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Title: The effect of the large-scale structure of the galaxy on star formation properties
Author: Eden , David Joseph
Awarding Body: Liverpool John Moores University
Current Institution: Liverpool John Moores University
Date of Award: 2013
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The production of a quantitative relationship between changes in the star-formation efficiency (SFE), and perhaps the stellar initial mass function (lMF), and the star-forming environment, whether it be pertaining to large-scale structure or local feedback effects, is required as the basis to a predictive model of star formation. The process of star formation is evolutionary from atomic gas --+ molecular clouds --+ clumps --+ stars, and each of these stages has an associated efficiency. If the environment as pertaining to the large-scale structure was changing the star formation process, at least one of these efficiencies should show some variation with environment. Foyle et at (2010). by studying nearby face-on galaxies, found that there was no evidence of an increased efficiency in forming molecular clouds from the atomic gas in and out of the spiral arms. implying that this initial stage was not affected by the largescale structure. The work of Moore et at (2012) implied that any increases would occur in either the cloud-to-clump stage, or the c1ump-to-star stage as it was found that an increase in the ratio of infrared luminosity to cloud mass occurs in the spiral arms. By combining Galactic Plane surveys from those surveying the molecular content of the Galaxy (Galactic Ring Survey, as well as new observations made with HARP on the JCMT), to the dust-continuum observations tracing the clump component (Bolocam Galactic Plane Survey), to the YSO-tracing infrared surveys (Spitzer GLIMPSE, WISE and Hi-GAL), the two possible stages responsible for the increase are investigated. The environments encompassed by this survey include multiple spiral arms, inter-arm regions and the end of the Galactic bar, within which the clump-formation efficiency (CFE; ratio of clump to cloud mass) and the SFE (ratio of infrared luminosity to clump mass) are evaluated. As well as the efficiencies, clump mass functions and luminosity functions for the different environments are presented. It is found that at the CFE shows no variation with large-scale structure environment, with any radical increases within clouds corresponding to their proximity to local sources of feedback, such as the W43 H 11 region. The SFE though shows an increase in the spiral arms compared to the inter-arm regions on the surface this implies that the spiral arms are affecting the last stage of star formation, the clamp-ta-stars stage. However, there are physical processes at work than just an increase in the efficiency of star formation. Moore et al. (2012) found that the majority of the increases in the arms were found to be . because of the presence of extreme-star forming regions (e.g. W49A) or simple source crowding. The increase may also be a result of the way that the SFE is measured. An increase in infrared luminosity-to-clump mass ratio can also be caused by a flatter luminosity function, which may not be an inherent increase in efficiency, just caused by more massive stars forming or more of the stellar initial mass function sampled, which would also result in more massive stars forming. It is then concluded that the most likely cause for the most radical and extreme efficiencies are the local feedback mechanisms. The spiral arms may be responsible for some of the increases but the predominant process controlling the increases is the presence of local feedback mechanisms.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available