A New Einstein Cross Gravitational Lens of a Lyman-break Galaxy

Abstract

We report the study of an “Einstein Cross” configuration first identified in a set of HST images by Cerny et al. Deep spectroscopic observations obtained at the Spanish 10.4 m Gran Telescopio Canarias telescope, allowed us to demonstrate the lens nature of the system, that consists of a Lyman-break galaxy (LBG), not a quasi-stellar object as is usually the case, at z = 3.03 lensed by a galaxy at z = 0.556. Combining the new spectroscopy with the archival HST data, it turns out that the lens is an elliptical galaxy with M <SUB> V </SUB> = -21.0, effective radius 2.8 kpc, and stellar velocity dispersion σ = 208 ± 39 km s<SUP>-1</SUP>. The source is an LBG with Lyα luminosity ∼L* at that redshift. From the modeling of the system, performed by assuming a singular isothermal ellipsoid (SIE) with external shear, we estimate that the flux source is magnified about 4.5 times, and the velocity dispersion of the lens is {σ }<SUB>SIE</SUB>}={197.9}<SUB>-1.3</SUB><SUP>+2.6</SUP> km s<SUP>-1</SUP>, in good agreement with the value derived spectroscopically. This is the second case known of an Einstein cross of an LBG.