Through the Looking Glass: Bright, Highly Magnified Galaxy Candidates at z ~ 7 behind A1703

Bradley, L. D., Bouwens, R. J., Zitrin, A., Smit, R., Coe, D., Ford, H. C., Zheng, W., Illingworth, G. D., Benitez, N., and Broadhurst, T. J.

Abstract

We report the discovery of seven strongly lensed Lyman-break galaxy (LBG) candidates at z ~ 7 detected in Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging of A1703. The brightest candidate, called A1703-zD1, has an observed (lensed) magnitude of 24.0 AB (26σ) in the WFC3/IR F160W band, making it 0.2 mag brighter than the z 850-dropout candidate recently reported behind the Bullet Cluster and 0.7 mag 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 mag, 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 μ ~ 3-40. Stellar population fits to the Advanced Camera for Surveys, WFC3/IR, and Spitzer/Infrared Array Camera data for A1703-zD1 and A1703-zD4 yield stellar masses (0.7 - 3.0) × 109 M &sun;, stellar ages 5-180 Myr, and star formation rates ~7.8 M &sun; yr-1, and low reddening with AV <= 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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