Spontaneous Generation of the Magnetic Field and Suppression of the Heat Conduction in Cold Fronts

We have determined the physical mechanism responsible for the plasmainstabilities, which was first found by Ramani and Laval (1978), associatedwith anisotropic velocity distributions induced by the temperature gradient inwhich there are growing low frequency transverse magnetic waves, even in theabsence of background magnetic fields. We have shown that the physicalmechanism responsible for the growth of one of the modes is identical to theWeibel instability. The nonlinear saturation level of the instability is alsoprovided by considering the wave-particle interactions. The non-linearevolutions of the magnetic fields after the saturation are speculated. Theresults are applied to the cold fronts which is one of the newly discoveredstructures in clusters of galaxies by the Chandra X-ray observatory. We predictthe existence of the magnetic field of $\sim 10\mu$G tangential to the surfaceover the entire region of the cold front surface and that the heat conductionis significantly suppressed by the trapping of the electrons by the generatedmagnetic fields. The instability may provide a new possibility on the origin ofcosmic magnetic field.Comment: 18 pages, 4 figures. Accepted for publication in the Astrophysical Journa