GH2005 Gas Dynamics in Clusters II Craig Sarazin Dept. of Astronomy University of Virginia A85 Chandra (X-ray) Cluster Merger Simulation

De-Projected Gas Profiles De-project X-ray surface brightness profile → gas density vs. radius,  (r) De-project X-ray spectra in annuli → T(r) Pressure P =  kT/(  m p )

Gas and Total Masses Gas masses → integrate  Total masses → hydrostatic equilibrium Dark matter M dm = M – M gal - M gas

Total Masses Profiles XMM/Newton (Pointecouteau et al) (curves are NFW fits)

Gas Fraction Profiles Chandra (Allen et al) (r 2500 ≈0.25 r vir )

Cluster total masses – M  3% stars and galaxies 15% hot gas 82% dark matter Clusters are dominated by dark matter Earliest and strongest evidence that Universe was dominated by dark matter Masses of Clusters

Mass gas ~ 5 x mass of stars & galaxies! Hot plasma is dominant form of observed matter in clusters Most of baryonic matter in Universe today is in hot intergalactic gas Compare baryon fraction in clusters to average value in Universe from Big Bang nucleosynthesis Ω M = 0.3, early evidence that we live in a low density Universe Compare fraction baryons high vs. low redshift, assume constant Evidence for accelerating Universe (dark energy) Masses of Clusters (cont.)

Central peaks in X-ray surface brightness Cooling Cores in Clusters cooling core non-cooling core (Coma) IXIX

Cooling Cores in Clusters Central peaks in X-ray surface brightness Temperature gradient, cool gas at center

Cooling Cores in Clusters Central peaks in X-ray surface brightness Temperature gradient, cool gas at center Radiative cooling time t cool < Hubble time t cool ~ 2 x 10 8 yr

Cooling Cores in Clusters Central peaks in X-ray surface brightness Temperature gradient, cool gas at center Radiative cooling time t cool < Hubble time Always cD galaxy at center Central galaxies generally have cool gas (optical emission lines, HI, CO), and are radio sources

Cooling Cores in Clusters (cont.) Theory: X-rays we see remove thermal energy from gas If not disturbed, gas cools & slowly flows into center Gas cools from ~10 8 K → ~10 7 K at ~100 M  /yr

Cooling Cores in Clusters (cont.) Steady-state cooling of homogeneous gas

Cooling Cores in Clusters (cont.) Bremsstrahlung cooling Reasonable fit to X-ray surface brightness Ṁ ~100 M  /yr ln I X r -1 ln r r -3

The Cooling Flow “Problem” Where does the cooling gas go? Central cD galaxies in cooling flows have cooler gas and star formation, but rates are ~1-10% of X-ray cooling rates from images Both XMM-Newton and Chandra spectra → lack of lines from gas below ~10 7 K

High-Res. Spectrum (XMM-Newton) Peterson et al. (2001) Brown line = data, red line = isothermal 8.2 keV model, blue line = cooling flow model, green line = cooling flow model with a low-T cutoff of 2.7 keV

How Much Gas Cools to Low Temperature? Gas cools down to ~1/2-1/3 of temperature of outer gas (~2 keV) Amount of gas cooling to very low temperatures through X-ray emission ≲ 10% of gas cooling at higher temperature Cooling gas now consistent with star formation rates and amount of cold gas

Heat source to prevent most of cooling gas from continuing to low temperatures: Heat conduction, could work well in outer parts of cool cores if unsuppressed Works best for hottest gas Q ∝ T 7/2, how to heat mainly cooler gas? Supernovae? AGN = Radio sources Heat Source to Balance or Reheat Cooling Gas?

Radio Sources in Cooling Flows ≳ 70% of cooling flow clusters contain central cD galaxies with radio sources, as compared to 20% of non-cooling flow clusters Could heating from radio source balance cooling?

A2052 (Chandra) Blanton et al.

Radio Contours (Burns)

Other Radio Bubbles Hydra A McNamara et al. Abell 262 Abell 133 Blanton et al. Fujita et al. Abell 2029 Clarke et al. Abell 85 Kempner et al.

Morphology – Radio Bubbles Two X-ray holes surrounded by bright X-ray shells From deprojection, surface brightness in holes is consistent with all emission projected (holes are empty) Mass of shell consistent with mass expected in hole X-ray emitting gas pushed out of holes by the radio source and compressed into shells

Buoyant “Ghost” Bubbles Fabian et al.McNamara et al. PerseusAbell 2597 Holes in X-rays at larger distances from center No radio, except at very low frequencies (Clarke et al.)

Buoyant “Ghost” Bubbles (Cont.) Abell 2597 – 327 MHz Radio in Green (Clarke et al.) Ghost bubbles have low frequency radio

Buoyant “Ghost” Bubbles Fabian et al.McNamara et al. PerseusAbell 2597 Holes in X-rays at larger distances from center No radio, except at very low frequencies (Clarke et al.) Old radio bubbles which have risen buoyantly

Entrainment of Cool Gas M87/Virgo Young et al. Columns of cool X-ray gas from cD center to radio lobe Gas entrained & lifted by buoyant radio lobe? A X-ray red, Radio green Fujita et al.

Temperatures & Pressures Gas in shells is cool Pressure in shells ≈ outside No large pressure jumps (shocks)

Temperatures & Pressures Gas in shells is cool Pressure in shells ≈ outside No large pressure jumps (shocks) Bubbles expand ≲ sound speed Pressure in radio bubbles ≈ pressure in X-ray shells Equipartition radio pressures are ~10 times smaller than X-ray pressures in shells!?

