A Lensed Arc in the Low‐Redshift Cluster Abell 2124

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Abstract
We report the discovery of an arclike object 27'' from the center of the cD galaxy in the redshift z=0.066 cluster A2124. Observations with the Keck II telescope reveal that the object is a background galaxy at z=0.573, apparently lensed into an arc of length ~85 and total R magnitude mR=20.86±0.07. The width of the arc is resolved; we estimate it to be ~06 after correcting for seeing. A lens model of the A2124 core mass distribution consistent with the cluster galaxy velocity dispersion reproduces the observed arc geometry and indicates a magnification factor 9. With this magnification, the strength of the [O II] λ3727 line implies a star formation rate of ~0.4 h−2 M☉ yr−1. A2124 thus appears to be the lowest redshift cluster known to exhibit strong lensing of a distant background galaxy.