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

Bettoni, D.; Falomo, Renato; Scarpa, R.; Negrello, Mattia; Omizzolo, Alessando; Corradi, R. L. M.; Reverte, D.; Vulcani, Benedetta
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The Astrophysical Journal Letters, Volume 873, Issue 2, article id. L14, 5 pp. (2019).

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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 V = ‑21.0, effective radius 2.8 kpc, and stellar velocity dispersion σ = 208 ± 39 km s‑1. 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 }SIE}={197.9}-1.3+2.6 km s‑1, in good agreement with the value derived spectroscopically. This is the second case known of an Einstein cross of an LBG.
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