Using quasar X-ray and UV flux measurements to constrain cosmological model parameters

Risaliti and Lusso have compiled X-ray and UV flux measurements of 1598 quasars (QSOs) in the redshift range 0.036 <= z <= 5.1003, part of which, z similar to 2.4 - 5.1, is largely cosmologically unprobed. In this paper we use these QSO measurements, alone and in conjunction with baryon acoustic oscillation (BAO) and Hubble parameter [H(z)] measurements, to constrain cosmological parameters in six different cosmological models, each with two different Hubble constant priors. In most of these models, given the larger uncertainties, the QSO cosmological parameter constraints are mostly consistent with those from the BAO + H(z) data. A somewhat significant exception is the non-relativistic matter density parameter Omega(m0) where QSO data favour Omega(m0) similar to 0.5 - 0.6 in most models. As a result, in joint analyses of QSO data with H(z) + BAO data the 1D Omega(m0) distributions shift slightly towards larger values. A joint analysis of the QSO + BAO + H(z) data is consistent with the current standard model, spatially-flat Lambda CDM, but mildly favours closed spatial hypersurfaces and dynamical dark energy. Since the higher Omega(m0) values favoured by QSO data appear to be associated with the z similar to 2 - 5 part of these data, and conflict somewhat with strong indications for Omega(m0) similar to 0.3 from most z < 2.5 data as well as from the cosmic microwave background anisotropy data at z similar to 1100, in most models, the larger QSO data Omega(m0) is possibly more indicative of an issue with the z similar to 2 - 5 QSO data than of an inadequacy of the standard flat Lambda CDM model.