Research found the most densely populated galaxy cluster in the primitive universe

A study led by researchers at the Instituto de Astrofisica de Canarias (IAC) and conducted with OSIRIS, an instrument on the Gran Telescopio Canarias (GTC), discovered the most densely populated galaxy cluster in formation in the early universe. The researchers predict that this structure, which is 12.5 billion light years away, will have evolved into a cluster similar to that of Virgo, a neighbor of the Milky Way’s Local Group of galaxies. The findings have been published in the specialized journal Monthly Notices of the Royal Astronomical Society (MNRAS).

Clusters of galaxies are groups of galaxies that remain together due to gravity. Scientists look for structures in formation, known as galaxy protoclusters, in the early universe to understand the evolution of these “cities of galaxies.”

A study has found the most densely populated galaxy cluster in formation in the primitive universe. The researchers predict that this structure, which is at a distance of 12.5 billion light-years from us, will have evolved into a cluster similar to that of Virgo, a neighbor of the Local Group of galaxies to which the Milky Way belongs.

An international team of astronomers determined the distance to the galaxy HDF850.1, known as one of the galaxies with the highest rate of star formation in the observable universe, in 2012. To their surprise, the scientists also discovered that this galaxy, known as the Hubble Deep Field/GOODS-North, is part of a group of around a dozen protogalaxies that formed during the first thousand million years of cosmic history. Only one other similar primordial group was known prior to its discovery.

Now, thanks to new research with the OSIRIS instrument on the Gran Telescopio Canarias (GTC, or GRANTECAN), the team has shown that it is one of the most densely populated regions populated with galaxies in the primitive Universe, and have conducted a detailed study of the physical properties of this system for the first time. “Surprisingly, we have discovered that all of the members of the cluster studied thus far, approximately two dozen, are galaxies with normal star formation, and that the central galaxy appears to dominate the production of stars in this structure,” explains Rosa Calvi, formerly a postdoctoral researcher at the IAC and the article’s first author.

Largest cluster of galaxies known in the early universe

Witnesses to the infancy of the local Universe

According to a recent study, this cluster of galaxies in formation is made up of various components, or “zones,” that differ in their evolution. Astronomers predict that this structure will gradually change into a galaxy cluster similar to Virgo, the central region of the supercluster of the same name in which the Milky Way is located, and to which the Milky Way belongs.

“We see this city being built just as it was 12,500 million years ago, when the Universe was less than 10% the age it is now, so we are seeing the childhood of a cluster of galaxies like those that are typical in the local Universe,” says Helmut Dannerbauer, an IAC researcher and co-author of this article.

The distance measured to these studied sources agrees perfectly with the predictions based on photometric observations taken previously on GRANTECAN by Pablo Arrabal Haro, formerly a doctoral student at the IAC, supervised by José Miguel Rodríguez Espinosa, an IAC researcher and Assistant General Secretary of the International Astronomical Union (IAU), and Casiana Muñoz-Tuñón, a researcher and Deputy Director of the IAC, all of them co-authors of the present article. Arrabal developed a method for selecting galaxies with normal star formation rates, based on the photometric survey SHARDS (Survey for High-z Absorption Red and Dead Sources), a Large Programme of the European Southern Observatory (ESO) carried out 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” states Arrabal.

Pablo Pérez-González, researcher at the Centro de Astrobiologa (CAB, CSIC-INTA) and co-author of the paper, led the SHARDS program. “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 before seen,” Pérez-González says.

Furthermore, Stefan Geier, GTC support astronomer and co-author of the paper, states that “this highly surprising result would not have been possible without the extraordinary capacity of OSIRIS combined with the large collating area of the GRANTECAN, the world’s largest optical and infrared telescope.”

The Gran Telescopio Canarias and the Observatorios del Instituto de Astrofisica de Canarias (IAC) are part of Spain’s network of Singular Scientific and Technical Infrastructures.