GASP XXX. The Spatially Resolved SFR-Mass Relation in Stripping Galaxies in the Local Universe

Abstract

The study of the spatially resolved star formation rate-mass ( ${{\rm{\Sigma }}}_{\mathrm{SFR}}$ - ${{\rm{\Sigma }}}_{* }$ ) relation gives important insights on how galaxies assemble at different spatial scales. Here, we present an analysis of the ${{\rm{\Sigma }}}_{\mathrm{SFR}}$ - ${{\rm{\Sigma }}}_{* }$ of 40 local cluster galaxies undergoing ram-pressure stripping drawn from the GAs Stripping Phenomena in galaxies (GASP) sample. Considering their integrated properties, these galaxies show an SFR enhancement with respect to undisturbed galaxies of similar stellar mass; we now exploit spatially resolved data to investigate the origin and location of the excess. Even on ˜1kpc scales, stripping galaxies present a systematic enhancement of ${{\rm{\Sigma }}}_{\mathrm{SFR}}$ (˜0.35 dex at ${{\rm{\Sigma }}}_{* }$ = ${10}^{8}{M}_{\odot }\,{\mathrm{kpc}}^{-2}$ ) at any given ${{\rm{\Sigma }}}_{* }$ compared to their undisturbed counterparts. The excess is independent of the degree of stripping and of the amount of star formation in the tails, and it is visible at all galactocentric distances within the disks, suggesting that the star formation is most likely induced by compression waves from ram pressure. Such excess is larger for less massive galaxies and decreases with increasing mass. As stripping galaxies are characterized by ionized gas beyond the stellar disk, we also investigate the properties of 411 star-forming clumps found in the galaxy tails. At any given stellar mass density, these clumps are systematically forming stars at a higher rate than in the disk, but differences are reconciled when we just consider the mass formed in the last few 10<SUP>8</SUP> yr ago, suggesting that on these timescales, the local mode of star formation is similar in the tails and in the disks.