Astronomers Discover a New Protocluster of Massive Quiescent Galaxies at a Redshift of 4.0

An international team of astronomers has reported the discovery of a new protocluster of massive quiescent galaxies at a redshift of approximately 4.0. This is the first detection of a protocluster of this type at such a high redshift. The finding was detailed in a paper published November 20 on the pre-print server arXiv.

Spectrum of SXDS2_19838 - one of the galaxies in the newfound protocluster. Credit: arXiv (2023). DOI: 10.48550/arxiv.2311.11569

Galaxy clusters are the most massive gravitationally bound structures in the universe, and they can contain hundreds to thousands of galaxies. Protoclusters are the early stages of galaxy cluster formation, and they are found at high redshifts.

The newly discovered protocluster, which has been designated SXDS2-19838, is located in the Subaru/XMM-Newton Deep Survey (SDXS) field. The protocluster contains at least five massive quiescent galaxies, which are galaxies that have stopped forming new stars. The most massive galaxy in the protocluster has a stellar mass of 113.1 billion solar masses.

The astronomers used the MOSFIRE spectrograph on the Keck I telescope to confirm the redshifts of the galaxies in the protocluster. They also used the Subaru telescope to measure the sizes and shapes of the galaxies.

The discovery of this protocluster is important because it provides new insights into the early formation of galaxy clusters. The astronomers believe that the protocluster will eventually collapse to form a massive galaxy cluster.

Journal Information: Masayuki Tanaka et al, A proto-cluster of massive quiescent galaxies at z=4, arXiv (2023). DOI: 10.48550/arxiv.2311.11569