Specific Star Formation Rate Profiles in Nearby Spiral Galaxies: Quantifying the Inside‐Out Formation of Disks

We present specific Star Formation Rate (sSFR) radial profiles for a sampleof 161 relatively face-on spiral galaxies from the GALEX Atlas of NearbyGalaxies. The sSFR profiles are derived from GALEX & 2MASS (FUV-K) colorprofiles after a proper SFR calibration of the UV luminosity and K-bandmass-to-light ratio are adopted. The (FUV-K) profiles were first corrected forforeground Galactic extinction and later for internal extinction using theratio of the total-infrared (TIR) to FUV emission. For those objects whereTIR-to-FUV-ratio radial profiles were not available, the (FUV-NUV) colorprofiles as a measure of the UV slope. The sSFR radial gradients derived fromthese profiles allow us to quantify the inside-out scenario for the growth ofspiral disks for the first time in the local Universe. We find a large dispersion in the slope of the sSFR profiles with a slightlypositive mean value, which implies a moderate inside-out disk formation. Thereis also a strong dependency of the value of this slope on the luminosity andsize of the disks, with large systems showing a uniform, slightly positiveslope in almost all cases and low-luminosity small disks showing a largedispersion with both positive and negative large values. While a majority ofthe galaxies can be interpreted as forming stars gradually either from insideout or from outside in, a few disks require episodes of enhanced recent growthwith scale lengths of the SFR (or gas infall) being significantly larger atpresent than in the past. We do not find any clear dependence of the sSFRgradient on the environment (local galaxy density or presence of closeneighbors).