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Optical Line Emission from z similar to 6.8 Sources with Deep Constraints on Ly alpha Visibility

Castellano, M., Pentericci, L., Fontana, A., Vanzella, E., Merlin, E., De Barros, S., Amorin, R., Caputi, K. I., Cristiani, S., Finkelstein, S. L., Giallongo, E., Grazian, A., Koekemoer, A., Maiolino, R., Paris, D., Pilo, S., Santini, P. & Yan, H., 20-Apr-2017, In : The Astrophysical Journal. 839, 2, 10 p., 73.

Research output: Contribution to journalArticleAcademicpeer-review

  • M. Castellano
  • L. Pentericci
  • A. Fontana
  • E. Vanzella
  • E. Merlin
  • S. De Barros
  • R. Amorin
  • K. I. Caputi
  • S. Cristiani
  • S. L. Finkelstein
  • E. Giallongo
  • A. Grazian
  • A. Koekemoer
  • R. Maiolino
  • D. Paris
  • S. Pilo
  • P. Santini
  • H. Yan

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 Ly alpha line. Deep IRAC observations at 3.6 and 4.5 mu m are used to determine the strength of optical emission lines affecting these bands at z similar to 6.5-6.9 in order to (1) investigate possible physical differences between Ly alpha 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]+H beta emission in the average (stacked) SEDs of galaxies both with and without Lya emission. The blue IRAC [3.6]-[4.5] color of the stack with detected Ly alpha line can be converted into a rest-frame equivalent width EW([O III]+ H beta) = 1500(-440) (+530) angstrom assuming a flat intrinsic stellar continuum. This strong optical line emission enables a first estimate of f(esc) less than or similar to 20% on the escape fraction of ionizing photons from Ly alpha detected objects. The objects with no Ly alpha line show less extreme EW([O III]+ H beta) = 520(-150)(+170) angstrom suggesting different physical conditions of the H II regions with respect to Ly alpha-emitting ones, or a larger f(esc). The latter case is consistent with a combined evolution of f(esc) and the. neutral hydrogen fraction as an. explanation of the lack of bright Lya emission at z > 6. A lower limit on the specific star formation rate, SSFR > 9.1 Gyr(-1) for M-star = 2 x 10(9) M-circle dot galaxies at these redshifts can be derived from the spectroscopically confirmed sample.

Original languageEnglish
Article number73
Number of pages10
JournalThe Astrophysical Journal
Volume839
Issue number2
Publication statusPublished - 20-Apr-2017

    Keywords

  • dark ages, reionization, first stars, galaxies: high-redshift, LYMAN BREAK GALAXIES, EXTRAGALACTIC LEGACY SURVEY, HUBBLE-SPACE-TELESCOPE, STAR-FORMATION RATE, IONIZING PHOTON ESCAPE, HIGH-REDSHIFT GALAXIES, BROAD-BAND PHOTOMETRY, SURVEY. SURVEY DESIGN, IRAC SOURCE COUNTS, GOODS-SOUTH FIELD

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