A Distant Echo of Milky Way Central Activity closes the Galaxy's Baryon
  Census
  We report on the presence of large amounts of million-degree gas in the Milky
Way's interstellar and circum-galactic medium. This gas (1) permeates both the
Galactic plane and the halo, (2) extends to distances larger than 60-200 kpc
from the center, and (3) its mass is sufficient to close the Galaxy's baryon
census.
  Moreover, we show that a vast, $\sim 6$ kpc radius, spherically-symmetric
central region of the Milky Way above and below the 0.16 kpc thick plane, has
either been emptied of hot gas or the density of this gas within the cavity has
a peculiar profile, increasing from the center up to a radius of $\sim 6$ kpc,
and then decreasing with a typical halo density profile. This, and several
other converging pieces of evidence, suggest that the current surface of the
cavity, at 6 kpc from the Galaxy's center, traces the distant echo of a period
of strong nuclear activity of our super-massive black-hole, occurred about 6
Myrs ago.
