Researchers study gravitational lensing around an extremely dense galaxy cluster | 7/20/2018 | Staff
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Dark matter halos are theoretical bodies inside which galaxies are suspended; the halo's mass dominates the total mass. These halos cannot be observed directly, but astronomers infer their presence by the phenomenon of gravity lensing—the distortion of background objects by strong gravitational sources that act as lenses. Astronomers can even study distant galaxies magnified by the gravitational lensing of closer gravitational objects.

Researchers have known for decades that the clustering of galaxies does not mirror the clustering of most of the matter in the universe. The concept that galaxy distribution correlates to matter density at a given site in the universe dates back to 1984. In a galaxy cluster, matter distribution is highly clustered, and halos form at the peak of this distribution. This is called the halo bias.

Halo - Bias - Relationship - Distribution - Galaxies

Halo bias can also be framed as the relationship between the spatial distribution of galaxies and the underlying dark matter density field. Clustering is enhanced relative to the general distribution of mass in the cluster. But there are other theorized properties besides mass that can affect clustering; physicists refer to these as secondary bias, but efforts at identifying them have been inconclusive.

Recently, a group of Italian researchers published a report in Nature Astronomy on a study of PSZ2 GO99.86+58.45, an extremely dense galaxy cluster with a very large gravitational lensing signal. They report that the system is extremely rare within the framework of galactic structure formation, and its characteristics strongly imply the effectiveness of enhancing mechanisms other than mass on dark matter halos.

Researchers - Data - Catalogs—the - CFHTLenS - RCSLens

The researchers analyzed data from two publicly available shear catalogs—the CFHTLenS and RCSLens. They found that the outskirts of the cluster have a very large gravitational lensing signal traceable up to 30 megaparsecs. Its high signal-to-noise ratio implies environment matter density that far exceeds the cosmological mean density. They report that...
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