Untangling the physical components of galaxies using infrared spectra

Hurley, Peter Donald (2014) Untangling the physical components of galaxies using infrared spectra. Doctoral thesis (PhD), University of Sussex.

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Abstract

The two main physical processes that underpin galaxy evolution are star formation and accretion of mass in active galactic nuclei (AGN). Understanding how contributions from these processes vary across cosmic time requires untangling their relative contributions.
The infrared part of the electromagnetic spectrum contains a number of AGN and star formation diagnostics e.g. emission lines from ionised gas or polyaromatic hydrocarbons (PAHs), and the shape of the continuum. Despite the higher resolution of data from Spitzer’s IRS spectrograph, separating out emission from star formation and AGN is carried out using limited spectral features or simplistic templates. In the first part of this thesis, I show how sophisticated data analysis techniques can make full use of the wealth of spectral data.
I demonstrate how the popular multivariate technique, Principal Component Analysis (PCA), can classify different types of ultra luminous infrared galaxies (ULIRGs), whilst providing a simple set of spectral components that provide better fits than state-of-the art
radiative transfer models. I show how an alternative multivariate technique, Non-Negative Matrix Factorisation (NMF) is more appropriate by applying it to over 700 extragalactic spectra from the CASSIS database and demonstrating its capability in producing spectral
components that are physically intuitive, allowing the processes of star formation and AGN activity to be clearly untangled. Finally, I show how rotational transition lines from carbon monoxide and water, observed
by the Herschel Space Observatory, provides constraints on the physical conditions within galaxies. By coupling the radiative transfer code, RADEX, with the nested
sampling routine, Multinest, I carry out Bayesian inference on the CO spectral line energy distribution ladder of the nearby starburst galaxy, IC342. I also show that water emission lines provide important constraints the conditions of the ISM of on one of the most distant
starburst galaxies ever detected, HFLS3.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy > QB0495 Descriptive astronomy
Q Science > QB Astronomy > QB0495 Descriptive astronomy > QB0799 Stars
Depositing User: Library Cataloguing
Date Deposited: 03 Dec 2014 15:11
Last Modified: 25 Sep 2015 14:13
URI: http://sro.sussex.ac.uk/id/eprint/51433

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