Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.mrao.cam.ac.uk/~mh475/poster.pdf
Дата изменения: Thu Oct 22 02:39:27 2009
Дата индексирования: Mon Oct 1 20:36:20 2012
Кодировка:
Modelling the effects of FR II radio jets on the turbulent magnetic fields in the intra-cluster medium
Mar tМn Huar te Espinosa , Mar tin Krause, Paul Alexander and Christian R. Kaiser.




Cambridge Cavendish Astrophysics Group,

Introduction
The Faraday rotation effect is observed on the AGN polarised radio emission traveling through the ICM, revealing magnetic fields of Mpc scale threading this media. RM maps are consistent with these cluster magnetic fields1 (CMFs): ·|B| µG, ·|B(r)| ICM (r), ·|B| Mcooling flow , · Turbulent structure. Open questions: The origin, evolution and role of the CMFs in the ICM stability. Since AGN jets have strong effects in the ICM in their vicinities, its not clear to what extent, and how, they affect both the CMFs and their RM characterisation.

The Model
Using Flash 3.12 we solve the equa- ties of 40 or 80 Mach permuted with tions of MHD with a constrained densities of 1в10-2 or 1в10-3 0 . transport scheme5 in a cubic Carte3 sian domain with 200 cells. The ICM is implemented as follows: · Monoatomic ideal gas ( = 5/3), 0 · King density profile ICM = (1+(r/a0 )2 ) , · Magnetohydrostatic equilibrium with central gravity, · Magnetic fields with a Kolmogorov turbulent structure (following [3]) and m 10. The plasma relaxes for a crossing time (118 Myr) and then we inject mass and x-momentum to a central control cylinder and experiment with the jets power: velociB µG

RM maps
We calculate RM= 812 dl rad m-2 from the jets' con3 tact discontinuity to the end of the domain along different viewing angles. This is done at different times with and without the jets to assess their effects on the CMFs. The fields in the region between the cocoon and the bow shock are amplified. The and RM increase as a function of the jets power. e.g. jets with a velocity of 80 Mach and density of 10-3 0 enhance and RM for 40% when viewed at 45 from the jets axis:
D/kpc 0 ne cm-

The evolution of the ICM energy
We calculate the ICM magnetic energy power spectra at different times with and without the jets. The initial spectrum is preserved except for numerical diffusion losses at scales 8 kpc. The jets enhance the magnetic energy in proportion to their power at all scales, specially at 40 kpc, where light-fast jets increase the magnetic energy for a factor of 1.9. Moreover, we follow the energetic evolution of the ICM. The jets transfer their kinetic energy to the thermal energy of the ambient quite efficiently at constant rates, approximately. However, we find again that only the fast jets manage to increase the total ambient magnetic energy by a factor of 2.

1.2e+54 Plasma kinetic energy [J]

light-slow heavy-slow light-fast heavy-fast

source source source source

1e+54

8e+53

6e+53

4e+53

118

120

122

124

126

128

130

132

134

Time [Myr] 6.1e+53 6e+53 5.9e+53 5.8e+53 5.7e+53 5.6e+53 5.5e+53 118 light-slow heavy-slow light-fast heavy-fast source source source source

Plasma magnetic energy [J]

120

122

124

126

128

130

132

134

Time [Myr]

The sources magnetic fields
Other example: 80 Mach, 10-2 0 and viewed at 90 from the jets axis: We do magnetic polarisation vector maps by integrating Stoke's parameters in the source and convolving the synchrotron emissivity 0 ptherm-jet B.7+1 with a passive tracer field which is injected along with the jets. We get polarisation angle distributions in good agreement with the observations of FR II objects. e.g. 3C34 from [4]:

References
[1] Carilli C. L., Taylor G. B., 2002, ARA&A, 40, 319; [2] Fryxell B. et al., 2000, ApJS, 131, 273; [3] Murgia et al. 2004, AAP, 424, 429; [4] Mullin, L. M., Hardcastle, M. J., Riley, J. M., 2006, MNRAS, 372, 113; [5] Lee D., Deaane A. E., 2008, Journal of Computational Physics, doi:10.1016/j.jcp.2008.08.026.

Acknowledgements
The software used in these investigations was in part developed by the DOE-supported ASC / Alliance Center for Astrophysical Thermonuclear Flashes at the University of Chicago. MHE acknowledges financial support from The Mexican National Council of Science and Technology, 196898/217314); Dongwook Lee for the 3D-USM-MHD solver of Flash 3.1.