X-ray Spectra of Clusters of Galaxies John Peterson Purdue University X-ray Gratings 2007 Boston, MA

Intracluster medium OpticalX-ray Heated due to large gravitational potentials Temperatures ~ 1-10 keV (10 7 to 10 8 K) Densities ~ to particles per cubic cm Sizes ~ 1 to 10 Mpc (10 24 to ) cm

<=X-ray Spectra (prior to 2000) At densities and temperatures (in core), t recombination = 10 6 years (for Fe XVII at 1 keV) t cool = (5/2 n k T)/(n 2  ) = 10 8 to 10 9 years t formation = years Collisional ionizations balanced by recombinations Line emission dominated by collisional excitations+cascades, Radiative recombination, and dielectronic recombination Same model as stellar coronae X-ray Spectrum dominated by line emission and Bremmstrahlung from collisionally ionized plasma Plasma out of LTE optically thin

Cooling Flows 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) Temperature Drops (e.g. Allen et al. 2001) Density rises and t cool is short (e.g. Voigt et al. 2002) from Images From CCD spectral fits

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

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)

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 Model Detailed studies best done with full Monte Carlo

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

Decompose into temperature bins and set limits

Hot clusters Peterson et al. 2003

Warm Clusters Peterson et al. 2003

Cool clusters/groups Peterson et al. 2003

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

Theoretical Intepretation: Essentially Three Fine-tuning Problems 1. Energetics: Need average heating or cooling power ~ L x 2.Dynamics: Either need energy source to work at low temperatures or at t ~ t cool (before complete cooling would occur) Cooling time ~ T 2 / (cooling function) If at 1/3 T max then why cool for 8/9 of the cooling time? or why at low temperatures? 3.Get Energetic and Dynamics right at all spatial positions Soft X-rays missing throughout entire cflow volume

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 Fabian et al. 2003

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

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) 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) Fabian et al Crawford et al. 2003

10.Dark Matter (huge energy source): Dark Matter-Baryon interactions (Qin & Wu 2001): Requires high cross-section (  /m ~ cm 2 /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

M87

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

Perseus

4 actual cooling flows: Mukai et al. 2003

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? Z i = Yield IA (z)+  dM Yield II (z,M) dN/dM

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 O/Fe Mg/Fe 0.8 Si/Fe S/Fe Tamura et al. 2004Matsushita et al Peterson et al Spatially resolved Abundances much more complicated

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 Sersic , de Plaa et al NGC 5044, Buote et al. 2005

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

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

Resonant Scattering  ~ n i  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. 2002Perseus, Churazov et al. 2004

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?