Model-independent Distance Calibration and Curvature Measurement Using Quasars and Cosmic Chronometers
Jun-Jie Wei, Fulvio Melia
Abstract
Abstract We present a new model-independent method to determine spatial curvature and to mitigate the circularity problem affecting the use of quasars as distance indicators. Cosmic-chronometer measurements are used to construct the curvature-dependent luminosity distance using a polynomial fit. Based on the reconstructed and the known ultraviolet versus X-ray luminosity correlation of quasars, we simultaneously place limits on the curvature parameter Ω K and the parameters characterizing the luminosity correlation function. This model-independent analysis suggests that a mildly closed universe ( ) is preferred at the 2.1 σ level. With the calibrated luminosity correlation, we build a new data set consisting of 1598 quasar distance moduli, and use these calibrated measurements to test and compare the standard ΛCDM model and the R h = ct universe. Both models account for the data very well, though the optimized flat ΛCDM model has one more free parameter than R h = ct , and is penalized more heavily by the Bayes Information Criterion. We find that R h = ct is slightly favored over ΛCDM with a likelihood of ∼57.7% versus 42.3%.