Nanjing, March 2003
Using the Sunyaev-Zel’dovich
effect to probe the gas in clusters
Mark Birkinshaw
University of Bristol
Nanjing, March 2003
Outline
1.
2.
3.
4.
5.
6.
The origin of the effect
SZ effect observations
SZ effect science: clusters
SZ effect science: cosmology
The future: dedicated SZ instruments
Summary
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
1. The origin of the effect
Clusters of galaxies
contain extensive hot
atmospheres
Te  6 keV
np 103 protons m-3
L  1 Mpc
Mark Birkinshaw, U. Bristol
2 Mpc
3
Nanjing, March 2003
Inverse-Compton scatterings
• Cluster atmospheres scatter photons passing
through them. Central iC optical depth
te  np sT L  10-2
• Scatterings changes the average photon
frequency by a fraction
  kBTe/mec2  10-2
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Microwave background spectrum
Fractional intensity change I/I = -2 (/) te  10-4
I

Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Thermal SZ effect
• Fractional intensity change in the CMB
I/I = -2 (/) te  10-4
• Effect in brightness temperature terms
TRJ = -2 Tr (/) te  -300 K
• Brightness temperature effect, TRJ, is
independent of redshift
• Flux density effect, S, decreases as DA-2, not
DL-2, and depends on redshift
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Spectrum of thermal effect
• spectrum related to
gradient of CMB
spectrum
• zero at peak of
CMB spectrum
(about 220 GHz)
• weak dependence
on Te
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Predicted SZ effect sky
SZ sky predicted
using structure
formation code (few
deg2, y = 0 – 10-4)
CMB primordial
fluctuations ignored
da Silva et al.
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
SZ effect and CMB power spectrum
thermal SZ
kinematic SZ
RS effect
Figure from Molnar & Birkinshaw 2000
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Attributes of SZ effect
• TRJ is a redshift-independent function of
cluster thermal energy, it is a calorimeter
• TRJ has a strong association with rich clusters
of galaxies, it is a mass finder
• TRJ contains a weak redshift-independent
kinematic effect, it is a radial speedometer
• TRJ has polarization with potentially more
uses, but signal is tiny
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
2. SZ effect observations
• Interferometers: e.g., Ryle, BIMA, OVRO
– structural information
– baseline range
• Single-dish radiometers: e.g., OVRO 40-m, OCRA
– speed
– systematic errors from spillover
• Bolometers: e.g., SuZIE, SCUBA, ACBAR
– speed
– structural and spectral information
– weather
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Ryle telescope
• first interferometric map
• Abell 2218
• brightness agrees with
single-dish data
• limited angular dynamic
range
Figure from Jones et al. 1993
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Interferometers
• restricted angular
dynamic range
• high signal/noise (long
integration possible)
• clusters easily detectable
to z  1
Figure from Carlstrom et al. 1999
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Interferometers
• restricted angular
dynamic range set
by baseline and
antenna size
• good rejection of
confusing radio
sources
available baselines
Abell 665 model, VLA observation
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Interferometers
• Good sky and ground noise rejection because
of phase data
• Long integrations and high signal/noise
possible
• 10 years of data, tens of cluster maps
• SZ detected for cluster redshifts from 0.02
(VSA) to 1.0 (BIMA)
• Could be designed with better baseline range
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Single-dish radiometers
• Potentially fast way to measure SZ effects of
particular clusters
• Multi-beams better than single beams at
subtracting atmosphere, limit cluster choice
• Less fashionable now than formerly: other
techniques have improved faster
• New opportunities: e.g., GBT
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Single-dish radiometers
• fast at measuring integrated
SZ effect of given cluster
• multi-beam limits choice of
cluster, but subtracts sky well
• radio source worries
• less used since early 1990s
• new opportunities, e.g. GBT
Figure from Birkinshaw 1999
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Distribution of central SZ effects
• Mixed sample of
37 clusters
• OVRO 40-m data,
18.5 GHz
• No radio source
corrections
• 40% of clusters
have observable
T < -100 K
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Bolometers
• Should be fast way to survey for SZ effects
• Wide frequency range possible on single
telescope, allowing subtraction of primary
CMB structures
• Atmosphere a problem at every ground site
• Several experiments continuing, SuZIE, MITO,
ACBAR, BOLOCAM, etc.
