A new Einstein Cross gravitational lens of a Lyman-break galaxy
  We report the study of an "Einstein Cross" configuration first identified in
a set of HST images by Cerny et al. 2018. Deep spectroscopic observations
obtained at the Spanish 10.4m GTC telescope, allowed us to demonstrate the lens
nature of the system, that consists of a Lyman-break galaxy, not a QSO 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_V =-21.0, effective radius 2.8 kpc and stellar
velocity dispersion sigma=208+-39 km/sec. The source is a Lyman break galaxy
with Ly_alpha 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 sigma_SIE=197.9-1.3+2.6 km/s, in good
agreement with the value derived spectroscopically. This is the second case
known of an Einstein cross of a Lyman-break galaxy.
