Quasar Cosmology and Physics

Abstract

In this thesis, we develop the VST ATLAS Quasar Survey, based on the VST ATLAS+NEOWISE imaging surveys and consisting of ∼ 1, 229, 000 quasar (QSO) candidates with 16 < g < 22.5 over ∼ 4700 deg2. We also probe the halo mass profiles of galaxy clusters, galaxies and Luminous Red Galaxies (LRGs) via the gravitational lensing of background VST ATLAS quasars. We show that disagreement between various authors as to whether the results of such cross-correlations are in tension with ΛCDM depend on whether a standard model HOD is assumed rather than simply assuming that galaxies trace mass. In the case of galaxy clusters we find that their mass profiles are well fitted by HODs with a 1-halo term based on the NFW profile. In the case of galaxies, we find that their mass profiles may be marginally more poorly fitted by HOD’s with 1-halo NFW profiles. In an attempt to study the 1-halo term directly, we measure the magnification bias of LRGs and find that the observed lensing amplitude may be too small to be explained by a standard HOD+NFW model at the smallest scales. We finally exploit the VST ATLAS QSO Survey to perform measurements of the QSO halo mass via the 2-point angular auto-correlation function and comparing with the mass clustering correlation function for the ΛCDM model, the cross-correlation with the Planck Cosmic Microwave Background (CMB) lensing convergence maps and scaling the model fits of comparable works, and finally by fitting HOD model parameters to our QSO auto-correlation function and from the derived QSO halo mass function estimating a QSO halo mass. These measurements give QSO halo masses of Mhalo = 8.5 × 1011h−1M⊙, Mhalo = 8.3 × 1011h−1M⊙, and Mhalo = 2.5 × 1012h−1M⊙ respectively. We further find that the sharp peak of our QSO halo mass function implies most (≈ 2/3) QSOs have halo masses within a factor of ≈ 3 of this average mass. Finally, we perform stacked reverberation mapping of QSOs in the eROSITA eFEDS field via optical to Broad Line cross-correlations and optical to X-ray cross-covariance. Simply by virtue of their existence, the 2 − 4σ peaks we find in these analyses provide further support for a narrow QSO black hole mass function. The continuum to Broad Line peak lags are 58±39 days for Hβ, 59±28 days for MgII, 35±25 days for CIV, and we see a peak at a continuum-X-ray lag of 35±12 days at 3−4σ significance and a smoother more continuous feature is seen at negative lags between -100 and -10 days at similarly high significance. The results for Hβ and CIV are in good agreement with other authors while the MgII lag is somewhat lower in these data than previous estimates. The X-ray lags are unexpectedly high, and the sharp X-ray peak being close to the CIV lag seems to suggest that X-rays may be associated as much with Broad Line Region scales as those of an ≈ 10× smaller accretion disk.