The EDGE-CALIFA Survey: The Resolved Star Formation Efficiency and Local Physical Conditions

Abstract

Abstract We measure the star formation rate (SFR) per unit gas mass and the star formation efficiency (SFEgas for total gas, SFEmol for the molecular gas) in 81 nearby galaxies selected from the EDGE-CALIFA survey, using 12CO (J = 1–0) and optical IFU data. For this analysis we stack CO spectra coherently by using the velocities of Hα detections to detect fainter CO emission out to galactocentric radii r gal ∼ 1.2r 25 (∼3R e) and include the effects of metallicity and high surface densities in the CO-to-H2 conversion. We determine the scale lengths for the molecular and stellar components, finding a close to 1:1 relation between them. This result indicates that CO emission and star formation activity are closely related. We examine the radial dependence of SFEgas on physical parameters such as galactocentric radius, stellar surface density Σ⋆, dynamical equilibrium pressure P DE, orbital timescale τ orb, and the Toomre Q stability parameter (including star and gas Q star+gas). We observe a generally smooth, continuous exponential decline in the SFEgas with r gal. The SFEgas dependence on most of the physical quantities appears to be well described by a power law. Our results also show a flattening in the SFEgas–τ orb relation at log [ τ orb ] ∼ 7.9 – 8.1 and a morphological dependence of the SFEgas per orbital time, which may reflect star formation quenching due to the presence of a bulge component. We do not find a clear correlation between SFEgas and Q star+gas.