What drives the velocity dispersion of ionized gas in star-forming
  galaxies?
  We analyze the intrinsic velocity dispersion properties of 648 star-forming
galaxies observed by the Mapping Nearby Galaxies at Apache Point Observatory
(MaNGA) survey, to explore the relation of intrinsic gas velocity dispersions
with star formation rates (SFRs), SFR surface densities ($\rm{\Sigma_{SFR}}$),
stellar masses and stellar mass surface densities ($\rm{\Sigma_{*}}$). By
combining with high z galaxies, we found that there is a good correlation
between the velocity dispersion and the SFR as well as $\rm{\Sigma_{SFR}}$. But
the correlation between the velocity dispersion and the stellar mass as well as
$\rm{\Sigma_{*}}$ is moderate. By comparing our results with predictions of
theoretical models, we found that the energy feedback from star formation
processes alone and the gravitational instability alone can not fully explain
simultaneously the observed velocity-dispersion/SFR and
velocity-dispersion/$\rm{\Sigma_{SFR}}$ relationships.
