A strong-lens survey in AEGIS: The influence of large-scale structure

We report on a visual search for galaxy-scale strong gravitational lenses over 650 arcmin(2) of HST ACS (V-606 and I-814) imaging in the DEEP2 Extended Groth Strip. This field has Keck DEIMOS spectroscopy of similar to 14,000 galaxies (similar to 75% complete to). We identify three strong galaxy-galaxy lenses: HST J141735 + 522646 is a previously known four-image lens (the Cross; z(1) = 0.8106, z(s) = 3.40); HST J141820 + 523611 (the Dew-drop; z(l) = 0.5798, z(s) = 0.9818) features two pairs of arcs; and HST J141833 + 524352 (the Anchor; z(l) = 0.4625, no z(s)) has one pair of arcs. Based on a normalized local density (1 + delta(3)), lenses are found to be in both under- and overdense local environments. All three lenses are fit well by singular isothermal ellipsoid models including external shear, with chi(2)(p) similar to 1. The model shears are similar to 10%. Approximating all line-of-sight galaxies as singular isothermal sphere halos truncated at 200 h(-1) kpc, with masses estimated through the Faber- Jackson relation, infers shears of similar to 2%, much smaller than those required by the models. Therefore, the corresponding convergence estimates must also be suspect. If more realistic treatment of galaxies (and the large-scale structure that they are embedded in) were to match the inferred shears to the model shears, then the true convergence could be measured and the mass-sheet degeneracy broken.