Synthetic $^{26}$Al emission from galactic-scale superbubble simulations
  Emission from the radioactive trace element $^{26}$Al has been observed
throughout the Milky Way with the COMPTEL and INTEGRAL satellites. In
particular the Doppler shifts measured with INTEGRAL connect $^{26}$Al with
superbubbles, which may guide $^{26}$Al flows off spiral arms in the direction
of Galactic rotation. In order to test this paradigm, we have performed
galaxy-scale simulations of superbubbles with $^{26}$Al injection in a Milky
Way-type galaxy. We produce all-sky synthetic $\gamma-$ray emission maps of the
simulated galaxies. We find that the 1809keV emission from the radioactive
decay of $^{26}$Al is highly variable with time and the observer's position.
This allows us to estimate an additional systematic variability of 0.2dex for a
star formation rate derived from $^{26}$Al for different times and measurement
locations in Milky Way-type galaxies. High-latitude morphological features
indicate nearby emission with correspondingly high integrated $\gamma-$ray
intensities. We demonstrate that the $^{26}$Al scale height from our simulated
galaxies depends on the assumed halo gas density. We present the first
synthetic 1809keV longitude-velocity diagrams from 3D hydrodynamic simulations.
The line-of-sight velocities for $^{26}$Al can be significantly different from
the line-of-sight velocities associated with the cold gas. Over time, $^{26}$Al
velocities consistent with the INTEGRAL observations, within uncertainties,
appear at any given longitude, broadly supporting previous suggestions that
$^{26}$Al injected into expanding superbubbles by massive stars may be
responsible for the high velocities found in the INTEGRAL observations. We
discuss the effect of systematically varying the location of the superbubbles
relative to the spiral arms.
