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Session 118 - Radiogalaxies.
Oral session, Thursday, January 16
Three-dimensional numerical simulations of light supersonic hydrodynamic jets have been performed to quantify the crucial roles of the interstellar medium (ISM) and intracluster medium (ICM) in defining the gross morphologies of powerful radio galaxies. Such a jet emerges through a power-law atmosphere (ISM) of its host galaxy and then crosses into a hotter, but less dense, ICM. These medium-resolution simulations are followed to lengths of 45 initial jet radii. To examine the role of the denser ISM in a jet's confinement and stability, simulations with different extension of the ISM (along the jet's axis) and different inclination angles of the ISM/ICM interface are compared.
The shear layer between the jet and the shock-processed gas is affected by non-linear hydrodynamical instabilities. It yields a complex pattern of asymmetric vortex rings, superimposed streamwise vortex tubes, and resulting internal shocks. The low Mach number jets have higher growth rates of instabilities in comparison with higher Mach number jets. In the low Mach number jets, the instabilities in the sheared flow eventually allow a smearing of the backflow plasma with the forward moving plasma and thus the jet decelerates. The growth of Rayleigh-Taylor instabilities along the contact discontinuity between the shocked ambient plasma and the shocked jet's plasma triggers the entrainment of heavier external gas into the jet.
Analytical estimates of the propagation speed of the jets within the ISM match rather well with a model which allows the expansion of the effective Mach disk in tune with the power law profile of the ISM. Non-zero initial opening angles yield broader morphologies. The effectiveness of the resonance modes in the presence of inviscid non-linear shear layer instabilities is discussed. The subsonic instabilities are strongly absorbed in a critical layer during the initial growth of the shear layer, providing one reason why such jets are observed to propagate for such large distances.
Program listing for Thursday