GASP - XX. From the loose spatially resolved to the tight global SFR-mass relation in local spiral galaxies

Abstract

Exploiting the sample of 30 local star-forming, undisturbed late-type galaxies in different environments drawn from the GAs Stripping Phenomena in galaxies with MUSE (GASP), we investigate the spatially resolved star formation rate-mass (Σ _{SFR}-Σ _\ast) relation. Our analysis includes also the galaxy outskirts (up to >4 effective radii, r<SUB>e</SUB>), a regime poorly explored by other Integral Field Spectrograph surveys. Our observational strategy allows us to detect H α out to more than 2.7r<SUB>e</SUB> for 75 per cent of the sample. Considering all galaxies together, the correlation between the Σ _{SFR} and Σ _\ast is quite broad, with a scatter of 0.3 dex. It gets steeper and shifts to higher Σ _\ast values when external spaxels are excluded and moving from less to more massive galaxies. The broadness of the overall relation suggests galaxy-by-galaxy variations. Indeed, each object is characterized by a distinct Σ _{SFR} -Σ _\ast relation and in some cases the correlation is very loose. The scatter of the relation mainly arises from the existence of bright off-centre star-forming knots whose Σ _{SFR}-Σ _\ast relation is systematically broader than that of the diffuse component. The Σ _{SFR}-Σ _{tot gas} (total gas surface density) relation is as broad as the Σ _{SFR}-Σ _\ast relation, indicating that the surface gas density is not a primary driver of the relation. Even though a large galaxy-by-galaxy variation exists, mean Σ _{SFR} and Σ _\ast values vary of at most 0.7 dex across galaxies. We investigate the relationship between the local and global SFR-M<SUB>*</SUB> relation, finding that the latter is driven by the existence of the size-mass relation.