  While dark matter (DM) is the key ingredient for a successful theory of
structure formation, its microscopic nature remains elusive. Indirect detection
may provide a powerful test for some strongly motivated DM particle models.
Nevertheless, astrophysical backgrounds are usually expected with amplitudes
and spectral features similar to the chased signals. On galactic scales, these
backgrounds arise from interactions of cosmic rays (CRs) with the interstellar
gas, both being difficult to infer and model in detail from observations.
Moreover, the associated predictions unavoidably come with theoretical errors,
which are known to be significant. We show that a trustworthy guide for such
challenging searches can be obtained by exploiting the full information
contained in cosmological simulations of galaxies, which now include baryonic
gas dynamics and star formation. We further insert CR production and transport
from the identified supernova events and fully calculate the CR distribution in
a simulated galaxy. We focus on diffuse gamma-rays, and self-consistently
calculate both the astrophysical galactic emission and the dark matter signal.
We notably show that adiabatic contraction does not necessarily induce large
signal-to-noise ratios in galactic centers, and could anyway be traced from the
astrophysical background itself. We finally discuss how all this may be used as
a generic diagnostic tool for galaxy formation.
