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Title: 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

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 {sub 1500}) ≳ 10 and S/N(Lyα) ≅ 10-15. Adopting μ > 5, the absolute magnitudes, M {sub 1500}, and Lyα fluxes are fainter than –18.7 and 2.8 × 10{sup –18} erg s{sup –1} cm{sup –2}, respectively. We find a very steep ultraviolet spectral slope β = –3.0 ± 0.5 (F {sub λ} = λ{sup β}), implying that these are very young, dust-free, and low metallicity objects, made of standard stellar populations or even extremely metal poormore » stars (age ≲ 30 Myr, E(B – V) = 0 and metallicity 0.0-0.2 Z/Z {sub ☉}). The objects are compact (<1 kpc{sup 2}) and with a stellar mass M {sub *} < 10{sup 8} M {sub ☉}. The very steep β, the presence of the Lyα line, and the intrinsic FWHM (<300 km s{sup –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.« less
Authors:
;  [1] ; ; ; ; ;  [2] ;  [3] ; ; ;  [4] ;  [5] ;  [6] ; ;  [7] ; ;  [8] ;  [9] ;  [10] ;  [11] more »; « less
  1. INAF-Bologna Astronomical Observatory, via Ranzani 1, I-40127 Bologna (Italy)
  2. INAF-Rome Astronomical Observatory, Via Frascati 33, I-00040 Monteporzio Roma (Italy)
  3. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, MS 249-17, Pasadena, CA 91125 (United States)
  4. STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
  5. Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
  6. Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, via Saragat 1, I-44122 Ferrara (Italy)
  7. INAF, Astronomical Observatory of Trieste, via G.B. Tiepolo 11, I-34143 Trieste (Italy)
  8. Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)
  9. INFN, National Institute of Nuclear Physics, via Valerio 2, I-34127 Trieste (Italy)
  10. Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)
  11. Institute of Astrophysics, Pontificia Universidad Catolica de Chile, V. Mackenna 4860, 22 Santiago (Chile)
Publication Date:
OSTI Identifier:
22363956
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 783; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMIC DUST; COSMOLOGY; ENERGY SPECTRA; GALAXIES; GALAXY CLUSTERS; LENSES; LYMAN LINES; METALLICITY; STARS; ULTRAVIOLET RADIATION