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The Evolution of Radio Sources in Clusters: Magnetic Fields and ICM Heating

This presentation highlights the evolution of radio sources in intracluster medium (ICM), discussing magnetic field components and the origins of ICM magnetic fields. It explores the amplification of magnetic fields by turbulent dynamos and the kinetic energy sources driving the process. The interaction between radio sources and ICM, including observations of cavities and bubbles, is also analyzed. The properties and models of buoyant bubbles, relic radio sources, and the consequences of magnetic fields in radio sources are discussed, emphasizing their impact on the stability and evolution of these phenomena.

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The Evolution of Radio Sources in Clusters: Magnetic Fields and ICM Heating

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  1. Radio Sources and the Evolution of the ICM David De Young US National Optical Astronomy Obs. Thomas W. Jones University of Minnesota Cosmic Magnetism Bologna - August 2005

  2. Radio Sources and the Evolution of the ICM • Two Major Topics: • Evolution of the Intracluster Medium • Evolution of Radio Sources

  3. Evolution of the Intracluster Medium • Magnetic Field Component • Origins of ICM Magnetic Field • Amplification by Turbulent Dynamos • Need Source of Kinetic Energy to Drive • Wakes from Cluster Galaxies? • Not Likely ((r,t) MHD Calculation - ApJ, 386,464) • Kinetic Energy From Extended Radio Sources?

  4. Reheating Cooling Flows In Clusters by AGN • Old Idea – Total AGN Energy Significant • Renewed Interest From Chandra Data • Observations of Cavities and Bubbles in ICM • Direct Evidence of Radio Source – ICM Interaction • But – • Cavities Imply Interaction • Cavities Do Not Provide Proof of ICM Heating • Issues: Details of Heating; Time Required

  5. Radio Source Cavities • Chandra A2052 + 6cm VLA (3C 317) Blanton et al. 2001, Burns 1990

  6. Radio Source Cavities • N1275 Fabian et al. 2000

  7. Properties of Radio Source Cavities and Shells • Morphology • Limb Brightened, “Relaxed” Structure • NOT Head-Tail or “Normal” FR-I • No Jets, but t ~ 10 yr • Tens of kpc in Diameter • Inferred Properties • In Pressure Equilibrium • Moving Subsonically (no Shocks) • Shell and Surroundings Cool 7 syn

  8. Inferred Physical Model of Radio Sources Cavities • Low Internal Density • High Internal Pressure • Energy Density ~ 10 x Equipartition • Thus… • Buoyant Bubbles

  9. Models of Buoyant Radio Source Bubbles • 3-D Hydrodynamic 10 x 10 x 30 kpc 8 Myr 25 Myr 41 Myr 59 Myr Density Brueggen et al. 2002

  10. Models of Buoyant Radio Source Bubbles Density • 2-D Hydrodynamic X-Y High Resolution Brueggen & Kaiser 2002

  11. Suggested Reheating Mechanisms • Mixing of ICM and Radio Source Material • Lifting of ICM in Wakes of Buoyant Bubbles • Entrainment of ICM Along Surface of Rising Bubbles • Self Consistent Mixing Calculation Not Yet Done; Hydro Results Suggestive • However….

  12. Relic Radio Sources in Clusters • A2597 VLA 1.4 GHz McNamara et al 2002.

  13. Relic Sources in Clusters • N1275 74 MHz Fabian et al. 2002

  14. Properties of Radio Relics • They Are Intact! At Times >> t • Reside 30-50 kpc From Cluster Center • Diameter 10-20 kpc • Buoyant Risetimes ~ 10 yr > Synchrotron Lifetimes • Reacceleration ? • Equilibrium Implies U >> U • PdV Work ~ 10 erg (or More) instab 8 int equip 59

  15. Consequences of Relic Radio Sources • Magnetic Field Cannot be Neglected • Bubble Expansion Creates Stabilizing Sheath • Linear Stability Analysis: • At r ~ 50 kpc, n = 0.01, B = 3 x 10 G: • R-T: l = 13 kpc, t = 7 x 10 yr • K-H: Stable for U ~ 0.1 c • Thus: No Fragmentation or Mixing for a Significant Fraction of Buoyant Risetime -6 7 O O s

