The Challenge of Detecting Intracluster Filaments with Faraday Rotation

Nicola Locatelli,Paola Domínguez-Fernández,Franco Vazza

doi:10.3390/galaxies6040128

Nicola Locatelli, Paola Domínguez-Fernández + Show 1 more

Open Access

https://doi.org/10.3390/galaxies6040128

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Abstract

The detection of filaments in the cosmic web will be crucial to distinguish between the possible magnetogenesis scenarios, and future large polarization surveys will be able to shed light on their magnetization level. In this work, we use numerical simulations of galaxy clusters to investigate their possible detection. We compute the Faraday Rotation signal in intracluster filaments and compare it to its surrounding environment. We find that the expected big improvement in sensitivity with the SKA-MID will in principle allow the detection of a large fraction of filaments surrounding galaxy clusters. However, the contamination of the intrinsic Faraday Rotation of background polarized sources will represent a big limiter to the number of objects that can be significantly detected. We discuss possible strategies to minimize this effect and increase the chances of detection of the cosmic web with the large statistics expected from future surveys.

Highlights

Magnetic fields in the Universe are observed to permeate a very wide range of spatial scales, from planetary (∼106 m) to galactic (∼kpc), up to galaxy cluster scales (∼Mpc)
We can assess the chances of detecting the magnetic cosmic web attached to massive galaxy clusters under realistic observing conditions, by focusing on the challenge of significantly distinguish the excess rotation measure (RM) in filaments compared to control fields
We computed the power spectra of magnetic fields in different 3-dimensional sub-volumes in the field of our cluster e18b, motivated by recent simulations by our group, in which the signature of magnetic dynamo in the innermost cluster regions clearly stems in power spectra [53]. in particular we selected a cubic 43 Mpc3 box coincident with a clearly detectable filament connected to the cluster, a similar box coincident with an undetectable filament, and a cubic volume on an empty “control field” located at the cluster virial radius of e18b

Summary

Introduction

Magnetic fields in the Universe are observed to permeate a very wide range of spatial scales, from planetary (∼106 m) to galactic (∼kpc), up to galaxy cluster scales (∼Mpc). The amplification of magnetic fields in cosmic structures might have proceeded in a bottom-up small-scale turbulent dynamo (e.g., [2]). Under such conditions, the dynamo should have erased most traces of the initial magnetization seeds, bringing the magnetic energy density close to equipartition with the plasma kinetic energy in galaxy clusters. The dynamo should have erased most traces of the initial magnetization seeds, bringing the magnetic energy density close to equipartition with the plasma kinetic energy in galaxy clusters This scenario well explains the observed magnetic fields in galaxy clusters, i.e., for densities and temperatures of n ≥ 10−4 (cm−3 ). Direct observations of magnetic fields in the IGM are made challenging by the very high sensitivity required for the imaging at most wavelengths

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