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

Abstract

We introduce SPARC ( Spitzer Photometry and Accurate Rotation Curves): a sample of 175 nearby galaxies with new surface photometry at 3.6  μ m and high-quality rotation curves from previous H i /H α 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.