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

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

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

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?

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

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

Radio Source Cavities • N1275 Fabian et al. 2000

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

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

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

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

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….

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

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

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

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

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

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

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

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

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

Initial Conditions

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

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

Relic Radio Bubble Evolution • Beta = 3000

Relic Radio Bubble Evolution • Beta = 120

Relic Radio Bubble Evolution • Bubble Deceleration

Lifting and Mixing Beta = 120K OptimallyCoupled

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

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

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

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

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

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

Radio Source Cavities • A2052

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

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

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