A panchromatic spatially resolved analysis of nearby galaxies - I. Sub-kpc-scale main sequence in grand-design spirals

We analyse the spatially resolved relation between stellar mass (M∗) and star formation rate (SFR) in disc galaxies (i.e. the main sequence, MS). The studied sample includes eight nearby face-on grand-design spirals, e.g. the descendant of high-redshift, rotationally supported starforming galaxies.We exploit photometric information over 23 bands, from theUVto the far-IR, from the publicly available DustPedia data base to build spatially resolved maps of stellarmass and SFRs on sub-galactic scales of 0.5-1.5 kpc, by performing a spectral energy distribution fitting procedure that accounts for both the observed and obscured star formation processes, over a wide range of internal galaxy environments (bulges, spiral arms, and outskirts). With more than 30 000 physical cells, we have derived a definition of the local spatially resolved MS per unit area for discs, log (σSFR)= 0.82log(σ∗) - 8.69. This is consistent with the bulk of recent results based on optical IFU, using the Ha line emission as an SFR tracer. Our work extends the analysis at lower sensitivities in both M∗and SFR surface densities, up to a factor of ~10. The self-consistency of the MS relation over different spatial scales, from sub-galactic to galactic, as well as with a rescaled correlation obtained for high-redshift galaxies, clearly proves its universality.