Variability in the stellar initial mass function at high mass: coalescence models for starburst clusters

A coalescence model using the observed properties of pre-stellar condensations (PSCs) shows how an initially steep IMF that might be characteristic of primordial cloud fragmentation can change into a Salpeter IMF or shallower IMF in a cluster of normal density after one dynamical time, even if the PSCs are collapsing on their own dynamical time. The model suggests that top-heavy IMFs in some starburst clusters originate with PSC coalescence.