Banerji, M.; (2010) Galaxies in the distant universe: colours, redshifts and star formation. Doctoral thesis , UCL (University College London).

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Abstract

This thesis explores the properties of distant galaxies in the Universe, in particular their redshifts, morphologies, evolutionary history and star formation processes within them. The first part is concerned with photometric redshift estimation. I present different photo-z methods and compare them using a sample of Luminous Red Galaxies (LRGs). Photo-z design studies are then carried out for the upcoming Dark Energy Survey as well as the planned space-based Euclid mission. I show the importance of adding near infra-red data to optical data in obtaining accurate redshift estimates for both these projects and how this may prove crucial for some of the cosmological analysis intended with them. In Chapter 5, I present automated morphological classifications for ∼ 1 million objects from the Sloan Digital Sky Survey and compare them to visual classifications of the same objects obtained as part of the Galaxy Zoo project. I find that a neural network is able to reproduce the human classifications to an accuracy of better than 90%. In Chapter 6 I study the evolution of the luminosity and mass functions of LRGs using spectroscopic data. I find that these objects are mainly composed of old stars that were formed very early in the history of the Universe and also that the most massive objects were already well assembled at redshifts of ∼0.8 in direct contradiction with predictions of most current models of galaxy formation. Chapter 7 presents an alternative means of determining the approximate nature of the stellar initial mass function of extragalactic systems by considering timescales for low-mass star formation in different environments. I find that a galaxy’s metallicity is a key parameter in determining the shape of its IMF and make some predictions about trends in molecular emission in different extragalactic systems with different IMFs.

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