Magneto-hydrodynamic Simulations of a Jet Drilling an HI Cloud: Shock Induced Formation of Molecular Clouds and Jet Breakup

摘要

The formation mechanism of the jet-aligned CO clouds found by NANTEN COobservations is studied by magnetohydrodynamical (MHD) simulations taking intoaccount the cooling of the interstellar medium. Motivated by the association ofthe CO clouds with the enhancement of HI gas density, we carried out MHDsimulations of the propagation of a supersonic jet injected into the dense HIgas. We found that the HI gas compressed by the bow shock ahead of the jet iscooled down by growth of the cooling instability triggered by the densityenhancement. As a result, cold dense sheath is formed around the interfacebetween the jet and the HI gas. The radial speed of the cold, dense gas in thesheath is a few km/s almost independent of the jet speed. Molecular clouds canbe formed in this region. Since the dense sheath wrapping the jet reflectswaves generated in the cocoon, the jet is strongly perturbed by the vortices ofthe warm gas in the cocoon, which breaks up the jet and forms a secondary shockin the HI-cavity drilled by the jet. The particle acceleration at the shock canbe the origin of radio and X-ray filaments observed near the eastern edge ofW50 nebula surrounding the galactic jet source SS433.