On the spatial and temporal non-locality of dynamo mean-field effects in
  supersonic interstellar turbulence
  The interstellar medium of the Milky Way and nearby disk galaxies harbours
large-scale coherent magnetic fields of Microgauss strength, that can be
explained via the action of a mean-field dynamo. As in our previous work, we
aim to quantify dynamo effects that are self-consistently emerging in realistic
direct magnetohydrodynamic simulations, but we generalise our approach to the
case of a non-local (non-instantaneous) closure relation, described by a
convolution integral in space (time). To this end, we leverage our
comprehensive simulation framework for the supernova-regulated turbulent
multi-phase interstellar medium. By introducing spatially (temporally)
modulated mean fields, we extend the previously used test-field method to the
spectral realm -- providing the Fourier representation of the convolution
kernels. The resulting spectra of the dynamo mean-field coefficients that we
obtain broadly match expectations and allow to rigorously constrain the degree
of scale separation in the Galactic dynamo. A surprising result is found for
the diamagnetic pumping term, which increases in amplitude when going to
smaller scales. Our results amount to the most comprehensive description of
dynamo mean-field effects in the Galactic context to date. Surveying the
relevant parameter space and quenching behaviour, this will ultimately enable
the development of assumption-free sub-grid prescriptions for otherwise
unresolved global galaxy simulations.
