Deriving the intrinsic properties of M51 with radiative transfer models

A quantitative derivation of the intrinsic properties of galaxies related to their fundamental building blocks, gas, dust, and stars is essential for our understanding of galaxy evolution. A fully self-consistent derivation of these properties can be achieved with radiative transfer (RT) methods that are constrained by panchromatic imaging observations. Here, we present an axi-symmetric RT model of the UV-optical-FIR/submm spectral and spatial energy distribution of the face-on spiral galaxy M51. The model reproduces reasonably well the azimuthally averaged radial profiles derived from the imaging data available for this galaxy, from GALEX, Sloan Digital Sky Survey, 2MASS, Spitzer, and Herschel. We model the galaxy with three distinct morphological components: a bulge, an inner disc, and a main disc. We derive the length parameters of the stellar emissivity and of the dust distribution. We also derive the intrinsic global and spatially resolved parameters of M51. We find a faint 'outer disc' bridging M51 with its companion galaxy M51b. Finally, we present and discuss an alternative model, with dust properties that change within the galaxy.