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
SCUBA
850 µm images: SZ effect measured in one; field too small
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
MITO
• MITO experiment at
Testagrigia
• 4-channel photometer:
separate components
• 17 arcmin FWHM
• Coma cluster detection
Figure from De Petris et al. 2002
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Viper + ACBAR
• Since 2001: 16-pixel
bolometer (ACBAR);
150, 220, 280 GHz
(+350 GHz in 2001)
• Dry air, 3º chopping
tertiary, large ground
shield
• 4 – 5 arcmin FWHM
• Excellent for SZ work
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
ACBAR cluster observations
2002 cluster observations: three of nine objects detected?
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
SZ effect status
• About 100 cluster detections
– high significance (> 10s) measurements
– multi-telescope confirmations
– interferometer maps, structures usually from X-rays
• Spectral measurements improving but still
rudimentary
– no kinematic effect detections
• Preliminary blind and semi-blind surveys
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
3. SZ effect science: clusters
• Integrated SZ effects
– total thermal energy content
– total hot electron content
• SZ structures
– not as sensitive as X-ray data
– need for gas temperature
• Mass structures and relationship to lensing
• Radial peculiar velocity via kinematic effect
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Integrated SZ effects
• Total SZ flux density
S RJ   d  neTe dz  U thermal
Thermal energy content immediately measured
in redshift-independent way
Virial theorem then suggests SZ flux density is
direct measure of gravitational potential energy
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Integrated SZ effects
• Total SZ flux density
S RJ   d  neTe dz  N eTe
If have X-ray temperature, then SZ flux density
measures electron count, Ne (and hence baryon
count)
Combine with X-ray derived mass to get fb
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
SZ effect structures
• Currently only crudely measured by SZ
methods (restricted angular dynamic range)
• X-ray based structures superior
• Structure more extended in SZ than X-ray: ne
rather than ne2 dependence. SZ should show
more about outer gas envelope, but need better
sensitivity
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
SZ effects and lensing
Weak lensing measures ellipticity field e, and so
-
1

crit  d θ  i (θ, θ) ei(θ)
2
Surface mass density as a function of position
can be combined with SZ effect map to give a
map of fb  SRJ/
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Total and gas masses
Inside 250 kpc:
XMM +SZ
Mtot = (2.0  0.1)1014 M
Lensing
Mtot = (2.7  0.9)1014 M
XMM+SZ
Mgas = (2.6  0.2)  1013 M
CL 0016+16 with XMM
Worrall & Birkinshaw 2002
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Cluster radial peculiar velocity
• Kinematic effect separable from thermal SZ
effect because of different spectrum
• Confusion with primary CMB fluctuations
limits velocity accuracy to about 150 km s-1
• Velocity substructure in atmospheres will
reduce accuracy further
• Statistical measure of velocity distribution of
clusters as a function of redshift in samples
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Cluster radial peculiar velocity
Need
• good SZ spectrum
• X-ray temperature
Confused by CMB
structure
Sample  vz2
Three clusters so far,
vz  1000 km s-1
A 2163; figure from LaRoque et al. 2002.
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
4. SZ effect science: cosmology
• Cosmological parameters
– cluster-based Hubble diagram
– cluster counts as function of redshift
• Cluster evolution physics
– evolution of cluster atmospheres via cluster counts
– evolution of radial velocity distribution
– evolution of baryon fraction
• Microwave background temperature elsewhere
in Universe
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Cluster Hubble diagram
X-ray surface brightness
X  ne2 Te½ L
SZ effect intensity change
I  ne Te L
Eliminate unknown ne
 L  I2 X-1 Te-3/2
 H0  X I-2 Te3/2 
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Cluster distances and masses
CL 0016+16
DA = 1.36  0.15 Gpc
H0 = 68  8  18 km s-1 Mpc-1
Worrall & Birkinshaw 2002
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Hubble diagram
• poor leverage for
other parameters
• need many
clusters at z > 0.5
• need reduced
random errors
• ad hoc sample
• systematic errors
From Carlstrom, Holder & Reese 2002
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Critical assumptions
• spherical cluster (or randomly-oriented sample)
• knowledge of density and temperature structure
to get form factors
• clumping negligible
• selection effects understood
need orientation-independent sample
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Blind surveys
• SZ-selected samples
– almost mass limited and orientation independent
• Large area surveys
– 1-D interferometer surveys slow, 2-D arrays better
– radiometer arrays fast, but radio source issues
– bolometer arrays fast, good for multi-band work
• Survey in regions of existing surveys
– XMM-LSS survey region ideal, many deg2
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Cluster counts and cosmology
Cluster counts
and redshift
distribution
provide strong
constraints on
s8, m, and
cluster heating.
dN/dz
m=1.0 L0 s80.52
m=0.3 L0.7 s80.93
m=0.3 L0 s80.87
z
Figure from Fan &
Chiueh 2000
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
ACBAR blind survey
CMB5 field, filtered, pointing source blanked. Features at s/n > 4.
