Observations of globular clusters show that they have universal lognormal mass functions with a characteristic peak at \sim 2 \times 10 ^ { 5 } { M _ { \odot } } , but the origin of this peaked distribution is highly debated .
Here we investigate the formation and evolution of star clusters in interacting galaxies using high-resolution hydrodynamical simulations performed with two different codes in order to mitigate numerical artifacts .
We find that massive star clusters in the range of \sim 10 ^ { 5.5 } -10 ^ { 7.5 } { M _ { \odot } } form preferentially in the highly-shocked regions produced by galaxy interactions .
The nascent cluster-forming clouds have high gas pressures in the range of P / k \sim 10 ^ { 8 } -10 ^ { 12 } { Kcm ^ { -3 } } , which is \sim 10 ^ { 4 } -10 ^ { 8 } times higher than the typical pressure of the interstellar medium but consistent with recent observations of a pre-super star cluster cloud in the Antennae Galaxies .
Furthermore , these massive star clusters have quasi-lognormal initial mass functions with a peak around \sim 10 ^ { 6 } { M _ { \odot } } .
The number of clusters declines with time due to destructive processes , but the shape and the peak of the mass functions do not change significantly during the course of galaxy collisions .
Our results suggest that gas-rich galaxy mergers may provide a favorable environment for the formation of massive star clusters such as globular clusters , and that the lognormal mass functions and the unique peak may originate from the extreme high-pressure conditions of the birth clouds and may survive the dynamical evolution .