A complete empirical understanding of large scale cosmic structure has long been hampered by the "missing baryon" problem: only a fraction of the total baryon density predicted by calculations of big bang nucleosynthesis and measured at high redshifts is observed in and near galaxies in the local Universe. Hydrodynamical simulations support the hypothesis that these baryons are not inside galaxy clusters, but diffusely spread along the cosmic web made of knots, voids, bridges and filaments between Galaxy clusters.

In addition, it is well established that weak (microGauss level) magnetic fields permeate the central regions of galaxy clusters, and diffuse radio sources associated with the intracluster medium are observed in an increasing number of merging systems. These synchrotron sources provide evidence for the presence of electrons with GeV energies diffused in the magneto-ionic medium. Direct manifestations of magnetic fields and relativistic particles have been also found along filaments connecting cluster pairs in two systems so far. Stacking techniques provide indication of the presence of a non-thermal component on cosmological filaments through radio observations in total intensity as well as in polarization. Image credits: TNG collaboration (https://www.tng-project.org/media/).

The study of cluster pairs in a pre-merging state and the bridges between them, is crucial to understanding the origin of thermal and non-thermal components in the cosmic web. What are the processes of heating and particle acceleration that transform "filaments" into "bridges"? What happens to the filament between two clusters when these collide? How the magnetic field is amplified and spread in bridges? These kinds of questions could be addressed by combining information from the Sunyaev-Zel'dovich effect, sensitive to low density environments, radio observations, sensitive to magnetic fields, and X-ray observations which trace the higher-density, lower-temperature thermal gas component.

The three listed observables are totally complementary and we call for experts on the Radio, millimetric, and X-ray observations, simulations and theoretical studies to share their view and their experience.

Programme

Invited speakers

Scientific organisers

Contact

elia.battistelli @ roma1.infn.it