| dc.description.abstract | My Ph.D. has been composed of work involving the use of far–IR and
submm observations of AGN. During this time it has focused on the in-
terplay between AGN and their host galaxies and cluster environments.
Understanding the role of AGN, and how they affect the evolution of both
their host galaxies and surrounding environments, is a pressing concern
in cosmological models of the universe, affecting as they do the chemical
makeup, star formation rate, and morphology of their host galaxies.
In Chapter 2, we focus on attempting to determine whether there is an
inherent physical difference between Broad Absorption Line Quasars and
non–BAL QSOs using Herschel observations taken at 250, 350 and 500 μm
as part of the H–ATLAS (Eales et al. 2010) survey. BAL QSOs have
been considered the most visible form of AGN feedback, and therefore are
a prime starting point for understanding how galaxy evolution may be
affected by the presence of an AGN. By using matched samples of 50 BAL
and 329 non–BAL QSOs, we create weighted stacks at each wavelength,
finding similar far–IR flux–densities for each sample within the errors. By
SED modelling using a simple modified black body (Hildebrand 1983) fit
to Mrk 231 and IZw1, we derive likely upper and lower limits for the BAL
and non–BAL QSOs in each wavelength, again finding they are consistent
within the errors. A bevy of statistical tests run on either population
similarly finds no evidence to reject the null hypothesis they are drawn from
the same parent population. These results would imply that HiBAL QSOs
can be unified with ordinary QSOs within a simple orientation dependent
scheme. We cannot make the same distinction for LoBALs or FeLoBALs,
which the literature suggests may well be a separate evolutionary phase.
In Chapter 3, we determine whether the presence of an AGN correlates to
an overdensity of star–forming galaxies in the FIR, as has been found at
shorter wavelengths (Falder et al. 2010). For the SHAGs study, 171 AGN
were observed and selected at z∼1. By using observations at 250 μm,
we are able to trace close to the peak of the grey–body SED created by
reprocessing by dust of radiation from young O and B stars. Following
data reduction, we determine number counts and correct for completeness
within a 1Mpc radius of the central AGN. We find an overdensity on the
order of around 0.4 sources per AGN, implying a degree of activity already
significantly lower than at higher redshifts. This overdensity appears to
be somewhat different between RL AGN and RQQ within 1Mpc. A cor-
relation is found between radio luminosity and star formation overdensity,
consistent with a stronger dependence found by Falder et al. (2010) at
3.6 μm, and there also appears to be a correlation between stellar mass
and star formation overdensity for radio–loud QSOs. The galaxies in the
environs of the AGN have LIRG–level luminosities, and are likely the pro-
genitors of modern day S0 galaxies, whose population increases steadily
from z∼1 to the present day (Postman et al. 2005; Smith et al. 2005).
Our work with SCUBA–2, presented in Chapter 4, follows on from a prior
sample of X–ray–absorbed QSOs (Stevens et al. 2005). This new sample
is composed of more highly–absorbed X–ray QSOs and covers a larger
area than the initial sample, so is ideal for an analysis of source counts
around AGN at high–redshift. Data from the JCMT have been reduced,
and completeness corrections and flux corrections applied to catalogues
to determine the number counts around AGN. A comparison background,
created using data from the Cosmology Legacy Survey has been used to
derive comparison counts. The AGN have been investigated, yet none are
detected above 3 at 850 μm, in contrast to the original sample. This may
suggest that star formation in their host galaxies has been suppressed.
Upon stacking in redshift and BAL classification, no difference in flux–
density is apparent and the sources studied here have a similar stacked
submm output to an unabsorbed QSO sample created for the original X–
ray absorbed QSOs. However, over half of the sources here are BAL QSOs
in contrast to the original absorbed QSO sample which contained only
1 BAL QSO. From the work in Chapter 2, one might expect BAL and
non–BAL QSOs to have similar flux–densities. We argue that the sources
studied in this thesis have likely undergone rapid evolution owing to a
strong outflow, and as such star formation has been suppressed sufficiently
that the submm emission is below the confusion noise. BAL winds may still
be present, but essentially, the show is already over. A similar mechanism
may already have occurred in unabsorbed QSOs if all QSOs pass through
an X–ray–absorbed phase. With regard to source counts, we find that there
is tentative evidence for an overdensity of sources around these AGN. The
SFRs of the companion sources have been calculated using several greybody
analogues, all of which imply a high degree of activity, suggesting these
fields will evolve to become some of the most massive regions at the present
epoch, in keeping with current theories of SMGs and high–redshift clusters. | en_US |
