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Title: Supermassive black holes and feedback in the high redshift universe
Author: Bradshaw, Emma J.
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2013
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In this thesis I use the UKIDSS Ultra-Deep Survey and complementary spectroscopic survey (the UDSz) to investigate AGN and galaxy evolution across a wide redshift range 1.0 < z < 2.5. The work presented here is divided broadly into two themes: a study of AGN and how they are affected by their environment, and a study of galactic winds and feedback processes. To explore how AGN are affected by their environment, I use angular crosscorrelation techniques to study X-ray and radio-loud AGN as a function of galaxy density in the red shift range 1.0 < z < 1.5. I find that AGN preferentially reside in over dense environments at these epochs, typically residing in dark matter halos of mass M2: 5x 1013 M0 . This is in contrast to what I find in the local Universe, where typical X-ray AGN reside in a range of environments, including small groups of galaxies and the outskirts of moderately dense clusters. To study galactic winds and feedback processes, I use spectra from the UDSz spectroscopic survey. This survey is a recent enhancement of the UDS, in which rv3500 high redshift galaxy spectra were obtained using the VIMOS and FORS2 spectrographs on the VLT. I discuss the data reduction and the process of redshift determination of the VIMOS data. rv1600 galaxy spectra are used in the work on feedback and galactic winds as a direct consequence of the reduction. Using the UDSz spectra, I then present a study of galactic-scale outflows at redshift 0.71 < z < 1.63. For this work, I use a large sample of galaxies with an average stellar mass of rv 109.5 M0 and spanning a wide range of rest-frame colours, which represent typical star-forming galaxies at this epoch. By stacking the data by galaxy property, I find that outflows are present in virtually all spectral stacks, with velocities ranging from 100-1000 km S-1. The highest velocity outflows (2:500 km S-1) are found in galaxies with the highest stellar masses and the youngest stellar populations. Our findings suggest that high velocity outflows are mostly driven by star-forming processes rather than AGN, with implied mass outflow rates COlTlparable to the rates of star formation. Such behaviour is consistent with models required to reproduce the high redshift mass-metallicity relation. To investigate the mass-metallicity relation further, I use the UV region of the electromagnetic spectrum to investigate metallicities of galaxies at redshifts 1.0 < z < 2.5. I confirm that, at this epoch, the most massive galaxies tend to be the most metal rich. I also find that these galaxies have a lower metallicity than analogous galaxies in the local Universe. From our investigation into galactic winds and feedback processes, I conclude that these mechanisms have an extremely important role to play in galaxy evolution. Consequently. disentangling the precise balance of star formation, galactic winds and AGN-driven winds in galaxies will remain a significant topic of research in astronomy in years to come. ix \.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available