Young Star Clusters In Nearby Molecular Clouds
  The SFiNCs (Star Formation in Nearby Clouds) project is an X-ray/infrared
study of the young stellar populations in 22 star forming regions with
distances <=1 kpc designed to extend our earlier MYStIX survey of more distant
clusters. Our central goal is to give empirical constraints on cluster
formation mechanisms. Using parametric mixture models applied homogeneously to
the catalog of SFiNCs young stars, we identify 52 SFiNCs clusters and 19
unclustered stellar structures. The procedure gives cluster properties
including location, population, morphology, association to molecular clouds,
absorption, age (AgeJX), and infrared spectral energy distribution (SED) slope.
Absorption, SED slope, and AgeJX are age indicators. SFiNCs clusters are
examined individually, and collectively with MYStIX clusters, to give the
following results. (1) SFiNCs is dominated by smaller, younger, and more
heavily obscured clusters than MYStIX. (2) SFiNCs cloud-associated clusters
have the high ellipticities aligned with their host molecular filaments
indicating morphology inherited from their parental clouds. (3) The effect of
cluster expansion is evident from the radius-age, radius-absorption, and
radius-SED correlations. Core radii increase dramatically from ~0.08 to ~0.9 pc
over the age range 1--3.5 Myr. Inferred gas removal timescales are longer than
1 Myr. (4) Rich, spatially distributed stellar populations are present in
SFiNCs clouds representing early generations of star formation. An Appendix
compares the performance of the mixture models and nonparametric Minimum
Spanning Tree to identify clusters. This work is a foundation for future
SFiNCs/MYStIX studies including disk longevity, age gradients, and dynamical
modeling.
