Abstract
We have discovered strong gravitational lensing by the galaxy ESO 325-G004, in images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope. The lens galaxy is a boxy group-dominant elliptical at z = 0.0345, making this the closest known galaxy-scale lensing system. The lensed object is very blue (B - IC ≈ 1.1), and forms two prominent arcs and a less extended third image. The Einstein radius is REin = 1.9 kpc (~3'' on the sky), much smaller than the lens galaxy effective radius of 8.5 kpc. Assuming a high redshift for the source, the mass within REin is 1.4 × 1011 M☉, and the mass-to-light ratio is 1.8 (M/L)☉, I. The equivalent velocity dispersion is σlens = 310 km s-1, in excellent agreement with the measured stellar dispersion σv = 320 km s-1. Modeling the lensing potential with a singular isothermal ellipse (SIE), we find close agreement with the light distribution. The best-fit SIE model reproduces the ellipticity of the lens galaxy to ~10%, and its position angle within 1°. The model predicts the broad features of the arc geometry as observed; the unlensed magnitude of the source is estimated at IC ~ 23.75. We suggest that ~60 similarly massive elliptical galaxies within z < 0.1 will exhibit such a luminous, multiply imaged source.
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