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A Review of the Observations: Cluster Cooling Flows 2003

A Review of the Observations: Cluster Cooling Flows 2003. Megan Donahue STScI and Michigan State University. The Riddle of Cooling Flows in Galaxies and Clusters of Galaxies. The Origins of “Cooling Flows”.

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A Review of the Observations: Cluster Cooling Flows 2003

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  1. A Review of the Observations:Cluster Cooling Flows 2003 Megan Donahue STScI and Michigan State University The Riddle of Cooling Flows in Galaxies and Clusters of Galaxies

  2. The Origins of “Cooling Flows” • Clusters discovered to be extended X-ray sources (Gursky et al. 1971, UHURU; Kellogg et al. 1972; Forman et al. 1972) • Thermal emission was the natural interpretation (Felten et al. 1966; Lea et al 1973; Lea 1975) given the spectrum (Davidsen et al. 1975; Gorenstein et al. 1973.) and extent. • Intracluster Fe detected: hot gas (Mitchell et al. 1976, Ariel V; Serlemitsos et al. 1976 OSO8) • Cooling times in many clusters very short. (Cowie & Binney 1977; Fabian & Nulsen 1977; Mathews & Bregman 1978; Cowie, Fabian, & Nulsen 1980) • Unusual optical nebulae associated with cluster cooling flows. (Hu, Cowie & Wang 1985; Heckman et al 1989;Fabian, Nulsen & Canizares 1984)

  3. NGC 1275 Baade & Minkowski 1954 See also: Hubble & Humason 1931

  4. WIYN image ChrisConselice WFPC2outline

  5. NGC 1275 Hubble HeritageMay 2003

  6. Trouble with “Cooling Flows”? • Cluster “cooling flows” were defined by an ICM cooling time shorter than a Hubble time. • If no heating counteracts the cooling, the mass cooling rates implied ~ 100-1000s solar masses per year in the centers of clusters. • Claim of soft X-ray absorption (White et al. 1991) • By the early 90s: the search was on.

  7. Search for cool baryonic matter • Ionized gas: 104-7 solar masses: Ha (Fabian & Nulsen 1977; Ford & Butcher 1979; Heckman 1981; Hu, Cowie, & Wang 1985; Heckman et al. 1989; Donahue, Stocke, & Gioia 1992; Crawford & Fabian 1992) • HI – limited to an occasional faint absorption line (21 cm, Lyman alpha) (Taylor et al 1999; Jaffe 1990; Laor 1997; McNamara, Bregman & O’Connell 1990; Dwarakanath, van Gorkhom, Owen 1994) • Metal line limits (Miller, Bregman, Knezek 2002)

  8. H-alpha: Curious correlations? • Only in clusters with short cooling times (Hu, Cowie & Wang 1985) • Correlated with X-ray mass cooling rates (Heckman et al 1989)

  9. Ha, [NII], [SII], [OI], [OII]… Too bright for simple cooling (FNC 1984; Heckman et al 1989) Hot stars (Johnstone et al. ; Voit & Donahue 1997) • Blue light (McNamara et al.) • Diluted stellar absorption lines (Cardiel et al.) Strong shocks not consistent with the data (molecular lines, X-ray imaging, temperature diagnostics)

  10. Search for cool baryonic matter • H2 – vibrationally excited, correlated with Ha (Elston & Maloney 1994; Jaffe & Bremer 1997 ) & extended (HST; Donahue et al. 2000; Falcke et al 2003) • CO upper limits (Bregman & Hogg 1988; McNamara & Jaffe 1994; O’Dea et al. 1994; Braine & Dupraz 1994; Antonucii & Barvainis 1994) • CO detections 109-1011.5 solar masses in some BCGs (Edge 2001; Salome’ & Combes 2003)

  11. “Cool” baryonic matter • Not in every “CF”; compact relative to the cooling region; low mass. • Nebulae extended, correlated: what’s heating them? Stars? Conduction from the hot phase? • What is their origin: condensation or cannibalism?

  12. Abell 2597 McNamara et al. 2002 Donahue et al. 2001

  13. X-ray and FUV Emission Lines • Individual X-ray emission lines can measure the cooling rate. • DL a [ dM/dt ] DT (Cowie et al. 1980) in a steady cooling flow • Early high resolution spectra (Canizares, Markert & Donahue 1988; Mushotzky & Szymkowiak 1988) • Recent XMM spectra (Peterson et al. 2003; Peterson et al. 2001; Kaastra et al. 2001; Tamura et al. 2001.)

