Dynamical evolution of star-forming regions

Abstract

We model the dynamical evolution of star-forming regions with a wide range of initial properties. We follow the evolution of the regions' substructure using the Q-parameter, we search for dynamical mass segregation using the ΛMSR technique, and we also quantify the evolution of local density around stars as a function of mass using the ΣLDR method. The amount of dynamical mass segregation measured by ΛMSR is generally only significant for subvirial and virialized, substructured regions - which usually evolve to form bound clusters. The ΣLDR method shows that massive stars attain higher local densities than the median value in all regions, even those that are supervirial and evolve to form (unbound) associations. We also introduce the Q - ΣLDR plot, which describes the evolution of spatial structure as a function of mass-weighted local density in a star-forming region. Initially dense (>1000 stars pc-2), bound regions always have Q < 1, ΣLDR > 2 after 5 Myr, whereas dense unbound regions always have Q < 1, ΣLDR > 2 after 5 Myr. Less dense regions (<100 stars pc-2) do not usually exhibit ΣLDR > 2 values, and if relatively high local density around massive stars arises purely from dynamics, then the Q - ΣLDR plot can be used to estimate the initial density of a star-forming region.