SPARC: MASS MODELS FOR 175 DISK GALAXIES WITH SPITZER PHOTOMETRY AND ACCURATE ROTATION CURVES

We introduce SPARC (Spitzer Photometry and Accurate Rotation Curves): a sample of 175 nearby galaxies with new surface photometry at 3.6. mu m and high-quality rotation curves from previous H I/H alpha studies. SPARC spans a broad range of morphologies (S0 to Irr), luminosities (similar to 5 dex), and surface brightnesses (similar to 4 dex). We derive [3.6] surface photometry and study structural relations of stellar and gas disks. We find that both the stellar massH I mass relation and the stellar radius-H I radius relation have significant intrinsic scatter, while the H I. massradius relation is extremely tight. We build detailed mass models and quantify the ratio of baryonic. to. observed velocity (V-bar/V-obs) for different characteristic radii and values of the stellar mass-to-light ratio (gamma(star)) at [3.6]. Assuming.gamma(star) 0.5 M-circle dot/L-circle dot (as suggested by stellar population models), we find that (i). the gas fraction linearly correlates with total luminosity;. (ii) the transition from star-dominated to gas-dominated galaxies roughly corresponds to the transition from spiral galaxies to dwarf irregulars, in line with density wave theory; and (iii). V-bar/V-obs varies with luminosity and surface brightness: high-mass, high-surface-brightness galaxies are nearly maximal, while low-mass, low-surface-brightness galaxies are submaximal. These basic properties are lost for low values