A conspicuous tangential alignment of galaxies in a STIS parallel Shear Survey field: A new dark-lens candidate?

We report the serendipituous discovery of a conspicuous alignment of galaxies in a eld obtained through the STIS Parallel Shear Survey. This project collects randomly distributed 50 00 50 00 elds to investigate the cosmic shear eect on this scale. Analyzing the parallel observations having the Seyfert galaxy NGC 625 as primary target, we recognized over the whole eld of view a strong apparent tangential alignment of galaxy ellipticities towards the image center. The eld shows several arclet-like features typical for images of massive galaxy clusters, but no obvious over-density of bright foreground galaxies. We also nd a multiple image candidate. On the basis of the possible strong and weak lensing eect within the data, we discuss whether this could be compatible with a massive halo with no clear optical counterpart.