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Large Area Survey for z=7 Galaxies in SDF and GOODS-N: Implications for Galaxy Formation and Cosmic Reionization
The Astrophysical Journal (2009)
  • Masami Ouchi
  • Bahram Mobasher
  • Kazuhiro Shimasaku
  • Henry C. Ferguson
  • S. Michael Fall
  • Yoshiaki Ono
  • Nobunari Kashikawa
  • Tomoki Morokuma
  • Kimihiko Nakajima
  • Sadanori Okamura
  • Mark Dickinson
  • Mauro Giavalisco, University of Massachusetts - Amherst
  • Kouji Ohta
We present results of our large-area survey for z'-band dropout galaxies at z=7 in a 1568 arcmin^2 sky area covering the SDF and GOODS-N fields. Combining our ultra-deep Subaru/Suprime-Cam z'- and y-band (lambda_eff=1um) images with legacy data of Subaru and HST, we have identified 22 bright z-dropout galaxies down to y=26, one of which has a spectroscopic redshift of z=6.96 determined from Lya emission. The z=7 luminosity function (LF) yields the best-fit Schechter parameters of phi*=0.69 +2.62/-0.55 x10^(-3) Mpc^(-3), Muv*=-20.10 +/-0.76 mag, and alpha=-1.72 +/-0.65, and indicates a decrease from z=6 at a >95% confidence level. This decrease is beyond the cosmic variance in our two fields, which is estimated to be a factor of <~2. We have found that the cosmic star formation rate density drops from the peak at z=2-3 to z=7 roughly by a factor of ~10 but not larger than ~100. A comparison with the reionization models suggests either that the Universe could not be totally ionized by only galaxies at z=7, or more likely that properties of galaxies at z=7 are different from those at low redshifts having, e.g., a larger escape fraction (>~0.2), and/or a flatter IMF. Our SDF z-dropout galaxies appear to form 60-Mpc long filamentary structures, and the z=6.96 galaxy with Lya emission is located at the center of an overdense region consisting of four UV bright dropout candidates, which might suggest an existence of a well-developed ionized bubble at z=7.
  • galaxies: formation,
  • galaxies: high-redshift,
  • cosmology: observations
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Publisher Statement
This paper was harvested from and ArXiv identifier is arXiv:0908.3191
Citation Information
Masami Ouchi, Bahram Mobasher, Kazuhiro Shimasaku, Henry C. Ferguson, et al.. "Large Area Survey for z=7 Galaxies in SDF and GOODS-N: Implications for Galaxy Formation and Cosmic Reionization" The Astrophysical Journal (2009)
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