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Structure and scaling of nearby clusters of galaxies – in X-rays

Structure and scaling of nearby clusters of galaxies – in X-rays Gabriel W. Pratt, MPE Garching, Germany. 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]. Rationale.

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Structure and scaling of nearby clusters of galaxies – in X-rays

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

  2. Introduction ΩM=1, ΩΛ=0, σ8=0.6 ΩM=0.3, ΩΛ=0.7, σ8=0.9 [Evrard et al. 2002] G.W. Pratt, Ringberg, 26/10/2005

  3. 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, LX-M) or proxies thereof (e.g., LX-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 G.W. Pratt, Ringberg, 26/10/2005

  4. 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 z=0 z=0.5 z=1 Bryan & Norman (1998); Navarro et al. (1995,1997) M  T3/2 G.W. Pratt, Ringberg, 26/10/2005

  5. LX  T2 Real clusters Real clusters are structurally similar, but the scaling laws are different ASCA/Ginga LX-T relation LX T3 (Arnaud & Evrard 1999; also Markevitch 1998) ROSAT X-ray EM profiles (Arnaud et al. 2002; also Vikhlinin et al. 1999) • Non-gravitational effects influence gas properties? G.W. Pratt, Ringberg, 26/10/2005

  6. Key questions • Is our basic understanding of cluster formation correct? • Are the dark matter properties consistent with predictions? • e.g., NFW ρDM  (r/rS)-1[1+ (r/rS)]-2 with c=R200/rs weakly dependent on mass • How good is our understanding of the gas physics? • Structure and scaling of entropy G.W. Pratt, Ringberg, 26/10/2005

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

  8. Universal profile 10 clusters 2—9 keV 13 clusters 0.7—9 keV ρ/ρc M/M200 R/R500 R/R200 [Vikhlinin et al. astro-ph/0507092; Chandra] [Pointecouteau et al. 2005; XMM] ~2 keV ~8 keV • Universal mass/density profile down to low mass • NFW model good description • < 15% dispersion in mass profiles at 0.1 R200 G.W. Pratt, Ringberg, 26/10/2005

  9. Concentration parameters <c500>= 3 (<c200> ~ 4.6) <c200>= 5 c200 c500 M500 M200 [Vikhlinin et al. astro-ph/0507092; Chandra] [Pointecouteau et al. 2005; XMM simulations by Dolag et al. 2004] • Concentration parameters in range expected • Dark matter properties consistent with predictions G.W. Pratt, Ringberg, 26/10/2005

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

  11. Context • Value of cosmological parameters measurable with clusters using number count methods (σ8, ΩM) depends sensitively on the normalisation of the cluster M-T relation • In X-rays, we get M from ne and T • Need to know the gas physics in detail σ8 M—T normalisation [Pierpaoli, Scott & White 2001] G.W. Pratt, Ringberg, 26/10/2005

  12. M500 (M) kT/10 (keV) M-T relation δ = 500 δ = 2500 Mδ (M) M  T1.7 M  T1.5 kT (keV) [Arnaud et al. 2005; XMM] [Vikhlinin et al. astro-ph/0507092; Chandra] • Slope under debate; observed normalisation no longer an issue • ~35% too low wrt pure gravitational simulations [Evrard et al. 1996] • Inclusion of non-gravitational physics[SN, radiative cooling; Borgani et al. (2004] improves situation; observational treatment [cf Rasia]??? G.W. Pratt, Ringberg, 26/10/2005

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

  14. Why entropy? • 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 ne-2/3 • Radiative cooling reduceskT ne-2/3 • Heat input (pre-heating, AGN, SNe, mixing) raiseskT ne-2/3 G.W. Pratt, Ringberg, 26/10/2005

  15. S  T S (0.1 R200) [Ponman et al, 2003] S  T Entropy scaling If clusters are self similar, ρgasρDMδc (0) = cst • S  T • Find S  T0.65 with slope stable to 0.5 R200 [see also Ponman et al. 2003] • S  T0.65  LX  T2.7 • Increased dispersion towards central regions [Pratt et al., astro-ph/0508234] G.W. Pratt, Ringberg, 26/10/2005

  16. 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 Adiabatic prediction (Voit 2005) [Pratt et al., astro-ph/0508234; also Pratt & Arnaud 2005] G.W. Pratt, Ringberg, 26/10/2005

  17. 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? G.W. Pratt, Ringberg, 26/10/2005

  18. 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 R200 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 R200 • Cool core systems represent lower envelope [see also Voit & Donahue 2005] • AGN heating probably has an effect G.W. Pratt, Ringberg, 26/10/2005

  19. Thanks: Monique Arnaud Hans Böhringer Judith Croston Etienne Pointecouteau 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 G.W. Pratt, Ringberg, 26/10/2005

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