2003A&A...407..913V

The gas hydrodynamics modeling of the Cartwheel ring galaxy is performed with the purpose to reproduce the measured intensity and radial distribution of Hα emission in the Cartwheel's disk. The star formation efficiency of ε=0.09-0.18 is derived for an assumed Schmidt law with power index N=1.5 and a full thickness of the Cartwheel's gas disk of z₀=250-1000pc, respectively. Simulations with a Schmidt law of star formation yield a higher Hα surface brightness (Σ_Hα) in the Cartwheel's inner ring as compared to the observed values. The Toomre criterion for star formation fails to account for the observed sharp drop of massive star formation (MSF) in the inner ring. Numerical simulations indicate that a large shear near/at the position of the inner ring can raise the gas threshold for star formation and suppress MSF in the Cartwheel's inner regions. Hence, the Schmidt law has to be supplemented with a shear criterion for star formation in order to reproduce the observed radial distribution of Σ_Hα in the Cartwheel's inner regions.