Abstract:
An international team of astronomers led by scientists from Purdue University in the United States discovered the most distant primitive galaxy cluster COSMOS-z3.1-A known to date. It was born when the universe was only 2.1 billion years old, and its mass is about 5,000 times that of the Milky Way. The discovery not only supports existing theories of the evolution of galaxy clusters, but also reveals how they are embedded in the larger cosmic web. The relevant paper was published in the latest issue of The Astrophysical Journal.
The picture shows the newly discovered primitive galaxy cluster COSMOS-z3.1-A. Image source: Tololo Inter-American Observatory/National Science Foundation, etc.
Galaxy clusters are the most massive gravitationally bound structures in the universe, consisting of hundreds or even thousands of galaxies. The galaxy clusters that people observe in recent space and time today are mature structures that evolved from the original galaxy clusters. The original galaxy cluster is a huge and loose collection of galaxies that is still merging and has not yet condensed into a stable galaxy cluster. Studying distant primitive galaxy clusters formed when the universe was young can help understand how modern galaxy clusters grew and evolved over time.
To search for these primitive galaxy clusters, the team systematically analyzed data obtained from the ODIN survey. ODIN is a project to observe galaxies in the early universe, using the Dark Energy Camera on the Victor Blanco 4-meter telescope at the Inter-American Observatory in Monte Tololo, Chile. With a large field of view and ultra-high resolution of 570 million pixels, the Dark Energy Camera has used more than 100 nights in the past three years to conduct in-depth imaging of large areas of the southern hemisphere.
The team identified a total of 150 distant primitive galaxy clusters, which were formed between about 1 billion and 3 billion years after the Big Bang. They further focused on two targets with unusually high galaxy densities: COSMOS-z3.1-A and COSMOS-z3.1-C.
The ODIN survey gave the two-dimensional position of these primitive galaxy clusters in the sky, and the team used data from the Dark Energy Spectrometer to draw three-dimensional images of these primitive galaxy clusters.
The results show that COSMOS-z3.1-A was born when the universe was only 2.1 billion years old. It is the earliest and most distant primitive galaxy cluster known so far, and is also one of the densest regions in the universe.
In addition, three-dimensional images show that these ancient primitive galaxy clusters are mostly located at the intersection of filaments of the cosmic web. This is the first time scientists have directly observed such structural features in the distant universe. The observational results are highly consistent with the theoretical predictions of how matter is distributed on the large scale of the universe.
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