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

Journal Article · Sat Mar 01 00:00:00 EST 2014 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/783/1/L12· OSTI ID:22363956

Vanzella, E.; Cusano, F. ^[1]; Fontana, A.; Grazian, A.; Castellano, M.; Pentericci, L.; Giallongo, E. ^[2]; Zitrin, A. ^[3]; Coe, D.; Bradley, L.; Postman, M. ^[4]; Giavalisco, M. ^[5]; Rosati, P. ^[6]; Nonino, M.; Cristiani, S. ^[7]; Smit, R.; Bouwens, R. ^[8]; Balestra, I. ^[9]; Zheng, W. ^[10]; Infante, L. ^[11] ; others, and

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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)

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 poor 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.

• OSTI ID: 22363956
• Journal Information: Astrophysical Journal Letters, Vol. 783, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COSMIC DUST
COSMOLOGY
ENERGY SPECTRA
GALAXIES
GALAXY CLUSTERS
LENSES
LYMAN LINES
METALLICITY
STARS
ULTRAVIOLET RADIATION