LARGE AREA SURVEY FOR z = 7 GALAXIES IN SDF AND GOODS-N: IMPLICATIONS FOR GALAXY FORMATION AND COSMIC REIONIZATION
- Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
- Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States)
- Department of Astronomy, School of Science, University of Tokyo, Tokyo 113-0033 (Japan)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan)
- NOAO, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States)
- Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
- Department of Astronomy, Kyoto University, Kyoto 606-8502 (Japan)
We present results of our large area survey for z'-band dropout galaxies at z = 7 in a 1568 arcmin{sup 2} sky area covering the SDF and GOODS-N fields. Combining our ultra-deep Subaru/Suprime-Cam z'- and y-band (lambda{sub eff} = 1 mum) images with legacy data of Subaru and Hubble Space Telescope, 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 Lyalpha emission. The z = 7 luminosity function yields the best-fit Schechter parameters of phi* = 0.69{sup +2.62}{sub -0.55} x 10{sup -3} Mpc{sup -3}, M*{sub UV} = -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 approx<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 approx10 but not larger than approx100. 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 (approx>0.2), a lower metallicity, and/or a flatter initial mass function. Our SDF z-dropout galaxies appear to form 60 Mpc long filamentary structures, and the z = 6.96 galaxy with Lyalpha 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.
- OSTI ID:
- 21378109
- Journal Information:
- Astrophysical Journal, Vol. 706, Issue 2; Other Information: DOI: 10.1088/0004-637X/706/2/1136; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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