An international collaboration between IRFU (Paris-Saclay University), the Institute of Astronomy at the University of Hawaii, LPC (Clermont Auvergne University), IP2I (Claude Bernard University Lyon 1), and Racah Institute of Physics (Hebrew University of Jerusalem), discovered a huge structure in the distribution of galaxies, giving it the name of the South Pole Wall.
Research in cosmology has been marked over the past forty years by the discovery of increasingly large structures, as the instruments made it possible to probe regions of the Universe which were increasingly large and distant: first in 1986 the discovery, by a team of the Smithsonian Center for Astrophysics, of the Great Wall, a structure of about 500 million light years connecting in particular the galaxy clusters between Hercules and the Hair of Berenice Constellations. Then in 2003, the Sloan Great Wall, has been discovered, thanks to the SDSS Sloan Digital Sky Survey. It is a filamentary structure 1.4 billion light-years in size and located about 1 billion light-years away. In 2016, as part of the Baryon Oscillation Spectroscopic Survey, the BOSS Great Wall has been discovered. It is a complex with a morphology similar to that of the Sloan Great Wall, but at a much greater distance.
In this history of discovery of large structures, a region of the sky remained essentially unexplored, an “Astra Incognita”, in the direction of the Celestial South Pole (that is to say along the line defined by the axis of rotation of our planet, in the Southern direction). This region, located at the observational limits of the telescopes located in the southernmost observatories, such as the Siding Springs Observatory in Australia, is characterized by the presence of thick clouds of galactic dust, such as the Cloud Complex in the constellation of the Chameleon, or the presence of the Magellanic Clouds, two satellite galaxies of our galaxy, which mask entire sections of the deep sky. The surveys of galaxies were therefore penalized by the presence of holes in their sky covers in this southernmost region.
However, a new study, based on the analysis of galaxy movements, has made possible to explore this region for the first time. Indeed, the movement of galaxies, generated by gravitation, betrays the presence of matter including in regions not directly observed. Using the latest generation of the galaxy velocity catalog, Cosmicflows-3, which includes approximately 18,000 measurements of galaxy velocities or groups of galaxies, a reconstruction of the distribution of matter in 3D in the southern sky has revealed the presence of a previously unknown wall: the South Pole Wall. It has a morphology and size similar to that of the Sloan Great Wall, while being twice as close to us. Its heart is located in the Constellation of the Chameleon, and it includes a long, almost straight filament connecting particularly dense sectors in the constellations of the Bird of Paradise and the Hare. Continuing in bending to reach the Eridan constellation sector near the celestial equator, it describes a huge arc that embraces the southern borders of Laniakea, the gravitational attraction basin in which our galaxy is located.
Continuing this Cosmos mapping endeavor, the collaboration is now working on the preparation of the next generation of galaxy speed catalogs, Cosmicflows-4, with the inclusion of new measurements obtained in the Northern Hemisphere with Green Bank radio telescopes and Arecibo.