# The whole picture of the large-scale structure of the CL1604 supercluster at z$\sim$0.9

## TL;DR

This study maps the extensive large-scale structure of the CL1604 supercluster at z~0.9, revealing it as part of a much larger network of galaxy clusters and analyzing the stellar populations of red-sequence galaxies within this structure.

## Contribution

It provides the first large-scale mapping of the CL1604 supercluster extending over 50 Mpc, confirming its connection to larger structures and analyzing galaxy stellar populations across this vast region.

## Key findings

- The supercluster is part of a larger structure extending beyond initial observations.
- Red-sequence galaxies are predominantly old (>2 Gyr) across the structure.
- Galaxies at similar redshifts have comparable stellar ages despite being 50 Mpc apart.

## Abstract

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.