ProFuse: physical multiband structural decomposition of galaxies and the mass-size-age plane

We present the new PROFUSE R package, a simultaneous spectral (ultraviolet to far-infrared) and spatial structural decomposition tool that produces physical models of galaxies and their components. This combines the functionality of the recently released PROFOUND (for automatic source extraction), PROFIT (for extended source profiling), and PROSPECT (for stellar population modelling) software packages. The key novelty of PROFUSE is that it generates images using a self-consistent model for the star formation and metallicity history of the bulge and disc separately, and uses target images across a range of wavelengths to define the model likelihood and optimize our physical galaxy reconstruction. The first part of the paper explores the PROFUSE approach in detail, and compares results to published structural and stellar population properties. The latter part of the paper applies PROFUSE to 6664 z < 0.06 GAMA galaxies. Using re-processed ugriZYJHKs imaging we extract structural and stellar population properties for bulges and discs in parallel. As well as producing true stellar mass based mass-size relationships, we further extend this correlation to explore the third dimensions of age and gas phase metallicity. The discs in particular demonstrate strong co-dependency between mass-size-age in a well-defined plane, where at a given disc stellar mass younger discs tend to be larger. These findings are in broad agreement with work at higher redshift, suggesting discs that formed earlier are physically smaller.