Xray Spectra of Clusters of Galaxies

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X-ray Spectra ofClusters of Galaxies

• John Peterson
• Purdue University
• X-ray Gratings 2007
• Boston, MA

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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
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ltX-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
excitationscascades, Radiative recombination,
and dielectronic recombination Same model as
stellar coronae
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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)

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
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• Cools unevenlygt Range of emperatures
  approximately at constant pressure
• Differential Luminosity predicted to be
• dLx/dT5/2 (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

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• Measuring a differential luminosity at keV
  temperatures
• gt Need Fe L ions (temperature sensitive)
• gt 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)
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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
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Failure of the Model
lt dL/dT constant model
8 keV ? 3 keV ? ?
Peterson et al. 2001
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Decompose into temperature bins and set limits
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Hot clusters
Peterson et al. 2003
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Warm Clusters
Peterson et al. 2003
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Cool clusters/groups
Peterson et al. 2003
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Peterson et al. 2003
Differential Luminosity vs. Fractional Temperature
Differential Luminosity vs. Temperature
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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

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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
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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
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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
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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
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M87
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M87
Use hundreds of gaussian blobs with own
properties (e.g. temperature) instead of a
parameterized model
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Perseus
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Perseus
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(No Transcript)
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4 actual cooling flows
Mukai et al. 2003
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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
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Abundances
Fegtmostly Ia O/Fe0.7/-0.2gt50
II Ne/Fe1.1/0.3gt100 II Mg/Fe1.0/0.3gt100
II Si/Fe2.3/1gt100 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
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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 lt 20 per 100 kpc
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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
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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
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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
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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?