The Discovery of Primeval Large-Scale Structures with Forming Clusters at Redshift 6

Abstract

We report the discovery of primeval large-scale structures (LSSs) including two protoclusters in a forming phase at z = 5.7. We carried out extensive deep narrowband imaging in the 1 deg2 sky of the Subaru/XMM-Newton Deep Field and obtained a cosmic map of 515 Lyα emitters (LAEs) in a volume with a transverse dimension of 180 Mpc × 180 Mpc and a depth of ~40 Mpc in comoving units. This cosmic map shows filamentary LSSs, including clusters and surrounding 10-40 Mpc scale voids, similar to the present-day LSSs. Our spectroscopic follow-up observations identify overdense regions in which two dense clumps of LAEs with a sphere of 1 Mpc diameter in physical units are included. These clumps show about 130 times higher star formation rate density, mainly due to a large overdensity, ~80, of LAEs. These clumps would be clusters in a formation phase involving a burst of galaxy formation.