A Spectral Atlas of Lyα Emitters at z = 5.7 and z = 6.6

Abstract

We present two uniformly observed spectroscopic samples of Ly α emitters (LAEs; 127 at z = 5.7 and 82 at z = 6.6), which we use to investigate the evolution of the LAE population at these redshifts. The observations cover a large field (44 deg ^2 ) in the North Ecliptic Pole, as well as several smaller fields. We have a small number of exotic LAEs in the samples: double-peaked Ly α profiles; very extended red wings; and one impressive lensed LAE cross. We also find three broad-line active galactic nuclei. We compare the Ly α line width measurements at the two redshifts, finding that the lower-luminosity LAEs show a strong evolution of decreasing line width with increasing redshift, while the high-luminosity LAEs do not, with a transition luminosity of log L (Ly α ) ≈ 43.25 erg s ^−1 . Thus, at z = 6.6, the high-luminosity LAEs may be producing large ionized bubbles themselves, or they may be residing in overdense galaxy sites that are producing such bubbles. In order to avoid losses in the red wing, the radius of the ionized bubble must be larger than 1 pMpc. The double-peaked LAEs also require transmission on the blue side. For the four at z = 6.6, we use models to estimate the proximity radii, R _a , where the ionizing flux of the galaxy is sufficient to make the surroundings have a low enough neutral fraction to pass the blue light. Since the required R _a are large, multiple ionizing sources in the vicinity may be needed.

Keywords

• Cosmological evolution
• Lyman-alpha galaxies
• Reionization