Faint Lyman-α (Lyα) emitters become increasingly rarer towards the re-ionisation epoch (z ∼ 6−7). However, observations from a very large (∼ 5 deg 2 ) Lyα narrow-band survey at z = 6.6 (Matthee et al. 2015) show that this is not the case for the most luminous emitters, capable of ionising their own local bubbles. Here we present follow-up observations of the two most luminous Lyα candidates in the COSMOS field: 'MASOSA' and 'CR7'. We used X-SHOOTER, SINFONI and FORS2 on the VLT, and DEIMOS on Keck, to confirm both candidates beyond any doubt. We find redshifts of z = 6.541 and z = 6.604 for 'MASOSA' and 'CR7', respectively. MASOSA has a strong detection in Lyα with a line width of 386 ± 30 km s −1 (FWHM) and with very high EW 0 (> 200Å), but undetected in the continuum, implying very low stellar mass and a likely young, metal-poor stellar population. 'CR7', with an observed Lyα luminosity of 10 43.92±0.05 erg s −1 is the most luminous Lyα emitter ever found at z > 6 and is spatially extended (∼ 16 kpc). 'CR7' reveals a narrow Lyα line with 266 ± 15 km s −1 FWHM, being detected in the NIR (rest-frame UV; β = −2.3 ± 0.1) and in IRAC/Spitzer. We detect a narrow HeII1640Å emission line (6σ, FWHM = 130±30 km s −1 ) in CR7 which can explain the clear excess seen in the J band photometry (EW 0 ∼ 80Å). We find no other emission lines from the UV to the NIR in our X-SHOOTER spectra (HeII/OIII]1663Å > 3 and HeII/CIII]1908Å > 2.5). We conclude that CR7 is best explained by a combination of a PopIII-like population which dominates the rest-frame UV and the nebular emission and a more normal stellar population which presumably dominates the mass. HST/WFC3 observations show that the light is indeed spatially separated between a very blue component, coincident with Lyα and HeII emission, and two red components (∼ 5 kpc away), which dominate the mass. Our findings are consistent with theoretical predictions of a PopIII wave, with PopIII star formation migrating away from the original sites of star formation.
We present the ancillary data and basic physical measurements for the galaxies in the ALMA Large Program to Investigate C + at Early Times (ALPINE) survey − the first large multi-wavelength survey which aims at characterizing the gas and dust properties of 118 main-sequence galaxies at redshifts 2 Faisst et al. 4.4 < z < 5.9 via the measurement of [C II] emission at 158 µm and the surrounding far-infrared (FIR) continuum in conjunction with a wealth of optical and near-infrared data. We outline in detail the spectroscopic data and selection of the galaxies as well as the ground-and space-based imaging products. In addition, we provide several basic measurements including stellar masses, star formation rates (SFR), rest-frame ultra-violet (UV) luminosities, UV continuum slopes (β), and absorption line redshifts, as well as Hα emission derived from Spitzer colors. Overall, we find that the ALPINE sample is representative of the 4 < z < 6 galaxy population and only slightly biased towards bluer colors (∆β ∼ 0.2). Using [C II] as tracer of the systemic redshift (confirmed for one galaxy at z = 4.5 for which we obtained optical [O II]λ3727 µm emission), we confirm red shifted Lyα emission and blue shifted absorption lines similar to findings at lower redshifts. By stacking the rest-frame UV spectra in the [C II] rest-frame we find that the absorption lines in galaxies with high specific SFR are more blue shifted, which could be indicative of stronger winds and outflows.
We present an analysis of 15 Type Ia supernovae (SNe Ia) at redshift > z 1 (9 at < < z 1.5 2.3) recently discovered in the CANDELS and CLASH Multi-Cycle Treasury programs using WFC3 on the Hubble Space Telescope. We combine these SNeIa with a new compilation of ∼1050 SNeIa, jointly calibrated and corrected for simulated survey biases to produce accurate distance measurements. We present unbiased constraints on the expansion rate at six redshifts in the range < < z 0.07 1.5 based only on this combined SNIa sample. The added leverage of our new sample at > z 1.5 leads to a factor of ∼3 improvement in the determination of the expansion rate at z=1.5, reducing its uncertainty to ∼20%, a measurement of2.69 0 0.52 0.86 . We then demonstrate that these six derived expansion rate measurements alone provide a nearly identical characterization of dark energy as the full SN sample, making them an efficient compression of the SNIa data. The new sample of SNeIa at > z 1.5 usefully distinguishes between alternative cosmological models and unmodeled evolution of the SNIa distance indicators, placing empirical limits on the latter. Finally, employing a realistic simulation of a potential Wide-Field Infrared Survey Telescope SN survey observing strategy, we forecast optimistic future constraints on the expansion rate from SNeIa.
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