Additional Pressure Sources Magnetic field larger than equipartition value? Lots of low-energy relativistic electrons? Lots of relativistic ions? Very hot, diffuse thermal gas? – Jet kinetic energy thermalized by “friction” or shocks? –Hard to detect hot gas in bubbles because of hot cluster gas in fore/background (but, may have been seen in MKW3s (Mazzotta et al.) In most clusters, just lower limits on kT ≳ 10 keV

Limits from Faraday Depolarization E pol B || Radio bubbles have large Faraday rotation, but strong polarization Faraday rotation ∝ n e B ∥ External thermal gas → strong Faraday rotation and polarization Internal thermal gas → Faraday depolarization Gives upper limit on n e Given pressure, gives lower limit on T kT ≳ 20 keV in most clusters if thermal gas is pressure source

Cooling Isobaric cooling time in shells are t cool ≈ 3 x 10 8 yr ≫ ages of radio sources Cooler gas at 10 4 K located in shells

Hα + [N II] contours (Baum et al.)

X-ray Shells as Radio Calorimeters Energy deposition into X-ray shells from radio lobes (Churazov et al.): E ≈ ergs in Abell 2052 ~Thermal energy in central cooling flow, ≪ total thermal energy of intracluster gas Repetition rate of radio sources ~ 10 8 yr (from buoyancy rise time of ghost cavities) Internal bubble energy Work to expand bubble

Can Radio Sources Offset Cooling? Compare –Total energy in radio bubbles, over –Repetition rate of radio source based on buoyancy rise time of bubbles –Cooling rate due to X-ray radiation

Examples A2052: E = erg E/t = 3 x erg/s kT = 3 keV, Ṁ = 42 M  /yr L cool = 3 x erg/s ☑ Hydra A: E = 8 x erg E/t = 2.7 x erg/s kT = 3.4 keV, Ṁ = 300 M  /yr L cool = 3 x erg/s ☑ A262: E = 1.3 x erg E/t = 4.1 x erg/s kT = 2.1 keV, Ṁ = 10 M  /yr L cool = 5.3 x erg/s ☒ (but, much less powerful radio source) Blanton et al. McNamara et al. Blanton et al.

X-ray Ripples How does radio source heat X-ray gas? Perseus (Fabian et al.) X-ray ripples = sounds waves or weak shocks Viscous damping heats gas? But, is Perseus unique? Abell 2052 (Blanton et al.) Also has ripples, ≈ 11 kpc, P ≈ 1.4 x 10 7 yr Blanton et al. Abell 2052 Chandra Unsharp Masked

Limit Cycle? X-ray cooling BH accretes Radio jets Heat X-ray gas Stop X-ray cooling Stop BH accretion BH inactive

Clusters from hierarchically, smaller things form first, gravity pulls them together Cluster Formation: Mergers and Accretion Virgo Consortium

Cluster Formation from Large Scale Structure Lambda CDM - Virgo Consortium z=2 z=1 z=0

Clusters form within LSS filaments, mainly at intersections of filaments Clusters form through mixture of small and large mergers Major mergers Accretion Clusters form today and in the past Cluster Formation (cont.) PS merger tree: Mass vs. time

Cluster Formation (cont.) Lambda CDM - Virgo Consortium z=2 z=1 z=0

Self-similar solution for spherical accretion of cold gas in E-dS Universe ( Bertschinger 1985; (earlier work Sunyaev & Zeldovich) Cold gas → very strong shocks Accretion shocks at very large radii (≳r vir ~2 Mpc) No direct observations so far Spherical Accretion Shocks  ≡ r / r ta (turn around radius)

Accretion Shocks (cont.) z=2 z=1 z=0 Growth of clusters not spherical Accretion episodic (mergers) IGM not cold

Accretion Shocks (cont.) Growth of clusters not spherical 40x40 Mpc Accretion episodic (mergers) IGM not cold 40x40 Mpc (Jones et al)

Accretion Shocks (cont.) ~40x40 Mpc External (accretion) & internal (merger) shocks (Ryu & Kang)

Accretion Shocks (cont.) Mach numbers ℳ ≡ v s / c s ~ 30 Y   = kinetic energy, Y th = thermal energy

Accretion Shocks (cont.) Accretion shocks at large radii in very low density gas X-ray emission ∝ (density) 2 → very faint, never seen so far Radio relics? Eventually, SZ images? (SZ ∝ pressure) Growth of LSS → most IGM is now hot, most baryons in diffuse, hot IGM

Clusters form hierarchically Major cluster mergers, two subclusters, ~10 15 M  collide at ~ 2000 km/s E (merger) ~ 2 x ergs E (shocks in gas) ~ 3 x ergs Cluster Mergers Major cluster mergers are most energetic events in Universe since Big Bang

Abell 85 Merger Chandra X-ray Image Kempner et al

Heat and compress ICM Increase entropy of gas Boost X-ray luminosity, temperature, SZ effect Mix gas Disrupt cool cores Produce turbulence Provide diagnostics of merger kinematics Thermal Effects of Mergers

Numerical N-body for collisionless dark matter, galaxies Numerical hydrodynamics for gas Initial conditions Draw from cosmological LSS simulations, resample at higher resolution Set up individual binary mergers to test physics Cooling by radiation Preheating, galaxy formation Numerical Hydrodynamics of Mergers

Additions Magnetic fields (MHD) Cosmic rays, particle acceleration Transport processes AGNs Issues Spatial resolution, particularly in cores (AMR, SPH) Overcooling, galaxy formation, feedback Numerical Hydrodynamics (cont.)