Investigating the Earliest Stages of High-Mass Star Formation

UoM administered thesis: Phd

Abstract

This thesis explores the deeply embedded early stages of high-mass star formation through two key observational projects. The first project characterises a sample of 731 high-mass star forming clumps hosting class II methanol masers. Masers detected with the Methanol Multibeam Survey are associated with counterparts in the Herschel Infrared Galactic Plane Survey (Hi-GAL), and the properties of these clumps are determined by fitting to the infrared spectral energy distribution. Compared to the entire population of protostellar YSOs visible with Hi-GAL, the maser sources are found to be generally more massive and more luminous in the infrared, but occupying a restricted luminosity-to-mass range within the bounds covered by the total Galactic population. Principal component analysis is used to explore the intra- and inter-sample trends and identifies a sample of 896 protostellar objects with properties consistent with the maser host sample. An average 70 micron flux density deficiency in the maserless protostellar objects suggests that the matched protostellar sources may recently have evolved beyond the point at which they can sustain a luminous 6.7GHz methanol maser. An apparent minimum 70 micron luminosity required to sustain a methanol maser of a given luminosity is seen. The addition of other observed masers to the analysis provides further evolutionary segregation within the sample and a proposed timeline of maser species is presented, including statistical lifetime estimates. The second project is a study of a single infrared dark cloud in an early stage of evolution with weak signatures of star formation activity, combining data from the Sub-millimeter Array, the Atacama Large Millimeter/sub-millimeter Array and the Atacama Compact Array. From the continuum emission, the clump has a low degree of internal fragmentation with only two cores detected, of masses 32 and 9 solar masses respectively. At least two developed outflows are clearly identified despite the early evolutionary stage, and have entrained comparable mass to more evolved objects of size, despite the dark nature of the object at 70 microns. The momentum and energy contained within the outflows is also calculated from the observations. The inferred accretion derived from outflows give an accretion rate onto the brightest embedded core is equal to 32% of the global infall rate observed towards the clump from single dish data. The momentum flux in the outflows against luminosity suggests that these cores are in the early stages of forming two high-mass stars of 50 and an 8 solar masses, and therefore this clump is likely an OB association precursor. The use of different molecular species as probes of temperature towards cold core regions in the presence of established outflows is also discussed.

Details

Original languageEnglish
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Supervisors/Advisors
Award date1 Aug 2022