Radial Variation of Attenuation and Star Formation in the Largest Late‐Type Disks Observed with GALEX

For a sample of 43 nearby, late-type galaxies, we have investigated theradial variation of both the current star formation rate and the dust-inducedUV light attenuation. To do this we have cross-correlated IRAS images and GALEXobservations for each of these galaxies, and compiled observations of the gas(CO and HI) and metal-abundance gradients found in the literature. We find thatattenuation correlates with metallicity. We then use the UV profiles, correctedfor attenuation, to study several variants of the Schmidt law and conclude thatour results are compatible with a simple law similar to the one of Kennicuttbut extending smoothly to lower surface densities, but with considerablescatter. We do not detect an abrupt break in the UV light at the thresholdradius derived from H-alpha data (at which the H-alpha profile shows a breakand beyond which only a few HII regions are usually found). We interpret theH-alpha sudden break not as a change in the star formation regime (as oftensuggested) but as the vanishingly small number of ionizing stars correspondingto low levels of star formation.