Predicted multiply-imaged X-ray AGNs in the XXL survey

TL;DR

This paper predicts the number and properties of multiply-imaged X-ray AGNs in the XXL survey using lensing models, estimating around 20 such sources with detailed statistical and cosmological considerations.

Contribution

It provides the first detailed prediction of multiply-imaged AGNs in the XXL survey, incorporating lensing models and survey detection probabilities.

Findings

Approximately 20 multiply-imaged AGNs expected in XXL survey.

Around 16 of these should be detectable in optical images.

Only one source predicted to have more than two images.

Abstract

We estimate the incidence of multiply-imaged AGNs among the optical counterparts of X-ray selected point-like sources in the XXL field. We also derive the expected statistical properties of this sample, such as the redshift distribution of the lensed sources and of the deflectors that lead to the formation of multiple images, modelling the deflectors using both spherical (SIS) and ellipsoidal (SIE) singular isothermal mass distributions. We further assume that the XXL survey sample has the same overall properties as the smaller XMM-COSMOS sample restricted to the same flux limits and taking into account the detection probability of the XXL survey. Among the X-ray sources with a flux in the [0.5-2] keV band larger than 3.0x10$^{-15}$ erg cm$^{-2}$ s$^{-1}$ and with optical counterparts brighter than an r-band magnitude of 25, we expect ~20 multiply-imaged sources. Out of these, ~16 should be detected if the search is made among the seeing-limited images of the X-ray AGN optical counterparts and only one of them should be composed of more than two lensed images. Finally, we study the impact of the cosmological model on the expected fraction of lensed sources.