Ministerio de Ciencia, Innovación y Universidades Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

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Gravitational lensing detection of an extremely dense environment around a galaxy cluster

Author/s: M. Sereno, C. Giocoli, L. Izzo, F. Marulli, A. Veropalumbo, S. Ettori, L. Moscardini, G. Covone, A. Ferragamo, R. Barrena, A. Streblyanska

Reference: 2018 Nature Astronomy 2 744 | Link

Differential surface density ΔΣ of PSZ2~G099.86+58.45 as a function of the proper projected distance from the center of the cluster. Black points are the measurements, while red points represent the averaged simulations. Blue curves plot the contribution by the main and the correlated matter, assuming a ΛCDM model. This plot shows how the distribution of the observed matter (black) is not well predicted by the numerical simulations (in red) beyond 5-7 Mpc.
Differential surface density ΔΣ of PSZ2~G099.86+58.45 as a function of the proper projected distance from the center of the cluster. Black points are the measurements, while red points represent the averaged simulations. Blue curves plot the contribution by the main and the correlated matter, assuming a ΛCDM model. This plot shows how the distribution of the observed matter (black) is not well predicted by the numerical simulations (in red) beyond 5-7 Mpc.

The matter in the Universe is organised in a complex network of sheets and filaments delineating large empty regions, the voids, while filamentary structures connect the densest regions of the Universe, so configuring a large network called the cosmic web. Galaxy clusters may contain thousands of galaxies, forming the most massive gravitationally bounded mass systems, and are essential pieces in the Large Scale Structure of the Universe. Disentangling the cosmic web is one of the most important challenges in Cosmology, because the properties of matter at such scales is not well known. Galaxy clusters form at the highest-density nodes of the cosmic web. The clustering of dark matter halos hosting these galaxy clusters is enhanced relative to the general mass distribution, with the matter density beyond the virial region being strongly correlated to the halo mass. Halo properties other than mass can further enhance the halo clustering. Today, observational campaigns have ascertained the haloes, but efforts to detect mass in the very external regions have been inconclusive. Here, we report the analysis of the environment in a sample of a massive cluster, PSZ2 G099.86+58.45, focusing on the detection of the environment dark matter correlated to a single cluster. The gravitational lensing signal of the outskirts is very large and can be traced up to 30 Mpc with a high signal-to-noise ratio, implying environment matter density in notable excess of the cosmological mean. Our finding reveals this system extremely rare in the current paradigm of structure formation and, implies that enhancing mechanisms around high-mass halos can be very effective.

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