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Near-Infrared Properties of I-Drop Galaxies in the Hubble Ultra Deep Field

Elizabeth Stanway·Richard McMahon·Andrew Bunker
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Abstract

We analyse near-infrared HST/NICMOS F110W (J) and F160W (H) band photometry of a sample of 27 i'-drop candidate z~6 galaxies in the central region of the HST/ACS Ultra Deep Field (HUDF). The infrared colours of the 20 objects not affected by near neighbours are consistent with a high redshift interpretation. This suggests that the low redshift contamination of this i'-drop sample is smaller than that observed at brighter magnitudes where values of 10-40% have been reported. The J-H colours are consistent with a slope flat in f_nu (f_lam \propto lam^{-2}), as would be expected for an unreddened starburst. There is, however, evidence for a marginally bluer spectral slope (f_lam propto lam^{-2.2) which is perhaps indicative of an extremely young starburst (~10 Myr old) or a top heavy initial mass function and little dust. The low levels of contamination, median photometric redshift of z~6.0 and blue spectral slope, inferred using the near-infrared data, supports the validity of the assumptions in our earlier work in estimating the star formation rates and, that the majority of the i-drop candidates galaxies lie at z~6.

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Elizabeth Stanway, Richard McMahon, Andrew Bunker. 2005-04-05. Near-Infrared Properties of I-Drop Galaxies in the Hubble Ultra Deep Field. https://doi.org/10.1111/j.1365-2966.2005.08977.x

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