Colloquium
Relativistic hydro and magnetohydrodynamic models for AGN jet propagation and deceleration
Resumen
I will present grid-adaptive computational studies of both magnetized and unmagnetized jet flows, with significantly relativistic bulk speeds, as appropriate for AGN jets. Our relativistic jet studies shed light on the observationally established classification of Fanaroff-Riley galaxies, where the appearance in radio maps distinguishes two types of jet morphologies. We investigate how density changes in the external medium can induce one-sided jet decelerations, explaining the existence of hybrid morphology radio sources. Our simulations explore under which conditions highly energetic FR II jets may suddenly decelerate and continue with FR I characteristics. In a related investigation, we explore the role of dynamically important, organized magnetic fields in the collimation of the relativistic jet flows. In that study, we concentrate on morphological features of the bow shock and the jet beam, for various jet Lorentz factors and magnetic field helicities. We show that the helicity of the magnetic field is effectively transported down the beam, with compression zones in between diagonal internal cross-shocks showing stronger toroidal field regions. For the high speed jets considered, significant jet deceleration only occurs beyond distances exceeding hundred jet radii, as the axial flow can reaccelerate downstream to internal cross-shocks. This reacceleration is magnetically aided, due to field compression across the internal shocks which pinch the flow.Sobre la charla
Centre for Plasma-Astrophysics, K. U. Leuven, Belgium
jets, galactic nuclei, cooling flows, active galaxies, outflows, magnetic fields, magnetohydrodynamics
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Sobre el conferenciante
Rony Keppens is professor at the Centre for Plasma-Astrophysics, K.U.Leuven, Belgium, affiliated with the FOM-Institute for Plasma Physics Rijnhuizen, and professor at the Astronomical Institute of Utrecht University. He headed Numerical Plasma Dynamics teams at Rijnhuizen and Leuven, and is frequently invited to lecture at postgraduate schools on computational methods in astrophysics. His expertise ranges from solar physics to high energy astrophysics, includes massively parallel computing, automated grid-adaptivity, as well as visualization of large-scale simulations. His research focuses on combined computational and analytical magnetofluid dynamics, with an eye towards astrophysically relevant applications encompassing stellar winds, astrophysical jets, and accretion disk dynamics.
He has been a key figure in various interdisciplinary collaborations on solar and space plasma physics, and his publication record includes studies of binary star systems, theory and applications of magnetoseismology in solar as well as accretion disk context, and state-of-the-art simulations of the ultra-relativistic plasmas encountered in Active Galactic Nuclei jets and Gamma Ray Bursts.
He teaches master level courses for Astronomy students in Leuven and Utrecht, and lectures in the Bachelor programme for physics and mathematics students at K.U.Leuven. He has been jury member for numerous PhD defenses at Utrecht, Leuven, Leiden, Edinburgh, Brussels, Oslo, Grenoble. His career started with research posts at the National Center for Atmospheric Research in Boulder, Colorado (US) and at the Kiepenheuer Institute for Solar Physics in Freiburg (Germany).
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