DIFFER
DIFFER Publication

Faranoff-Riley type I jet deceleration at density discontinuities Relativistic hydrodynamics with a realistic equation of state

Label Value
Author
Abstract

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.

Year of Publication
2008
Journal
Astronomy & Astrophysics
Volume
491
Number
2
Number of Pages
321-U33
Date Published
Nov
Type of Article
Article
ISBN Number
0004-6361
Accession Number
ISI:000260761100011
URL
PId
f23a3fbe3fc41b424a298b5702c40c3a
Alternate Journal
Astron. Astrophys.
Journal Article
Download citation