Nanjing, March 2003 Using the Sunyaev-Zeldovich effect to probe the gas in clusters Mark Birkinshaw...

Nanjing, March 2003

Using the Sunyaev-Zel’dovich effect to probe the gas in clusters

Mark Birkinshaw

University of Bristol

Mark Birkinshaw, U. Bristol 2

Nanjing, March 2003

Outline

1. The origin of the effect

2. SZ effect observations

3. SZ effect science: clusters

4. SZ effect science: cosmology

5. The future: dedicated SZ instruments

6. Summary


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

2 Mpc


Nanjing, March 2003

Inverse-Compton scatterings

• Cluster atmospheres scatter photons passing through them. Central iC optical depth

enpT L

• Scatterings changes the average photon frequency by a fraction

kBTe/mec2


Nanjing, March 2003

Microwave background spectrum

I

Fractional intensity change I/I = -2 (/ e 10-4


Nanjing, March 2003

Thermal SZ effect• Fractional intensity change in the CMB

I/I = -2 (/ e 10-4

• Effect in brightness temperature terms

TRJ = -2 Tr (/ e -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


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


Nanjing, March 2003

SZ sky predicted using structure formation code (few deg2, y = 0 – 10-4)

CMB primordial fluctuations ignored

da Silva et al.

Predicted SZ effect sky


Nanjing, March 2003

SZ effect and CMB power spectrum

Figure from Molnar & Birkinshaw 2000

thermal SZ

kinematic SZ

RS effect


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


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


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


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


Nanjing, March 2003

Interferometers

• restricted angular dynamic range set by baseline and antenna size

• good rejection of confusing radio sources

Abell 665 model, VLA observation

available baselines


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


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


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


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


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.


Nanjing, March 2003

SCUBA

850 µm images: SZ effect measured in one; field too small


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


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


Nanjing, March 2003

ACBAR cluster observations

2002 cluster observations: three of nine objects detected?


Nanjing, March 2003

SZ effect status• About 100 cluster detections

– high significance (> 10) 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


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


Nanjing, March 2003

Integrated SZ effects• Total SZ flux density

thermaleeRJ UdzTndS Thermal energy content immediately measured in redshift-independent wayVirial theorem then suggests SZ flux density is direct measure of gravitational potential energy


Nanjing, March 2003

Integrated SZ effects• Total SZ flux density

eeeeRJ TNdzTndS 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


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 ne

2 dependence. SZ should show more about outer gas envelope, but need better sensitivity


Nanjing, March 2003

SZ effects and lensingWeak lensing measures ellipticity field e, and so

)(),(1 2

crit θθθθ ii ed

Surface mass density as a function of position can be combined with SZ effect map to give a map of fb SRJ/


Nanjing, March 2003

Total and gas massesInside 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 XMMWorrall & Birkinshaw 2002


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


Nanjing, March 2003

Cluster radial peculiar velocityNeed• good SZ spectrum• X-ray temperature

Confused by CMB structure

Sample vz2

Three clusters so far, vz 1000 km s

A 2163; figure from LaRoque et al. 2002.


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


Nanjing, March 2003

Cluster Hubble diagram

X-ray surface brightness

X ne2 Te

½ L SZ effect intensity change

I ne Te L

Eliminate unknown ne

L I2 X1 Te

3/2

H0 X I2 Te

3/2


Nanjing, March 2003

Cluster distances and massesCL 0016+16

DA = 1.36 0.15 Gpc

H0 = 68 8 18 km s-1 Mpc-1

Worrall & Birkinshaw 2002


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


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


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


Nanjing, March 2003

Cluster counts and cosmologyCluster counts and redshift distribution provide strong constraints on 8, m, and cluster heating.

z

dN/dzm=1.0

m=0.3

m=0.3

Figure from Fan & Chiueh 2000


Nanjing, March 2003

ACBAR blind survey

CMB5 field, filtered, pointing source blanked. Features at s/n > 4.


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

Figure from Carlstrom et al. 1999.

b/m


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)


Nanjing, March 2003

Microwave background temperature• Test T (1 + z)

• SZ results for two clusters plus results from molecular excitation

Battistelli et al. (2002)


Nanjing, March 2003

5. The future: dedicated SZ instruments

Today Future

CBI MITO/MAD AMiBA APEX

OVRO 40-m Ryle OCRA ALMA

VSA ACBAR AMI etc.

MAP BOLOCAM Planck

SuZIE etc. SZA


Nanjing, March 2003

Survey speeds

• OCRA will be fastest survey radiometer

• AMiBA will be fastest survey interferometer

• Frequencies complementary


Nanjing, March 2003

New SZ interferometers

AMiBA

SZA

AMI

solid nearby high-M clusterdashed high-z low-M cluster

AMIBA 90 GHzSZA 30 GHzAMI 15 GHz

Complementary spectral coverage

Short baselines crucial for SZ detection

Long baselines for radio sources


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


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?


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(5)

z


Nanjing, March 2003

OCRA

Torun Observatory, Jodrell Bank, Bristol, Bologna

OCRA-p


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


Nanjing, March 2003

APEXMPI project at

Chajnantor

300-element bolometer array at 870 m ideal for SZ

(117-element prototype shown)


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


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


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


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


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

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Nanjing, March 2003 Using the Sunyaev-Zeldovich effect to probe the gas in clusters Mark Birkinshaw...

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