Comparing simulated $^{26}$Al maps to gamma-ray measurements
  Context. The diffuse gamma-ray emission of $^{26}{\rm Al}$ at 1.8 MeV
reflects ongoing nucleosynthesis in the Milky Way, and traces massive-star
feedback in the interstellar medium due to its 1 Myr radioactive lifetime.
Interstellar-medium morphology and dynamics are investigated in astrophysics
through 3D hydrodynamic simulations in fine detail, as only few suitable
astronomical probes are available. Aims. We compare a galactic-scale
hydrodynamic simulation of the Galaxy's interstellar medium, including feedback
and nucleosynthesis, with gamma-ray data on $^{26}{\rm Al}$ emission in the
Milky Way extracting constraints that are only weakly dependent on the
particular realisation of the simulation or Galaxy structure. Methods. Due to
constraints and biases in both the simulations and the gamma-ray observations,
such comparisons are not straightforward. For a direct comparison, we perform
maximum likelihood fits of simulated sky maps as well as observation-based
maximum entropy maps to measurements with INTEGRAL/SPI. To study general
morphological properties, we compare the scale heights of $^{26}{\rm Al}$
emission produced by the simulation to INTEGRAL/SPI measurements.} Results. The
direct comparison shows that the simulation describes the observed inner Galaxy
well, but differs significantly from the observed full-sky emission morphology.
Comparing the scale height distribution, we see similarities for small scale
height features and a mismatch at larger scale heights. We attribute this to
the prominent foreground emission sites that are not captured by the
simulation.
