An overdensity of Lyα emitters at redshift z ≈ 5.7 near the Hubble Ultra Deep Field

We have identified an obvious and strong large-scale structure at redshift z approximate to 5.75 in a wide (31' x 33') field, narrowband survey of the Chandra Deep Field-South region. This structure is traced by 17 candidate Ly alpha emitters, among which 12 are found in an 823 nm filter (corresponding to Lya at z = 5.77 +/- 0.03) and five in an 815 nm image (z = 5.70 +/- 0.03). The Ly alpha emitters in both redshift bins are concentrated in one quadrant of the field. The Hubble Ultra Deep Field, the Chandra Deep Field-South, and the Great Observatories Origins Deep Survey-South fields all lie near the edge of this overdensity region. Our results are consistent with reports of an overdensity in the Ultra Deep Field region at z approximate to 5.9. This structure is the highest redshift overdensity found so far.