Merging time-scales of stellar sub-clumps in young star-forming regions
  Recent observations and hydrodynamical simulations of star formation inside a
giant molecular cloud have revealed that, within a star forming region, stars
do not form evenly distributed throughout this region, but rather in small
sub-clumps. It is generally believed that these sub-clumps merge and form a
young star cluster. The time-scale of this merging process is crucial for the
evolution and the possible survival of the final star cluster. The key issue is
whether this merging process happens faster than the time needed to remove the
residual gas of the cloud. A merging time-scale shorter than the gas-removal
time would enhance the survival chances of the resulting star cluster. In this
paper we show by means of numerical simulations that the time-scale of the
merging is indeed very fast. Depending on the details of the initial sub-clump
distribution, the merging may occur before the gas is expelled from the
newly-formed cluster either via supernovae or the winds from massive stars. Our
simulations further show that the resulting merger-objects have a higher
effective star formation efficiency than the overall star forming region and
confirm the results that mass-segregated sub-clumps form mass-segregated
merger-objects.
