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Discovery of a very bright strongly lensed galaxy candidate at z ~ 7.6

By Bradley LD, Bouwens RJ, Ford HC, Illingworth GD, Jee MJ, Benitez N, Broadhurst TJ, Franx M, Frye BL, Infante L, Motta V, Rosati P, White RL and Zheng W


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 similar to 7.6 in the field of the massive galaxy clusterAbell 1689 (z = 0.18). The galaxy candidate, which we refer to as A1689-zD1, shows a strong z(850) - J(110) break of at least 2.2 mag and is completely undetected (< 1 sigma) in HST Advanced Camera for Surveys (ACS) g(475), r(625), i(775), and z(850) data. These properties, combined with the very blue J(110) - H(160) and H(160) - [4.5 mu m] colors, are exactly the properties of an z similar to 7.6 LBG, and can only be reasonably fit by a star- forming galaxy at z = 7.6 +/- 0.4 (chi(2)(nu) = 1.1). Attempts to reproduce these properties with a model galaxy at z < 4 yield particularly poor fits (chi(2)(nu) >= 25). . A1689- zD1 has an observed (lensed) magnitude of 24.7 AB (8 sigma) in the NICMOS H(160) band and is similar to 1.3 mag brighter than the brightest known z(850)-dropout galaxy. When corrected for the cluster magnification of similar to 9.3 at z similar to 7.6, the candidate has an intrinsic magnitude of H(160) = 27.1 AB, or about an L(*) galaxy at z similar to 7: 6. The source- plane deprojection shows that the star formation is occurring in compact knots of size less than or similar to 300 pc. The best- fit stellar population synthesis models yield a median redshift of 7.6, stellar masses (1.6-3.9) x 10(9) M(circle dot), stellar ages 45-320 Myr, star formation rates less than or similar to 7.6M(circle dot) yr(-1), and low reddening with A(V) <= 0.3. These properties are generally similar to those of LBGs found at z similar to 5-6. The inferred stellar ages suggest a formation redshift of z similar to 8-10 (t less than or similar to 0.63 Gyr). A1689-zD1 is the brightest observed, highly reliable z > 7.0 galaxy candidate found to date

Year: 2008
DOI identifier: 10.1086/533519
OAI identifier: oai:iris.unife.it:11392/1854055
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