Browsing by Author "Fan, Xiaohui"
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Item Physical properties of spectroscopically confirmed galaxies at Z ≥ 6. I. Basic characteristics of the rest-frame UV continuum and lyman-alpha emission(American Astronomical Society, 2013) Jiang, Linhua; Egami, Eiichi; Mechtley, Matthew; Fan, Xiaohui; Cohen, Seth H.; Windhorst, Rogier A.; Dave, Romeel; Finlator, Kristian; Kashikawa, Nobunari; Ouchi, Masami; Shimasaku, KazuhiroWe 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.Item Physical properties of spectroscopically-confirmed galaxies at z >= 6. II. Morphology of the rest-frame UV continuum and Lyman-alpha emission(IOP Science, 2013) Jiang, Linhua; Egami, Eiichi; Fan, Xiaohui; Dave, RomeelWe present a detailed structural and morphological study of a large sample of spectroscopicallyconfirmed galaxies at z ≥ 6, using deep HST near-IR broad-band images and Subaru optical narrowband images. The galaxy sample consists of 51 Ly_ emitters (LAEs) at z ≃ 5.7, 6.5, and 7.0, and 16 Lyman-break galaxies (LBGs) at 5.9 ≤ z ≤ 6.5. These galaxies exhibit a wide range of restframe UV continuum morphology in the HST images, from compact features to multiple component systems. The fraction of merging/interacting galaxies reaches 40% ∼ 50% at the brightest end of M1500 ≤ −20.5 mag. The intrinsic half-light radii rhl,in, after correction for PSF broadening, are roughly between rhl,in ≃ 0.′′05 (0.3 kpc) and 0.′′3 (1.7 kpc) at M1500 ≤ −19.5 mag. The median rhl,in value is 0.′′16 (∼0.9 kpc). This is consistent with the sizes of bright LAEs and LBGs at z ≥ 6 in previous studies. In addition, more luminous galaxies tend to have larger sizes, exhibiting a weak size-luminosity relation rhl,in ∝ L0.14 at M1500 ≤ −19.5 mag. The slope of 0.14 is significantly flatter than those in fainter LBG samples. We discuss the morphology of z ≥ 6 galaxies with nonparametric methods, including the CAS system and the Gini and M20 parameters, and demonstrate their validity through simulations. We search for extended Ly_ emission halos around LAEs at z ≃ 5.7 and 6.5, by stacking a number of narrow-band images. We do not find evidence of extended halos predicted by cosmological simulations. Such Ly_ halos, if they exist, could be weaker than predicted. Finally, we investigate any positional misalignment between UV continuum and Ly_ emission in LAEs. While the two positions are generally consistent, several merging galaxies show significant positional differences. This is likely caused by a disturbed ISM distribution due to merging activity.