The Milky Way as a distant galaxy: an IFU and panchromatic view

Understanding the structure and evolution of galaxies increasingly benefits from placing the Milky Way (MW), the best-studied stellar system, in an external-galaxy context. To analyse the MW as an extragalactic system, we construct an integrated-light view of it using two complementary approaches: composite stellar populations built from a selection-function-free orbit-superposition solution constrained by APOGEE DR17, and full SKIRT radiative-transfer modelling of a hydrodynamical MW simulation initialised from the same solution. In both cases, the MW data are assembled into mock IFU datacubes and analysed with with full spectral fitting (pPXF). We find, however, that the underlying LOSVD is more complex than can be captured by a Gauss-Hermite parametrisation, as is likely the case in MW-like late-type barred galaxies. For the composite-population mocks, we recover the main large-scale kinematic structures, including the rotation and velocity-dispersion patterns associated with the thin and thick discs and the bar/bulge, together with the mean stellar-population maps. The known disc chemical bimodality in [α/M]-[M/H] cannot be recovered directly from the IFU, regardless of the α-resolution of the SSP templates, but its MW-like spatially varying double-sequence behaviour is recovered across the disc. The broad global star-formation history is reproduced, although artificial bursts, likely driven by the age-metallicity degeneracy, remain even after regularisation. For the radiative-transfer mocks, the main kinematic maps are recovered with moderate accuracy, whereas higher-order moments and stellar-population properties remain difficult to constrain, primarily because of the lower spectral resolution and lower statistical SNR of the datacubes. These results indicate that forward panchromatic modelling remains challenging for high-resolution IFU-like observations.