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A simple model of gas accretion in young galaxy disks suggests that fastturbulent motions can be driven by accretion energy for a timet_acc~2(epsilon^{0.5} GM^2/xi V^3)^{0.5} where epsilon is the fraction of theaccretion energy going into disk turbulence, M and V are the galaxy mass androtation speed, and xi is the accretion rate. After t_acc, accretion isreplaced by disk instabilities as a source of turbulence driving, and shortlyafter that, energetic feedback by young stars should become important. The starformation rate equilibrates at the accretion rate after 1 to 2 t_acc, dependingon the star formation efficiency per dynamical time. The fast turbulence thatis observed in high redshift starburst disks is not likely to be driven byaccretion because the initial t_acc phase is over by the time the starburst ispresent. However, the high turbulent speeds that must have been presentearlier, when the observed massive clumps first formed, could have been drivenby accretion energy. The combined observations of a high relative velocitydispersion in the gas of z~2 clumpy galaxies and a gas mass comparable to thestellar mass suggests that either the star formation efficiency is fairly high,perhaps 10x higher than in local galaxies, or the observed turbulence ispowered by young stars.

Accretion-Driven Turbulence and the Transition to Global Instability in Young Galaxy Disks