Large Cosmic Variance in the Clustering Properties of Lyα Emitters at z ≃ 5

We reported in a previous paper the discovery of a large-scale structure of Lyα emitters (LAEs) at z = 4.86 ± 0.03 with a projected size of 20 h Mpc × 50 h Mpc in narrowband data of a 25′ × 45′ area of the Subaru Deep Field (Ω0 = 0.3, λ0 = 0.7, and H0 = 70 h70 km s-1 Mpc-1). However, the surveyed area, which corresponds to 55 h Mpc × 100 h Mpc, was not large enough to conclude that what we were seeing was a typical distribution of z ≃ 5 LAEs. In this Letter, we report the results of follow-up imaging of the same sky area using a new narrowband filter (NB704, λc = 7046 Å and FWHM = 100 Å) to detect LAEs at z = 4.79, i.e., LAEs lying closer to us by 39 h Mpc on average than the z = 4.86 objects. We detect 51 LAEs at z = 4.79 ± 0.04 down to NB704 = 25.7, and we find that their sky distribution is quite different from the z = 4.86 LAEs'. The clustering of z = 4.79 LAEs is very weak on any scale, and there is no large-scale high-contrast structure. The shape and the amplitude of the angular correlation function are thus largely different between the two samples. These results demonstrate a large cosmic variance in the clustering properties of LAEs on scales of ~50 h Mpc.