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X-ray Spectra of Clusters of Galaxies

X-ray Spectra of Clusters of Galaxies. John Peterson Purdue University X-ray Gratings 2007 Boston, MA. Intracluster medium. Optical. X-ray. Heated due to large gravitational potentials Temperatures ~ 1-10 keV (10 7 to 10 8 K) Densities ~ 10 -5 to 10 -1 particles per cubic cm

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X-ray Spectra of Clusters of Galaxies

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  1. X-ray Spectra ofClusters of Galaxies John Peterson Purdue University X-ray Gratings 2007 Boston, MA

  2. Intracluster medium Optical X-ray Heated due to large gravitational potentials Temperatures ~ 1-10 keV (107 to 108 K) Densities ~ 10-5 to 10-1 particles per cubic cm Sizes ~ 1 to 10 Mpc (1024 to 1025) cm

  3. <=X-ray Spectra (prior to 2000) X-ray Spectrum dominated by line emission and Bremmstrahlung from collisionally ionized plasma Plasma out of LTE optically thin At densities and temperatures (in core), trecombination = 106 years (for Fe XVII at 1 keV) tcool= (5/2 n k T)/(n2) = 108 to 109 years tformation= 5 109 years Collisional ionizations balanced by recombinations Line emission dominated by collisional excitations+cascades, Radiative recombination, and dielectronic recombination Same model as stellar coronae

  4. Long-standing prediction that cores of clusters should cool by emitting X-rays in less than a Gyr (Fabian & Nulsen 1977, Cowie & Binney 1977, Mathews & Bregman 1978) Cooling Flows Density rises and tcool is short (e.g. Voigt et al. 2002) from Images Temperature Drops (e.g. Allen et al. 2001) From CCD spectral fits

  5. Cools unevenly=>Range of emperatures approximately at constant pressure • Differential Luminosity predicted to be: • dLx/dT=5/2 (Mass Deposition Rate) k/(mp) • Predicts a unique X-ray spectrum; Free parameters: Tmax, Abundances • The major assumption is that the emission of X-rays is the dominate heating or cooling term

  6. Measuring a differential luminosity at keV temperatures => Need Fe L ions (temperature sensitive) => Need to resolve each ion separately (i.e. / ~ 100) Very difficult to do in detail with CCD instrument (ASCA, XMM-Newton EPIC, Chandra ACIS) Works with XMM-Newton RGS (for subtle reasons)

  7. RGS (dispersive spectrometer) : High dispersion angles (3 degrees) / ~ 3 degrees / ang. size ~ 100 for arcminute size Soft X-ray band from Si K to C K; FOV: 5 arcminutes by 1 degree Analysis not simple: dispersive, background, few counts Data Detailed studies best done with full Monte Carlo Model

  8. Failure of the Model <= dL/dT= constant model 8 keV  3 keV  ? Peterson et al. 2001

  9. Decompose into temperature bins and set limits

  10. Hot clusters Peterson et al. 2003

  11. Warm Clusters Peterson et al. 2003

  12. Cool clusters/groups Peterson et al. 2003

  13. Peterson et al. 2003 Differential Luminosity vs. Fractional Temperature Differential Luminosity vs. Temperature

  14. Theoretical Intepretation: Essentially Three Fine-tuning Problems 1. Energetics: Need average heating or cooling power ~ Lx Dynamics: Either need energy source to work at low temperatures or at t ~ tcool (before complete cooling would occur) Cooling time ~ T2 / (cooling function) If at 1/3 Tmax then why cool for 8/9 of the cooling time? or why at low temperatures? • Get Energetic and Dynamics right at all spatial positions Soft X-rays missing throughout entire cflow volume

  15. Current Models 1. AGN reheating: relativistic flows inflate subsonic cosmic ray bubbles & cause ripples; dissipation efficiency? & feedback mechanism? (Rosner & Tucker 1989; Binney & Tabor 1995; Tabor & Binney 1995; Churazov et al. 2001, Bruggen & Kaiser 2001; Quilis et al. 2001, David et al 2001; Nulsen 2002; Kaiser & Binney 2002; Ruszkowski & Begelman 2002; Soker & David 2003; Brighenti & Mathews 2003) McNamara et al. 2000 Fabian et al. 2003

