Model Selection based on the Angular-Diameter Distance to the Compact Structure in Radio Quasars

TL;DR

This paper uses radio quasar data to measure the angular-diameter distance and its maximum, supporting the R_h=ct universe model over flat LCDM through statistical analysis.

Contribution

It introduces a new catalog of 140 radio quasars for model selection and provides observational evidence favoring the R_h=ct universe model.

Findings

Measured z_max=1.69 in flat LCDM consistent with Planck

z_max=1.718 in R_h=ct universe closely matches observations

Bayes factor favors R_h=ct universe over flat LCDM with 81% likelihood

Abstract

Of all the distance and temporal measures in cosmology, the angular-diameter distance, d_A(z), uniquely reaches a maximum value at some finite redshift z_max 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 0 < z < 3 for model selection and the measurement of z_max. In flat LCDM, we find that Omega_m= 0.24^{+0.1}_{-0.09}, fully consistent with Planck, with z_max=1.69. Both of these values are associated with a d_A(z) indistinguishable from that predicted by the zero active mass condition, rho+3p=0, in terms of the total pressure p and total energy density rho of the cosmic fluid. An expansion driven by this constraint, known as the R_h=ct universe, has z_max=1.718, which differs from the measured value by less than ~1.6%. Indeed, the Bayes Information Criterion favours R_h=ct over flat LCDM with a likelihood of ~81% versus 19%, suggesting that the optimized parameters in Planck LCDM mimic the constraint p=-rho/3.