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HOT TIMES FOR COOLING FLOWS

This study explores the dynamics of cooling flows and heating mechanisms within galaxy clusters, focusing on the interplay between gas radiation, pressure support, and temperature equilibria. We discuss the "cooling flow problem," addressing evidence against mass dropout and the heating mechanisms, including AGN heating and turbulent mixing. We introduce the concept of "effervescent heating," detailing how rising gas bubbles contribute to cluster heating while stabilizing cooling flows. The findings are supported by advanced simulations and observational data, revealing crucial insights on entropy floors and bubble dynamics.

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HOT TIMES FOR COOLING FLOWS

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  1. HOT TIMES FOR COOLING FLOWS MateuszRuszkowski

  2. Cooling flow cluster Non-cooling flow cluster COOLING FLOW PROBLEM • gas radiates X-rays & loses pressure support against gravity • gas sinks towards the center to adjust to a new equilibrium

  3. PROBLEMS • “COOLING FLOWS” • No evidence for large mass dropout • Stars, absorbing gas • Temperature “floor’’ Sanders & Fabian 2002 Temp. drops by factor ~3

  4. CLUSTER HEATING appears to be: • RELATIVELY GENTLE • No shock heating • Cluster gas convectively stable • Abundance gradients not washed out • DISTRIBUTED WIDELY – not too centrally concentrated • Entropy “floor” manifest on large scales • Needed to avoid cooling “catastrophe”

  5. HEATING CANDIDATES • AGN heating (Tabor & Binney, Churazov et al.) • Thermal conduction (Bertschinger & Meiksin, Zakamska & Narayan, Fabian et at., Loeb) • Turbulent mixing (Kim & Narayan)

  6. WE CALL THIS “EFFERVESCENT HEATING” • Cluster gas heated by pockets of very buoyant (relativistic?) gas rising subsonically through ICM pressure gradient • Expanding bubbles do pdV work • Dependent on two conditions: • Buoyant fluid does not mix (much) with cluster gas persistent X-ray “holes” • Acoustic & potential energy is converted to heat by damping and/or mixing

  7. EFFERVESCENT HEATING: 1D MODEL • “Bubbles” rise on ~ free-fall time • Assume • Number flux of CR conserved • Energy flux decreases due to adiabatic losses • Dissipation converts motion to heat ~locally

  8. HEATING MODEL TARGETS PRESSURE GRADIENT STABILIZES COOLING • Volume heating rate: • Compare to cooling rate:

  9. 1D ZEUS SIMULATIONS Ruszkowski & Begelman 2002 Includes: Conductivity @ Spitzer/4 Simple feedback in center

  10. Ruszkowski & Begelman 2002 AGN, not conduction, dominates heating

  11. Possible solutions: • Cooling --- gas cools and forms galaxies, • low entropy gas is removed; Voit et al. • Turbulent mixing (Kim & Narayan) • AGN heating --- gas is heated; entropy increases ENTROPY PROBLEM IN THE ICM • entropy “floor” • Supernova heating may be inadequate Roychowdhury, Ruszkowski, Nath & Begelman 2003

  12. relation ? Roychowdhury, Ruszkowski, Nath & Begelman 2003

  13. Testing assumptions of the model ‘‘Pure’’ theory requires • Lateral spreading of the buoyant gas must be significant • Spreading must occur on the timescale comparable to or shorter than the cooling timescale BUT Heating must be consistent with observations • No convection • Preserved abundance gradients • Cool rims around rising bubbles • Radio emission less extended spatially than X-rays • Sound waves

  14. THE TOOL – the FLASH code • Crucial to model mixing and weak shocks accurately • PPM code with Adaptive Mesh Refinement, e.g., FLASH, better than lower-order, diffusive code, e.g., ZEUS

  15. Note multiple “fossil” bubbles, not aligned with current radio jets 3C 84 and Perseus Cluster Fabian et al. 2000 Chandra image

  16. RAPID ISOTROPIZATION – buoyant gas spreads laterally on dynamical timescale until it covers steradians Ruszkowski, Kaiser & Begelman 2003

  17. Cold rims, not strong shocks 3C 84 and Perseus Cluster Fabian et al. 2000 Chandra image

  18. COOL RIMS – entrainment of lower temperature gas Ruszkowski, Kaiser & Begelman 2003

  19. THE DEEPEST VOICE FROM THE OUTER SPACE Unsharp masked Chandra image X-ray temperatures 131 kpc Fabian et al. 2003

  20. MEDIA CRAZE

  21. SOUND WAVES Ruszkowski, Kaiser & Begelman 2003

  22. 3C 338 and Abell 2199 Johnstone et al. 2002 Chandra image +1.7 GHz radio “fossil” bubbles

  23. Conditions emulate Abell 2199, with cooling; Ruszkowski, Kaiser & Begelman 2003 X-ray Radio 244 Myr 127 186 303

  24. Radio: Higher contrasts, detectable only close to jet axis X-rays: spread out laterally 3C 338 + Abell 2199 (Johnstone et al. 2002) “Ghost cavities” do not trace previous jet axis

  25. CONCLUSIONS • SEMI-ANALYTICAL MODELS • No need for large mass deposition rates • Minimum temperatures around 1 keV • Entropy floor • Significant and fast lateral spreading • Sound waves • Cool rims • Mismatch between X-ray and radio emission • NUMERICAL SIMULATIONS

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