Using three-dimensional hydrodynamic simulations , we investigate heating and turbulence driving in an intracluster medium ( ICM ) by orbital motions of galaxies in a galaxy cluster .
We consider N _ { g } member galaxies on isothermal and isotropic orbits through an ICM typical of rich clusters .
An introduction of the galaxies immediately produces gravitational wakes , providing perturbations that can potentially grow via resonant interaction with the background gas .
When N _ { g } ^ { 1 / 2 } M _ { 11 } \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } 100 , where { M _ { 11 } } is each galaxy mass in units of 10 ^ { 11 } { M _ { \odot } } , the perturbations are in the linear regime and the resonant excitation of gravity waves is efficient to generate kinetic energy in the ICM , resulting in the velocity dispersion \sigma _ { v } \sim 2.2 N _ { g } ^ { 1 / 2 } { M _ { 11 } } { km s ^ { -1 } } .
When N _ { g } ^ { 1 / 2 } M _ { 11 } \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 100 , on the other hand , nonlinear fluctuations of the background ICM destroy galaxy wakes and thus render resonant excitation weak or absent .
In this case , the kinetic energy saturates at the level corresponding to \sigma _ { v } \sim 220 { km s ^ { -1 } } .
The angle-averaged velocity power spectra of turbulence driven in our models have slopes in the range of -3.7 to -4.3 .
With the nonlinear saturation of resonant excitation , none of the cooling models considered are able to halt cooling catastrophe , suggesting that the galaxy motions alone are unlikely to solve the cooling flow problem .