Assessing cosmic acceleration with the Alcock–Paczyński effect in the SDSS-IV quasar catalogue

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 less than or similar to 1.5 in the Sloan Digital Sky Survey IV, with a possible extension to higher redshifts and improved precision when this catalogue is expanded by upcoming surveys. We here use this method to probe the redshift-dependent expansion rate in three pertinent Friedmann-Lemaitre-Robertson-Walker cosmologies: Lambda cold dark matter (Lambda CDM), which predicts a transition from deceleration to acceleration at z similar to 0.7; Einstein-de Sitter, in which the Universe is always decelerating; and the R-h = ct universe, which expands at a constant rate. Lambda CDM is consistent with these data, but R-h = ct is favoured overall.