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

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Abstract

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 (US)
Article number56
JournalAstrophysical Journal
Volume768
Issue number1
DOIs
StatePublished - May 1 2013

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Tilvi, V., Papovich, C., Tran, K. V. H., Labbé, I., Spitler, L. R., Straatman, C. M. S., Persson, S. E., Monson, A., Glazebrook, K., Quadri, R. F., Van Dokkum, P., Ashby, M. L. N., Faber, S. M., Fazio, G. G., Finkelstein, S. L., Ferguson, H. C., Grogin, N. A., Kacprzak, G. G., Kelson, D. D., ... Willner, S. P. (2013). Discovery of Lyman break galaxies at z ∼ 7 from the zFourGE survey. Astrophysical Journal, 768(1), [56]. https://doi.org/10.1088/0004-637X/768/1/56