Properties of wide-separation lensed quasars by clusters of galaxies in the Sloan Digital Sky Survey

Abstract

We use high-resolution N-body numerical simulations to study the number of predicted large-separation multiply imaged systems produced by clusters of galaxies in the Sloan Digital Sky Survey (SDSS) photometric and spectroscopic quasar samples. We incorporate the condensation of baryons at the centre of clusters by (artificially) adding a brightest cluster galaxy (BCG) as a truncated isothermal sphere. We make predictions in two flat cosmological models: a Lambda cold dark matter (Lambda CDM) model with a matter density Omega(m,0) = 0.3, sigma(8) = 0.9 (Lambda CDM 0) and a model favoured by the Wilkinson Microwave Anisotropy Probe (WMAP) three-year data with Omega(m,0) = 0.238 and sigma(8)= 0.74 (WMAP3). We found that the predicted multiply imaged quasars with separation > 10 arcsec is about 6.2 and 2.6 for the SDSS photometric (with an effective area of 8000 deg(2)) and spectroscopic (with an effective area of 5000 deg(2)) quasar samples, respectively, in the Lambda CDM0 model; the predicted numbers of large-separation lensed quasars agree well with the observations. These numbers are reduced by a factor of 7 or more in the WMAP3 model, and are consistent with the data at less than or similar to 8 per cent level. The predicted cluster lens redshift peaks around redshift 0.5, and 90 per cent are between 0.2 and 1. The ratio of systems with at least four image systems (N-img >= 4) and those with N-img >= 2 is about 1/3.5 for both the Lambda CDM0 and the WMAP3 models, and for both the photometric and the spectroscopic quasar samples. We find that the BCG creates a central circular region, comparable to the Einstein ring of the BCG, where the central image disappears in the usual three- and five-image configurations. If we include four image systems as an extreme case of five-image systems (with an infinitely demagnified central image), we find that 68 per cent of the central images are fainter by a factor of 100 than the brightest image and about 80 per cent are within 1.5 arcsec of the BCG.