Chinese Researchers Detect the Largest Number of Galaxy Clusters (Astronomy)

Galaxy clusters are the largest gravitationally bound systems in the universe, which contain a lot of galaxies, gas, and dark matter. They are ideal laboratories to study galaxy formation and evolution in dense environments and also excellent probes to explore the large-scale structure, dark matter, and dark energy. 

A large sample of galaxy clusters at z < 1, when the universe is about 5.7 billion years old, is fundamental for accurately analyzing the late evolution of galaxies in dense environment, especially for those brightest cluster galaxies (BCGs). 

Recently, a research team led by Dr. ZOU Hu from National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) has utilized the deep imaging data from the Dark Energy Spectroscopic Instrument (DESI) imaging surveys and detected more than 540,000 galaxy clusters at z < 1. These clusters are by far the largest sample that has been found. 

Fig. 1 Redshift distribution of the galaxy clusters detected in the study. Others are the redshift distributions of the clusters that are found using the SDSS imaging data. The distributions are scaled by the survey area. (Image by NAOC) 

Their work was published in The Astrophysical Journal Supplement Series on April 13. 

The galaxy clusters detected in this work will be used for further studying the properties of member galaxies, evolution of massive central galaxies, mass assembly and star formation in dense environment, and gas properties in clusters, etc. 

Through international collaboration, Dr. ZOU Hu has participated the DESI project and conducted large-scale multi-wavelength imaging surveys, including the Beijing-Arizona Sky Survey (BASS). 

Before using the imaging data to detect galaxy clusters, the team has accurately estimated the photometric redshifts and stellar masses of about 300 million galaxies with r<23, which is about 6 million times fainter than the stars that the human eyes can see. Based on the photometric redshift catalog, they adopted a new fast peak clustering algorithm and detected more than 540,000 galaxy clusters with the number of members larger than 10. 

By contrast with those cluster finders based on red sequence, the researchers can detect the clusters that are lack of red galaxies. Compared with traditional overdensity detecting methods, the speed performance of the new method is better and member galaxies can be easily identified. In addition, they have preliminarily found more than a hundred strong lensing systems among these clusters. 

This work will play an important role in data analyses and scientific studies of future Chinese large telescopes and large-scale surveys, such as Chinese Space Station Telescope (CSST). 

Featured image: One of the detected clusters at the redshift of about 0.4. Some properties of the cluster and the brightest cluster galaxy (BCG) are displayed. The position of the BCG is marked by the small circle, the average position of the member galaxies by the cross, and the distance of 0.5 Mpc from the BCG by the big circle. (Image by NAOC) 


Reference: Hu Zou, Jinghua Gao, Xin Xu, Xu Zhou, Jun Ma, Zhimin Zhou, Tianmeng Zhang, Jundan Nie, Jiali Wang, and Suijian Xue, “Galaxy Clusters from the DESI Legacy Imaging Surveys. I. Cluster Detection”, Astrophysical Journal, Volume 253, Number 2, 2021. Link to paper


Provided by Chinese Academy of Sciences

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