Testing the cosmic curvature at high redshifts: the combination of LSST strong lensing systems and quasars as new standard candles

TL;DR

This paper introduces a model-independent method combining high-redshift quasars and LSST strong lensing systems to precisely constrain cosmic curvature, highlighting the importance of lens mass models.

Contribution

It proposes a novel approach using quasars as standard candles and analyzes the impact of lens models on curvature constraints, achieving higher precision at high redshifts.

Findings

Quasars can serve as standard candles up to z=5.1 with high precision.

The choice of lens model significantly affects the cosmic curvature constraints.

Power-law lens models yield the most stringent constraints.

Abstract

The cosmic curvature, a fundamental parameter for cosmology could hold deep clues to inflation and cosmic origins. We propose an improved model-independent method to constrain the cosmic curvature by combining the constructed Hubble diagram of high-redshift quasars with galactic-scale strong lensing systems expected to be seen by the forthcoming LSST survey. More specifically, the most recent quasar data are used as a new type of standard candles in the range $0.036<z<5.100$, whose luminosity distances can be directly derived from the non-linear relation between X-ray and UV luminosities. Compared with other methods, the proposed one involving the quasar data achieves constraints with higher precision ($\Delta \Omega_k\sim 10^{-2}$) at high redshifts ($z\sim 5.0$). We also investigate the influence of lens mass distribution in the framework of three types of lens models extensively used in strong lensing studies (SIS model, power-law spherical model, and extended power-law lens model), finding the strong correlation between the cosmic curvature and the lens model parameters. When the power-law mass density profile is assumed, the most stringent constraint on the cosmic curvature $\Omega_k$ can be obtained. Therefore, the issue of mass density profile in the early-type galaxies is still a critical one that needs to be investigated further.