Physical properties of spectroscopically confirmed galaxies at z ≥ 6. I. basic characteristics of the rest-frame UV continuum and Lyα emission

Linhua Jiang, Eiichi Egami, Matthew Mechtley, Xiaohui Fan, Seth H. Cohen, Rogier A. Windhorst, Romeel Davé, Kristian Finlator, Nobunari Kashikawa, Masami Ouchi, Kazuhiro Shimasaku

Research output: Contribution to journalArticlepeer-review

60 Scopus citations


We present deep Hubble Space Telescope near-IR and Spitzer mid-IR observations of a large sample of spectroscopically confirmed galaxies at z ≥ 6. The sample consists of 51 Lyα emitters (LAEs) at z ≃ 5.7, 6.5, and 7.0, and 16 Lyman break galaxies (LBGs) at 5.9 ≤ z ≤ 6.5. The near-IR images were mostly obtained with WFC3 in the F125W and F160W bands, and the mid-IR images were obtained with IRAC in the 3.6 μm and 4.5 μm bands. Our galaxies also have deep optical imaging data from Subaru Suprime-Cam. We utilize the multi-band data and secure redshifts to derive their rest-frame UV properties. These galaxies have steep UV-continuum slopes roughly between β ≃ -1.5 and -3.5, with an average value of β ≃ -2.3, slightly steeper than the slopes of LBGs in previous studies. The slope shows little dependence on UV-continuum luminosity except for a few of the brightest galaxies. We find a statistically significant excess of galaxies with slopes around β ≃ -3, suggesting the existence of very young stellar populations with extremely low metallicity and dust content. Our galaxies have moderately strong rest-frame Lyα equivalent width (EW) in a range of ∼10 to ∼200 Å. The star formation rates are also moderate, from a few to a few tens of solar masses per year. The LAEs and LBGs in this sample share many common properties, implying that LAEs represent a subset of LBGs with strong Lyα emission. Finally, the comparison of the UV luminosity functions between LAEs and LBGs suggests that there exists a substantial population of faint galaxies with weak Lyα emission (EW < 20 Å) that could be the dominant contribution to the total ionizing flux at z ≥ 6.

Original languageEnglish (US)
Article number99
JournalAstrophysical Journal
Issue number2
StatePublished - Aug 1 2013


  • cosmology: observations
  • galaxies: evolution
  • galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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