DISCOVERY OF A VERY BRIGHT STRONGLY LENSED GALAXY CANDIDATE AT z ≈

Using Hubble Space Telescope (HST) and Spitzer IRAC imaging, we report the discovery of a very bright strongly lensed Lyman break galaxy (LBG) candidate at z ∼ 7.6 in the field of the massive galaxy cluster Abell 1689 (z = 0.18). The galaxy candidate, which we refer to as A1689-zD1, shows a strong z850 − J110 break of at least 2.2 mag and is completely undetected (< 1 σ) in HST Advanced Camera for Surveys (ACS) g475, r625, i775, and z850 data. These properties, combined with the very blue J110−H160 and H160− [4.5μm] colors, are exactly the properties of an z ∼ 7.6 LBG and can only be reasonably fit by a star-forming galaxy at z = 7.6± 0.4 (χ ν = 1.1). Attempts to reproduce these properties with a model galaxy at z < 4 yield particularly poor fits (χν ≥ 25). A1689-zD1 has an observed (lensed) magnitude of 24.7 AB (8 σ) in the NICMOS H160 band and is ∼ 1.3 mag brighter than the brightest-known z850-dropout galaxy. When corrected for the cluster magnification of ∼ 9.3 at z ∼ 7.6, the candidate has an intrinsic magnitude of H160 = 27.1 AB, or about an L∗ galaxy at z ∼ 7.6. The source-plane deprojection shows that the star formation is occurring in compact knots of size . 300 pc. The best-fit stellar population synthesis models yield a median redshift of 7.6, stellar masses (1.6− 3.9)× 10M⊙, stellar ages 45− 320 Myr, star-formation rates . 7.6M⊙ yr, and low reddening with AV ≤ 0.3. These properties are generally similar to those of LBGs found at z ∼ 5− 6. The inferred stellar ages suggest a formation redshift of z ∼ 8− 10 (t . 0.63 Gyr). A1689-zD1 is the brightest observed, highly reliable z > 7.0 galaxy candidate found to date. Subject headings: cosmology: observations — galaxies: evolution — galaxies: formation — galaxies: high-redshift