ATTENUATION OF LUMINOSITY OF DISTANT GALAXIES BY MULTIPLE GRAVITATIONAL LENSING

We investigated the change of luminosity of distant galaxies due to mu ltiple gravitational lensing. We obtained the luminosity change by cal culating the orbits of photons in a model universe in which lensing ob jects are uniformly distributed. We found that luminosities of galaxie s are, in most cases, attenuated by multiple gravitational lensing. Th ere are a few galaxies whose luminosity is amplified through multiple lensing. The number of attenuated galaxies is much larger than that of amplified galaxies. We also found that the median value of attenuatio n ratio of the distant galaxies is well approximated by (1 + z)-1.3(OM EGA(l))1/2, where OMEGA(l), is the density parameter of lensing object s. This result shows that the gravitational lensing introduces an ''at tenuation bias'' into the luminosity function of distant galaxies and quasars.