Transcript 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 (107 to 108 K)
Densities ~ 10-5 to 10-1 particles per cubic cm
Sizes ~ 1 to 10 Mpc (1024 to 1025) cm
<=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
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)
From CCD spectral fits
Density rises and
tcool is short
(e.g. Voigt et al. 2002)
from Images
•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
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
Detailed studies best
done with full Monte
Carlo
Model
Failure of the Model
<= dL/dT= constant
model
8 keV  3 keV  ?
Peterson et al. 2001
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
Peterson et al. 2003
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 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
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 Xrays?
(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
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
M87
M87
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Use hundreds of gaussian blobs
with own properties (e.g.
temperature) instead of a
parameterized model
Perseus
Perseus
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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 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
Mg/Fe
Si/Fe 1.4
S/Fe 1.1
0.5
0.8
1.2
1.1
Spatially resolved
Abundances much more
complicated
Peterson et al. 2003
Sersic 159-03, de Plaa 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
NGC 5044, Buote et al. 2005
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
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
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
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?