Physical properties of spectroscopically confirmed galaxies at Z ≥ 6. I. Basic characteristics of the rest-frame UV continuum and lyman-alpha emission
Date
2013Author
Jiang, Linhua
Egami, Eiichi
Mechtley, Matthew
Fan, Xiaohui
Cohen, Seth H.
Windhorst, Rogier A.
Dave, Romeel
Finlator, Kristian
Kashikawa, Nobunari
Ouchi, Masami
Shimasaku, Kazuhiro
Metadata
Show full item recordAbstract
We present deep HST near-IR and Spitzer mid-IR observations of a large sample of spectroscopically-
confirmed galaxies at z ≥ 6. The sample consists of 51 Ly-alpha 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 3.6μm and 4.5μm 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 ≃ −1.5 and –3.5, with an average
value of ≃ −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 ≃ −3, suggesting the existence of
very young stellar populations with extremely low metallicity and dust content. Our galaxies have
moderately strong rest-frame Ly equivalent width (EW) in a range of ∼10 to ∼200 °A. The star-
formation rates are also moderate, from a few to a few tens 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 Ly-alpha 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 Ly-alpha emission
(EW < 20 °A) that could be the dominant contribution to the total ionizing flux at z ≥ 6.