Mark Birkinshaw, U. Bristol
40
Nanjing, March 2003
Baryon mass fraction
SRJ  Ne Te
Total SZ flux  total
electron count  total
baryon content.
Compare with total
mass (from X-ray or
gravitational lensing)
 baryon fraction
b/m
Figure from Carlstrom et al. 1999.
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Microwave background temperature
• Ratio of SZ effects at two different frequencies
is a function of CMB temperature (with slight
dependence on Te and cluster velocity)
• So can use SZ effect spectrum to measure CMB
temperature at distant locations and over range
of redshifts
• Test T  (1 + z)
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Microwave background temperature
• Test T  (1 + z)
• SZ results for two
clusters plus results
from molecular
excitation
Battistelli et al. (2002)
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
5. The future: dedicated SZ
instruments
Today
CBI
Future
MITO/MAD AMiBA
APEX
OVRO 40-m Ryle
OCRA
ALMA
VSA
ACBAR
AMI
etc.
MAP
BOLOCAM Planck
SuZIE
etc.
SZA
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Survey speeds
• OCRA will be
fastest survey
radiometer
• AMiBA will be
fastest survey
interferometer
• Frequencies
complementary
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
New SZ interferometers
AMIBA
SZA
AMI
90 GHz
30 GHz
15 GHz
AMiBA
SZA
Complementary spectral
coverage
AMI
Short baselines crucial
for SZ detection
Long baselines for radio
sources
solid nearby high-M cluster
dashed high-z low-M cluster
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
AMiBA
• ASIAA/NTU project
• Operational in 2004, prototype
2002
• 19(?) dishes, 1.2/0.3 m
diameters, 1.2 – 6 m baselines
•  = 95 GHz,  = 20 GHz
• Dual polarization
• 1.3 mJy/beam in 1 hr
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
XMM-LSS survey SZ follow-up
• XMM survey of 64 deg2 to 5  10-15 erg cm-2 s-1
(0.5 – 2.0 keV)
• Expect 300 sources deg-2, 12% clusters  2000
clusters
• SZ imaging will give Hubble diagram to z = 1
• Combining X-ray, SZ, shear mapping at z < 0.5
will give baryon fraction and total masses
• possible SZ detection of IGM filaments?
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Cluster finding: X-ray vs SZ
• AMiBA is better
than XMM for
clusters at z > 0.7
• interferometers
provide almost
mass limited
catalogues
• may find X-ray
dark clusters
LX(5s)
Mark Birkinshaw, U. Bristol
z
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Nanjing, March 2003
OCRA
OCRA-p
Torun Observatory, Jodrell Bank, Bristol, Bologna
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
OCRA
• 30 GHz
• Tsys = 40 K
• 1 arcmin FWHM
beam
• 5 mJy sensitivity in
10 sec
• now on telescope
• OCRA-F in progress
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
APEX
MPI project at
Chajnantor
300-element
bolometer
array at 870
m ideal for
SZ
(117-element prototype
shown)
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
6. Summary (1)
• SZ effect is a major cluster and cosmological
probe
• SZ maps dominated by massive objects at z 
0.5, filaments and groups tend to average out
• SZ effect easily detectable to z > 1
• SZ effects appear on lumpy background, adds
noise
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Summary (2)
• Individual cluster SZ effects give
–
–
–
–
–
total thermal energy contents
total electron contents
structural information (especially on large scales)
cluster masses
microwave background temperature at distant points
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Summary (3)
• Sample studies give
–
–
–
–
–
–
Hubble diagram and cosmological parameters
cluster number counts and cosmological parameters
baryon mass fraction
evolution of cluster atmospheres
evolution of radial velocities
redshift-dependence of microwave background
temperature
Mark Birkinshaw, U. Bristol
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Nanjing, March 2003
Summary (4)
• Improved SZ data could give
–
–
–
–
radio source energetics (non-thermal SZ effect)
radial velocities of clusters (kinematic effect)
transverse velocities of clusters (polarization effect)
detections of gas in in-falling filaments
• Many new SZ facilities will come on-line in the
next 5 – 10 years
Mark Birkinshaw, U. Bristol
56
Nanjing, March 2003
Attributes of SZ effect
• TRJ is a redshift-independent function of
cluster thermal energy, it is a calorimeter
• TRJ has a strong association with rich clusters
of galaxies, it is a mass finder
• TRJ contains a weak redshift-independent
kinematic effect, it is a radial speedometer
• TRJ has polarization with potentially more
uses, but signal is tiny
Mark Birkinshaw, U. Bristol
57