IAFE   05512
INSTITUTO DE ASTRONOMIA Y FISICA DEL ESPACIO
Unidad Ejecutora - UE
artículos
Título:
Magnetic Field Amplification and Evolution in Turbulent Collisionless Magnetohydrodynamics: An Application to the Intracluster Medium
Autor/es:
R. SANTOS-LIMA; E. M. DE GOUVEIA DAL PINO; G. KOWAL; D. FALCETA-GONÇALVES; A. LAZARIAN; M. S. NAKWACKI
Revista:
ASTROPHYSICAL JOURNAL
Editorial:
IOP PUBLISHING LTD
Referencias:
Lugar: Chicago; Año: 2014 vol. 781 p. 1 - 21
ISSN:
0004-637X
Resumen:
The amplification of magnetic fields (MFs) in the intracluster medium
(ICM) is attributed to turbulent dynamo (TD) action, which is generally
derived in the collisional-MHD framework. However, this assumption is
poorly justified a priori, since in the ICM the ion mean free path
between collisions is of the order of the dynamical scales, thus
requiring a collisionless MHD description. The present study uses an
anisotropic plasma pressure that brings the plasma within a parametric
space where collisionless instabilities take place. In this model, a
relaxation term of the pressure anisotropy simulates the feedback of the
mirror and firehose instabilities, in consistency with empirical
studies. Our three-dimensional numerical simulations of forced transonic
turbulence, aiming the modeling of the turbulent ICM, were performed for
different initial values of the MF intensity and different relaxation
rates of the pressure anisotropy. We found that in the high-β
plasma regime corresponding to the ICM conditions, a fast anisotropy
relaxation rate gives results that are similar to the collisional-MHD
model, as far as the statistical properties of the turbulence are
concerned. Also, the TD amplification of seed MFs was found to be
similar to the collisional-MHD model. The simulations that do not employ
the anisotropy relaxation deviate significantly from the collisional-MHD
results and show more power at the small-scale fluctuations of both
density and velocity as a result of the action of the instabilities. For
these simulations, the large-scale fluctuations in the MF are mostly
suppressed and the TD fails in amplifying seed MFs.