SDSS-IV MaNGA: Understanding Ionized Gas Turbulence using Integral Field
  Spectroscopy of 4500 Star-Forming Disk Galaxies
  The Sloan Digital Sky Survey MaNGA program has now obtained integral field
spectroscopy for over 10,000 galaxies in the nearby universe. We use the final
MaNGA data release DR17 to study the correlation between ionized gas velocity
dispersion and galactic star formation rate, finding a tight correlation in
which sigma_Ha from galactic HII regions increases significantly from ~ 18-30
km/s broadly in keeping with previous studies. In contrast, sigma_Ha from
diffuse ionized gas (DIG) increases more rapidly from 20-60 km/s. Using the
statistical power of MaNGA, we investigate these correlations in greater detail
using multiple emission lines and determine that the observed correlation of
sigma_Ha with local star formation rate surface density is driven primarily by
the global relation of increasing velocity dispersion at higher total SFR, as
are apparent correlations with stellar mass. Assuming HII region models
consistent with our finding that sigma_[O III] < sigma_Ha < sigma_[O I], we
estimate the velocity dispersion of the molecular gas in which individual HII
regions are embedded, finding values sigma_Mol = 5-30 km/s consistent with ALMA
observations in a similar mass range. Finally, we use variations in the
relation with inclination and disk azimuthal angle to constrain the velocity
dispersion ellipsoid of the ionized gas sigma_z/sigma_r = 0.84 +- 0.03 and
sigma_phi/sigma_r = 0.91 +- 0.03, similar to that of young stars in the
Galactic disk. Our results are most consistent with theoretical models in which
turbulence in modern galactic disks is driven primarily by star formation
feedback.
