ 1.3 mm continuum image reveals that G34.24+0.13MM is a single compact core, with a size of 4700 AU and a mass of 12.5 M⊙. Molecular lines are detected towards the source, possibly indicating ordered motions of the gaseous envelope or unresolved multiplicity. The uniquely high luminosity-mass ratio of G34.24+0.13MM requires future higher-resolution multi-wavelength observations to properly explain.