Abstract
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.
Highlights
The formation and survival of young, embedded star clusters is an important issue for the star cluster community and has implications for our understanding of the formation and evolution of galaxies as a whole
The time-scale of this merging process is crucial for the evolution and the possible survival of the final star cluster
While the star formation efficiency (SFE; i.e. the fraction of gas which ends up in the star(s)) in these cores is high, the overall SFE measured over the whole molecular cloud is very low, of the order of a few per cent (Clark & Bonnell 2004), and 40 per cent in cluster-forming clumps
Summary
The formation and survival of young, embedded star clusters is an important issue for the star cluster community and has implications for our understanding of the formation and evolution of galaxies as a whole. While the star formation efficiency (SFE; i.e. the fraction of gas which ends up in the star(s)) in these cores is high, the overall SFE measured over the whole molecular cloud is very low, of the order of a few per cent (Clark & Bonnell 2004), and 40 per cent in cluster-forming clumps (i.e. embedded star clusters, Lada & Lada 2003). Dissolving sub-clumps (due to the fast two-body relaxation) will distribute their stars preferentially in the centre, i.e. in and around the merger object This process would tend to reduce the time-scale for star cluster formation rather than prolonging it. Where Tcsrc is the crossing time of the star forming cloud
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