Fermi Bubbles in the Milky Way: the closest AGN feedback laboratory
  courtesy of Sgr A*?
  Deposition of a massive ($10^4$ to $10^5 \msun$) giant molecular cloud (GMC)
into the inner parsec of the Galaxy is widely believed to explain the origin of
over a hundred unusually massive young stars born there $\sim 6$ Myr ago. An
unknown fraction of that gas could have been accreted by Sgr A*, the
supermassive black hole (SMBH) of the Milky Way. It has been recently suggested
that two observed $\gamma$-ray-emitting bubbles emanating from the very center
of our Galaxy were inflated by this putative activity of Sgr A*. We run a suite
of numerical simulations to test whether the observed morphology of the bubbles
could be due to the collimation of a wide angle outflow from Sgr A* by the
disc-like Central Molecular Zone (CMZ), a well known massive repository of
molecular gas in the central $\sim 200$ pc. We find that an Eddington-limited
outburst of Sgr A* lasting $\simeq 1$ Myr is required to reproduce the
morphology of the {\it Fermi} bubbles, suggesting that the GMC mass was $\sim
10^5 \msun$ and it was mainly accreted by Sgr A* rather than used to make
stars. We also find that the outflow from Sgr A* enforces strong angular
momentum mixing in the CMZ disc, robustly sculpting it into a much narrower
structure -- a ring -- perhaps synonymous with the recently reported "Herschel
ring". In addition, we find that Sgr A* outflow is likely to have induced
formation of massive star-forming GMCs in the CMZ. In this scenario, the Arches
and Quintuplet clusters, the two observed young star clusters in the central
tens of parsecs of the Galaxy, and also GMCs such as Sgr B2, owe their
existence to the recent Sgr A* activity.
