Interaction of an accelerating layer with a cloud: formation of tails and cumulative jets

Abstract

ABSTRACT We consider the penetration of spherical dense cloud into a planar layer of gas that is in gravitational equilibrium in a constant field of gravity with acceleration W. We take into account the compressibility of the medium in contrast to the classical problem of a drop falling on the surface of an incompressible fluid. Our goal is to study the formation of cumulative jets in relation to the conditions on the borders of H ii regions. We determine those features of motion that would distinguish jet streams from inhomogeneities of a different origin. Our simulation has shown that cumulative jets may arise in the presence of an acceleration layer W. The gas in jet moves in the direction opposite to the initial velocity Vc. At the same time, there are both a cumulative jet and tails, teardrop-shaped condensations, caused, respectively, by gas inflow in the wake behind the cloud and the classical Rayleigh–Taylor instability. We assume the model, according to which the H ii RCW 82 region formed in an initially homogeneous cloud. In framework of this model, we estimated the characteristic time of a cumulative jet formation ts ≈ 0.15 Myr. This is less than the present age of the H ii RCW 82 region, which is about 0.4 Myr. From the obtained estimates, it follows that the conditions at the periphery of the H ii RCW 82 region are favourable for the manifestation of cumulative effects on scales of ∼1.4 × 1017 cm, which are significantly smaller than the layer thickness.