2017MNRAS.467.3544S

We constrain the origin of Fermi bubbles using 2D hydrodynamical simulations of both star formation-driven and black hole accretion-driven wind models. We compare our results with recent observations of O VIII to O VII line ratio within and near Fermi bubbles. Our results suggest that independent of the driving mechanisms, a low-luminosity ( L ∼0.7-1×10⁴¹ erg s^–1) energy injection best reproduces the observed line ratio for which the shock temperature is ≃3 x 10⁶ K. Assuming the Galactic halo temperature to be 2 x 10⁶ K, we estimate the shock velocity to be ∼300 km s^–1 for a weak shock. The corresponding estimated age of the Fermi bubbles is ∼15-25 Myr. Such an event can be produced either by a star formation rate of ∼0.5 M_☉ yr^–1 at the Galactic Centre or a very low-luminosity jet/accretion wind arising from the central black hole. Our analysis rules out any activity that generates an average mechanical luminosity >=10⁴¹ erg s^–1 as a possible origin of the Fermi bubbles.