Model-independent distance calibration and curvature measurement using quasars and cosmic chronometers

Jun Jie Wei, Fulvio Melia

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


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 DL cal (WK, z) using a polynomial fit. Based on the reconstructed DL cal (WK, z) and the known ultraviolet versus X-ray luminosity correlation of quasars, we simultaneously place limits on the curvature parameter ΩK and the parameters characterizing the luminosity correlation function. This model-independent analysis suggests that a mildly closed universe (WK = -0.918 ± 0.429) is preferred at the 2.1σ 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 Rh = ct universe. Both models account for the data very well, though the optimized flat ΛCDM model has one more free parameter than Rh = ct, and is penalized more heavily by the Bayes Information Criterion. We find that Rh = ct is slightly favored over ΛCDM with a likelihood of ∼57.7% versus 42.3%. Unified Astronomy Thesaurus concepts: Quasars (1319); Cosmological parameters (339); Cosmological models (337); Distance indicators (394); Observational cosmology (1146).

Original languageEnglish (US)
Article numberab5e7d
JournalAstrophysical Journal
Issue number2
StatePublished - Jan 10 2020

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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