HI and CO observations of M33 interstellar medium

We find that the HI turbulent energy surface density inside 8kpc is ~1-3x10^46^erg/pc^2^, and has no strong dependence on galactocentric radius because of the lack of variation in HI surface density and HI velocity dispersion. Then, we consider the energies injected by supernovae (SNe), the magneto-rotational instability (MRI), and the gravity-driven turbulence from accreted materials as the sources of turbulent energy.

For a constant dissipation time of turbulence, the SNe energy can maintain turbulence inside ~4kpc radius (equivalent to ~0.5R_25_), while the MRI energy is always smaller than the turbulent energy within 8kpc radius. However, when we let the dissipation time to be equal to the crossing time of turbulence across the HI scale height, the SNe energy is enough to maintain turbulence out to 7kpc radius, and the sum of SNe and MRI energies is able to maintain turbulence out to 8kpc radius.