GH2005 Gas Dynamics in Clusters II

1. GH2005Gas Dynamics in Clusters II Craig Sarazin Dept. of Astronomy University of Virginia Cluster Merger Simulation A85 Chandra (X-ray)

2. De-Projected Gas Profiles • De-project X-ray surface brightness profile → gas density vs. radius, r(r) • De-project X-ray spectra in annuli → T(r) • Pressure P = rkT/(mmp)

3. Gas and Total Masses • Gas masses → integrate r • Total masses → hydrostatic equilibrium • Dark matter Mdm = M – Mgal - Mgas

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

5. Gas Fraction Profiles Chandra (Allen et al) (r2500≈0.25 rvir)

6. Masses of Clusters • Cluster total masses 1014 – 1015 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

7. Masses of Clusters (cont.) • 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 • ΩM=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)

8. Cooling Cores in Clusters IX • Central peaks in X-ray surface brightness cooling core non-cooling core (Coma)

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

10. Cooling Cores in Clusters • Central peaks in X-ray surface brightness • Temperature gradient, cool gas at center • Radiative cooling time tcool < Hubble time • tcool ~ 2 x 108 yr

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

12. 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 ~108 K → ~107 K at ~100 M/yr

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

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

15. 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 ~107 K

16. 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

17. 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

18. Heat Source to Balance or Reheat Cooling 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 ∝ T7/2, how to heat mainly cooler gas? • Supernovae? • AGN = Radio sources

19. 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?

20. A2052 (Chandra) Blanton et al.

21. Radio Contours (Burns)

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

23. 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

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

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

26. Buoyant “Ghost” Bubbles Perseus Abell 2597 Fabian et al. McNamara et al. • 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

27. Entrainment of Cool Gas M87/VirgoYoung et al. A133 --- X-ray red, Radio greenFujita et al. • Columns of cool X-ray gas from cD center to radio lobe • Gas entrained & lifted by buoyant radio lobe?

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

30. 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!?

31. 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

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

33. Cooling • Isobaric cooling time in shells are tcool≈ 3 x 108 yr≫ ages of radio sources • Cooler gas at 104 K located in shells

34. Hα + [N II] contours (Baum et al.)

35. X-ray Shells as Radio Calorimeters • Energy deposition into X-ray shells from radio lobes (Churazov et al.): • E ≈ 1059 ergs in Abell 2052 • ~Thermal energy in central cooling flow, ≪ total thermal energy of intracluster gas • Repetition rate of radio sources ~ 108 yr(from buoyancy rise time of ghost cavities) Internal bubble energy Work to expand bubble

36. 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

37. Examples • A2052: E = 1059 erg E/t = 3 x 1043 erg/s kT = 3 keV, Ṁ = 42 M/yr Lcool = 3 x 1043 erg/s ☑ • Hydra A: E = 8 x 1059 erg E/t = 2.7 x 1044 erg/s kT = 3.4 keV, Ṁ = 300M/yr Lcool = 3 x 1044 erg/s ☑ • A262: E = 1.3 x 1057 erg E/t = 4.1 x 1041 erg/s kT = 2.1 keV,Ṁ = 10M/yr Lcool = 5.3 x 1042 erg/s ☒ (but, much less powerful radio source) Blanton et al. McNamara et al. Blanton et al.

38. X-ray Ripples Abell 2052 Chandra Unsharp Masked 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, l≈ 11 kpc, P ≈ 1.4 x 107 yr Blanton et al.

39. Limit Cycle?

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

41. Cluster Formation fromLarge Scale Structure Lambda CDM - Virgo Consortium z=2 z=1 z=0

42. Cluster Formation (cont.) • 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 PS merger tree: Mass vs. time

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

44. Spherical Accretion Shocks • 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 (≳rvir~2 Mpc) • No direct observations so far l ≡ r / rta (turn around radius)

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

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

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

48. Accretion Shocks (cont.) • Mach numbers ℳ ≡ vs / cs ~ 30 • Yf= kinetic energy, Yth = thermal energy

49. 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

50. Cluster Mergers • Clusters form hierarchically • Major cluster mergers, two subclusters, ~1015 M collide at ~ 2000 km/s • E (merger) ~ 2 x 1064 ergs • E (shocks in gas) ~ 3 x 1063 ergs Major cluster mergers are most energetic events in Universe since Big Bang