Probing star formation and radio activity using faint galaxy redshift surveys

Abstract

In this thesis, we study the evolution of radio luminosity functions (RLF) for AGN and star forming galaxies (SFG), the colour-magnitude distributions of radio and X-ray sources at redshift z ~1, the star formation rate density in dwarf galaxies at z ~1 and investigate downsizing. In chapter 1 we give the background to our studies. We describe the Big Bang model before going on to examine different types of galaxies and looking at their star formation rates and the variation of their properties with their envirorunents. We summarise the elements of modern astronomy methodology used throughout this thesis in chapter 2. In this chapter we describe the methods of measuring star formation rates, galaxy environments and luminosity functions. In chapter 3 we match the AEGIS20 radio survey to the DEEP2 optical spectroscopic survey in the extended Groth Strip (EGS) to create a sample of radio-emitting galaxies that we separate into AGN and SFGs. We derive the RLFs of each of these at two redshift intervals and measure their evolution out to z ~1. We also compare the colour-magnitude distribution of the radio sources to that of the general galaxy population at this redshift and compare these to their local Universe equivalents. We found the evolution of the RLFs to be consistent with pure luminosity evolution with the form L x (1 + z)(^a) where a = 1.0 ± 0.9 for the AGN and a = 3.7 ± 0.3 for the SFGs. We analyse the variations of these radio sources' properties with their environments in chapter 4. Using the projected n(^th) nearest neighbour method to estimate the density of the environments, we find a strong trend of SFG numbers dropping with density. The final science chapter is chapter 5 in which we describe the Redshift One LDSS3 Emission-line Survey (ROLES). This survey targets the [OII] emission line in dwarf galaxies with log (M(_*)/M(_ʘ) )<9.5. We convert the [OII] luminosity to a star formation rate (SFR) and then proceed to analyse the mass-dependence of the global star formation rate at redshift z ~ 1 We find that SFR turns over with stellar mass at this redshift. By also comparing to similar studies in the local Universe, we investigate the empirical "downsizing" picture of galaxy evolution. Finally, we present our conclusions and suggestions for future work in chapter 6.