DISSECTING GALAXY COLORS WITH GALEX, SDSS, AND SPITZER

We combine data from the Sloan Digital Sky Survey (SDSS), the Galaxy Evolution Explorer (GALEX), and the Spitzer Space Telescope to create a sample of galaxies observed homogeneously from the UV to the far-IR. This sample, consisting of similar to 460 galaxies observed spectroscopically by the SDSS, provides us with a multi-wavelength (0.15-24 mu m) view of obscured and unobscured star formation in nearby (z < 0.3) galaxies with star formation rates (SFRs) ranging from 0.01 to 100 M-circle dot yr(-1). We calculate a robust dust measure from the infrared-to-UV ratio (or infrared excess [IRX]) and explore the influence of star formation history (SFH) on the dust-UV color relation (i.e., the IRX-beta relation). We find that the UV colors of galaxies are only weakly dependent on their SFH as measured by the 4000 angstrom break. However, we find that the contributions of dust and SFH are A distinguishable when colors at widely separated wavelengths (e.g., 0.23-3.6 mm) are introduced. We show this explicitly by recasting the IRX-b relation as a more general IRX-SFH-color relation, which we examine in different projections. We also determine simple fits to this relation.