1. G.W. Pratt, Ringberg, 26/10/2005 Structure and scaling of nearby clusters of galaxies – in X-rays Gabriel W. Pratt, MPE Garching, Germany

2. G.W. Pratt, Ringberg, 26/10/2005 Introduction Ω M =1, Ω Λ =0, σ 8 =0.6 Ω M =0.3, Ω Λ =0.7, σ 8 =0.9 [Evrard et al. 2002]

3. G.W. Pratt, Ringberg, 26/10/2005 Rationale Cluster mass is most fundamental characteristic  most useful for cosmology (whatever the cosmological test) We will never measure the mass of every cluster  need mass- observable relations (e.g., M-T, L X -M) or proxies thereof (e.g., L X -T) We need to establish robust scaling relations (local and distant)  Detailed structural investigation only possible at low-z  astrophysics of the ICM & its evolution

4. G.W. Pratt, Ringberg, 26/10/2005 Introduction Simplest model of structure formation is dark matter-driven hierarchical gravitational collapse Gas ‘follows’ DM Expect simple self-similar scaling of haloes with mass (& redshift)  scaling laws, structural similarity Bryan & Norman (1998); Navarro et al. (1995,1997) M  T 3/2 z=0 z=0.5 z=1

5. G.W. Pratt, Ringberg, 26/10/2005 ROSAT X-ray EM profiles (Arnaud et al. 2002; also Vikhlinin et al. 1999) Real clusters are structurally similar, but the scaling laws are different ASCA/Ginga L X -T relation L X  T 3 (Arnaud & Evrard 1999; also Markevitch 1998)  Non-gravitational effects influence gas properties? Real clusters L X  T 2

6. G.W. Pratt, Ringberg, 26/10/2005 Is our basic understanding of cluster formation correct? Are the dark matter properties consistent with predictions? e.g., NFW ρ DM  (r/r S ) -1 [1+ (r/r S )] -2 with c=R 200 /r s weakly dependent on mass How good is our understanding of the gas physics? Structure and scaling of entropy Key questions

7. G.W. Pratt, Ringberg, 26/10/2005 Converging observational support for dark matter predictions

8. G.W. Pratt, Ringberg, 26/10/2005 Universal profile Universal mass/density profile down to low mass NFW model good description < 15% dispersion in mass profiles at 0.1 R 200 ~2 keV ~8 keV 13 clusters 0.7—9 keV [Vikhlinin et al. astro-ph/0507092; Chandra] R/R 500 ρ/ρcρ/ρc [Pointecouteau et al. 2005; XMM] R/R 200 M/M 200 10 clusters 2—9 keV

9. G.W. Pratt, Ringberg, 26/10/2005 M 500 M 200 c 500 c 200 Concentration parameters [Pointecouteau et al. 2005; XMM simulations by Dolag et al. 2004] [Vikhlinin et al. astro-ph/0507092; Chandra] = 3 ( ~ 4.6) = 5 Concentration parameters in range expected  Dark matter properties consistent with predictions

10. G.W. Pratt, Ringberg, 26/10/2005 The M—T relation: cosmological connection

11. G.W. Pratt, Ringberg, 26/10/2005 Context [Pierpaoli, Scott & White 2001] Value of cosmological parameters measurable with clusters using number count methods (σ 8, Ω M ) depends sensitively on the normalisation of the cluster M-T relation  In X-rays, we get M from n e and T  Need to know the gas physics in detail M—T normalisation σ8σ8

12. G.W. Pratt, Ringberg, 26/10/2005 M δ (M  ) kT (keV) δ = 500 δ = 2500 M-T relation M 500 (M  ) kT/10 (keV) [Arnaud et al. 2005; XMM] Slope under debate; observed normalisation no longer an issue pure gravitational simulations [Evrard et al. 1996] ~35% too low wrt pure gravitational simulations [Evrard et al. 1996] non-gravitational physics Inclusion of non-gravitational physics [SN, radiative cooling; Borgani et al. (2004] improves situation; observational treatment [cf Rasia]??? [Vikhlinin et al. astro-ph/0507092; Chandra] M  T 1.7 M  T 1.5

13. G.W. Pratt, Ringberg, 26/10/2005 Non-gravitational processes and entropy

14. G.W. Pratt, Ringberg, 26/10/2005 Gas entropy is generated in shocks and compression as the gas accretes into the dark matter potential well It preserves the gravitational accretion history and any subsequent modification by non-gravitational processes Useful X-ray observable S = kT n e -2/3 Why entropy? Radiative cooling reduces kT n e -2/3 Heat input (pre-heating, AGN, SNe, mixing) raises kT n e -2/3

15. G.W. Pratt, Ringberg, 26/10/2005 [Pratt et al., astro-ph/0508234] Entropy scaling S  T If clusters are self similar, ρ gas  ρ DM  δ c (0) = cst  S  T Find S  T 0.65 with slope stable to 0.5 R 200 [see also Ponman et al. 2003] S  T 0.65  L X  T 2.7 Increased dispersion towards central regions S   T S (0.1 R 200 ) [Ponman et al, 2003]

16. G.W. Pratt, Ringberg, 26/10/2005 Entropy scaling: comparison with adiabatic simulations Hotter systems in relatively good agreement (slope & normalisation) Clear excess normalisation at all measured radii in poorer systems (x2.5 at 2 keV) Increased dispersion in central regions Need mechanism which increases normalisation ar large R and dispersion at small R [Pratt et al., astro-ph/0508234; also Pratt & Arnaud 2005] Adiabatic prediction (Voit 2005)

17. G.W. Pratt, Ringberg, 26/10/2005 Conclusions: dark matter Universal mass/density profile in clusters, well described by standard NFW model, c in range expected from simulations  dark matter collapse understood Normalisation of M-T relation has converged, but is consistently lower than simulations  are simulations correctly reproducing the thermal structure in clusters?  how do the observational assumptions (particularly HE) affect final mass estimate?

18. G.W. Pratt, Ringberg, 26/10/2005 Conclusions: gas physics Slope of M—T relation is stable (universal mass profile), but steeper if lower mass objects (kT < 3 keV) are included in fit S—T relation is shallower than self-similar at all radii probed Entropy profiles are self-similar (~20% dispersion) outside ~0.2 R 200 except for a normalisation factor  some non-gravitational processes boost entire entropy profile, preferentially in low mass systems (filamentary preheating?) Dispersion increases to >60% at < 0.05 R 200  Cool core systems represent lower envelope [see also Voit & Donahue 2005]  AGN heating probably has an effect

19. G.W. Pratt, Ringberg, 26/10/2005 For more information: Pratt, Arnaud & Pointecouteau, 2005, A&A, in press (astro-ph/0508234) Arnaud, Pointecouteau & Pratt, 2005, A&A, 441, 893 Pointecouteau, Arnaud & Pratt, 2005, A&A, 435, 1 Thanks: Monique Arnaud Hans Böhringer Judith Croston Etienne Pointecouteau