Dynamic cores in hydrostatic disguise

Abstract

(Abrigded) We discuss the column density profiles of "cores" in 3D SPH numerical simulations of turbulent molecular clouds. The SPH scheme allows us to perform a high spatial resolution analysis of the density maxima (cores) at scales between ~0.003 and 0.3pc. We analyze simulations in three different physical conditions: large scale driving, small scale driving, and random Gaussian initial conditions without driving; each one at two different timesteps: just before self-gravity is turned-on, and when gravity has been operating such that 5% of the total mass in the box has been accretted into cores. For this dataset, we perform Bonnor-Ebert fits to the column density profiles of cores. We find that 65% of the cores can be matched to Bonnor-Ebert profiles, and of these, 47% correspond to stable equilibrium configurations with xi_max < 6.5, even though the cores analyzed in the simulations are not in equilibrium, but instead are dynamically evolving. We also find in some cases substantial superposition effects when we analyze the projection of the density structures. As a consequence, different projections of the same core may give very different values of the BE fits. Finally, we briefly discuss recent results claiming that Bok globule B68 is in hydrostatic equilibrium, stressing that they imply that this core is unstable by a wide margin. We conclude that fitting BE profiles to observed cores is not an unambiguous test of hydrostatic equilibrium, and that fit-estimated parameters of the BE sphere may differ significantly from the actual values in the cores.