Assessing Cosmic Acceleration with the Alcock-Paczynski Effect in the SDSS-IV Quasar Catalog

TL;DR

This paper introduces a new cosmological test using the Alcock-Paczynski effect with SDSS-IV quasar data, aiming to measure the Universe's expansion history and compare different cosmological models.

Contribution

It presents a novel AP effect-based method that avoids spatially bound systems, utilizing quasar sub-samples at z < 1.5 for cosmological model testing.

Findings

LCDM is consistent with the data

R_h=ct universe is favored overall

Method can be extended with future surveys

Abstract

The geometry of the Universe may be probed using the Alcock-Paczynski (AP) effect, in which the observed redshift size of a spherical distribution of sources relative to its angular size varies according to the assumed cosmological model. Past applications of this effect have been limited, however, by a paucity of suitable sources and mitigating astrophysical factors, such as internal redshift-space distortions and poorly known source evolution. In this Letter, we introduce a new test based on the AP effect that avoids the use of spatially bound systems, relying instead on sub-samples of quasars at redshifts z < 1.5 in the Sloan Digital Sky Survey IV, with a possible extension to higher redshifts and improved precision when this catalog is expanded by upcoming surveys. We here use this method to probe the redshift-dependent expansion rate in three pertinent Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmologies: LCDM, which predicts a transition from deceleration to acceleration at z ~ 0.7; Einstein-de Sitter, in which the Universe is always decelerating; and the R_h=ct universe, which expands at a constant rate. LCDM is consistent with these data, but R_h=ct is favoured overall.