Star formation is boosted (and quenched) from the inside-out: radial star formation profiles from MaNGA

The tight correlation between total galaxy stellar mass and star formation rate (SFR) has become known as the star-forming main sequence. Using similar to 487 000 spaxels from galaxies observed as part of the Sloan Digital Sky Survey Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we confirm previous results that a correlation also exists between the surface densities of star formation (Sigma(SFR)) and stellar mass (Sigma(star)) on kpc scales, representing a 'resolved' main sequence. Using a new metric (Delta Sigma(SFR)), which measures the relative enhancement or deficit of star formation on a spaxel-by-spaxel basis relative to the resolved main sequence, we investigate the SFR profiles of 864 galaxies as a function of their position relative to the global star-forming main sequence (Delta SFR). For galaxies above the global main sequence (positive Delta SFR) Delta Sigma(SFR) is elevated throughout the galaxy, but the greatest enhancement in star formation occurs at small radii (<3 kpc, or 0.5R(e)). Moreover, galaxies that are at least a factor of 3 above the main sequence show diluted gas phase metallicities out to 2R(e), indicative of metal-poor gas inflows accompanying the starbursts. For quiescent/passive galaxies that lie at least a factor of 10 below the star-forming main sequence, there is an analogous deficit of star formation throughout the galaxy with the lowest values of Delta Sigma(SFR) in the central 3 kpc. Our results are in qualitative agreement with the 'compaction' scenario in which a central starburst leads to mass growth in the bulge and may ultimately precede galactic quenching from the inside-out.