Milliarcsecond compact structure in radio quasars and the geometry of the universe

TL;DR

This study uses a new model-independent approach with VLBI quasar data to measure cosmic curvature up to redshift 3.0, finding results consistent with a flat universe and projecting high-precision future constraints.

Contribution

It introduces an improved, model-independent method utilizing intermediate-luminosity quasars to measure cosmic curvature at high redshift, achieving higher precision than previous techniques.

Findings

Measured cosmic curvature consistent with zero.

Method achieves higher precision constraints.

Future surveys could refine the measurement to ΔΩ_k~10^{-2}.

Abstract

In this paper, by using the recently compiled set of 120 intermediate-luminosity quasars (ILQSO) observed in a single-frequency VLBI survey, we propose an improved model-independent method to probe cosmic curvature parameter $\Omega_k$ and make the first measurement of the cosmic curvature referring to a distant past, with redshifts up to $z\sim 3.0$. Compared with other methods, the proposed one involving the quasar data achieves constraints with higher precision in this redshift range. More importantly, our results indicate that the measured $\Omega_k$ is in good agreement with zero cosmic curvature, implying that there is no significant deviation from a flat Universe. Finally, we investigate the possibility of testing $\Omega_k$ with a much higher accuracy using quasars observed in the future VLBI surveys. It is shown that our method could provide a reliable and tight constraint on the prior $\Omega_k$ and one can expect the zero cosmic curvature to be established at the precision of $\Delta\Omega_k\sim 10^{-2}$ with 250 well-observed radio quasars.