Feedback in Galaxy Clusters Brian Morsony University of Maryland 1
Not talking about Galaxy-scale feedback Local accretion disk feedback 2
Outline Galaxy cluster properties Cooling flows the need for feedback Feedback candidates AGN feedback Conduction instabilities AGN and conduction 3
Galaxy Cluster Properties Massive, 10 14 10 15 Solar masses total Close to cosmological baryon fraction, 85-90% dark matter 10-30% of baryons in stars Most baryons (70-90%) in hot ICM gas Gas is pressure supported 4
Cluster Example - Perseus 5 Ken Crawford
Cluster Example - Perseus a 6 Fabian et al. 2011
Cooling Flows For some clusters, cooling time of gas in center less than age of universe See X-ray temperature decreasing towards the cluster center Cool-core cluster 7
Cool-core vs. non-cool core a 8 Fabian et al 2009
Cool-core vs. non-cool core 9 Sanderson et al. 2006
Cool-core vs. non-cool core 10 Cavagnolo et al. 2009
Cooling Flows Gas in cool-core cluster should continue to cool Pressure decreases, hot gas will flow in to replace it - Cooling flow Should be either Lots of cold gas in cluster center Lots of stars and star formation 11
Need for feedback Cooling flows are not seen Cluster have a large elliptical central galaxy 10 12 M Sun of stars Form 10 100 stars/year Have some (10 10 M Sun ) cold gas Should have: 10 13 M Sun of stars or gas Form 1000+ stars/year 12
Filaments in Perseus 13 C. Conselice
Filaments in Perseus 14 Fabian et al. 2008
Feedback What does feedback mean to me? Need a heat source Powerful enough to balance cooling Able to maintain cool core Knows how much cooling is going on and adjust its self Fairly stable on long time scales 15
Example: Thermostat Metal contracts, triggers a switch Heat source turns on, gets warm Metal expands, turns heat off Room cools, repeat Heater needs to be powerful enough, but not too powerful 16
Feedback Candidates Supernova Gravitational heating Dynamical friction / sloshing AGN Conduction 17
Supernova Gas cools -> gas forms stars -> stars make SN -> SN drive winds and heat gas Very important in galaxy-scale feedback Cluster are a very deep potential Stars are a small fraction of baryons Not enough energy 18
Gravitational heating and Dynamical friction / sloshing 19 Gravitational heating As galaxies fall into cluster, gas is stripped Gas has excess potential energy, converted to heat Dynamical friction / sloshing As galaxies or sub-clusters move through the cluster, they create tides Tidal energy dissipated as heat Gas displaced from dark matter potential, sloshing releases energy
Sloshing Abell 2052 20 Blanton et al. 2011
Gravitational heating and Dynamical friction / sloshing These are sources of heat, not feedback Galaxy infall or cluster mergers don t know about gas cooling rate Should see some cluster catastrophically cooling 21
AGN Jets Cool gas falls in, accretes onto SMBH Accretion powers AGN jets Kinetic energy of jets injected into cluster core Jets heat gas, shut off cooling Accretion rate deceases, shuts of jets 22
AGN Jets 23 Perseus Cluster X-ray Image Multiple X-ray cavities Sound waves extending out from cluster center
AGN Jets Inner cavities filled with radio emission Radio bubbles 24
AGN jet advantages They exists, ~all cool core clusters have X- ray cavities Have a clear feedback loop Have (maybe) enough energy to balance cooling 25
AGN jet problems 26 Jets are not isotropic is energy well distributed? How is jet energy converted into heat? Shocks? Mixing? Gravitational uplift? Cosmic rays? Do they really produce enough energy to balance cooling?
AGN Jets in hydrostatic cluster Morsony et al. 2010 27
AGN Jets in realistic cluster Morsony et al. 2010 28
Conduction Hot gas in outer cluster has lots of energy compared to cooling gas in core If you can tap into that, can stop cooling Spitzer conduction time is short compared to cooling time But, clusters are (weakly) magnetized 29
Conduction Conduction is anisotropic, along field lines Effectiveness depends on field structure For a tangled magnetic field, conduction suppressed by 100+, not effective For radial field, conduction not suppressed, effective For azimuthal field, conduction suppressed, not effective 30
Magnetic field structure 31 Thermal instabilities alter field structure Clusters are stable to convection in absence of magnetic fields In outer cluster, magnetic fields lead to magnetothermal instability (MTI), create turbulence In inner cluster, heat flux-driven buoyancy instability (HBI), creates stable azimuthal field
MTI Magnetic field structure HBI 32 McCourt et al. 2011
Conduction field structure From Karen Yang Preliminary 33
AGN Jets + Conduction Jets have magnetic fields Partially aligned with jet Jets are long, ~100 kpc Could create connection for conduction to happen Jets generate turbulence Could disrupt HBI fields (more conduction) Create tangled fields (less conduction) 34
AGN Jets From Karen Yang Preliminary 35
AGN Jets + Conduction From Karen Yang Preliminary 36
AGN vs. AGN + Conduction From Karen Yang Hot mode w/o conduction Hot mode with conduction 37
Summary Feedback is needed in galaxy clusters Type of feedback uncertain AGN accretion is an important part, either: Direct feedback from jet energy Indirect feedback from impact on conduction Quasar mode feedback? Other heating may also contribute 38
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