A luminous Lyα-emitting galaxy at redshift z = 6.535: Discovery and spectroscopic confirmation

We present a redshift z = 6.535 galaxy discovered by its Lyα emission in a 9180 Å narrowband image from the Large Area Lyman Alpha survey. The Lyα line luminosity (1.1 × 10⁴³ ergs s^-1) is among the largest known for star-forming galaxies at z ≈ 6.5. The line shows the distinct asymmetry that is characteristic of high-redshift Lyα. The 2 σ lower bound on the observer-frame equivalent width is greater than 530 Å. This is hard to reconcile with a neutral intergalactic medium (IGM) unless the Lyα line is intrinsically strong and is emitted from its host galaxy with an intrinsic Doppler shift of several hundred km s^-1. If the IGM is ionized, it corresponds to a rest-frame equivalent width greater than 40 Å after correcting for Lyα forest absorption. We also present a complete spectroscopic follow-up of the remaining candidates with line flux greater than 2 × 10^-17 ergs cm^-2 s^-1 in our 1200 arcmin² narrowband image. These include another galaxy with a strong emission line at 9136 Å and no detected continuum flux, which, however, is most likely an [O III] λ5007 source at z = 0.824, on the basis of a weak detection of the [O III] λ4959 line.