Model selection based on the angular-diameter distance to the compact structure in radio quasars

Abstract

Of all the distance and temporal measures in cosmology, the angular-diameter distance, dA(z), uniquely reaches a maximum value at some finite redshift and then decreases to zero towards the Big Bang. This effect has been difficult to observe due to a lack of reliable, standard rulers, though refinements to the identification of the compact structure in radio quasars may have overcome this deficiency. In this letter, we assemble a catalog of 140 such sources with for model selection and the measurement of . In flat ΛCDM, we find that , fully consistent with the Planck optimized value, with . Both of these values are associated with a dA(z) indistinguishable from that predicted by the zero active mass condition, , in terms of the total pressure p and total energy density ρ of the cosmic fluid. An expansion driven by this constraint, known as the universe, has , which differs from the ΛCDM optimized value by less than . Indeed, the Bayes Information Criterion favours over flat ΛCDM with a likelihood of vs. , suggesting that the optimized parameters in Planck ΛCDM mimic the constraint .