Scaling relations for globular clusters ( GCs ) differ from scaling relations for pressure supported ( elliptical ) galaxies .
We show that two-body relaxation is the dominant mechanism in shaping the bivariate dependence of density on mass and Galactocentric distance for Milky Way GCs with masses \lesssim 10 ^ { 6 } M _ { \odot } , and it is possible , but not required , that GCs formed with similar scaling relations as ultra-compact dwarf galaxies .
We use a fast cluster evolution model to fit a parameterised model for the initial properties of Milky Way GCs to the observed present-day properties .
The best-fit cluster initial mass function is substantially flatter ( power-law index \alpha = -0.6 \pm 0.2 ) than what is observed for young massive clusters ( YMCs ) forming in the nearby Universe ( \alpha \simeq - 2 ) .
A slightly steeper CIMF is allowed when considering the metal-rich GCs separately ( \alpha \simeq - 1.2 \pm 0.4 ) .
If stellar mass loss and two-body relaxation in the Milky Way tidal field are the dominant disruption mechanisms , then GCs formed differently from YMCs .