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 Lyalpha emitters (LAEs) at z = 4.86 +/- 0.03 with a projected size of 20 h(70)(-1) Mpc x 50 h(70)(-1) Mpc in narrowband data of a 25' x 45' area of the Subaru Deep Field (Ohm(0) = 0.3, lambda(0) = 0.7, and H-0 = 70 h(70) km s(-1) Mpc(-1)). However, the surveyed area, which corresponds to 55 h(70)(-1) Mpc, was not large enough to conclude that what we were seeing was a typical distribution of z similar or equal to 5 LAEs. In this Letter, we report the results of follow-up imaging of the same sky area using a new narrowband filter (NB704, lambda(c) = 7046 Angstrom and FWHM = 100 Angstrom) to detect LAEs at z = 4.79, i.e., LAEs lying closer to us by 39 h(70)(-1) 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 fun tion are thus largely different between the two samples. The results demonstrate a large cosmic variance in the clustering properties of LAEs on scales of similar to50 h(70)(-1) Mpc.