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Title: Methanol masers and the environments of massive star formation
Author: Avison, Adam Matthew
ISNI:       0000 0004 2698 5936
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2011
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This thesis presents an investigation into the environments of massive young stellar objects during the period of their evolution where 6.7GHz methanol masers form. Radio observations (both spectral line and continuum data) from the Methanol MultiBeam Survey (MMB) and multiple wavelength infrared data are used to characterise the physical conditions of environments associated with methanol masers. The velocity structures of methanol masers with velocity spreads spanning over 10km/s from the MMB-ATCA dataset are investigated. These sources are seen to have more structure than those with small velocity distributions, providing more information on the physical characteristics of the maser environments. A number of possible morphologies including potential disk, ring and outflow types are suggested for these source from both their velocity structure and position velocity distributions. The MMB-8GHz continuum dataset is used to define the size (e.g Hyper Compact, Ultra Compact or Compact) for Hii regions observed within the MMB-ATCA data. These Hii regions are found to be predominantly in the UCHii or HCHii size regime. Statistical testing to assess any difference in Hii region sizes between sources with maser/continuum source separation of > 0.2 parsecs and those of separation >0.2 parsecs, finds (at between the 80% and 93% significance level) that Hii sources with closely associated maser and continuum emission are smaller in size, suggesting that these sources are less evolved. MIPS 24 and 70µm data are used to define the colour magnitude space inhabited by MMB masers and Hii regions which are found to occupy a large region of log(F70 /F24 ) colour space between a lower limit value of 0.4 and up to 5. Kolmogorov-Smirnov testing of these data show statistically significant differences in the infrared (IR) environments between isolated masers and masers with associated Hii regions, indicating that isolated masers trace younger less evolved protostellar objects. Tests are conducted of 10 degree regions in galactic longitude of the Galactic Plane finding regions with statistically different IR environments indicating the relative ages of the star forming regions in the Galaxy. A null results was found for differing IR environments of masers based on the masers luminosity. An initial study of the IR environments of methanol masers using early data from the Hi-GAL survey, using the PACS and SPIRE instruments onboard the Herschel space telescope. With this investigation the colour-colour space characteristics and spectral energy distributions of the seven MMB masers in the PACS dataset are found and compared to non-maser Herschel sources, providing the basis for further investigation as more Herschel data becomes available.
Supervisor: Fuller, Gary Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available