HOT TIMES
FOR COOLING FLOWS
Mateusz Ruszkowski
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)
• 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
WE CALL THIS
“EFFERVESCENT HEATING”
EFFERVESCENT HEATING:
1D MODEL
• “Bubbles” rise on ~ free-fall time  tcool
• 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:

1/ 4
ECR
p d ln p
 ~  
 3
2
4r
r d ln r
• Compare to cooling rate:
2
  n (T )   T
2

1D ZEUS
SIMULATIONS
Ruszkowski &
Begelman 2002
Includes:
Conductivity @
Spitzer/4
 feedback
Simple M
in center
Ruszkowski &
Begelman 2002
AGN, not
conduction,
dominates
heating
ENTROPY PROBLEM IN THE ICM
LX  T 3
entropy “floor”
– Supernova heating may be inadequate
–
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
Roychowdhury, Ruszkowski, Nath & Begelman 2003
M BH  M cluster
relation ?
Roychowdhury, Ruszkowski, Nath & Begelman 2003
L  0.1LEdd
M BH  4  104 M bulge
M bulge  2  103 M cluster
 M cluster 
erg  s 1
L  10 
 M sun 
45
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
3C 84 and
Perseus Cluster
Fabian et al. 2000
Note multiple
“fossil” bubbles,
not aligned with
current radio jets
Chandra
image
RAPID ISOTROPIZATION – buoyant gas
spreads laterally on dynamical timescale until
it covers 4 steradians
Ruszkowski, Kaiser &
Begelman 2003
3C 84 and Perseus Cluster
Fabian et al. 2000
Cold rims, not
strong shocks
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
“fossil” bubbles
Chandra image
+1.7 GHz radio
44
L

10
erg / s
Conditions emulate Abell 2199, with cooling; AGN
Ruszkowski, Kaiser & Begelman 2003
127
186
244
303
Myr
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
NUMERICAL SIMULATIONS
•
•
•
•
Significant and fast lateral spreading
Sound waves
Cool rims
Mismatch between X-ray and radio emission