Speaker
Description
The evolution of the Universe proceeds along the filaments of the cosmic web, where enormous amount of energy is dissipated through complex plasma processes that can be traced by radio emitting electrons. While the central regions of galaxy clusters, located at the knots of the cosmic web, have been studied in fair detail, their outskirts are still poorly explored, and cosmic filaments have remained elusive so far. The initial step in this direction has arrived thanks to the Low Frequency Array (LOFAR). LOFAR has recently discovered that some clusters host Megahalos, diffuse sources filling the volume of clusters up to their periphery (Cuciti et al. 2022, Nature). In a few cases, LOFAR detected large radio structures connecting pre-merging clusters, called “radio bridges” (Botteon et al., 2020; Govoni et al. 2019, Science). Galaxy clusters and filaments are expected to be surrounded by strong accretion shocks that should be able to accelerate cosmic rays. The signatures of accretion shocks however have been only detected by stacking radio surveys in polarisation (Vernstrom et al. 2023, Science Adv.). These discoveries represent the first steps in the exploration of the large scale structure of the Universe in the radio band. SKA, with its unprecedented sensitivity, is going to enable the systematic observation of these sources and possibly open the possibility to detect cosmic filaments. Given that the synchrotron diffuse sources beyond galaxy clusters typically have steep spectra (alpha <-1), SKA-LOW and band 1 of SKA-MID will be the most suitable for this kind of studies. We estimated that with 1 hour integration time SKA-LOW in stage AA* will be about 6 times more sensitive than LOFAR, at a comparable resolution. The combination of SKA-LOW and SKA-MID will ensure a proper characterisation of the spectral properties of these sources, which is paramount to understand the acceleration mechanisms at play outside galaxy clusters.
| Topics | Galaxy Clusters & LSS (relativistic particles and magnetic fields) |
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