We present the large-scale structure over a 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 the 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 via follow-up spectroscopy with Subaru/FOCAS and Gemini-N/GMOS. This suggests that the structure known as the CL1604 supercluster is the tip of the iceberg. We investigate the stellar population of the red-sequence galaxies using 4000 Å break and Balmer H$\delta$ absorption lines. Almost all of the red-sequence galaxies brighter than $21.5\:$mag in the z band show an old stellar population of $\gtrsim\! 2\:$Gyr. The comparison of composite spectra of the red-sequence galaxies in the individual clusters show that the galaxies at a similar redshift have a 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 on a 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.
This paper reports our discovery of the most massive supercluster, termed the King Ghidorah Supercluster (KGSc), at z = 0.50–0.64 in the Third Public Data Release of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP PDR3) over 690 deg2, as well as an initial result for a galaxy and dark matter mapping. The primary structure of the KGSc comprises triple broad weak-lensing (WL) peaks over 70 comoving Mpc. Such extensive WL detection at z > 0.5 can only currently be achieved using the wide-field high-quality images produced by the HSC-SSP. The structure is also contiguous with multiple large-scale structures across a ∼400 comoving Mpc scale. The entire field has a notable overdensity (δ = 14.7 ± 4.5) of red-sequence clusters. Additionally, large-scale underdensities can be found in the foreground along the line of sight. We confirmed the overdensities in stellar mass and dark matter distributions to be tightly coupled and estimated the total mass of the main structure to be 1 × 1016 solar masses, according to the mock data analyses based on large-volume cosmological simulations. Further, upcoming wide-field multi-object spectrographs such as the Subaru Prime Focus Spectrograph may aid in providing additional insights into distant superclusters beyond the 100 Mpc scale.
more » « less- NSF-PAR ID:
- 10384393
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society: Letters
- Volume:
- 519
- Issue:
- 1
- ISSN:
- 1745-3925
- Format(s):
- Medium: X Size: p. L45-L50
- Size(s):
- p. L45-L50
- Sponsoring Org:
- National Science Foundation
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