COSMOLOGICAL MAGNETOHYDRODYNAMIC SIMULATIONS OF CLUSTER FORMATION WITH ANISOTROPIC THERMAL CONDUCTION
- Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
- Department of Astronomy, ASC/Flash Center, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States)
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen 05233 (Germany)
- Astronomy Department and Theoretical Astrophysics Center, 601 Campbell Hall, University of California, Berkeley, CA 94720 (United States)
The intracluster medium (ICM) has been suggested to be buoyantly unstable in the presence of magnetic field and anisotropic thermal conduction. We perform first cosmological simulations of galaxy cluster formation that simultaneously include magnetic fields, radiative cooling, and anisotropic thermal conduction. In isolated and idealized cluster models, the magnetothermal instability (MTI) tends to reorient the magnetic fields radially whenever the temperature gradient points in the direction opposite to gravitational acceleration. Using cosmological simulations of cluster formation we detect radial bias in the velocity and magnetic fields. Such radial bias is consistent with either the inhomogeneous radial gas flows due to substructures or residual MTI-driven field rearrangements that are expected even in the presence of turbulence. Although disentangling the two scenarios is challenging, we do not detect excess bias in the runs that include anisotropic thermal conduction. The anisotropy effect is potentially detectable via radio polarization measurements with LOFAR and the Square Kilometer Array and future X-ray spectroscopic studies with the International X-ray Observatory. We demonstrate that radiative cooling boosts the amplification of the magnetic field by about two orders of magnitude beyond what is expected in the non-radiative cases. This effect is caused by the compression of the gas and frozen-in magnetic field as it accumulates in the cluster center. At z = 0 the field is amplified by a factor of about 10{sup 6} compared to the uniform magnetic field that evolved due to the universal expansion alone. Interestingly, the runs that include both radiative cooling and thermal conduction exhibit stronger magnetic field amplification than purely radiative runs. In these cases, buoyant restoring forces depend on the temperature gradients rather than the steeper entropy gradients. Thus, the ICM is more easily mixed and the winding up of the frozen-in magnetic field is more efficient, resulting in stronger magnetic field amplification. We also demonstrate that thermal conduction partially reduces the gas accretion driven by overcooling despite the fact that the effective conductivity is suppressed below the Spitzer-Braginskii value.
- OSTI ID:
- 21587361
- Journal Information:
- Astrophysical Journal, Vol. 740, Issue 2; Other Information: DOI: 10.1088/0004-637X/740/2/81; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
AMPLIFICATION
ANISOTROPY
CLUSTER MODEL
GALAXIES
GALAXY CLUSTERS
INSTABILITY
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
RADIATIVE COOLING
SIMULATION
TEMPERATURE GRADIENTS
THERMAL CONDUCTION
COOLING
ENERGY TRANSFER
FLUID MECHANICS
HEAT TRANSFER
HYDRODYNAMICS
MATHEMATICAL MODELS
MECHANICS
NUCLEAR MODELS