Discovery of Lyman break galaxies at z ∼ 7 from the zFourGE survey

V. Tilvi*, C. Papovich, K. V H Tran, I. Labbé, 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. KoekemoerD. Murphy, P. J. McCarthy, J. A. Newman, B. Salmon, S. P. Willner

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

39 Citations (Scopus)


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 arcmin2 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 Hubble Space Telescope 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 broadband-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 (M UV ∼ -21.6 mag) from z ∼ 7 to z ∼ 5. Fitting the galaxies' spectral energy distributions, we predict Lyα equivalent widths for the two brightest LBGs, and find that the presence of a Lyα 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 broadband photometry. The derived specific star-formation rates for the bright LBGs are ∼13 Gyr-1, slightly higher than the lower-luminosity LBGs, implying that the star-formation rate increases with stellar mass for these galaxies.

Original languageEnglish
Article number56
Pages (from-to)1-17
Number of pages17
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 1 May 2013
Externally publishedYes


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