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dc.contributor.authorDodd, Elizabeth Frances
dc.date.accessioned2015-03-14T18:34:52Z
dc.date.available2015-03-14T18:34:52Z
dc.date.issued2014-05-27
dc.identifier.urihttp://hdl.handle.net/2299/15622
dc.description.abstractThe overall aim of this thesis is to investigate the environments of AGN, in particular, the density of galaxies in the environments of radio-loud and radio-quiet AGN. This determines whether AGN trace dense environments at high redshifts and whether the environments are important in addressing the problem of radio-loud dichotomy. I extend my research by investigating whether star-formation evolves differently in high-redshift AGN environments compared to the field. I begin by investigating the environments of 169 AGN using Spitzer data at z ∼ 1. I investigate the source density of star-forming galaxies in the environments of radio galaxies, radio-loud quasars and radio- quiet quasars. I do not find any significant overdensity of star-forming galaxies in these environments, although I find tentative evidence for a diff erence in the colours of galaxies in the radio galaxy environments compared to the quasar and field environments. I next use VIDEO data to investigate the environments of the quasars out to z ∼ 3. Firstly, I use a training sample of QSOs and galaxies, which trains a neural network to detect QSOs in the VIDEO data. I detect 274 possible QSOs in the VIDEO data using this method. I am able to determine that the efficiency of the neural network clas- sification is 95 per cent using the training sample. I compare these results to a colour selection method, which detects 88 QSOs in the VIDEO data, and find that the neural network is able to detect ∼ 80 per cent of the colour selected QSOs at Ks = 21. I then investigate the source overdensity using a radial analysis on the environments of the VIDEO QSOs. I find a significant overdensity of galaxies in the environments of the whole QSO sample and in the environments of the radio-loud quasars compared to the radio-quiet quasars. I extend the density analysis by using a second density measure, called the spatial clustering amplitude technique, to compare the environments of the quasars with their radio luminosities, absolute magnitudes and redshifts. I do not fi any significant correlations between environmental density and radio luminosity, absolute magnitude or redshift for the QSOs. I extend this research to investigate the type of galaxies found in the AGN environments. However, I do not find any significant differences between the type of galaxies found in the QSO environments and the background field.en_US
dc.language.isoenen_US
dc.publisherUniversity of Hertfordshireen_US
dc.rightsinfo:eu-repo/semantics/openAccessen_US
dc.subjectQuasarsen_US
dc.subjectAGNen_US
dc.subjectNeural networksen_US
dc.subjectHigh redshiften_US
dc.subjectGalaxy clustersen_US
dc.subjectStar formationen_US
dc.subjectStatisticsen_US
dc.titleThe Environments of Active Galaxies over Cosmic Timeen_US
dc.typeinfo:eu-repo/semantics/doctoralThesisen_US
dc.type.qualificationlevelDoctoralen_US
dc.type.qualificationnamePhDen_US
herts.preservation.rarelyaccessedtrue


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