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

X-ray Spectra ofClusters of Galaxies

John Peterson

Purdue UniversityX-ray Gratings 2007

Boston, MA

Intracluster medium

Optical X-ray

Heated due to large gravitational potentialsTemperatures ~ 1-10 keV (107 to 108 K)Densities ~ 10-5 to 10-1 particles per cubic cmSizes ~ 1 to 10 Mpc (1024 to 1025) cm

<=X-ray Spectra (prior to 2000)

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 yearstformation= 5 109 years

Collisional ionizations balanced by recombinationsLine emission dominated by collisional excitations+cascades, Radiative recombination, and dielectronic recombinationSame model as stellar coronae

X-ray Spectrum dominated by line emission andBremmstrahlung from collisionally ionized plasmaPlasma out of LTE optically thin

Cooling FlowsLong-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 tcool 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:

dLx/dT=5/2 (Mass Deposition Rate) k/(mp) Predicts a unique X-ray spectrum; Free parameters: Tmax, AbundancesThe 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 sizeSoft X-ray band from Si K to C K; FOV: 5 arcminutes by 1 degreeAnalysis 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. 2001

<= dL/dT= constant model

Decomposeinto temperaturebins and setlimits

Hot clusters


Warm Clusters


Cool clusters/groups


Differential Luminosity vs. Temperature

Differential Luminosity vs.Fractional Temperature


Theoretical Intepretation: Essentially Three Fine-tuning Problems

1. Energetics: Need average heating or cooling power ~ Lx

2. 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?3. Get Energetic and Dynamics right at all spatial positions

Soft X-rays missing throughout entire cflow volume

Current Models1. 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

2. Heat transfer from the outside to the core: probably through conductionStability & 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. 2002

Crawford et al. 2003

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 particlesRequires a high central density for neutralino

Dark Matter-Baryon Interactions (Chuzhoy & Nusser 2004):same cross-section but makemass of dark matter ~ 1/3 of proton mass

M87

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

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.







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?

Zi = YieldIA(z)+ dM YieldII (z,M) dN/dM

Abundances

Fe=>mostly IaO/Fe=0.7+/-0.2=>50% IINe/Fe=1.1+/0.3=>100% IIMg/Fe=1.0+/0.3=>100% IISi/Fe=2.3+/1=>100% II

O/Fe 0.6 0.5 Mg/Fe 0.8 Si/Fe 1.4 1.2 S/Fe 1.1 1.1

Tamura et al. 2004 Matsushita et al. 2003


Spatially resolvedAbundances much morecomplicated

Spatial Distribution of Abundances

Abundances depend on temperature model sensitivelyGradient in Metals ~ 100% per 100 kpcGradient in O/Fe or Si/Fe < 20% per 100 kpc

Sersic 159-03, de Plaa et al. 2005NGC 5044, Buote et al. 2005

Evidence for a Low T (0.7 keV) diffuse thermal component (WHIM) still unsettled

Absorption (3 sigma) behindComa, Takei et al. 2007

OVII emission, Kaastra et al. 2001

Subtleties of particlebackground in CCD fits, de Plaa et al 2005

Large soft X-ray background from within the galaxy (McCammon et al. 2002)

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

SummaryCooling 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?

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

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