High resolution imaging of massive young stellar objects and a sample of molecular outflow sources

This thesis contains a study of millimetre wavelength observations of massive young stellar objects (MYSOs) both via interferometric and single dish observations. First, the high angular resolution observations ( up to ∼0.1”) from a variety of interferometers of the MYSO, S140
IRS1, are presented. This source is one of only two prototypes that have ionised equatorial emission from a radiatively driven disc wind. The observations confirm that IRS1 has a dusty disc at a position angle compatible with that of the disc wind emission, and confirms the disc
wind nature for the first time.
Secondly, the observations of S140 IRS1 are modelled using a 2D axisymmetric radiative transfer code. Extensive models producing synthetic data at millimetre wavelengths were developed. These models show that on the largest scales, typically accessible with single dish observations or compact interferometric configurations, the spectral
energy distribution is relatively unchanged by the addition of a compact dust disc. However, a disc is required to match the interferometric visibilities at the smaller scales. The position angle of the disc is well constrained via a newly developed 2D visibility fitting method. The
models however, are degenerate and there are a range of realistic best fitting discs.
The third section presents the single dish observations of the core material traced by C18O around 99 MYSOs and compact HII regions from the RMS survey. A method to calculate the core masses and velocity extent is reported. The method is accurate and robust, and can be applied to any molecular line emission. An updated distance limited
sample contains 87 sources and is complete to 103 L⊙. It is a representative sample of MYSOs and HII regions. All of the cores harbour at least one massive protostar.
Finally, methodologies to establish outflow parameters via 12CO (3-2) and 13CO (3-2) data are investigated. Multiple techniques are trialed for a well studied test source, IRAS 20126+4104, and a repeatable outflow analysis pathway is described. In more complex regions using the 12CO emission to identify outflows and determine the mass is more difficult and an alternative method is suggested. Moreover, the dynamical timescale of the outflows and the dynamical parameters are estimated in a spatial sense rather than using a simple average. Such analysis will aid in categorising different outflows from the full sample.