SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844-7.213: DEMOGRAPHICS OF Ly{alpha} EMISSION IN z {approx} 7 GALAXIES

Journal Article · Tue Jan 10 04:00:00 EST 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/744/2/83· OSTI ID:22004298

Ono, Yoshiaki; Shimasaku, Kazuhiro; Nakajima, Kimihiko ^[1]; Ouchi, Masami ^[2]; Mobasher, Bahram; Nayyeri, Hooshang ^[3]; Dickinson, Mark; Kartaltepe, Jeyhan S ^[4]; Penner, Kyle ^[5]; Weiner, Benjamin J ^[6]; Stern, Daniel ^[7]; Kashikawa, Nobunari ^[8]; Spinrad, Hyron ^[9]

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1. Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo 113-0033 (Japan)
2. Institute for Cosmic Ray Research, University of Tokyo, Kashiwa 277-8582 (Japan)
3. Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States)
4. National Optical Astronomical Observatories, Tucson, AZ 85719 (United States)
5. Department of Astronomy, University of Arizona, Tucson, AZ 85721 (United States)
6. Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
7. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
8. Optical and Infrared Astronomy Division, National Astronomical Observatory of Japan, Tokyo 181-8588 (Japan)
9. Department of Astronomy, University of California, Berkeley, CA 94720 (United States)

We present the results of our ultra-deep Keck/DEIMOS spectroscopy of z-dropout galaxies in the Subaru Deep Field and Great Observatories Origins Deep Survey's northern field. For 3 out of 11 objects, we detect an emission line at {approx}1 {mu}m with a signal-to-noise ratio of {approx}10. The lines show asymmetric profiles with high weighted skewness values, consistent with being Ly{alpha}, yielding redshifts of z = 7.213, 6.965, and 6.844. Specifically, we confirm the z = 7.213 object in two independent DEIMOS runs with different spectroscopic configurations. The z = 6.965 object is a known Ly{alpha} emitter, IOK-1, for which our improved spectrum at a higher resolution yields a robust skewness measurement. The three z-dropouts have Ly{alpha} fluxes of 3 Multiplication-Sign 10{sup -17} erg s{sup -1} cm{sup -2} and rest-frame equivalent widths EW{sup Ly{alpha}}{sub 0} = 33-43 A. Based on the largest spectroscopic sample of 43 z-dropouts, which is the combination of our and previous data, we find that the fraction of Ly{alpha}-emitting galaxies (EW{sup Ly{alpha}}{sub 0} > 25 A) is low at z {approx} 7; 17% {+-} 10% and 24% {+-} 12% for bright (M{sub UV} {approx_equal} -21) and faint (M{sub UV} {approx_equal} -19.5) galaxies, respectively. The fractions of Ly{alpha}-emitting galaxies drop from z {approx} 6 to 7 and the amplitude of the drop is larger for faint galaxies than for bright galaxies. These two pieces of evidence would indicate that the neutral hydrogen fraction of the intergalactic medium increases from z {approx} 6 to 7 and that the reionization proceeds from high- to low-density environments, as suggested by an inside-out reionization model.

• OSTI ID: 22004298
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 744; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COSMOLOGY
EMISSION
GALACTIC EVOLUTION
GALAXIES
HYDROGEN
ORIGIN
RED SHIFT
SIGNAL-TO-NOISE RATIO
SPECTRA
SPECTROSCOPY