2018MNRAS.479..435M

We present a detailed study of an unusually bright, lensed galaxy at z = 5.424 discovered within the CFHTLS imaging survey. With an observed flux of i_AB = 23.0, J141446.82+544631.9 is one of the brightest galaxies known at z > 5. It is characterized by strong Ly α emission, reaching a peak in (observed) flux density of >10^–16erg s^–1 cm^–2Å^–1. A deep optical spectrum from the Large Binocular Telescope places strong constraints on N V and C IV emission, disfavouring an Active Galactic Nucleus (AGN) source for the emission. However, a detection of the N IV] λ1486 emission line indicates a hard ionizing continuum, possibly from hot, massive stars. Resolved imaging from HST deblends the galaxy from a foreground interloper; these observations include narrowband imaging of the Ly α emission, which is marginally resolved on approximately few kpc scales and has EW₀ ∼ 260 Å. The Ly α emission extends over ∼2000 km s^–1 and is broadly consistent with expanding shell models. Spectral energy distribution fitting that includes Spitzer/IRAC photometry suggests a complex star formation history that includes both a recent burst and an evolved population. J1414+5446 lies 30 arcsec from the centre of a known lensing cluster in the CFHTLS; combined with the foreground contribution, this leads to a highly uncertain estimate for the lensing magnification in the range 5 <= µ <= 25. Because of its unusual brightness, J1414+5446 affords unique opportunities for detailed study of an individual galaxy near the epoch of re-ionization and a preview of what can be expected from upcoming wide-area surveys that will yield hundreds of similar objects.