Evidence against a redshift z > 6 for the galaxy STIS123627+621755

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Abstract

The identification of galaxies at extreme distances provides the most direct information about the earliest phases of galaxy formation. But at redshifts z > 5 even the most luminous galaxies appear faint; the interpretation of low signal-to-noise ratio data is difficult and misidentifications do occur. Here we report optical and near-infrared observations of the source STIS123627+621755, which was previously suggested to be at a redshift of 6.68 (ref. 1). At that redshift, and with the reported1 spectral energy distribution, the galaxy should be essentially invisible at wavelengths less than 9,300 Å, because the intervening intergalactic medium absorbs almost all light energetic enough to ionize neutral hydrogen—that is, with wavelengths less than the redshifted Lyman limit of λ = (1 + z) × 912 Å. At near-infrared wavelengths, however, the galaxy should be relatively bright. Here we report a detection of the galaxy at 6,700 Å and a non-detection at a wavelength of 1.2 µm, contrary to expectations for z ≈ 6.68. The data conservatively require that STIS123627+621755 has a redshift z < 6.

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Figure 1: Imaging of STIS123627+621755 showing that the galaxy is detected at R, below the Lyman limit if z = 6.68.
Figure 2: The photometric detection of STIS123627+621755 at 6,700 Å is not consistent with z > 6.

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Acknowledgements

We acknowledge H. W. Chen and K. Lanzetta, who have been generous with information and supportive of our follow-up efforts on this intriguing source. We thank J. Gardner and J. Bloom for comments on the STIS data. We thank the staff of Keck Observatory for their help in obtaining the data. The W.M. Keck Observatory is operated as a scientific partnership among the University of California, the California Institute of Technology, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. We especially thank G. Punawai and X. Jerome for their assistance during the observing runs. The work of D.S. and P.E. were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. The work of W.v.B. and W.d.V. at the Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory was performed under the auspices of the US Department of Energy by University of California Lawrence Livermore National Laboratory. This work has been supported by a grant from the NSF (H.S.).

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Correspondence to Daniel Stern.

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