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Gravitational Lensing in Low-Redshift Clusters of Galaxies: The Arclike Object in Abell 3408 and Its Lensing Interpretation

We analyze the seldom discussed lensing effects expected in low-z clusters (z = 0.05-0.15), using as an example the bright arc (z=0.073) discovered by Campusano & Hardy near the central elliptical galaxy of the cluster Abell 3408 (z=0.042). The photometric and spectroscopic observations for both the central elliptical and the arc are presented. The mass distribution in A3408 is modeled by scaled versions of two representative distributions derived from studies of clusters at higher redshifts: (i) a "minimum" mass case where the mass distribution follows 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 arc is well reproduced by both models, but rather small magnifications of the source galaxy are implied. The source galaxy is tentatively identified in both the lensing and nonlensing scenarios as being a spiral. The smaller lensed spiral (14.6 h50−1 kpc, MB = -18.2) predicted by the dark halo model appears to fit the observations marginally better. Furthermore, we found that only the dark halo model predicts a measurable amount of weak shear in the images of faint background galaxies. We conclude that observations, under very good seeing conditions, of weak shear in faint background galaxies in the direction of low-redshift galaxy clusters are possible. The combination of the latter with X-ray data can provide a powerful tool for probing the mass distribution in the very central region of galaxy clusters.