GRAVITATIONAL LENSING IN LOW-REDSHIFT CLUSTERS OF GALAXIES - THE ARC-LIKE OBJECT IN ABELL-3408 AND ITS LENSING INTERPRETATION

We analyze the seldom discussed lensing effects expected in low-z clus ters (z = 0.05-0.15), using as an example the bright are (z = 0.073) d iscovered by Campusano & Hardy near the central elliptical galaxy of t he cluster Abell 3408 (z = 0.042), The photometric and spectroscopic o bservations for both the central elliptical and the are are presented. The mass distribution in A3408 is modeled by scaled versions of two r epresentative distributions derived from studies of clusters at higher redshifts: (i) a ''minimum'' mass case where the mass distribution fo llows the light profile of the central elliptical galaxy and (ii) a '' maximum'' mass case where a typical massive dark halo is added to the previous case. The observed are is well reproduced by both models, but rather small magnifications of the source galaxy are implied, The sou rce galaxy is tentatively identified in both the lensing and nonlensin g scenarios as being a spiral. The smaller lensed spiral (14.6h(50)(-1 )kpc,M-B = -18.2) predicted by the dark halo model appears to fit the observations marginally better. Furthermore, we found that only the da rk halo model predicts a measurable amount of weak shear in the images of faint background galaxies. We conclude that observations, under ve ry good seeing conditions, of weak shear in faint background galaxies in the direction of low-redshift galaxy clusters are possible. The com bination of the latter with X-ray data can provide a powerful tool for probing the mass distribution in the very central region of galaxy cl usters.