| dc.description.abstract | In this thesis I study the links between Active Galactic Nuclei (AGN) and
their surrounding large scale environments mainly at high redshift. I firstly
use Spitzer space telescope data for one of the largest and most uniformly
selected samples of radio-loud and radio-quiet AGN at high redshift. It
consists of 173 AGN of both type-1 Sloan Digital Sky Survey (SDSS) Quasi-
Stellar-Objects (QSOs) and type-2 radio-galaxies at the single cosmic epoch
of z ∼ 1. I find significant (8 σ) over-densities of galaxies in the AGNs’
environments when compared to an offset field. Further to this I address
the question of whether radio-loud AGN are found, on average, in denser
environments than their radio-quiet counterparts. I show that there is a link
between the environment and radio luminosity of the most powerful radioloud
QSOs and RGs in the sample, and also reconcile the conflicting results
in the literature by suggesting that there is only a link to the environment
at the highest radio powers.
I extend this work to higher redshift with data from the Spitzer extragalactic
Representative Volume Survey (SERVS) and type-1 SDSS QSOs in
the regions covered by SERVS. This deep data allowed me to study the environments
of QSOs in the redshift range 1 < z < 4. Again I find significant
(4 σ) over-densities of galaxies around the QSOs in this sample, this time
making use of the 3.6-4.5 μm colour to select galaxies more likely to reside
at the redshifts of interest.
I show that the environments of these QSOs are comparable to those predicted
for similarly large black holes in the Durham semi-analytic galaxy
formation model (Galform).
Finally I use data from the Herschel-Astrophysical Terahertz Large Area
Survey with the recently launched Herschel space observatory to study the
environments of type-1 QSOs in the far-infrared (FIR). I find a small excess
of galaxies around the QSOs for which I find that the star-formation rate
increases with increasing redshift. The star-formation rates are estimated
by modelling the FIR spectral energy distribution of the galaxies with a
modified black-body spectrum. This follows the general increase in starformation
rate with redshift observed in the Universe as a whole. I also
compare these findings with those made by the Submillimeter Common-User
Bolometer Array (SCUBA) of higher redshift QSOs. | en_US |
