The Complex Distribution of Recently Formed Stars. Bimodal Stellar
  Clustering in the Star-Forming Region NGC 346
  We present a detailed stellar clustering analysis with the application of the
two-point correlation function on distinct young stellar ensembles. Our aim is
to understand how stellar systems are assembled at the earliest stages of their
formation. Our object of interest is the star-forming region NGC 346 in the
Small Magellanic Cloud. It is a young stellar system well-revealed from its
natal environment, comprising complete samples of pre--main-sequence and upper
main-sequence stars, very close to their formation. We apply a comprehensive
characterization of the autocorrelation function for both centrally condensed
stellar clusters and self-similar stellar distributions through numerical
simulations of stellar ensembles. We interpret the observed autocorrelation
function of NGC 346 on the basis of these simulations. We find that it can be
best explained as the combination of two distinct stellar clustering designs, a
centrally concentrated, dominant at the central part of the star-forming
region, and an extended self-similar distribution of stars across the complete
observed field. The cluster component, similar to non-truncated young star
clusters, is determined to have a core radius of ~2.5 pc and a density profile
index of ~2.3. The extended fractal component is found with our simulations to
have a fractal dimension of ~2.3, identical to that found for the interstellar
medium, in agreement to hierarchy induced by turbulence. This suggests that the
stellar clustering at a time very near to birth behaves in a complex manner. It
is the combined result of the star formation process regulated by turbulence
and the early dynamical evolution induced by the gravitational potential of
condensed stellar clusters.
