Lens magnification by CL0024+1654 in the and band

¹ Astrophysics Group, Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2BW, UK
² Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
³ Astronomical Observatory, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
⁴ Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁵ NORDITA, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark
⁶ Science Institute, Dunhaga 3, 107 Reykjavik, Iceland

Corresponding author: S. Dye, sdye01@ic.ac.uk

Received: 28 August 2001
Accepted: 8 February 2002

Abstract

We estimate the total mass distribution of the galaxy cluster CL0024+1654 from the measured source depletion due to lens magnification in the R band. Within a radius of , a total projected mass of (EdS) is measured. The error here includes shot noise, source clustering, uncertainty in background count normalisation and contamination from cluster and foreground galaxies. This corresponds to a mass-to-light ratio of . We compute the luminosity function of CL0024+1654 in order to estimate contamination of the background source counts from cluster galaxies. Three different magnification-based reconstruction methods are employed: 1) an estimator method using a local calculation of lens shear; 2) a non-local, self-consistent method applicable to axi-symmetric mass distributions; 3) a non-local, self-consistent method for derivation of 2D mass maps. We have modified the standard single power-law slope number count theory to incorporate a break and applied this to our observations. Fitting analytical magnification profiles of different cluster models to the observed number counts, we find that CL0024+1654 is best described either by a NFW model with scale radius and normalisation or a power-law profile with slope , central surface mass density and assuming a core radius of . The NFW model predicts that the cumulative projected mass contained within a radius R scales as . Finally, we have exploited the fact that flux magnification effectively enables us to probe deeper than the physical limiting magnitude of our observations in searching for a change of slope in the U band number counts. We rule out both a total flattening of the counts with a break up to and a change of slope, reported by some studies, from up to with 95% confidence.