Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Institute. STScI is operated by the association of Universities for Research in Astronomy, Inc., under the NASA contract NAS 5-26555.

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Fitting a function of the form ${\rm log}~(N(r)) = a+b\cdot{\rm log}~(r)$ results in $b=-\eta$ . However, using logarithmic binning, one fits ${\rm log}~(N({\rm log}~(r))) = a+b\cdot{\rm log}~(r)$ , in which $b=1-\eta$ . This extra term +1 can easily cause confusion when comparing different distributions. Also see B05 and Elmegreen & Falgarone (1996).

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... IRAF

The Image Reduction and Analysis Facility (IRAF) is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.

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... distribution

Strictly speaking, the term distribution refers to linear intervals, i.e. $N(R){\rm d} R$ , and the term function refers to logarithmic intervals, i.e. $N(R){\rm d}{\rm log}~R$ . In this work, however, we will not make this distinction. We will only use the term distribution and we will specify the type of interval used when necessary.

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... clouds

Between 0.5 and $\sim$ 10 pc a log-normal distribution provides a reasonable fit to the data (not shown here).

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... radii

If one would actually quantify any age-radius relation one needs to be aware of possible biases, due to a slight mass-radius relation or size-of-sample effects. E.g. at older ages, the low-mass clusters will first fade below the detection limit, so any observed age-radius relation could then result from a possible mass-radius relation. Also, if one would let the absolute age intervals increase with age (i.e. logarithmic binning), one would sample the radius distribution up to larger radii for older ages and the average radius would seem to increase with age.

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