http://arxiv.org/abs/1403.2129
A pair of giant gamma-ray bubbles which extend ~50 degrees above and below the Galactic plane with a width of ?~40 degrees are revealed by the Fermi Gamma-ray Space Telescope. The formation mechanism of the bubbles is still under debate. Many observations have strongly indicated that the activity of the supermassive black hole located in the Galactic center, Sgr A*, is likely much stronger than the present time, and the Fermi bubbles may be the result of this activity. Speci?cally, the previous independent quantitative studies to the past activity show that while Sgr A* was also in a hot accretion regime, the accretion rate should be 3-4 orders of magnitude higher than the present value and last for 10^7 yr. Recent MHD numerical simulations of hot accretion flows have shown the existence of winds from hot accretion flows and obtained their main properties such as mass flux and velocity. Based on these knowledge and constraints, in this paper we have performed three-dimensional hydrodynamical numerical simulations to study the formation of the Fermi bubbles. We ?find that the winds can well explain the main observational features of the Fermi bubbles. The active phases is required to last for about 10 million years and the later quiescent state should last for no more than 0.2 million years. Disc-like and massive Central Molecular Zone (CMZ) changes the outflow orientation, to be approximately towards Galactic poles. Viscosity suppresses the Rayleigh- Taylor (RT) instability and Kelvin-Helmholtz (KH) instability, which induces a smooth edge. The observed ROSAT X-ray features can be interpreted by the shocked interstellar medium (ISM) and the interaction region between outflow gas and CMZ gas. Moreover, the thermal pressure and the temperature are in very good consistency with the recent Suzaku observational results.
G. Mou, F. Yuan, D. Bu, et. al.
Tue, 11 Mar 14
7/66