2008/08/18 by Z. Méliani, Z. Meliani, Rony Keppens +3 · 3 citations
Mathematics · Physics and Astronomy · #Active galactic nucleus #Astrophysical Phenomena and Observations #Astrophysical jet #Astrophysics #Astrophysics and Cosmic Phenomena #Classical mechanics #Classification of discontinuities #Equation of state #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae #Geology #Jet (fluid) #Lorentz factor #Lorentz transformation #Mathematical analysis #Mathematics #Mechanics #Physics #Polytropic process #Quantum mechanics #Type (biology) #astro-ph
paper · pdf · doi:10.1051/0004-6361:20079185
accepted in A&A
arxiv created 2008/08/18 · openalex publication_date 2008/11/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Aims. We propose a model that could explain the sudden jet deceleration in active galactic nuclei, thereby invoking density discontinuities. Motivated particularly by recent indications from HYbrid MOrphology Radio Sources (HYMORS) that Fanaroff-Riley classification is induced in some cases by variations in the density of the external medium. We explore how one-sided jet deceleration and a transition to FR I type can occur in HYMORS, which start as FR II (and remain so on the other side). Methods. We implemented the Synge-type equation of state introduced in the general polytropic case by Meliani et al. (2004, A&A, 425, 773) into the relativistic hydrodynamic grid-adaptive AMRVAC code. To demonstrate its accuracy, we set up various test problems in an appendix, which we compare to exact solutions that we calculate as well. We use the code to analyse the deceleration of jets in FR II/FR I radio galaxies, following them at high resolution across several hundred jet beam radii. Results. We present results for 10 model computations that vary the inlet Lorentz factor from 10 to 20, include uniform or decreasing density profiles, and allow for cylindrical versus conical jet models. As long as the jet propagates through uniform media, we find that the density contrast sets most of the propagation characteristics, fully consistent with previous modelling efforts. When the jet runs into a denser medium, we find a clear distinction in the decelaration of high-energy jets depending on the encountered density jump. For fairly high-density contrast, the jet becomes destabilised and compressed, decelerates strongly ( up to subrelativistic speeds), and can form knots. If the density contrast is too weak, the high-energy jets continue with FR II characteristics. The trend is similar for the low-energy jet models, which start as underdense jets from the outset, and decelerate by entrainment into the lower region as well. We point out differences that are found between cylindrical and conical jet models, together with dynamical details like the Richtmyer-Meshkov instabilities developing at the original contact interface.