Galactic Outflows by Alfvénic Poynting Flux: Application to Fermi Bubbles [GA]

We investigate roles of magnetic activity in the Galactic bulge region in driving large-scale outflows of size ~ 10 kpc. Magnetic buoyancy and breakups of channel flows formed by magnetorotational instability excite Poynting flux by the magnetic tension force. A three-dimensional global numerical simulation shows that the average luminosity of such Alfvenic Poynting flux is 10^{40} – 10^{41} erg s^{-1}. We examine the energy and momentum transfer from the Poynting flux to the gas by solving time-dependent hydrodynamical simulations with explicitly taking into account low-frequency Alfvenic waves of period of 0.5 Myr in a one-dimensional vertical magnetic flux tube. The Alfvenic waves propagate upward into the Galactic halo, and they are damped through the propagation along meandering magnetic field lines. If the turbulence is nearly trans-Alfvenic, the wave damping is significant, which leads to the formation of an upward propagating shock wave. At the shock front, the temperature >~ 5 x 10^6 K, the density ~ 1 cm^{-3}, and the outflow velocity ~ 400-500 km/s at a height ~10 kpc, which reasonably explain the basic physical properties of the thermal component of the Fermi bubbles.

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T. Suzuki and A. Lazarian
Thu, 12 Oct 17

Comments: 14 pages, 9 figures included; comments are welcome