Scientists of Chinese Academy of Sciences have detected the largest number of galaxy clusters so far

In addition, it is necessary for us to Recently, Zou Hu, an associate researcher at the National Astronomical Observatory, a team of scientists from the Chinese Academy of Sciences, and other DESI depth image survey data based on international cooperation, The redshift z < 1 and more than 540,000 cluster samples were detected, and the total mass of cluster samples was effectively estimated. This is the largest cluster sample detected so far. The research results have been received by the Supplement of Astrophysics Journal.

As the first article in the series, the cluster samples detected in this study will be used to explore the properties of member galaxies in the cluster, the evolution of massive central galaxies, mass assembly and star formation in dense environment, and the properties of gas in the cluster, so as to understand the late evolution of member galaxies in the cluster. At the same time, the sample will also play an application role in the research of dark matter, large-scale structure and cosmological parameter limitation.

Galaxy clusters are the largest self-gravitational binding system in the universe, including a large number of galaxies, gases and dark matter. Galaxy cluster is an ideal place to study the formation and evolution of galaxies in high density environment, and it is also an effective probe to study the large-scale structure of the universe, dark matter and dark energy. Large samples of galaxy clusters with redshift z < 1 are the premise of accurately studying the late evolution of galaxies in dense environment, especially the brightest cluster galaxies (BCG) in galaxy clusters. They are the largest and brightest galaxies in the universe, and most of them are located in the center of gravitational potential wells of galaxy clusters. Limited by samples, more observations have given contradictory conclusions about their late evolution.

Based on international cooperation, Zou Hu and others participated in the Dark Energy Spectral Sky Survey (DESI) project and carried out a large-scale deep sky survey, of which the leading Beijing-Arizona Sky Survey is a part. The total area of the image survey is about 20,000 square degrees, which is 2-3 magnitude deeper than the SDSS survey in Si Long on average. Before using the survey data to detect galaxy clusters, Zou Hu and others carried out high-precision photometric redshift and star mass measurement on 300 million galaxies with R < 23 magnitude. The accuracy of photometric redshift was less than 0.02, and the accuracy of logarithmic star mass was 0.2 dex. The relevant research results were published in the Supplement of Astrophysics Journal. Based on the photometry redshift catalog, researchers adopted a new fast peak clustering algorithm, and detected more than 540,000 galaxy clusters with more than 10 member galaxies. Compared with the cluster search method based on red sequence, this algorithm can detect clusters lacking red galaxies. Compared with the traditional density search method, this algorithm is more efficient and can effectively detect member galaxies. Based on the observation data of X-ray and radio SZ effect, the total mass of galaxy clusters is effectively estimated by using the optical luminosity of member galaxies. The red shift range of the sample is z < 1, and the total mass range is 1013.5-1014.8 M. Compared with the previous catalogue of the largest galaxy cluster based on SDSS survey, the sample of this galaxy cluster has expanded by about 4 times, and the peak value of redshift distribution has expanded from 0.4 to 0.7. Monte Carlo simulation shows that the error rate of galaxy clusters is about 3%.

At the same time, Yang Xiaohu, a professor at Shanghai Jiaotong University, cooperated with Zou Hu and adopted an improved galaxy cluster search algorithm based on dark matter halo, and detected galaxy clusters of similar size (with more than 10 members), which was recently received by Astrophysics Journal. Synthesizing two different detection methods can give a more reliable judgment of galaxy clusters and members, which is beneficial to analyze the systematic influence of different galaxy cluster detection methods on various studies.

Hundreds of strong gravitational lens systems have been preliminarily discovered from the detected galaxy clusters. In addition, DESI is carrying out spectral survey observation and plans to acquire the spectra of 35 million galaxies and quasars. Large-scale spectral data combined with deep multi-band image data will ensure detailed study of the properties of galaxy clusters and member galaxies, the correlation of galaxy properties and the mass assembly history of member galaxies in the future. Our research work will prepare for data analysis and scientific research of large telescope equipment and large-scale sky surveys such as CSST in China.

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The redshift distribution of galaxy clusters detected by Zou Hu et al. is compared with the photometric galaxy clusters based on SDSS survey in the past, and the survey area is reduced here

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Galaxy clusters with redshift of about 0.4 were detected, and some properties of galaxy clusters and BCG were also marked on the map. The small circle in the center gives the position of BCG galaxy, the cross marks the average position of the member galaxies of the cluster, and the large circle shows the distance range of 0.5 Mpc. Around the central BCG, the arc signal of the strong gravitational lens can be seen

(Source: Chinese Academy of Sciences)

Source: China Hi-Tech

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