  16. Non-Linear R-T Instability t = 0 Beta = 1.3 M Beta = 1.3 K 130 ~ ICM 1 kpc slices T = 10M K t = 15 Myr

  17. Prior MHD Calculations • 2-D MHD – Pre-formed Bubble • Tangential Field Inserted “By Hand” • Self Consistent MHD (Robinson et al. 2004) Breuggen & Kaiser 2001

  18. Current MHD Calculations • Time Dependent Evolution of Buoyant Radio Relics in a Stratified ICM • R – T Instability • Lifting and Mixing of Different Elements of the ICM • Destruction of Relic and Mixing with ICM • Includes Effects of Central Galaxy + Cluster • Includes Inflation of Radio Relic Bubble

  19. Initial & Boundary Conditions • Gravitation – Includes Dark Matter • Central Galaxy • King Model; Rc = 3 kpc; M = 3.5 x 10(12) Mo at 20 kpc • Cluster • NFW Model; alpha = 0; M = 3.5 x 10(10) Mo at 10 kpc • ICM – Equilibrium Configuration • Isothermal – T = 3 keV = 3.5 x10(7) K • Density n = 0.1 at z = 5 kpc

  20. Initial & Boundary Conditions • ICM – Equilibrium Configuration • Magnetic Field • Orientation: Phi = 0, 45, 90 • B = const or Beta = const (120 – 75K) • |B| = 0.2, 1, 5 MicroGauss (Beta = 7.5(4), 3(3), 120) • Bubble • R = 2 kpc • P = Pext at z = 15 kpc • n = 0.01n at z = 15 kpc • Inflation time ~ 10 Myr • dE/dt ~ 10 (42) erg/s

  21. Initial Conditions

  22. Relic Radio Bubble Evolution • Beta = 3000 • Bo = 1 Microgauss

  23. Relic Radio Bubble Evolution • Beta = 120 • Bo = 5 Microgauss

  24. Relic Radio Bubble Evolution • Beta = 3000

  25. Relic Radio Bubble Evolution • Beta = 120

  26. Relic Radio Bubble Evolution • Bubble Deceleration

  27. Lifting and Mixing Beta = 120K OptimallyCoupled

  28. Relic Radio Bubble Evolution • Three Dimensions • Beta = 3000 • t(infl) = 10 Myr • No Major Changes From 2-D

  29. Relic Radio Bubble Evolution • Three Dimensions vs. Two • Beta = 3000

  30. Consequences of B Fields • For Radio Sources • Dynamically Unimportant B (Beta>>1) Can Have Dramatic Late Time Effects • Suppression of R-T and K-H Instabilities • Deceleration of Buoyant RS Bubbles • Detailed Evolution Dependent both |B| and B • Buoyant Lifetimes can be > t Rad, Equip

  31. Consequences of B Fields • For Cluster ICM Reheating • Onset of Instability and Mixing Delayed • Initial Scale Length Large: l ~ 10 kpc • Mixing Time to Reheat Will Be Long • How Long? • Time Required for Turbulent Cascade to Go From Energy Range to Dissipation Range • l /v ~ 3 x 10 yr Large Eddy Turnover Time o 7 o turb

  32. Lifting and Magnetic Fields • Weak Field Limit – Maximal Coupling • Most Lifting Occurs in Wake of Rising Relic • Volume of Lifted Material Limited to Column Smaller than Bubble Cap • Changing Beta Alters Bubble Geometry but Not the Volume Lifted (to zeroth order) • Repeated Outbursts and/or Additional Mixing Mechanisms Will be Required to Reheat ICM

  33. Conclusions • Relic Radio Source Cavities Provide Evidence for Interaction with a Magnetized ICM • Radio Lobe Interaction With a Magnetized ICM Indicates: • Delay of Onset of Destructive Instabilities • Long Times to Reheat the ICM • Volume of Lifted ICM Limited to Wake Region

  34. Radio Source Cavities • A2052

  35. Relic Sources in Clusters • 200 kpc Cavities (McNamara et al. 2005) • Z = 0.22 • pdV ~ 10 erg 62

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