Morphologies of extragalactic jets

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1 MOMENTUM TRANSPORT IN TURBULENT HYDRO JETS AND EXTRAGALACTIC SOURCES MORPHOLOGY Attilio Ferrari University of Torino University of Chicago JETSET - CMSO with G. Bodo, S. Massaglia, A. Mignone, P. Rossi 8-10 July 2008 CMSO - Princeton 1 Morphologies of extragalactic jets 1

2 MHD jet acceleration with resistivity (Zanni et al. 2007) a m = 0.1 (low resistivity) Low diffusivity, footpoints of field lines advected towards the center Differential rotation along the lines triggers a magnetic tower effect Intermittent pinches a m = 1 (large resistivity) Field lines gently wrapped around magnetic surfaces 3 Fanaroff-Riley morphological classes FR I or jet dominated 3C 31 VLA FR II or lobe dominated (classical doubles) 3C 98 VLA Low-power sources Strong interaction with ambient High-power sources Weak interaction with ambient 8-10 July 2008 CMSO - Princeton 4 2

3 Interaction with external medium Light supersonic jets interacting with a denser medium Confinement by external pressure (magnetic?) Shears, matter entrainment, mixing Jet deceleration Activity of jet s head and energy deposition 8-10 July 2008 CMSO - Princeton 5 Shear instabilities in supersonic flows experiments (Brown & Roshko 1974) nonlinear simulations of jets (Bodo et al. 1998) with and without magnetic fields Jet disruption by local instabiltiies 8-10 July 2008 CMSO - Princeton 6 3

4 Astrophysical jets may suffer decollimation and deceleration due to intrinsic instabilities (e.g. Pringle, Blandford, Ferrari, Hardee, Birkinshaw, Hughes, Toth, Keppens, Martí, Jones ) Shear instabilities as the origin of knots and wiggles and relativistic electron acceleration (e.g. Benford et al. 1980, Hardee 1990) 8-10 July 2008 CMSO - Princeton 7 Overpressured cocoons stabilize jets and define morphologies Shear instabilities as origin of different types of radiogalaxies, FR I, FR II, CSS, etc. (De Young 1997) light jets 8-10 July 2008 CMSO - Princeton 8 4

5 Relativistic jets 0.1 pc 1 pc 100 pc 1 kpc 10 kpc γ γ 3-20 γ 5 γ 2 (FR I) β.2 (F I) γ (FR II) γ larger for FR II γ > 4 (FR II) How do relativistic jets decelerate? Mass injection from ambient, stars, etc. (Komissarov 1994) Mass entrainment from the ambient medium across an unstable boundary layer (De Young 1996) Connecting morphologies with deceleration 8-10 July 2008 CMSO - Princeton 9 High-resolution 3D simulations outflow Jet Injection + perturbations outflow outflow Homogeneous external medium Pressure equilibrium at inlet Physical domain: -12 R j < x <12 R j 0 < y < 120 (180) R j -12 R j < z < 12 R j Equivalent Reynolds number??? (10-100) 8-10 July 2008 CMSO - Princeton 10 5

6 Set of simulations M = v b c s M r = " b v b " s v s relativistic Mach number Perturbations at the jet inlet: pinching helical fluting g b = g b (1+e) Þ e» July 2008 CMSO - Princeton 11 Turbulence, mixing, entrainment, deceleration High-resolution 3D relativistic hydro jets (Mignone et al 2003, Rossi et al 2008, PLUTO code) γ in = 10, Mach = 3, ρ jet = 10-3 ρ amb Lorentz β, t fin = 750 t cross MHD simulations with rotation in progress 8-10 July 2008 CMSO - Princeton 12 6

7 Mixing by shear instabilities (3D rendering of passive tracer) η = 10 2 η = 10 4 Relativistic spine surrounded by a turbulent mixing layer 0 η = July 2008 CMSO - Princeton 13 η = 10 2 η = η = July 2008 CMSO - Princeton 14 7

8 The case η = 10 4 Transverse velocity distribution 20 R j 30 R j 40 R j 8-10 July 2008 CMSO - Princeton 15 Longitudinal momentum transport outside the jet 20 R j 30 R j 40 R j h = 10 4 Inner region = turbulent transport Outer regions = bow shock effect 16 8

9 Radial momentum flux 20 R j 30 R j 40 R j h = 10 4 Inner region = turbulent transport Outer regions = bow shock effect 17 Comparison with observations Emissivity integration along the line of sight at different projection angles α Agreement with Bridle & Laing empirical models -> spine + layer a = 20º a = 60º 8-10 July 2008 CMSO - Princeton 18 9

10 3D cocoons and FR II lobes Spearhead Low ratio between thermal and kinetic energies (η,m ) Fat (low pressure) High ratio between thermal and kinetic energies Fat (high pressure) Inhomogeneous ambient 8-10 July 2008 CMSO - Princeton 19 Results Relativistic jets maintain high bulk Lorentz factors over long propagtion lengths The critical parameter is density ratio: η 10 2 is required for strong deceleration In all cases a spine-layer configuration is obtained that can explain the morphology of FR I sources Critical value of jet power above which no dissipation occurs and the FR II morphology appears 2 2 # R P j,crit =1.3"10 44 j & # )b & # n &# % ( % ( % ( + & crit % ( $ 1 pc' $ 10' $ 1 cm *3 ' $ 10 3 ' *1 erg s *1 For η η crit ~ 10 3 the turbulent layer is very weak, and correspondingly FR II morphology is obtained for P j P j,crit ~ erg s -1 Fat lobes in FR II for high pressure or high temperature jets or strongly inhomogeneous ambient 20 10

11 Final comments Many physical issues still unresolved Simulations: global: morphologies local: microphysics Beyond MHD Happy birthday, Russell! 8-10 July 2008 CMSO - Princeton 21 11