1. Preventing Star and Galaxy Formation Michael Balogh Department of Physics and Astronomy University of Waterloo

2. Outline Part I: The problem –Composition of the Universe –Galaxy formation in a nutshell –The importance of galaxy clusters Part II: Energetics –How much energy is required to explain the observed properties of clusters Part III: A Unified model

3. We observe starlight – which results from the condensation of baryonic matter

4. Matter and Energy Baryons make up less than 5% of the matter and energy in the Universe Spergel et. al 2003, 2006

5.  >95% of baryons are dark The matter budget: stars Cole et. al 2002  stars = 0.0014 ± 0.00013

6. Dark matter Springel, Frenk & White 2006

7. The halo model Radiative cooling Hot baryons Dark matter ~10 6 K for galaxies, hence invisible

8. The cooling catastrophe Cooling occurs primarily through bremsstrahlung radiation, so t cool  T 1/2  -1 The typical density of haloes is higher at early times:   (1+z) 3 Thus, gas cools very efficiently in small haloes at high redshift. White & Frenk (1991) Balogh et al. (2001)

9. Why so few stars? Balogh et al. (2001) Observations imply  * /  b  0.05 f cool 0.1 0.6 0.5 0.4 0.3 0.2 Fraction of condensed gas in simulations is much larger, depending on numerical resolution Pearce et al. (2000) Lewis et al. (2000) Katz & White (1993) kT (keV) 110

10. Galaxy Luminosity Function Benson et al. 2003 Number density of galaxies Luminosity Theory Data

11. The intracluster medium The brightest galaxies reside in the centres of massive clusters We can see the hot gas directly, in X-ray emission

12. Galaxy clusters Coma: XMM-Newton ObservatoryComa cluster Can use the hot gas as a sort of calorimeter, measuring the heat associated with galaxy formation, because:  Clusters form a nearly closed-box system  Hydrostatic equilibrium is a good approximation  The shape of the gravitational potential is precisely known The Perseus cluster

13. Galaxy clusters Can use the hot gas as a sort of calorimeter, measuring the heat associated with galaxy formation, because:  Clusters form a nearly closed-box system  Hydrostatic equilibrium is a good approximation  The shape of the gravitational potential is precisely known The Perseus cluster

14. Galaxy clusters Coma: XMM-Newton ObservatoryComa cluster Can use the hot gas as a sort of calorimeter, measuring the heat associated with galaxy formation, because:  Clusters form a nearly closed-box system  Hydrostatic equilibrium is a good approximation  The shape of the gravitational potential is precisely known The Perseus cluster

15. Cooling Up to 50% of clusters have sharply peaked gas density profiles –Gas should be cooling rapidly –As pressure support is lost, hotter gas flows in and is compressed. Conselice et al. 2003 H  filaments in the Perseus cluster may be a sign that gas is cooling (Fabian & Nulsen 1997). Fabian 1994

16. Cooling – not so much Line emission from cooling gas not seen Low star-formation rates, cold gas mass Peterson et al. 2003 Edge & Frayer 2003

17. Black holes Some cooling clusters show depressions in X-ray emission, often filled with radio emission. Attributed to outflows from massive black hole accretion Most energetic can provide up to 6x10 54 J

18. Non-cooling clusters >50% have diffuse X-rays, with cooling times of at least several billion years. Cooling disrupted by mergers? Or extreme heating? XMM image of Coma

19. Part II Energy requirements

20. Gas profiles Can measure the gas density and temperature as a function of radius, from X-ray data. Normalized gas density Normalized radius Normalized Temperature

21. Entropy Keeps track of heat gain/loss –Radiative cooling reduces entropy –Heating raises entropy Low entropy gas sinks to the bottom of the potential well

22. Entropy and density Gas temperature of gravitationally confined gas needs to be ~T vir However, density can be arbitrarily normalized by changing the entropy (if potential is dark-matter dominated) Hydrostatic equilibrium equation: Entropy definition:

23. Entropy profiles Cooling only: slope of entropy distribution determined by potential and cooling function. –Both are known quite well. Assumes steady supply of gas (may not be true for low-mass clusters, or groups) McCarthy, Fardal & Babul 2005

24. Observed entropy profiles Good agreement at large radius Excess entropy at small radius, r<200 kpc. McCarthy et al. 2007 Pure cooling model

25. Energetics How much energy would it take to transform the pure-cooling model to match the observations? –Recall the most energetic outbursts can provide up to 6x10 54 J. McNamara et al. 2005

26. Energetics How much energy would it take to transform the pure-cooling model to match the observations? –About 5x10 55 J, within the central ~300 kpc (10 55 J) 6x10 54 J

27. Recall: AGN Most energetic can provide up to 6x10 54 J But these are rare; most outbursts are much less energetic McNamara et al. 2005 Perseus: 2x10 52 J

28. Preheating Heating the gas before it falls into the cluster (when it has a low density) can reduce energy requirements by factors of ~10-100, to ~10 54 J. 6x10 54 J

29. Non-cooling clusters There are few non- cooling clusters with high resolution X-ray data. Instead, we compare total luminosity to mass Clusters with short cooling times are brighter in X-rays McCarthy et al. 2006 X-ray luminosity Cluster mass

30. Non-cooling clusters Compare with models in which gas is preheated to some initial entropy E~0.5-5x10 54 J of preheating required to account for the lowest luminosity clusters Balogh et al. 2006 6x10 54 J X-ray luminosity Cluster mass

31. Part III A unified model

32. Circulation flows Simulation of energetic bubbles every 10 8 years. Gas near the centre is heated, and it rises bouyantly E.g. Brighenti & Mathews 2002 Mass-weighted temperature (simulation) Sijacki & Springel 2006

33. Maintaining steady-state Only ~2x10 38 W required to balance cooling ~5x10 53 J outburst every 10 8 years will do the job 6x10 54 J McCarthy et al. 2007 X-ray luminosity Model based on fit to entropy profiles Pure cooling model

34. Circulation flow model Heat gas that cools to random entropy below some threshold parameter Move gas to its appropriate adiabat McCarthy et al. 2007

35. Circulation flow model Gets centre right – but not enough entropy at intermediate radius (also Voit & Donahue 2005) R (kpc) S (keV cm 2 ) Observations Model McCarthy et al. 2007

36. Solutions? Need to raise the adiabat of gas at ~200 kpc. –Lower the baryon fraction? Changes normalization, but not shape. Strongly constrained –Conduction? Cannot accommodate low-mass clusters Causes cooling at large radii Cannot explain non-cooling systems –Preheating

37. Preheating Preheating + circulation flows, works. McCarthy et al. 2007 S (keV cm 2 ) R (kpc)

38. A unified model Not sensitive to parameters A range of preheating energy (z=2) of 1-5x10 54 J can explain cooling clusters. Heating at a higher level may be responsible for the non-cooling clusters. McCarthy et al. 2007 Increasing circulation flow energy Increasing preheating level 6x10 54 J

39. Summary A unified heating model for clusters: –AGN at z~2 heat the IGM to S=100-700 keV cm 2 (up to 10 55 J required) –Those with S<300 keV cm 2 (about 3x10 54 J) become cooling flow clusters by the present day. Regulated by AGN outflows. –Others are non-cooling clusters. Prediction: there should be no cooling flow clusters at z~1 or beyond. –May be supported by recent claims for few cooling flow clusters at z>0.5 by Vikhlinin et al. 2006 6x10 54 J

40. Collaborators Ian McCarthy (University of Durham) Richard Bower (University of Durham) Arif Babul (University of Victoria) Mark Voit (Michigan State University)