GALAXY-CLUSTER ASSOCIATIONS FROM GRAVITATIONAL LENSING

We investigate the associations between background galaxies and foregr ound clusters of galaxies due to the effect of gravitational lensing b y clusters of galaxies. Similar to the well-known quasar-galaxy ones, these associations depend sensitively on the shape of galaxy number-ma gnitude or number-flux relation, and both positive and ''negative'' as sociations are found to be possible, depending on the limiting magnitu de and/or the flux threshold in the surveys. We calculate the enhancem ent factors assuming a singular isothermal sphere model for clusters o f galaxies and a pointlike model for background sources selected in th ree different wavelengths, B, K and radio. Our results show that K- se lected galaxies might constitute the best sample to test the ''negativ e'' associations while it is unlikely that one can actually observe an y association for blue galaxies. We also point out that bright radio s ources (S > 1 Jy) can provide strong positive associations, which may have been already detected in 3CR sample.