Gravity‐driven Turbulence in Galactic Disks

High-resolution, 2-D hydrodynamical simulations with a large dynamic rangeare performed to study the turbulent nature of the interstellar medium (ISM) ingalactic disks. The simulations are global, where the self-gravity of the ISM,realistic radiative cooling, and galactic rotation are taken into account. Inthe analysis undertaken here, feedback processes from stellar energy source areomitted. We find that the velocity field of the disk in a non-linear phaseshows a steady power-law energy spectrum over three-orders of magnitude in wavenumber. This implies that the random velocity field can be modeled asfully-developed, stationary turbulence. Gravitational and thermal instabilitiesunder the influence of galactic rotation contribute to form the turbulentvelocity field. The Toomre effective Q value, in the non-linear phase, rangesover a wide range, and gravitationally stable and unstable regions aredistributed patchily in the disk. These results suggest that large-scalegalactic rotation coupled with the self-gravity of the gas can be the ultimateenergy sources that maintain the turbulence in the local ISM. We find that ourmodels of turbulent rotating disks are consistent with the velocity dispersionof an extended HI disk in the dwarf galaxy, NGC 2915, where there is noprominent active star formation. Numerical simulations show that the stellarbar in NGC 2915 enhances the velocity dispersion, and it also drives spiralarms as observed in the HI disk.