On the Gravitational Boundedness of Small Scale Structures in Molecular Clouds

Abstract

We investigate, in a set of 3D numerical simulations of driven, magnetized, isothermal, and self-gravitating molecular clouds (MCs), the statistical correlations between the energy ratios (thermal/gravity, and kinetic/gravity) of clumps and cores (CCs) identified in the simulations and gravitational binding indicators commonly used in observational studies such as the Jeans number, J_{c}, and the virial parameter, alpha_{vir}. In the energy ratios, we consider the surface energy terms which account for the effects of the environment on the clump gravitational boundedness. We find that: a) J_{c} and the thermal/gravitational energy ratios are well correlated, b) alpha_{vir} and the (thermal+kinetic)/gravity or kinetic/gravity energy ratios are poorly correlated, additionally affected by the ambiguity of the compressive or dispersive effect of the velocity field. This result suggest that the use of alpha_{vir} estimates in the observations is only useful to assess the kinetic+thermal energy content of a CC and not its gravitational boundedness. Finally, we discuss briefly the possibility of measuring the kinetic energy surface term directly in the observations.