A Strong-lens Survey in Aegis: the Influence of Large Scale Structure

We report on the results of a visual search for galaxy-scale strong gravitational lenses over 650 arcmin of HST/ACS imaging in the Extended Groth Strip (EGS). These deep F606Wand F814W-band observations are in the DEEP2-EGS field. In addition to a previously-known Einstein Cross also found by our search (the “Cross,” HSTJ141735+52264, with zlens = 0.8106 and a published zsource = 3.40), we identify two new strong galaxy-galaxy lenses with multiple extended arcs. The first, HSTJ141820+52361 (the “Dewdrop”; zlens = 0.5798), lenses two distinct extended sources into two pairs of arcs (zsource = 0.9818 by nebular [O II] emission), while the second, HSTJ141833+52435 (the “Anchor”; zlens = 0.4625), produces a single pair of arcs (source redshift not yet known). Four less convincing arc/counter-arc and two-image lens candidates are also found and presented for completeness. All three definite lenses are fit reasonably well by simple singular isothermal ellipsoid models including external shear, giving χν values close to unity. Using the three-dimensional line-of-sight (LOS) information on galaxies from the DEEP2 data, we calculate the convergence and shear contributions κlos and γlos to each lens, assuming singular isothermal sphere halos truncated at 200h −1 kpc. These are compared against a robust measure of local environment, δ3, a normalized density that uses the distance to the third nearest neighbor. We find that even strong lenses in demonstrably underdense local environments may be considerably affected by LOS contributions, which in turn, under the adopted assumptions, may be underestimates of the effect of large scale structure. Subject headings: gravitational lensing – galaxies: high-redshift – large-scale structure of universe – galaxies: individual (HST J141735+52264) – galaxies: individual (HST J141820+52361) – galaxies: individual (HSTJ141833+52435)