Study Reveals the Largest Galaxy Cluster Formed in the Early Universe

A new study headed by scientists from the Instituto de Astrofísica de Canarias (IAC) and performed with OSIRIS—an instrument on the Gran Telescopio Canarias (GTC) —has identified the formation of the most thickly populated cluster of galaxies in the primitive universe.

Image of the studied galaxy cluster in formation, 12.5 billion light-years from us. The circles indicate the new members discovered with the GTC; 4 of them are shown in detail. Image Credit: NASA/ESA/GOODS-N+3DHST+CANDELS Team/Daniel López/IAC.

The investigators predict that such a structure, which is located at a distance of 12.5 billion light-years from Earth, could have evolved and become a cluster almost the same as that of Virgo—a neighbor of the Local Group of galaxies which also includes the Milky Way galaxy. The new study has been published in the leading journal, Monthly Notices of the Royal Astronomical Society (MNRAS).

Galaxy clusters are sets of galaxies that continue to remain together due to the action of gravity. To figure out the evolution of such “cities of galaxies,” investigators search for structures in the supposed protoclusters of galaxies formed in the early universe.

Back in 2012, an international group of astronomers precisely determined the distance of the galaxy, called HDF850.1, which was believed to be one among the galaxies with a maximum rate of star formation in the visible universe.

To their amazement, the researchers also found that the HDF850.1 galaxy, which is one of the most researched areas on the sky, called the Hubble Deep Field/GOODS-North, is also a part of a set of about a dozen protogalaxies, which evolved during the first thousand million years of galactic history. But prior to its discovery, only one other analogous primordial group was recognized.

But now thanks to the latest study performed with the OSIRIS instrument on the Gran Telescopio Canarias (GRANTECAN or GTC), the researchers have demonstrated that it is one of the most thickly populated areas inhabited with galaxies in the primitive Universe, and for the first time, they were able to perform a comprehensive analysis of the physical characteristics of this system.

Surprisingly we have discovered that all the members of the cluster studied up to now, around two dozen, are galaxies with normal star formation, and that the central galaxy appears to dominate the production of stars in this structure.

Rosa Calvi, Study First Author and Former Postdoctoral Researcher, Instituto de Astrofísica de Canarias

Witnesses to the Infancy of the Local Universe

The latest research work demonstrates that the formation of this galaxy cluster is composed of numerous “zones” or components with variations in their evolution.

It was predicted by the astronomers that this structure will slowly change until it turns into a galaxy cluster that is analogous to Virgo—the core area of the supercluster of the same name in which the Local Group of galaxies is located, including the Milky Way galaxy.

We see this city in construction just as it was 12,500 million years ago, when the Universe had less than 10% of its present age, so we are seeing the childhood of a cluster of galaxies like those which are typical in the local Universe.

Helmut Dannerbauer, Study Co-Author and Researcher, Instituto de Astrofísica de Canarias

The distance quantified to these analyzed sources perfectly matches with the predictions based on photometric observations that were taken before on the GRANTECAN by Pablo Arrabal Haro, previously a doctoral student at the IAC, managed by José Miguel Rodríguez Espinosa, Assistant General Secretary of the International Astronomical Union (IAU) and an IAC scientist, and Casiana Muñoz-Tuñón, a researcher and Deputy Director of the IAC. All of them are co-authors of the new article.

Arrabal designed a technique for choosing galaxies with standard rates of star formation, based on the photometric survey SHARDS (short for Survey for High-z Absorption Red and Dead Sources)—a Large Programme of the European Southern Observatory (ESO)—performed on the GTC.

I am very happy to see that the method developed during my doctoral thesis works so well in finding and confirming a region highly populated with galaxies in the distant Universe,” Arrabal stated.

Pablo Pérez-González, the author of the article and a researcher from the Centro de Astrobiología (CAB, CSIC-INTA) has headed the SHARDS programme.

Measuring exactly how these structures are forming, especially at the beginning of the Universe, is not easy, and we need exceptional data such as those we are taking with the GTC telescope as part of the SHARDS and SHARDS Frontier Fields projects, which allow us to determine distances to galaxies and between galaxies at the edge of the Universe with a precision never achieved before.

Pablo Pérez-González, Study Author and Researcher, Centro de Astrobiología

Stefan Geier, a GTC support astronomer and the study co-author, also pointed out that, “this highly surprising result would not have been possible without the extraordinary capacity of OSIRIS together with the large colllecting area of the GRANTECAN, the largest optical and infrared telescope in the world.”

The Observatories of the Instituto de Astrofísica de Canarias (IAC) and the Gran Telescopio Canarias are part of the web of Singular Scientific and Technical Infrastructures of Spain.

Journal Reference:

Calvi, R., et al. (2021) Probing the existence of a rich galaxy overdensity at z = 5.2. Monthly Notices of the Royal Astronomical Society.


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