Exploring galaxy mass profiles in strongly lensed quasars with upcoming Roman Space Telescope observations

¹ Department of Mathematics and Physics, Faculty of Natural and Human Sciences, “Fan S. Noli” University of Korça, Albania
² Department of Physics, Faculty of Natural Sciences, University of Tirana, Albania

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 15 April 2026

Abstract

Strong gravitational lensing of quasars is a powerful tool for probing cosmological parameters, tracing galaxy evolution, and investigating the internal structure of quasars. In this work, we examine the galaxy mass profiles in doubly lensed quasars expected to be detected by the Roman Space Telescope. Our previous studies suggest that, for Roman, approximately one in every 150 observed quasars will be strongly lensed by foreground galaxies, with about 85% of these events produced by a single lensing galaxy. Here, we focus on calculating the angular positions of lensed images, the time delays between them, and their magnification ratios, considering three mass density profiles: the Singular Isothermal Sphere (SIS), the Non-Singular Isothermal Sphere (NIS), and the Singular Isothermal Ellipsoid (SIE), restricted to double quasars. We simulated such systems using Monte Carlo techniques, based on observed redshift distributions of quasars and galaxies, galaxy stellar masses, and the empirical relation between stellar mass and velocity dispersion. Our results show that the SIS, NIS, and SIE models yield nearly identical predictions for angular separations, time delays, and magnification ratios. These findings suggest that future observations of doubly lensed quasars with the Roman Space Telescope may not provide clear statistical discrimination between different galaxy mass profiles, although Roman will remain a powerful instrument for collecting valuable data on gravitational lensing systems.