Discovery of a Supercluster at $z\sim$0.91 and Testing the $\Lambda$CDM Cosmological Model

TL;DR

This paper reports the discovery of a massive supercluster at redshift 0.91, providing observational evidence to test the predictions of the $ ext{Lambda}$CDM cosmological model regarding large-scale structure formation.

Contribution

It presents the first confirmed detection of a supercluster at $z\,\sim\,0.91$ and compares its properties with $ ext{Lambda}$CDM model predictions, highlighting the need for further observational tests.

Findings

Discovery of a supercluster at $z\sim0.91$ with three massive clusters.

The supercluster spans approximately 100 Mpc in the galaxy density map.

The observed supercluster is consistent with $ ext{Lambda}$CDM predictions, but more candidates are needed for confirmation.

Abstract

The $\Lambda$CDM cosmological model successfully reproduces many aspects of the galaxy and structure formation of the universe. However, the growth of large-scale structures (LSSs) in the early universe is not well tested yet with observational data. Here, we have utilized wide and deep optical--near-infrared data in order to search for distant galaxy clusters and superclusters ($0.8<z<1.2$). From the spectroscopic observation with the Inamori Magellan Areal Camera and Spectrograph (IMACS) on the Magellan telescope, three massive clusters at $z\sim$0.91 are confirmed in the SSA22 field. Interestingly, all of them have similar redshifts within $\Delta z\sim$0.01 with velocity dispersions ranging from 470 to 1300 km s$^{-1}$. Moreover, as the maximum separation is $\sim$15 Mpc, they compose a supercluster at $z\sim$0.91, meaning that this is one of the most massive superclusters at this redshift to date. The galaxy density map implies that the confirmed clusters are embedded in a larger structure stretching over $\sim$100 Mpc. $\Lambda$CDM models predict about one supercluster like this in our surveyed volume, consistent with our finding so far. However, there are more supercluster candidates in this field, suggesting that additional studies are required to determine if the $\Lambda$CDM cosmological model can successfully reproduce the LSSs at high redshift.