SPECTROSCOPIC CONFIRMATION OF z {approx} 7 LYMAN BREAK GALAXIES: PROBING THE EARLIEST GALAXIES AND THE EPOCH OF REIONIZATION

Journal Article · Tue Dec 20 04:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/743/2/132· OSTI ID:22004444

Pentericci, L; Fontana, A; Castellano, M; Grazian, A; Boutsia, K; Giallongo, E; Maiolino, R; Paris, D; Santini, P ^[1]; Vanzella, E; Cristiani, S ^[2]; Dijkstra, M ^[3]; Dickinson, M ^[4]; Giavalisco, M ^[5]; Moorwood, A ^[6]

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1. INAF Osservatorio Astronomico di Roma, Via Frascati 33,00040 Monteporzio (Italy)
2. INAF Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34131 Trieste (Italy)
3. Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching (Germany)
4. National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726 (United States)
5. Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States)
6. European Southern Observatory, Karl-Schwarzschild Strasse, 85748 Garching (Germany)

We present the final results from our ultra-deep spectroscopic campaign with FORS2 at the ESO Very Large Telescope (VLT) for the confirmation of z {approx_equal} 7 'z-band dropout' candidates selected from our VLT/Hawk-I imaging survey over three independent fields. In particular, we report on two newly discovered galaxies at redshift {approx}6.7 in the New Technology Telescope Deep Field. Both galaxies show an Ly{alpha} emission line with rest-frame equivalent widths (EWs) of the order of 15-20 A and luminosities of (2-4) Multiplication-Sign 10{sup 42} erg s{sup -1}. We also present the results of ultra-deep observations of a sample of i-dropout galaxies, from which we set a solid upper limit on the fraction of interlopers. Out of the 20 z-dropouts observed we confirm 5 galaxies at 6.6 < z < 7.1. This is systematically below the expectations drawn on the basis of lower redshift observations: in particular, there is a significant lack of objects with intermediate Ly{alpha} EWs (between 20 and 55 A). We conclude that the observed trend for the rising fraction of Ly{alpha} emission in Lyman break galaxies from z {approx} 3 to z {approx} 6 is most probably reversed from z {approx} 6 to z {approx} 7. Explaining the observed rapid change in the Ly{alpha} emitter fraction among the dropout population with reionization requires a fast evolution of the neutral fraction of hydrogen in the universe. Assuming that the universe is completely ionized at z = 6 and adopting a set of semi-analytical models, we find that our data require a change of the neutral hydrogen fraction of the order of {Delta}{chi}{sub H{sub i}}{approx}0.6 in a time {Delta}z {approx} 1, provided that the escape fraction does not increase dramatically over the same redshift interval.

• OSTI ID: 22004444
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 743; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
GALACTIC EVOLUTION
GALAXIES
HYDROGEN
LUMINOSITY
RED SHIFT
TELESCOPES
UNIVERSE