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Description
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 HI/H{alpha} studies. SPARC spans a broad range of morphologies (S0 to Irr), luminosities (~5dex), and surface brightnesses (~4dex). We derive [3.6] surface photometry and study structural relations of stellar and gas disks. We find that both the stellar mass-HI mass relation and the stellar radius-HI radius relation have significant intrinsic scatter, while the HI 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 ({Upsilon}_*_) at [3.6]. Assuming {Upsilon}_*_{simeq}0.5M_{Sun}_/L_{Sun}_ (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 {Upsilon}_*_ {simeq}0.2M_{Sun}_/L_{Sun}_ as suggested by the DiskMass survey. The mean maximum-disk limit in bright galaxies is {Upsilon}_*_{simeq}0.7M_{Sun}_/L_{Sun}_ at [3.6]. The SPARC data are publicly available and represent an ideal test bed for models of galaxy formation.
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