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Register a new userDetermining the range of validity of quasar X-ray and UV flux measurements for constraining cosmological model parameters
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We use six different cosmological models to study the recently-released compilation of X-ray and UV flux measurements of 2038 quasars (QSOs) which span the redshift range $0.009 leq z leq 7.5413$. We find, for the full QSO data set, that the parameters of the X-ray and UV luminosities $L_X-L_{UV}$ relation used to standardized these QSOs depend on the cosmological model used to determine these parameters, i.e, it appears that the full QSO data set include QSOs that are not standardized and so cannot be used for the purpose of constraining cosmological parameters. Subsets of the QSO data, restricted to redshifts $z lesssim 1.5-1.7$ obey the $L_X-L_{UV}$ relation in a cosmological-model-independent manner, and so can be used to constrain cosmological parameters. The cosmological constraints from these lower-$z$, smaller QSO data subsets are mostly consistent with, but significantly weaker than, those that follow from baryon acoustic oscillation and Hubble parameter measurements.
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Risaliti and Lusso have compiled X-ray and UV flux measurements of 1598 quasars (QSOs) in the redshift range $0.036 leq z leq 5.1003$, part of which, $z sim 2.4 - 5.1$, 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 $H(z)$ + BAO data. A somewhat significant exception is the non-relativistic matter density parameter $Omega_{m0}$ where the QSO data favors $Omega_{m0} sim 0.5 - 0.6$ in most models. Consequently in joint analyses of QSO data with $H(z)$ + BAO data the one-dimensional $Omega_{m0}$ distributions shift slightly toward larger values. A joint analysis of the QSO + $H(z)$ + BAO data is consistent with the current standard model, spatially-flat $Lambda$CDM, but mildly favors closed spatial hypersurfaces and dynamical dark energy. Since the higher $Omega_{m0}$ values favored by the QSO data appear to be associated with the $z sim 2 - 5$ part of these data, and conflict somewhat with strong indications for $Omega_{m0} sim 0.3$ from most $z < 2.5$ data as well as from the cosmic microwave background anisotropy data at $z sim 1100$, in most models, the larger QSO data $Omega_{m0}$ is possibly more indicative of an issue with the $z sim 2 - 5$ QSO data than of an inadequacy of the standard flat $Lambda$CDM model.
The recent compilation of quasar (QSO) X-ray and UV flux measurements include QSOs that appear to not be standardizable via the X-ray luminosity and UV luminosity ($L_X-L_{UV}$) relation and so should not be used to constrain cosmological model parameters. Here we show that the largest of seven sub-samples in this compilation, the SDSS-4XMM QSOs that contribute about 2/3 of the total QSOs, have $L_X-L_{UV}$ relations that depend on the cosmological model assumed and also on redshift, and is the main cause of the similar problem discovered earlier for the full QSO compilation. The second and third biggest sub-samples, the SDSS-Chandra and XXL QSOs that together contribute about 30% of the total QSOs, appear standardizable, but provide only weak constraints on cosmological parameters that are not inconsistent with the standard spatially-flat $Lambda$CDM model or with constraints from better-established cosmological probes.
We use the Risaliti & Lusso (2015) compilation of 808 X-ray and UV flux measurements of quasars (QSOs) in the redshift range $0.061 leq z leq 6.28$, alone and in conjuction with baryon acoustic oscillation (BAO) and Hubble parameter [$H(z)$] measurements, to constrain cosmological parameters in six cosmological models. The QSO data constraints are significantly weaker than, but consistent with, those from the $H(z)$ + BAO data. A joint analysis of the QSO + $H(z)$ + BAO data is consistent with the current standard model, spatially-flat $Lambda$CDM, but mildly favors closed spatial hypersurfaces and dynamical dark energy.
We use 78 reverberation-measured Mg II time-lag quasars (QSOs) in the redshift range $0.0033 leq z leq 1.89$ to constrain cosmological parameters in six different cosmological models. The basis of our method is the use of the radius-luminosity or $R-L$ relation to standardize these 78 Mg II QSOs. In each cosmological model we simultaneously determine $R-L$ relation and cosmological model parameters, thus avoiding the circularity problem. We find that the $R-L$ relation parameter values are independent of the cosmological model used in the analysis thus establishing that current Mg II QSOs are standardizable candles. Cosmological constraints obtained using these QSOs are significantly weaker than, but consistent with, those obtained from a joint analysis of baryon acoustic oscillation (BAO) observations and Hubble parameter [$H(z)$] measurements. So, we also analyse these QSOs in conjunction with the BAO + $H(z)$ data and find cosmological constraints consistent with the standard spatially-flat $Lambda$CDM model as well as with mild dark energy dynamics and a little spatial curvature. A larger sample of higher-quality reverberation-measured QSOs should have a smaller intrinsic dispersion and so should provide tighter constraints on cosmological parameters.
We use measurements of the peak photon energy and bolometric fluence of 119 gamma-ray bursts (GRBs) extending over the redshift range of $0.3399 leq z leq 8.2$ to simultaneously determine cosmological and Amati relation parameters in six different cosmological models. The resulting Amati relation parameters are almost identical in all six cosmological models, thus validating the use of the Amati relation in standardizing these GRBs. The GRB data cosmological parameter constraints are consistent with, but significantly less restrictive than, those obtained from a joint analysis of baryon acoustic oscillation and Hubble parameter measurements.
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