Abstract
We report the discovery of seven strongly lensed Lyman break galaxy (LBG) candidates at z~7 detected in Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging of Abell 1703. The brightest candidate, called A1703-zD1, has an observed (lensed) magnitude of 24.0 AB (26 sigma) in the WFC3/IR F160W band, making it 0.2 magnitudes brighter than the z_850-dropout candidate recently reported behind the Bullet Cluster and 0.7 magnitudes brighter than the previously brightest known z~7.6 galaxy, A1689-zD1. With a cluster magnification of ~9, this source has an intrinsic magnitude of H_160 = 26.4 AB, a strong z_850 - J_125 break of 1.7 magnitudes, and a photometric redshift of z~6.7. Additionally, we find six other bright LBG candidates with H_160 band magnitudes of 24.9-26.4, photometric redshifts z~6.4 - 8.8, and magnifications mu~3-40. Stellar population fits to the ACS, WFC3/IR, and \Spitzer/IRAC data for A1703-zD1 and A1703-zD4 yield stellar masses (0.7 - 3.0) x 10^{9} M_sun, stellar ages 5-180 Myr, and star-formation rates ~7.8 M_sun/yr, and low reddening with A_V <= 0.7. The source-plane reconstruction of the exceptionally bright candidate A1703-zD1 exhibits an extended structure, spanning ~4 kpc in the z~6.7 source plane, and shows three resolved star-forming knots of radius r~0.4 kpc.
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