THE LACK OF INTENSE Ly{alpha} IN ULTRADEEP SPECTRA OF z = 7 CANDIDATES IN GOODS-S: IMPRINT OF REIONIZATION?
- INAF Osservatorio Astronomico di Roma, Via Frascati 33000 40 Monteporzio (Italy)
- INAF Osservatorio Astronomico di Trieste, Via G.B.Tiepolo 11, 34131 Trieste (Italy)
- Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States)
- National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726 (United States)
- European Southern Observatory, Karl-Schwarzschild Strasse, 85748 Garching bei Munchen (Germany)
We present ultradeep optical spectroscopy obtained with FORS2 on the Very Large Telescope (VLT) of seven Lyman-break galaxy (LBG) candidates at z>6.5 selected in the GOODS-S field from Hawk-I/VLT and WFC3/HST imaging. For one galaxy we detect a low significance emission line (S/N {<=} 7), located at {lambda} = 9691.5 {+-} 0.5 A and with flux 3.4 x 10{sup -18} erg cm{sup -2} s{sup -1}. If identified as Ly{alpha}, it places the LBG at redshift z = 6.972 {+-} 0.002, with a rest-frame equivalent width EW{sub rf} = 13 A. Using Monte Carlo simulations and conservative EW distribution functions at 2 < z < 6, we estimate that the probability of observing no galaxies in our data with S/N>10 is {approx_equal}2%, and that of observing only one galaxy out of seven with S/N = 5 is {approx_equal}4%, but these can be as small as {approx}10{sup -3}, depending on the details of the EW distribution. We conclude that either a significant fraction of the candidates is not at high redshift or that some physical mechanism quenches the Ly{alpha} emission emerging from the galaxies at z>6.5, abruptly reversing the trend of the increasing fraction of strong emitters with increasing redshift observed up to z {approx} 6.5. We discuss the possibility that an increasingly neutral intergalactic medium is responsible for such quenching.
- OSTI ID:
- 21454870
- Journal Information:
- Astrophysical Journal Letters, Vol. 725, Issue 2; Other Information: DOI: 10.1088/2041-8205/725/2/L205; ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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