1 / 29

Stability and evolution of parsec and kiloparsec-scale jets

Stability and evolution of parsec and kiloparsec-scale jets. Manuel Perucho i Pla Departament d’Astronomia i Astrofísica Universitat de València Spain VLBI Group Max-Planck-Institut für Radioastronomie Germany December 14th 2005. OUTLINE OF THE TALK. Jet stability. Vortex sheet limit.

leora
Download Presentation

Stability and evolution of parsec and kiloparsec-scale jets

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Stability and evolution of parsec and kiloparsec-scale jets Manuel Perucho i Pla Departament d’Astronomia i Astrofísica Universitat de València Spain VLBI Group Max-Planck-Institut für Radioastronomie Germany December 14th 2005

  2. OUTLINE OF THE TALK • Jet stability. • Vortex sheet limit. • Sheared flows. • Application to extragalactic jets. • Parsec-scale: 3C 273. • Kiloparsec-scale: 3C 31. • Recent developments and future prospects. • Relativistic Magnetohydrodynamics.

  3. JETS AND KELVIN-HELMHOLTZ INSTABILITIES (i) • Kelvin-Helmholtz instabilities grow in the interface between two flows in relative motion. • They may grow after any small perturbation, generating observable structures and eventual mass loading and disruption of the flow. • In 2D: • Cylindrical jets: pinching modes. • Slab jets: pinching and helical modes. Birkinshaw (1991)

  4. JETS AND KELVIN-HELMHOLTZ INSTABILITIES (ii) • KH modes might be present in: • Kiloparsec scale structures: • Knots in radio jets. • Responsible of mass entrainment in decelerated jets: FRI-FRII dichotomy (e.g., Komissarov 1994, Bicknell 1994). • Parsec scale structures: Helical patterns (Lobanov & Zensus 2001, Hardee et al. 2005), trailing components (Agudo et al. 2001). • Linear analysis has proven to be a powerful tool to extract information from observations and numerical simulations (e.g., Hardee 2000, 2003, Hardee et al. 2005). • Observations can provide us with wavelengths and transversal structure which could be interpreted using linear perturbation theory (Lobanov & Zensus 2001) and numerical simulations (Perucho et al. 2005) in order to obtain physical parameters of the jet.

  5. OBJECTIVES OF THE WORK • Our purpose was to study the transition of KH instabilities in relativistic jets from the linear to the non-linear regimes and to perform a systematic study in terms of the jet/ambient parameters. • From this study, we could gain insight in • the mechanisms of jet disruption, • the long term stability properties of jets in terms of the physical parameters, • the formation of observed structures in relativistic jets (knots, helices, shear layers,...).

  6. JET STABILITYVORTEX SHEET LIMIT

  7. VORTEX SHEET STABILITY (i) • Linear regime (Perucho et al. 2004a) • Initial setup of simulations. • Solve the dispersion relation • frequencies and growth rates in terms of wavelength. • Select first body mode at maximum growth rate. • Parameters: • Lorentz factor (velocity). • Rest mass density contrast. • Specific internal energy. • Pressure equilibrium. • Performed simulations sweeping beam specific internal energy (0.07-60 c^2), and Lorentz factor (from 5 to 20). Pressure pert. Axial velocity pert. Perp. velocity pert. • -The numerical code reproduces linear growth (temporal view, high resolution). • -KH instabilities saturate when the amplitude of the perturbation of axial velocity (in the jet reference frame) reaches the speed of light (Hanasz 1995, 1997).

  8. VORTEX SHEET STABILITY (ii) • Evolution of Kelvin-Helmholtz instabilities in relativistic flows: • PHASES: LINEAR, SATURATION, NON-LINEAR

  9. VORTEX SHEET STABILITY (iii) • Evolution of Kelvin-Helmholtz instabilities in relativistic flows: • PHASES: LINEAR, SATURATION, NON-LINEAR

  10. VORTEX SHEET STABILITY (iv) • Evolution of Kelvin-Helmholtz instabilities in relativistic flows: • PHASES: LINEAR, SATURATION, NON-LINEAR

  11. VORTEX SHEET STABILITY (v) During the transition to the non-linear regime, the formation of a shock wave in the jet/ambient boundary (mainly in colder and slower jets) is previous to jet disruption. • We followed the non-linear evolution • of the instabilities (Perucho et al. 2004b) and characterised it with two criteria: • - Transfer of axial momentum. • Width of the shear/mixing layer. • Results show faster, cold/warm jets as the most stable, and slower, colder jets as the most unstable (high momentum transfer and wide mixing layers).

  12. JET STABILITYSHEARED FLOWS

  13. STABILITY OF SHEARED FLOWS (i, see poster) • Simulations perturbing several helical and pinching modes in slab jets with shear layer (Perucho et al. 2005). • Linear stability solutions reveal the presence of fast growing, small wavelength resonances, mostly important in faster jets. • The code • develops those small scale structures as harmonics of the longer excited wavelengths. • reproduces the growth rates of perturbed modes in the simulations, excepting for the resonances, where non-linear effects might be taking place. Snapshot of a simulation in the linear phase Theoretical representation of a non-resonant mode Theoretical representation of a resonant mode

  14. STABILITY OF SHEARED FLOWS (ii) • Non linear regime • Resonant modes are crucial in the non-linear evolution. They appear in higher Lorentz factor and relativistic Mach number jets.

