The effects of a compressive velocity pulse on a collapsing turbulent clump

Abstract

High-resolution hydrodynamical simulations are presented to follow the gravitational collapse of a uniform turbulent clump, upon which a purely radial compressive velocity pulse is activated in the midst of the evolution of the clump, when its turbulent state has been fully developed. The shape of the velocity pulse is determined basically by two free parameters: the velocity $V_0$ and the initial radial position $r_0$. In the present paper, models are considered in which the velocity $V_0$ takes the values 2, 5, 10, 20, and 50 times the speed of sound of the clump $c_0$, while $r_0$ is fixed for all the models. The collapse of the model with $2 \, c_0$ goes faster as a consequence of the velocity pulse, while the cluster formed in the central region of the isolated clump mainly stays the same. In the models with greater velocity $V_0$, the evolution of the isolated clump is significantly changed, so that a dense shell of gas forms around $r_0$ and moves radially inward. The radial profile of the density and velocity as well as the mass contained in the dense shell of gas are calculated, and it is found that (i) the higher the velocity $V_0$, the less mass is contained in the shell; (ii) there is a critical velocity of the pulse, around $10 \, c_0$, such that for shock models with a lower velocity, there will be a well defined dense central region in the shocked clump surrounded by the shell.