Feedback from winds and supernovae in massive stellar clusters

This thesis contains a study of the mechanical feedback from winds and supernovae on inhomogeneous molecular material left over from the formation of a massive stellar cluster. Firstly, the mechanical input from a cluster with three massive O-stars into a giant molecular cloud (GMC) clump containing 3240M⊙ of molecular material within a 4 pc radius is investigated using a 3D hydrodynamcial model.
The cluster wind blows out of the molecular clump along low-density channels, into which denser clump material is entrained. The densest regions are surprisingly resistant to ablation by the cluster wind, in part due to shielding by other dense regions close to the cluster.
Nonetheless, molecular material is gradually removed by the cluster wind during which mass-loading factors in excess of several hundred are obtained. Because the clump is very porous, 60-75% of the injected wind energy escapes the simulation domain. After 4.4Myrs the massive stars in the simulation start to explode as supernovae. The highly structured environment into which the SN energy is released
allows even weaker coupling to the remaining dense material
and practically all of the SN energy reaches the wider environment. Secondly, the X-ray emission from the simulated stellar cluster is presented.
The GMC clump causes short–lived attenuation effects on
the X-ray emission of the cluster. However, once most of the material has been ablated away by the winds the remaining dense clumps do not have a noticable effect on the attenuation compared with the assumed interstellar medium (ISM) column. The evolution of the X-ray luminosity and spectra are presented, and synthetic images of the emission are generated. The X-ray luminosity is initially high whilst the winds are “bottled up”, but reduce to a near constant value once the GMC clump has been mostly destroyed. The luminosity decreases slighly during the red supergiant phase of the stars due to the depressurization of the hot gas. However, the luminosity dramatically increases during the Wolf-Rayet stage of each star.
The X-ray luminosity is enhanced by 2-3 orders of magnitude for at least 466 yrs after each supernova explosion, at which time the blast wave leaves the grid. Comparisons between the simulated cluster and both theoretical models and observations of young stellar clusters are
presented.
Thirdly, the radio emission from the simulated cluster is presented. Similar to the X-ray emission, the thermal radio emission is intially high when the winds are confined in the GMC clump and reduce as the material is ablated away. The evolution of the radio flux density and spectra are presented, and synthetic images of the emission are
generated. The radio emission is compared with the X-ray results throughout the evolution of the cluster. The flux density increases during the RSG phase, and remains high during the WR phgase of the stars. The radio flux density is enhanced by three orders of magnitude during the first supernova explosion. Comparisons between the simulated cluster and observations of young stellar clusters are made.
Finally, a preliminary investigation of the interaction of stellar winds within a massive cluster are presented. The hydrodynamcial simulations examine the energy and mass input of a stellar cluster into the ISM.