Himiko

The angular size of the Lyα nebula is ≥ 17 proper kpc
(§3.2), which is comparable to the diameter of the stellar
disk of the present-day Milky Way. It is impressive, if we
consider that the age of the Universe at z = 6.595 is only
6% of the one of the present-day Universe. Moreover,
such an extended Lyα source is very rare in the cosmological
volume only with the number density of 1.2×10⁻⁶
comoving Mpc⁻³ at z = 6.6 (§2.2). If our selection of
large Lyα nebula does not miss a significant fraction of
massive galaxies at this early epoch (z = 6.6), our object
could be an ancestor of a bright-cluster or cD galaxy, and
should be a good laboratory of massive-galaxy formation
near the reionization epoch.