Magnetohydrodynamic Simulations of a Jet Drilling an H I Cloud: Shock Induced Formation of Molecular Clouds and Jet Breakup

Abstract

The formation mechanism of the jet-aligned CO clouds found by NANTEN CO observations is studied by magnetohydrodynamical (MHD) simulations taking into account the cooling of the interstellar medium. Motivated by the association of the CO clouds with the enhancement of HI gas density, we carried out MHD simulations of the propagation of a supersonic jet injected into the dense HI gas. We found that the HI gas compressed by the bow shock ahead of the jet is cooled down by growth of the cooling instability triggered by the density enhancement. As a result, cold dense sheath is formed around the interface between the jet and the HI gas. The radial speed of the cold, dense gas in the sheath is a few km s −1 almost independent of the jet speed. Molecular clouds can be formed in this region. Since the dense sheath wrapping the jet reflects waves generated in the cocoon, the jet is strongly perturbed by the vortices of the warm gas in the cocoon, which breaks up the jet and forms a secondary shock in the HI-cavity drilled by the jet. The particle acceleration at the shock can be the origin of radio and X-ray filaments observed near the eastern edge of W50 nebula surrounding the galactic jet source SS433.Subject headings: ISM: clouds -ISM: jets and outflows -magnetohydrodynamics (MHD) -shock waves -stars: individual(SS433)

Magnetohydrodynamic Simulations of the Formation of Molecular Clouds toward the Stellar Cluster Westerlund 2: Interaction of a Jet with a Clumpy Interstellar Medium

“…They carried out axisymmetric 2D simulations taking into account the radiative cooling in the temperature range 10 4 K < T < 10 6 K. They showed that cooling enhanced by shock compression at the head of the jet forms cool shell with temperature T ∼ 10 4 K. Axisymmetric 2D MHD simulations of the protostellar jets taking into account the radiative cooling were carried out by Frank et al (1998), Stone & Hardee (2000), and Teşileanu et al (2008). Asahina et al (2014) presented the results of two-dimensional axisymmetric magneto-hydrodynamic (MHD) simulations of the interaction of a jet and neutral hydrogen (HI) cloud by taking into account the interstellar cooling. They adopted a cooling function applicable to the high density gas with T < 10 4 K (Inoue et al 2006).…”

Bow Shock Fragmentation Driven by a Thermal Instability in Laboratory Astrophysics Experiments

“…This effect has previously been studied mostly through numerical simulations (see e.g. ; Blondin et al (1990), Stone & Norman (1993), de Gouveia dal Pino & Benz (1993), Frank et al (1998), Teşileanu et al (2008) and Asahina et al (2014)).…”

A Hydrochemical Hybrid Code for Astrophysical Problems. I. Code Verification and Benchmarks for a Photon-Dominated Region (Pdr)

“…However, chemistry plays an important role in some astrophysical flows, because chemical abundance of the gas affects thermodynamics, and consequently dynamics, of flows. For instance, atomic or molecular cooling is crucial for shock induced formation of molecular clouds (Asahina et al 2014) and stars (Vanhala & Cameron 1998). As shown in this paper, photoevaporation flow of interstellar gas caused by strong external radiation field is also typical example in which chemical evolution affects thermal and hydrodynamical evolutions.…”