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Title: Dust and star formation in NGC 4449
Author: Karczewski, O. L.
Awarding Body: University College London (University of London)
Current Institution: University College London (University of London)
Date of Award: 2013
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The low degree of processing of the interstellar medium (ISM) in nearby metal-poor galaxies, such as NGC 4449, allow them to be viewed as local analogues of the first galaxies formed in the Universe. In this work we present a study of dust and star formation in NGC 4449, both on global and local scales. We present the spectral energy distribution (SED) of NGC 4449 from the FUV to the sub-mm. Our analysis of a global optical spectrum of NGC 4449 suggests an early onset of star formation, while our results from a chemical evolution dust model provide an indication of the chemical composition of dust globally. These results were used as constraints in constructing a photoionization and radiative transfer MOCASSIN model of NGC 4449. The presented iterative scheme allowed us to infer a total mass of the youngest stellar population which is likely to reside in the centre, in the SW and in the N of NGC 4449. The derived global recent star formation rate is in good agreement with previous estimates. We conclude that our scheme is a new tool, which is particularly suitable for deriving integrated properties of galaxies. Based on spectroscopic observations from the Spitzer Space Telescope and the Herschel Space Telescope we obtained a detailed view of the ionized regions, the photo-dissociation regions and the dust emission within NGC 4449. Our results suggest a deficit of ionized polycyclic aromatic hydrocarbons (PAHs) near the centre of NGC 4449 and bright [OIII]88 emission dominating the ISM cooling locally. Additionally, we examined a sample of type Ibc supernovae to assess their possible contribution to dust formation in the early Universe. We found that the estimated dust masses are too low to consider type Ibc supernovae as major dust producers.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available