Kinematics of massive star ejecta in the Milky Way as traced by 26Al
  Massive stars form in groups and their winds and supernova explosions create
superbubbles up to kpc in size. Their ejecta are important for the dynamics of
the interstellar medium and chemical evolution models. However, ejecta
kinematics and the characteristic scales in space and time are rather
unexplored beyond ~10 ka.
  Through measurement of radioactive 26Al with its decay time constant of ~10^6
years, we aim to trace the kinematics of massive-star and supernova ejecta over
million-year time scales. Our goal is to identify the mixing time scale and the
spatio-kinematics of such ejecta from the pc to kpc scale.
  We use the SPI spectrometer on INTEGRAL and its observations along the
Galactic ridge to trace the line shape of the 1808.63 keV gamma-ray line from
26Al decay. We determine line centroids and compare these to Doppler shift
expectations from large-scale systematic rotation around the Galaxy's center,
as observed in other Galactic objects.
  We measure the radial velocities of gas traced by 26Al, averaged over the
line of sight, as a function of Galactic longitude. We find substantially
higher velocities than expected from Galactic rotation, the average bulk
velocity being ~200 km s^-1 larger than the Galactic-rotation prediction. The
observed radial velocity spread implies a Doppler-broadening of the gamma-ray
line that is consistent with our measurements of the overall line width. We can
reproduce the observed characteristics with 26Al sources located along the
inner spiral arms, when we add a global blow-out into the forward direction
away from arms, such as expected from massive stars offset towards the
spiral-arm leading edge. The superbubbles-halo connection implies
angular-momentum transfer in the disk-halo system and also radial gas flows.
