The luminosity and redshift dependence
of quasar clustering

Abstract

Our aim in this thesis is to measure the dependence of quasar clustering with redshift and
luminosity. We employ the two-point correlation function to measure the clustering of
quasars and compare our results to models of quasar activity.
Firstly, we present the photometry of the VST-ATLAS survey. This survey aims to
image 4700 deg2 of the Southern Sky to approximately the same depth as SDSS with the
second data release covering 60% of the planned survey. The VST-ATLAS median ‘seeing’
is on average 0.4'' less than that of SDSS images and the median point-source depth
is on average 0.4mag fainter. The r-band has 0.9'' median seeing (cf. 1.24'' in SDSS)
and median 5s depth for point-sources of 22.67 [AB] (cf. 22.31 [AB] in SDSS). The use
of gri imaging from the AAVSO Photometric All-Sky Survey has been used to improve
the accuracy of the zero-point calibration such that VST-ATLAS photometry agrees with
SDSS to the 0.02mag level. We verify the CASU generated catalogue parameters such
as the morphological classifications, aperture fluxes and aperture magnitude corrections
against the SDSS and we demonstrate that the flat fielding and scattered light correction
result in photometry uniform to 0.006mag.
We go on to present a new redshift survey, the 2dF Quasar Dark Energy Survey pilot
(2QDESp), which consists of 10000 quasars from 150 deg2 of the Southern Sky,
based on VST-ATLAS imaging and 2dF/AAOmega spectroscopy. Combining our optical
photometry with the WISE (W1,W2) bands we can select essentially contamination free
quasar samples with 0.8<z<2.5 and g<20.5. At fainter magnitudes, optical UVX selection
is still required to reach our g~22.5 limit. Using both these techniques we observed
quasar redshifts at sky densities up to 90 deg-2.
Further, we use the two-point correlation function to measure the clustering of quasars.
By comparing 2QDESp with other surveys (SDSS, 2QZ and 2SLAQ) we find that quasar
clustering is approximately luminosity independent, with results for all four surveys consistent with a correlation scale of r0=6.1+/-0.1 h-1 Mpc, despite their decade range in luminosity.
We find a significant redshift dependence of the correlation scale, particularly
when BOSS data with r0=7.3+/-0.1 h-1Mpc are included at z~2.4. All quasars remain
consistent with having a single host halo mass of 2+/-1 x10^12 h^-1 M. This result implies
that either quasars do not radiate at a fixed fraction of the Eddington luminosity
or AGN black hole and dark matter halo masses are weakly correlated. No significant
evidence is found to support fainter, X-ray selected quasars at low redshift having larger
halo masses as predicted by the ‘hot halo’ mode AGN model of Fanidakis et al. (2013).
Finally, although the combined quasar sample reaches an effective volume as large as that
of the original SDSS LRG sample, we do not detect the Baryonic Acoustic Oscillation
(BAO) feature in these data.