Discovery of a giant Lyα emitter near the reionization EPOCH

We report the discovery of a giant Lyα emitter (LAE) with a Spitzer/Infrared Array Camera (IRAC) counterpart near the reionization epoch at z = 6.595. The giant LAE is found from the extensive 1 deg² Subaru narrowband survey for z = 6.6 LAEs in the Subaru/XMM-Newton Deep Survey (SXDS) field, and subsequently identified by deep spectroscopy of Keck/DEIMOS and Magellan/IMACS. Among our 207 LAE candidates, this LAE is not only the brightest narrowband object with L(Lyα) = 3.9 ± 0.2 × 10⁴³ erg s^-1 in our survey volume of 10⁶ Mpc³, but also a spatially extended Lyα nebula with the largest isophotal area whose major axis is at least ≃3″. This object is more likely to be a large Lyα nebula with a size of ≳17 kpc than to be a strongly lensed galaxy by a foreground object. Our Keck spectrum with medium-high spectral and spatial resolutions suggests that the velocity width is v _FWHM = 251 ± 21 km s^-1, and that the line-center velocity changes by ≃60 km s^-1 in a 10 kpc range. The stellar mass and star formation rate are estimated to be 0.9-5.0 × 10¹⁰ M _⊙ and >34 M _⊙ yr^-1, respectively, from the combination of deep optical to infrared images of Subaru, UKIDSS-Ultra Deep Survey, and Spitzer/IRAC. Although the nature of this object is not yet clearly understood, this could be an important object for studying cooling clouds accreting onto a massive halo, or forming-massive galaxies with significant outflows contributing to cosmic reionization and metal enrichment of intergalactic medium.