event
Wednesday 27 Jun 2012: The Supershell/Molecular cloud connection in the Milky Way and Beyond (+ Making a SPLASH with the Parkes Telescope)
Dr Joanne Dawson - University of Tasmania
Physics, 4th floor 14:00-14:30
Throughout the Milky Way and other neighbouring galaxies we routinely observe expanding, rim-brightened structures in the neutral ISM, which are up to hundreds of parsecs in diameter. These "supershells", which are generally held to be formed by the combined influence of clustered supernovae and stellar winds, play a number of roles in the ecosystem of a galaxy; including providing energy and mass to galactic halos, injecting energy to power turbulence, and sweeping-up and cooling the atomic ISM. In this talk I will examine the role of supershells in the formation of molecular clouds. The theoretical context for this is the compression, cooling and fragmentation of the atomic medium in turbulent shocks and flows, of which shells swept-up by large-scale stellar feedback are but one example. I will first report the results of CO(J=1-0) and HI 21cm observations of the molecular and atomic ISM in two Milky Way supershells, which demonstrate an enhanced level of molecularisation over both objects, and hence provide the first quantitative observational evidence of increased molecular cloud production in volumes of space affected by supershell activity. However, it is still far from clear whether these two systems are representative of the general case, either in the Milky Way, or elsewhere. For the second part of my presentation I will discuss recent results on supergiant shells in the LMC, which suggest that while they do indeed help to organise the ISM into over-dense structures, their influence in global molecular cloud production is not a dominant one. Finally, I will briefly introduce first results from SPLASH, a new high-sensitivity survey of the Galactic Plane in the 18cm ground state transitions of OH, which promises to provide insight into the evolution of molecular gas in the Milky Way.
