Exploiting the IRT-THESEUS capability to observe lensed Quasars

TL;DR

This paper assesses the potential of the IRT-THESEUS telescope to observe and analyze lensed quasars, predicting the detection of up to 214,000 quasars and 140 lensed cases, which could advance understanding of quasars and galaxy mass distributions.

Contribution

It introduces a novel simulation-based approach to estimate the number of lensed quasars observable by IRT-THESEUS, highlighting its capability for extragalactic and gravitational lensing studies.

Findings

Up to 214,000 quasars could be observed during the survey.

Approximately 140 of these quasars may be gravitationally lensed.

The study demonstrates the potential of IRT-THESEUS for probing quasar properties and galaxy mass models.

Abstract

THESEUS is an ESA space based project, aiming to explore the early universe by unveiling a complete census of Gamma-Ray Burst (GRB) population in the first billion years. This goal is expected to be achieved by combined observations of its three instruments: the Soft X-ray Imager (SXI), the X and Gamma Imaging Spectrometer (XGIS) and the InfraRed Telescope (IRT). In particular, the IRT instrument will help to identify, localise and study the afterglow of the GRBs detected by SXI and XGIS, and about $40\%$ of its time will be devoted to an all-sky photometric survey, which will certainly detect a relevant number of extragalactic sources, including Quasars. In this paper, we focus on the capability of IRT-THESEUS Telescope to observe Quasars and, in particular, those objects lensed by foreground galaxies. In our analysis, we consider the Quasar Luminosity Function (QLF) in the infrared band based obtained by the Spitzer Space Telescope imaging survey. Furthermore, by using the mass-luminosity distribution function of galaxies and the galaxy/Quasar redshift distributions, we preformed Monte Carlo simulations to estimate the number of lensed Quasars. We predict that up to $2.14 \times 10^5$ Quasars can be observed during gthe IRT-Theseus sky survey, and about $140$ of them could be lensed by foreground galaxies. Detailed studies of these events would provide a powerful probe of the physical properties of Quasars and the mass distribution models of the galaxies.