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

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

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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. - PowerPoint PPT Presentation

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

  • Structure and scaling of nearby clusters of galaxies in X-raysGabriel W. Pratt, MPE Garching, Germany

  • IntroductionM=1, =0, 8=0.6M=0.3, =0.7, 8=0.9[Evrard et al. 2002]

  • 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

  • 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 similarityBryan & Norman (1998); Navarro et al. (1995,1997)

    M T3/2z=0z=0.5z=1

  • ROSAT X-ray EM profiles(Arnaud et al. 2002; also Vikhlinin et al. 1999)Real clusters are structurally similar, but the scaling laws are differentASCA/Ginga LX-T relation LX T3(Arnaud & Evrard 1999; also Markevitch 1998)

    Non-gravitational effects influence gas properties?

    Real clusters

  • Is our basic understanding of cluster formation correct? Are the dark matter properties consistent with predictions? e.g., NFW DM (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 entropyKey questions

  • Converging observational support for dark matter predictions

  • Universal profile Universal mass/density profile down to low mass NFW model good description < 15% dispersion in mass profiles at 0.1 R200~2 keV~8 keV

  • M500M200c500c200Concentration 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

  • The MT relation: cosmological connection

  • Context[Pierpaoli, Scott & White 2001]Value of cosmological parameters measurable with clusters using number count methods (8, M) 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

    MT normalisation8

  • M (M)kT (keV) = 500 = 2500M-T relation[Arnaud et al. 2005; XMM] 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]???[Vikhlinin et al. astro-ph/0507092; Chandra]M T1.7M T1.5

  • Non-gravitational processes and 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-2/3Why entropy? Radiative cooling reduces kT ne-2/3 Heat input (pre-heating, AGN, SNe, mixing) raises kT ne-2/3

  • [Pratt et al., astro-ph/0508234]Entropy scalingIf clusters are self similar,gas DM c (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

  • 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)

  • 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?

  • Conclusions: gas physics Slope of MT relation is stable (universal mass profile), but steeper if lower mass objects (kT < 3 keV) are included in fit ST 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

  • For more information:

    Pratt, Arnaud & Pointecouteau, 2005, A&A, in press (astro-ph/0508234)Arnaud, Pointecouteau & Pratt, 2005, A&A, 441, 893Pointecouteau, Arnaud & Pratt, 2005, A&A, 435, 1Thanks:Monique ArnaudHans BhringerJudith CrostonEtienne Pointecouteau

    To put the work into context.Most of my recent work has been on testing the self-similar modelWork breaks down into two main themes: the properties of the dark matter, and the properties of the ICM

    Clusters are self-similar beyond 0.1 R200, but with altered scaling.May not be one single mechanism