The EDGE-CALIFA survey: the influence of galactic rotation on the
  molecular depletion time across the Hubble sequence
  We present a kpc-scale analysis of the relationship between the molecular
depletion time ($\tau_\mathrm{dep}^\mathrm{mol}$) and the orbital time
($\tau_\mathrm{orb}$) across the field of 39 face-on local galaxies, selected
from the EDGE-CALIFA sample. We find that, on average, 5% of the available
molecular gas is converted into stars per orbital time, or
$\tau_\mathrm{dep}^\mathrm{mol}\sim20\tau_\mathrm{orb}$. The resolved relation
shows a scatter of $\sim0.5$ dex. The scatter is ascribable to galaxies of
different morphologies that follow different
$\tau_\mathrm{dep}^\mathrm{mol}-\tau_\mathrm{orb}$ relations which decrease in
steepness from early- to late-types. The morphologies appear to be linked with
the star formation rate surface density, the molecular depletion time, and the
orbital time, but they do not correlate with the molecular gas content of the
galaxies in our sample. We speculate that in our molecular gas rich, early-type
galaxies, the morphological quenching (in particular the disc stabilization via
shear), rather than the absence of molecular gas, is the main factor
responsible for their current inefficient star formation.
