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 μm and high-quality rotation curves from previous H I/Hα studies. SPARC spans a broad range of morphologies (S0 to Irr), luminosities (∼5 dex), and surface brightnesses (∼4 dex). We derive [3.6] surface photometry and study structural relations of stellar and gas disks. We find that both the stellar mass-H I mass relation and the stellar radius-H I radius relation have significant intrinsic scatter, while the H I mass-radius 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 (ϒ_⋆) at [3.6]. Assuming ϒ_⋆ ≃ 0.5 M _⊙/L _⊙ (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 of ϒ_⋆ ≃ 0.2 M _⊙/L _⊙ as suggested by the DiskMass survey. The mean maximum-disk limit in bright galaxies is ϒ_⋆ ≃ 0.7 M _⊙/L _⊙ at [3.6]. The SPARC data are publicly available and represent an ideal test bed for models of galaxy formation.