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Published November 1, 2014 | Published
Journal Article Open

Young Galaxy Candidates in the Hubble Frontier Fields. I. A2744

Abstract

We report the discovery of 24 Lyman-break candidates at 7 ≾ z ≾ 10.5, in the Hubble Frontier Fields (HFF) imaging data of A2744 (z = 0.308), plus Spitzer/IRAC data and archival ACS data. The sample includes a triple image system with a photometric redshift of z ≃ 7.4. This high redshift is geometrically confirmed by our lens model corresponding to deflection angles that are 12% larger than the lower-redshift systems used to calibrate the lens model at z = 2.019. The majority of our high-redshift candidates are not expected to be multiply lensed given their locations in the image plane and the brightness of foreground galaxies, but are magnified by factors of ~1.3-15, so that we are seeing further down the luminosity function than comparable deep-field imaging. It is apparent that the redshift distribution of these sources does not smoothly extend over the full redshift range accessible at z < 12, but appears to break above z = 9. Nine candidates are clustered within a small region of 20'' across, representing a potentially unprecedented concentration. Given the poor statistics, however, we must await similar constraints from the additional HFF clusters to properly examine this trend. The physical properties of our candidates are examined using the range of lens models developed for the HFF program by various groups including our own, for a better estimate of underlying systematics. Our spectral-energy-distribution fits for the brightest objects suggest stellar masses of ≃ 10^9 M_☉, star formation rates of ≃ 4 M_☉ yr^(–1), and a typical formation redshift of z ≾ 19.

Additional Information

© 2014 American Astronomical Society. Received 2014 February 25; accepted 2014 September 10; published 2014 October 15. The work presented in this paper is based on observations made with the NASA/ESA Hubble Space Telescope, and has been supported by award AR-13279 from the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. It is also based on data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This work utilizes gravitational lensing models produced by PIs Bradac, Ebeling, Merten & Zitrin, Sharon, and Williams, funded as part of the HST Frontier Fields program conducted by STScI. These models were calibrated using arcs identified in archival HST imaging by Merten et al. (2011), spectroscopic redshifts of arcs obtained using the VLT/FORS2 spectrograph (Richard et al. 2014), and VLT and Subaru/Suprimecam imaging of the A2744 field (Cypriano et al. 2004; Okabe & Umetsu 2008; Okabe et al. 2010a, 2010b). X.S. acknowledges support from FP7-SPACE-2012-ASTRODEEP-312725, and NSFC grants 11103017 and 11233002. Support for A.Z. is provided by NASA through Hubble Fellowship grant HST-HF-51334.01-A awarded by STScI. F.E.B. acknowledges support from Basal- CATA PFB-06/2007, CONICYT-Chile grants (FONDECYT 1141218, ALMA-CONICYT 31100004, Gemini-CONICYT 32120003, Anillo ACT1101), and the Millennium Institute of Astrophysics (Project IC120009). J.M.D. acknowledges support from the Spanish consolider project CAD2010-00064 and AYA2012-39475-C02-01. We thank M. Meneghitti for helpful comments.

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