Speaker
Description
Magnetic fields are everywhere in the Universe, but little is know about their origin and amplification, particularly on the largest scales. Proto-clusters, the distant progenitors of local galaxy clusters, offer a unique environment to study magnetic fields during the first phases of structure formation and especially to understand the magnetic field amplification during this process. However, little is known at present about magnetic fields in proto-clusters.
Using the Jansky Very Large Array, we have started the first systematic study of magnetic fields in proto-clusters, selected from the CARLA (Clusters Around Radio-Lod AGN) sample. Our sample comprises 9 spectroscopically confirmed objects within $1.37 < z < 2.80$, with masses $13.6 < \mathrm{log_{10}M_{halo} \ [M_{\odot}]} < 14.6$, and that host a powerful polarised radio-loud AGN.
To study magnetic fields in proto-clusters, we analyse the Faraday rotation effect of the polarised emission from the central AGN jets and lobes. As this radiation propagates through the hot, sparse, and magnetised proto-intra-cluster medium (proto-ICM), its polarisation angle is rotated by the Rotation Measure (RM), which traces the line-of-sight magnetic field and electron density. Measuring the RM and its dispersion allows us to probe the magnetic field structure and disentangle contributions from the AGN and the surrounding medium.
In one of these objects, CARLA J1510+5958, we find uniform RM and well-ordered magnetic field vectors in one of the radio lobes, indicating that the AGN may be compressing a magnetised medium in its vicinity. In contrast, the opposite lobe shows complete depolarisation, which is consistent with it being embedded in a hot, low-density, and turbulent magnetised plasma. Together, these results point to the existence of a magnetised proto-ICM. By comparing our observations with 3D semi-analytical simulations, we estimate a lower limit on the physical magnetic field strength of approximately 0.05 $\mu$G.
In the talk, I will present these preliminary findings and outline how the SKA Observatory, with its high sensitivity, resolution, and wide bandwidth, will open a new window to map magnetic fields in proto-clusters and help our understanding of the cosmic magnetism.
| Topics | Galaxy Clusters & LSS (relativistic particles and magnetic fields) |
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