Optical Line Emission from z ∼ 6.8 Sources with Deep Constraints on Lyα Visibility

Journal Article · Thu Apr 20 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA696E· OSTI ID:22872792

Castellano, M.; Pentericci, L.; Fontana, A.; Merlin, E.; Amorin, R.; Giallongo, E.; Grazian, A.; Paris, D.; Pilo, S.; Santini, P. ^[1]; Vanzella, E.; Barros, S. De ^[2]; Caputi, K. I. ^[3]; Cristiani, S. ^[4]; Finkelstein, S. L. ^[5]; Koekemoer, A. ^[6]; Maiolino, R. ^[7]

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1. INAF—Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone (RM) (Italy)
2. INAF—Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127, Bologna (Italy)
3. Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands)
4. INAF Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, I-34143, Trieste (Italy)
5. Department of Astronomy, The University of Texas at Austin, C1400, Austin, TX 78712 (United States)
6. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
7. Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

We analyze a sample of z-dropout galaxies in the CANDELS GOODS South and UDS fields that have been targeted by a dedicated spectroscopic campaign aimed at detecting their Lyα line. Deep IRAC observations at 3.6 and 4.5 μm are used to determine the strength of optical emission lines affecting these bands at z ∼ 6.5–6.9 in order to (1) investigate possible physical differences between Lyα emitting and non-emitting sources; (2) constrain the escape fraction of ionizing photons; and (3) provide an estimate of the specific star formation rate at high redshifts. We find evidence of strong [O iii]+Hβ emission in the average (stacked) SEDs of galaxies both with and without Lyα emission. The blue IRAC [3.6]–[4.5] color of the stack with detected Lyα line can be converted into a rest-frame equivalent width EW([O iii]+Hβ) = 1500{sub −440}{sup +530} Å assuming a flat intrinsic stellar continuum. This strong optical line emission enables a first estimate of f{sub esc}≲20% on the escape fraction of ionizing photons from Lyα detected objects. The objects with no Lyα line show less extreme EW([O iii]+Hβ) = 520{sub −150}{sup +170} Å, suggesting different physical conditions of the H ii regions with respect to Lyα-emitting ones, or a larger f{sub esc}. The latter case is consistent with a combined evolution of f{sub esc} and the neutral hydrogen fraction as an explanation of the lack of bright Lyα emission at z > 6. A lower limit on the specific star formation rate, SSFR > 9.1 Gyr{sup −1} for M{sub star}=2×10{sup 9} M{sub ⊙} galaxies at these redshifts can be derived from the spectroscopically confirmed sample.

• OSTI ID: 22872792
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 839; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
EMISSION
GALAXIES
HYDROGEN
LYMAN LINES
PHOTONS
RED SHIFT
STARS