Is the Hubble diagram of quasars in tension with concordance cosmology?

TL;DR

This study reanalyzes quasar-based Hubble diagram data to assess its tension with the standard cosmological model, finding indications of higher matter density but questioning the reliability of quasars as cosmological probes.

Contribution

It provides a model-independent analysis of quasar data, confirming potential tension in matter density estimates and highlighting limitations of quasars for cosmological conclusions.

Findings

Indicates a higher matter density ($7e47e47e47e47e47e47e47e47e47e47e47e47e47e47e4$) suggested by the data.

Weak role of the dark energy equation of state ($w_{de}$) in the tension.

Quasar data currently unreliable for confirming cosmic acceleration.

Abstract

Recently Risaliti \& Lusso [Nature Astron. 3 (2019) 3 272] reported new measurements of the expansion rate of the Universe by constructing the Hubble diagram of 1598 quasars in the redshift range $0.5<z<5.5$. It is claimed a $4\sigma$ tension with the standard concordance $\Lambda$CDM concerning both the fractionary matter density $\Omega_{m0}$ and the dark energy equation of state parameter $w_{de}$ standard values. In this work we promote an independent analysis of the same data set using a model-independent estimator for cosmic acceleration. Our results corroborate that the source of such tension can be related to the $\Omega_{m0}$ value with a reasonable indication of a higher $\Omega_{m0}$ value ($\Omega_{m0} \gtrsim 0.4$). On the other hand, we find that the role played by $w_{de}$ on the claimed tension is weak. We also discuss the use of this estimator as a "quality tool" to test the robustness of Hubble diagrams. We conclude claiming that the Quasars data can not yet be seen as a reliable cosmological tool since they can not even state the universe experienced an accelerated expansion phase.