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Title: The luminosity and redshift dependence of quasar clustering
Author: Chehade, Benjamin Thomas
ISNI:       0000 0004 5923 141X
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 2016
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available