  14. Isobaric Multiphase Cooling-Flow Model Peterson, et al. 2003

  15. Isobaric Multiphase Cooling-Flow Model (T-ranges) Peterson et al. 2003

  16. XMM spectroscopy • Peterson, et al. 2003 • FeXVII and other lines from 1 keV gas not present. • Two-temperature or “truncated” cooling flow (at ~T/3 - T/2)

  17. FeXVII in Perseus: then and now • XMM/RGS 60 cm2 • FPCS1 cm2

  18. Cooling rates are reduced • Chandra grating spectra results are consistent with XMM. (e.g. Hicks et al. 2002; Wise 2003) • Chandra low resolution spectra also implies lowered dM/dt. (e.g. Lewis et al. 2002; McNamara et al. 2000) • FUSE OVI limits and faint detections record very low dM/dt (10%). (Oergerle et al. 2002) • Are they consistent with the baryon limits and detections of gas at cooler temperatures? (Close!) • But are we asking the right question anymore?

  19. New Name: Cool core clusters? • In a steady cooling flow: DL ~ DT . dM/dt • XMM and Chandra spectra show that gas cooler than Tx/3 is not there in quantities consistent with DT . dM/dt • Cluster gas does not simply cool and flow toward the center: the simple cooling flow model is wrong • The correlations with M-dot should be revisited! • But maybe call it the “Cooling Term” instead.

  20. Some gas still cools… • Temperature gradients in the core are confirmed by Chandra and XMM. • The virial temperatures are hotter than the core temperatures. • Gas cooler than ~1 keV not seen or is very faint. • The minimum core temperature seems to be related to the ICM temperature: Tcore = Tx/3 - Tx/2 • The cooling time is still short.

  21. Temperature Gradients Horner, Donahue, & Voit 2003

  22. Entropy (S=T/n2/3) Gradients

  23. Core entropy gradients from fits

  24. Core entropy gradients by enclosed gas mass

  25. Cool cores mean something …more curious correlations • “Cooling flows” center on BCG • While “cooling flows” often have… • Optical emission line nebulae consistent with star formation but not strong shocks • Molecular gas (both warm and cold) & dust • Excess blue light and hot star absorption features • Central radio sources = AGN …Clusters with tc > tH don’t have these things

  26. Clues from morphology? • Central radio sources • Some are powerful, most are relatively weak (some are faint to non-existent) • Radio power correlates with cooling rate; M87’s cool X-ray filament & radio source have similar structure • Radio structure anti-correlated with: • X-ray emission (cavities) • Ha and infrared H2 emission

  27. M87 • Single phase? • 2nd temperature associated with filament (~1 keV) • Radio source & cavities (Young et al. 2002; Matsushita et al. 2002; Molendi 2002 Young et al. 2002

  28. Abell 1795 CXC/SAO/Fabian et al. 2001 Institute for Astronomy/Cowie

  29. Clues from dust? • Dust has a short lifetime in hot dense gas (Draine & Salpeter 1979; Dwek & Arendt 1992). • Existence of dusty optical filaments with Galactic extinction properties suggests the origin of the filaments is not the ICM (Donahue & Voit 1993; Sparks et al. 1989; Voit & Donahue 1997). • If the cool gas is dusty, could it have been cannibalized from other galaxies? Or does it condense from an dust-enriched ICM (See limits from extinction (Maoz 1995), ISOPHOT emission (Stickel et al. 2002) • ICM could be contaminated with dust via winds, stripping; but with a small covering factor?

  30. Physics of structure formation? • Assembly of a cD: cannibalism, mergers • Effect of an AGN on structure formation • Effect of star formation on galaxy formation • Signature of hierarchical assembly on clusters: contribution of in-falling groups, galaxies? Time dependence?

  31. Spectral Emission Measure • Spectral luminosity dL/dT  dM/dT * Ta • a = 0 expected • a =1-2 observed: what is the physical explanation? • Is there really a relationship to the virial temperature? (Good to confirm!) Peterson, et al. 2003

  32. Entropy Profile The distribution of entropy with radius and time is a prediction of the heating process: convection, conduction, gravitational processes have different effects. Kaiser & Binney 2003: Episodic heating

  33. Questions for discussion this week • Is “M-dot” a valid cluster core property? • Are there model-independent quantities that can be used to describe the spectral and imaging characteristics of cluster cores? • How does gas cool from the hot phase?

  34. Questions for the committed • Do the X-ray spectra consistently suggest that T_low scales with the virial temperature? • How are metallicity gradients affected by convective processes? • What heats the optical and infrared nebulae? How does that mechanism affect the hot gas? • If temperature gradients exist in most of the cool cores, how quickly must the cool gas be replenished if conductive evaporation is important? • What are the roles of stars and AGN?

  35. Summary • New observations from XMM and Chandra have ruled out the steady cooling flow model. • Time to divorce the model from the observations: cool cores, high central densities… • Observations: dT/dr, spectra of T/3 but not T/2 gas, entropy gradients, correlations of radio, IR, and optical phenomena with short cooling times. • The same observations have introduced a new problem: what are the heating terms in the energy equation? (Alternative: is it possible to cool the gas but not allow it to radiate X-rays and FUV?)

  36. A2597: FUSE spectrum

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