Abstract
The intracluster medium (ICM) is the
low-density diffuse gas that fills
the space between galaxies within galaxy clusters.
It is primarily composed of magnetized plasma, which reaches virial temperatures
of up to $10^8 K $, probably due to mergers of subhalos.
Under these conditions, the plasma is weakly collisional and therefore has
an anisotropic pressure tensor with
respect to the local direction of the magnetic field.
This triggers very fast, Larmor-scale, pressure-anisotropy-driven kinetic instabilities that alter magnetic field amplification. We aim to study magnetic field amplification through a turbulent, small-scale dynamo, including the effects of the kinetic instabilities, during the evolution of a typical massive galaxy cluster.
A specific aim of this work is to establish a redshift limit from
which a dynamo has to start to amplify the magnetic field up to
equipartition with the turbulent velocity field at redshift $z=0$. We implemented one-dimensional radial profiles for various plasma quantities for
merger trees generated with the modified GALFORM
algorithm. We assumed that turbulence is driven by successive mergers of dark matter halos and
constructed effective models for the Reynolds number $ Re eff $ dependence
on the magnetic field in three different magnetization regimes
(unmagnetized, magnetized ``kinetic'' , and magnetized ``fluid''),
including the effects of kinetic instabilities.
The magnetic field growth rate is calculated for the different $ Re eff $ models. The model results in a higher magnetic field growth rate at higher redshift.
For all scenarios considered in this study, to reach equipartition at $z=0$, it is sufficient for the amplification of the magnetic field to start at redshift $z_ start 1.5$ and above. The time to reach equipartition can be significantly shorter in cases with systematically smaller turbulent forcing scales and for the highest $ Re eff $ models. The origin of magnetic fields in the weakly collisional ICM can be explained
by the small-scale turbulent dynamo, provided that the dynamo
process starts beyond a given redshift.
Merger trees are useful tools for studying
the evolution of magnetic fields in weakly collisional plasmas,
and could also be used to constrain the different
stages of the dynamo that could potentially be observed by future radio telescopes.
Subject
Space and Planetary Science,Astronomy and Astrophysics
Cited by
1 articles.
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