  A single ferromagnetic kagome layer is predicted to realize a Chern insulator
with quantized Hall conductance, which upon stacking can become a
Weyl-semimetal with large anomalous Hall effect (AHE) and magneto-optical
activity. Indeed, in the kagome bilayer material Fe$_3$Sn$_2$, a large AHE was
detected, however, it still awaits the direct probing of the responsible band
structure features by bulk sensitive methods. We measure the optical, both
diagonal and Hall, conductivity spectra over a broad spectral range and
identify the origin of the intrinsic AHE with the help of momentum- and
band-decomposed first-principles calculations. We find that low-energy
transitions, tracing "helical volumes" in momentum space reminiscent of the
formerly predicted helical nodal lines, substantially contribute to the AHE,
which is further increased by contributions from multiple higher-energy
interband transitions. Our study also reveals that local Coulomb interactions
lead to band reconstructions near the Fermi level.