  15. STABILITY OF SHEARED FLOWS (iii) • UST1 models: mixed and slowed down after shock. • UST2 models: progressive mixing and slowing. • ST models: resonant modes avoid disruption and generate a hot shear layer which protects the fast core. • Separation of models is observed in the evolution of axial momentum, final shear layer structure (next slide) and in a relativistic Mach number-Lorentz factor plot:

  16. STABILITY OF SHEARED FLOWS (iv) ST UST1 UST2 • Shear layer (mean profiles of variables). • Upper panels: thermodynamical variables. • Lower panels: dynamical variables. specific internal energy tracer rest mass density Axial velocity Norm. Lorentz factor Norm. Axial momentum

  17. I, P intensities in J1-J4 region I P STABILITY OF SHEARED FLOWS (v) • Mean velocities and structures found point towards the following: • UST1 models • Disrupted, thick shear layers: FRI’s? (e.g., Laing and Bridle 2002a,b). • ST models • Stable: FRII’s? • hot shear layers: observed? (kpc, Swain et al. 1998; pc, Attridge et al. 1999). • Relativistic thin (~2Rj) hot shear layers confirm results found in 3D simulations of Aloy et al. (1999, 2000) 3C31, Laing & Bridle 2002 3C 353, Swain et al. 1998 1055+018, Attridge et al. 1999

  18. PARSEC-SCALE JETS3C 273

  19. High resolution observations with space VLBI resolve transversal structure of jets, allowing for interpretation of structures in terms of KH instabilitites (e.g., 3C 273, Lobanov and Zensus 2001, LZ01). Consistency of the linear approach. Are the observed structures linear KH instabilities? Are the approximations used in the linear approach valid? We have shown that numerical codes reproduce the linear regime. We have tested in two simulations whether thestructures found in 3C 273 by LZ01 are due to KH instabilities or to the periodicities of precession and ejection of fast components (Abraham et al. 1996, Krichbaum et al. 2000). Our results reinforce the interpretation in LZ01 of KH instabilities as the origin of the structures. Source periodicities have difficulties in generating observed wavelengths. Parsec scale jets: 3C 273 (see poster)

  20. KILOPARSEC-SCALE JETS 3C 31

  21. 3C31, Laing & Bridle 2002 Observations and modelling (Laing and Bridle 2002a,b) Laing and Bridle (2002a,b) compare VLA data of total intensity and polarization of 3C 31 with theoretical one-dimensional models. • Models: • - Axisymmetric, time-stationary, relativistic jet. • Parametrized distributions of velocity, emission and magnetic field. • Apply conservation of mass, momentum and energy to infer variations of pressure, density, Mach number and entrainment rate. • - External density and pressure from Hardcastle et al. (2002). • - Pressure equilibrium with the external medium in the outermost studied region. Results: - Jet axial structure: inner, flaring, outer. - 52º to line of sight. - Transversal structure (spine+shear layer). - Spine velocity decreasing due to entrainment after the steady shock (from 0.9 to 0.25 c). THE OBSERVATION THE MODEL I F O

  22. Observations and modelling (Laing and Bridle 2002a,b) • Dynamics: • The jet is overpressured at the inlet and expands rapidly. • Recollimation occurs when the jet becomes underpressured. • Recollimation is accompanied by a peak in the entrainment rate. • The jet is slowly entrained and decelerated outwards. • Jet composition is probably purely leptonic, but picks up thermal plasma. FRI paradigm: free expansion, recollimation at shock, mass entrainment and deceleration to transonic speeds.

  23. Numerical simulations (i) • The jet is injected with the values at 500 pc from injection. • Jet Lkin~ 10^44 erg/s (FRI). • Implemented Synge equation of state in the code, which allows for two families of particles (electron/positron and proton, following Scheck et al. 2002, Falle & Komissarov 1996). • 2D simulations (axisymmetric jet): • Resolution: 8 cells/R_j axially and 16 cells/R_j radially • A: 2880x1800 cells, 18 kpc x 6 kpc (v=0.87 c). • B: 672x480 cells, 4.2 x 1.8 kpc (v=0.5 c). Initial set of parameters External medium (Hardcastle et al. 2002) rm=7.8kpc μ=0.5 mass p.p. X=1. H abundance

  24. Numerical simulations (ii) evolution A A: The bow shock is still supersonic by the end of the simulation M~2-3 B: the bow shock is only slightly supersonic. ~ constant advance speed (A: ~ 0.007c) (B: ~ 0.0025c) self-similar evolution (A: L/r ~2.5) (B: L/r ~1.6) B

  25. SIMULATION B jet disruption, mass load and deceleration jet expansion growth of instabilities recollimation shock Numerical simulations (iii)

  26. Numerical simulation (results v) Oscillations around pressure equilibrium Mass loading Recollimation shock SIMULATION A SIMULATION B

  27. THE FUTURERELATIVISTIC MAGNETOHYDRODYNAMICS

  28. Relativistic Magnetohydrodynamics(see poster Roca-Sogorb et al.) • An RMHD code developed in València and the MPA in Garching (Antón et al. 2005, Leismann et al. 2005) is now available for our work. • This code has been parallelised for the use in share memory machines and adapted to our needs in the last weeks. Work still in progress… • 3D version. • Relativistic equation of state (realistic atmospheres). • Combination of these elements along with the use of two dimensional analysis of high resolution VLBI observations (e.g., Lobanov & Zensus 2001)will allow us to reconstruct in detail the physical conditions in jets and to interprete emission patterns and transversal structure in terms of physical facts. • In Roca-Sogorb et al. we show our first results on the emission and polarization of magnetised jets.

  29. Relativistic Magnetohydrodynamics(see poster Roca-Sogorb et al.) Helical magnetic field with pitch angle of 20º. vj=0.99 Mj=15.05 Pj/Pa=2.0 Γ=4/3 ρj/ρa=0.001 Θ=43.8 º Θ=8.1 º Θ=1.4 º

More Related