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Characterizing Faint Galaxies in the Reionization Epoch: LBT Confirms Two L < 0.2 L* Sources at z = 6.4 Behind the CLASH/Frontier Fields Cluster MACS0717.5+3745

Vanzella, E. and Fontana, A. and Zitrin, A. and Coe, D. and Bradley, L. and Postman, M. and Grazian, A. and Castellano, M. and Pentericci, L. and Giavalisco, M. and Rosati, P. and Nonino, M. and Smit, R. and Balestra, I. and Bouwens, R. and Cristiani, S. and Giallongo, E. and Zheng, W. and Infante, L. and Cusano, F. and Speziali, R. (2014) Characterizing Faint Galaxies in the Reionization Epoch: LBT Confirms Two L < 0.2 L* Sources at z = 6.4 Behind the CLASH/Frontier Fields Cluster MACS0717.5+3745. Astrophysical Journal Letters, 783 (1). Art. No. L12. ISSN 2041-8205. doi:10.1088/2041-8205/783/1/L12.

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We report the LBT/MODS1 spectroscopic confirmation of two images of faint Lyα emitters at z = 6.4 behind the Frontier Fields galaxy cluster MACSJ0717.5+3745. A wide range of lens models suggests that the two images are highly magnified, with a strong lower limit of μ > 5. These are the faintest z > 6 candidates spectroscopically confirmed to date. These may also be multiple images of the same z = 6.4 source as supported by their similar intrinsic properties, but the lens models are inconclusive regarding this interpretation. To be cautious, we derive the physical properties of each image individually. Thanks to the high magnification, the observed near-infrared (restframe ultraviolet) part of the spectral energy distributions and Lyα lines are well detected with S/N(m _(1500)) ≳ 10 and S/N(Lyα) ≃ 10-15. Adopting μ > 5, the absolute magnitudes, M _(1500), and Lyα fluxes are fainter than –18.7 and 2.8 × 10^(–18) erg s^(–1) cm^(–2), respectively. We find a very steep ultraviolet spectral slope β = –3.0 ± 0.5 (F _λ = λ^β), implying that these are very young, dust-free, and low metallicity objects, made of standard stellar populations or even extremely metal poor stars (age ≾ 30 Myr, E(B – V) = 0 and metallicity 0.0-0.2 Z/Z_☉). The objects are compact (<1 kpc^2) and with a stellar mass M_* < 10^8 M_☉. The very steep β, the presence of the Lyα line, and the intrinsic FWHM (<300 km s^(–1)) of these newborn objects do not exclude a possible leakage of ionizing radiation. We discuss the possibility that such faint galaxies may resemble those responsible for cosmic reionization.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Zitrin, A.0000-0002-0350-4488
Coe, D.0000-0001-7410-7669
Postman, M.0000-0002-9365-7989
Giavalisco, M.0000-0002-7831-8751
Nonino, M.0000-0001-6342-9662
Smit, R.0000-0001-8034-7802
Bouwens, R.0000-0002-4989-2471
Cusano, F.0000-0003-2910-6565
Additional Information:© 2014 American Astronomical Society. Received 2013 December 23; accepted 2014 January 27; published 2014 February 14. The Large Binocular Telescope (LBT) is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia. We acknowledge the support from the LBT-Italian Coordination Facility for the execution of observations, data distribution, and reduction. We thank Gianni Zamorani, Marco Mignoli, and Francesco Calura for useful discussions. This work utilizes gravitational lensing models produced by PIs Bradac, Ebeling, Zitrin & Merten, Sharon, and Williams funded as part of the HST Frontier Fields program conducted by STScI. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. The lens models were obtained from the Mikulski Archive for Space Telescopes (MAST). Support for A.Z. is provided by NASA through Hubble Fellowship grant #HST-HF-51334.01-A awarded by STScI. A.F. acknowledges the contribution of the EC FP7 SPACE project ASTRODEEP (Ref. No: 312725). L.I. is partially supported by CATA-Basal, Conicyt. We acknowledge financial contribution from PRIN-INAF-2010 and PRIN-INAF-2012.
Funding AgencyGrant Number
Hubble Space TelescopeUNSPECIFIED
NASANAS 5-26555
NASA Hubble FellowshipHST-HF-51334.01-A
European Research Council (ERC)312725 ASTRODEEP
BASAL Center for Astrophysics and Associated Technologies (CATA)UNSPECIFIED
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)UNSPECIFIED
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Subject Keywords:cosmology: observations, dark ages, reionization, first stars, galaxies: formation
Issue or Number:1
Record Number:CaltechAUTHORS:20140429-083728610
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Official Citation:Characterizing Faint Galaxies in the Reionization Epoch: LBT Confirms Two L < 0.2 L Sources at z = 6.4 Behind the CLASH/Frontier Fields Cluster MACS0717.5+3745 E. Vanzella et al. 2014 ApJ 783 L12
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45269
Deposited By: Ruth Sustaita
Deposited On:29 Apr 2014 17:23
Last Modified:10 Nov 2021 17:02

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