Three Lyα Emitters at z ≈ 6: Early GMOS/Gemini Data from the GLARE Project

We report spectroscopic detection of three z ~ 6 Lyα-emitting galaxies, in the vicinity of the Hubble Ultra Deep Field, from the early data of the Gemini Lyman Alpha at Reionisation Era (GLARE) project. Two objects, GLARE 3001 (z = 5.79) and GLARE 3011 (z = 5.94), are new detections and are fainter in z′ (z = 26.37 and 27.15) than any Lyman break galaxy previously detected in Lyα. A third object, GLARE 1042 (z = 5.83), has previously been detected in line emission from the ground; we report here a new spectroscopic continuum detection. Gemini/GMOS-South spectra of these objects, obtained using nod and shuffle, are presented together with a discussion of their photometric properties. All three objects were selected for spectroscopy via the i-drop Lyman break technique, the two new detections from the GOODS version 1.0 imaging data. The red i′-z′ colors and high equivalent widths of these objects suggest a high-confidence z > 5 Lyα identification of the emission lines. This brings the total number of known z > 5 galaxies within 9' of the Hubble Ultra Deep Field to four, of which three are at the same redshift (z = 5.8 within 2000 km s-1), suggesting the existence of a large-scale structure at this redshift.