V. Tilvi, C. Papovich, K. -V. H. Tran, I. Labbe, L. R. Spitler, C. M. S. Straatman, S. E. Persson, A. Monson, K. Glazebrook, R. F. Quadri, P. van Dokkum, M. L. N. Ashby, S. M. Faber, G. G. Fazio, S. L. Finkelstein, H. C. Ferguson, N. A. Grogin, G. G. Kacprzak, D. D. Kelson, A. M. Koekemoer, D. Murphy, P. J. McCarthy, J. A. Newman, B. Salmon, S. P. Willner
Star-forming galaxies at redshifts z>6 are likely responsible for the reionization of the universe, and it is important to study the nature of these galaxies. We present three candidates for z~7 Lyman-break galaxies (LBGs) from a 155 arcmin^2 area in the CANDELS/COSMOS field imaged by the deep FourStar Galaxy Evolution (zFourGE) survey. The FourStar medium-band filters provide the equivalent of R~10 spectroscopy, which cleanly distinguishes between z~7 LBGs and brown dwarf stars. The distinction between stars and galaxies based on an object's angular size can become unreliable even when using HST imaging; there exists at least one very compact z~7 candidate (FWHM~0.5-1 kpc) that is indistinguishable from a point source. The medium-band filters provide narrower redshift distributions compared with broad-band-derived redshifts. The UV luminosity function derived using the three z~7 candidates is consistent with previous studies, suggesting an evolution at the bright end (MUV -21.6 mag) from z~7 to z~5. Fitting the galaxies' spectral energy distributions, we predict Lyman-alpha equivalent widths for the two brightest LBGs, and find that the presence of a Lyman-alpha line affects the medium-band flux thereby changing the constraints on stellar masses and UV spectral slopes. This illustrates the limitations of deriving LBG properties using only broad-band photometry. The derived specific star-formation rates for the bright LBGs are ~13 per Gyr, slightly higher than the lower-luminosity LBGs, implying that the star-formation rate increases with stellar mass for these galaxies.
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http://arxiv.org/abs/1304.4227
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