Features of collisionless turbulence in the intracluster medium from simulated Faraday Rotation maps

NAKWACKI, M. S.; G. KOWAL; R. SANTOS-LIMA; E. M. DE GOUVEIA DAL PINO; D. FALCETA-GONÇALVES

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2015 vol. 455 p. 3702 - 3723

0035-8711

Observations of the intracluster medium (ICM) in galaxy clusters suggest for the presence ofturbulence and the magnetic fields? existence has been proved through observations of FaradayRotation (FR) and synchrotron emission. The ICM is also known to be filled by a rarefiedweakly collisional plasma. In this work, we study the possible signatures left on FR mapsby collisionless instabilities. For this purpose, we use a numerical approach to investigatethe dynamics of the turbulence in collisionless plasmas based on an magnetohydrodynamical(MHD) formalism taking into account different levels of pressure anisotropy. We considermodels covering the sub/super-Alfv ́enic and trans/supersonic regimes, one of them represent-ing the fiducial conditions corresponding to the ICM. From the simulated models, we computeFR maps and analyse several statistical indicators in order to characterize the magnetic fieldstructure and compare the results obtained with the collisionless model to those obtainedusing standard collisional MHD framework. We find that important imprints of the pressureanisotropy prevails in the magnetic field and also manifest in the associated FR maps whichevidence smaller correlation lengths in the collisionless MHD case. These points are remark-ably noticeable for the case mimicking the conditions prevailing in ICM. Nevertheless, inthis study we have neglected the decrease of pressure anisotropy due to the feedback of theinstabilities that naturally arise in collisionless plasmas at small scales. This decrease may notaffect the statistical imprint differences described above, but should be examined elsewhere.