HOT TIMES FOR COOLING FLOWS

HOT TIMES FOR COOLING FLOWS MateuszRuszkowski

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

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

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”

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

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

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

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

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

Ruszkowski & Begelman 2002 AGN, not conduction, dominates heating

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

relation ? Roychowdhury, Ruszkowski, Nath & Begelman 2003

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

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

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

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

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

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

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

MEDIA CRAZE

SOUND WAVES Ruszkowski, Kaiser & Begelman 2003

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

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

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

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

HOT TIMES FOR COOLING FLOWS