Analysis of Maser Properties Associated with High-Mass Star Formation

The main aim of this thesis was to see if more insight could be drawn from the maser properties than just their association statistics. We explore the properties and distributions of the 6.7 GHz methanol masers from the Methanol MultiBeam (MMB) survey and the 22.235 GHz water masers from the H2O Southern Galactic Plane Survey (HOPS) within the massive and dense clumps detected by the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL), and what this tells us about the physical properties of the star forming regions that generate them. We find that clumps containing both water and methanol masers are significantly more luminous, more evolved and more massive than clumps only containing one of these maser species. This leads us to the conclusion that combinations of other maser species may also represent different star forming stages. We compare our results to the current “straw man” model (Ellingsen et al., 2007) and after finding some differences, we suggest some modifications. We investigate the nature of masers that are offset far from the centre of the clump, and find that these are generally a result of large Hii regions or unresolved sub-structures contained in the ATLASGAL clump. We have identified a sample of positionally and kinematically associated masers located on the edge of their clumps that have no clear infrared (IR) or submillimetre counterpart. Further work is required to identify the driving source of these masers. We also look at clumps that contain a significantly high quantity of water masers, and find that the majority of these clumps contain Hii regions that are shocking these water masers. These clumps also show significantly higher luminosities, masses and luminosity-to-mass ratios than clumps with both maser species, which suggests that these are some of the most intense and evolved star forming regions in the ATLASGAL database. Our results are useful, since we have proven that the properties of masers can tell us about the nature of their star forming environments, which opens up possibilities for targeted searches by using maser properties. This will improve our understanding of massive star formation going forward.