The whole picture of the large-scale structure of the CL1604
  supercluster at z$\sim$0.9
  We present the large-scale structure over more than 50 comoving Mpc scale at
z $\sim$ 0.9 where the CL1604 supercluster, which is one of the largest
structures ever known at high redshifts, is embedded. The wide-field deep
imaging survey by the Subaru Strategic Program with Hyper Suprime-Cam reveals
that the already-known CL1604 supercluster is a mere part of larger-scale
structure extending to both the north and the south. We confirm that there are
galaxy clusters at three slightly different redshifts in the northern and
southern sides of the supercluster by determining the redshifts of 55
red-sequence galaxies and 82 star-forming galaxies in total by the follow-up
spectroscopy with Subaru/FOCAS and Gemini-N/GMOS. This suggests that the
structure ever known as the CL1604 supercluster is the tip of the iceberg. We
investigate stellar population of the red-sequence galaxies using 4000 A break
and Balmer H$\delta$ absorption line. Almost all of the red-sequence galaxies
brighter than 21.5 mag in $z$-band show an old stellar population with
$\gtrsim2$ Gyr. The comparison of composite spectra of the red-sequence
galaxies in the individual clusters show that the galaxies at a similar
redshift have similar stellar population age, even if they are located $\sim$50
Mpc apart from each other. However, there could be a large variation in the
star formation history. Therefore, it is likely that galaxies associated with
the large-scale structure at 50 Mpc scale formed at almost the same time, have
assembled into the denser regions, and then have evolved with different star
formation history along the hierarchical growth of the cosmic web.