  16. 2. Heat transfer from the outside to the core: probably through conduction Stability & is conduction coefficient realistic (Tucker & Rosner 1983, Stewart et al. 1984, Zakamska & Narayan 2001; Voigt et al.2002; Fabian, Voigt, & Morris 2002; Soker 2003; Kim & Narayan 2003) Voigt et al. 2003

  17. 3. Cooling through non radiative interactions with cold material: Avoids producing soft X-rays? (Begelman & Fabian 1990; Norman & Meiskin 1996; Fabian et al. 2001, 2002; Mathews & Brighenti 2003) Fabian et al. 2002 4. Cluster Mergers (Markevitch et al. 2001) 5. Inhomogenous Metals (Fabian et al. 2001; Morris et al.200) 6. Differential Absorption (Peterson et al. 2001) 7. Cosmic Rays Interactions (Gitti et al. 2002) 8. Photoionization (Oh 2004) 9. Non-maxwellian particle ionization (Oh 2004) Crawford et al. 2003

  18. 10. Dark Matter (huge energy source): Dark Matter-Baryon interactions (Qin & Wu 2001): Requires high cross-section (/m ~ 10-25 cm2/GeV ) Dark Matter (Neutralino) Annihilations (Totani 2004): Converts to relativistic particles Requires a high central density for neutralino Dark Matter-Baryon Interactions (Chuzhoy & Nusser 2004): same cross-section but make mass of dark matter ~ 1/3 of proton mass

  19. M87

  20. M87 Use hundreds of gaussian blobs with own properties (e.g. temperature) instead of a parameterized model

  21. Perseus

  22. Perseus

  23. 4 actual cooling flows: Mukai et al. 2003

  24. Abundances Long-standing problem of the origin of metals in the ICM: Supernovae Ia (what fraction?)+ Type II (of what mass?) and of what metallicity (and therefore when)?+Stellar winds (for CNO)+ Hypernovae? Zi = YieldIA(z)+  dM YieldII (z,M) dN/dM

  25. Abundances Fe=>mostly Ia O/Fe=0.7+/-0.2=>50% II Ne/Fe=1.1+/0.3=>100% II Mg/Fe=1.0+/0.3=>100% II Si/Fe=2.3+/1=>100% II Tamura et al. 2004 Matsushita et al. 2003 O/Fe 0.6 0.5 Mg/Fe 0.8 Si/Fe 1.4 1.2 S/Fe 1.1 1.1 Spatially resolved Abundances much more complicated Peterson et al. 2003

  26. Sersic 159-03, de Plaa et al. 2005 NGC 5044, Buote et al. 2005 Spatial Distribution of Abundances Abundances depend on temperature model sensitively Gradient in Metals ~ 100% per 100 kpc Gradient in O/Fe or Si/Fe < 20% per 100 kpc

  27. Evidence for a Low T (0.7 keV) diffuse thermal component (WHIM) still unsettled OVII emission, Kaastra et al. 2001 Absorption (3 sigma) behind Coma, Takei et al. 2007

  28. Large soft X-ray background from within the galaxy (McCammon et al. 2002) Subtleties of particle background in CCD fits, de Plaa et al 2005

  29. Resonant Scattering • ~ ni i (cluster size) ~ few for some transitions ( Fe XXV He r, Fe XXIV 3d-2p, Fe XVIII 3d-2p, Fe XVII 3d-2p, possibly some Ly alpha transitions) But doppler velocities can lower this (thermal width ~ 100 km/s, sound speed ~ 1000 km/s) NGC 4636, Xu et al. 2002 Perseus, Churazov et al. 2004

  30. Summary Cooling flow model fails to reproduce X-ray spectrum; Several strong observational constraints (factor of 20!) Fails despite very simple theoretical arguments Much more theoretical work needed for fine-tuning challenges Much more observational work is needed to constrain the spatial distribution and to connect to other wavelengths Abundances still need more study Soft excess inconclusive Resonant scattering inconclusive Note: radiative cooling is supposed to form galaxies through tiny cooling flows. Do we understand this now?

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