The Sunyaev-Zel’dovich effect: background and issues

SZ effect and ALMA

The Sunyaev-Zel’dovich effect:background and issues

Mark Birkinshaw

University of Bristol

7 April 2005 Mark Birkinshaw, U. Bristol 2

SZ effect and ALMA

1. Simple observables: shape

The SZ effects are the results of inverse-Compton scattering by hot electrons on cold CMB photons. The principal (thermal) SZ effect has an amplitude proportional to the Comptonization parameter, ye, the dimensionless electron temperature weighted by the scattering optical depth


SZ effect and ALMA

1. Simple observables: shape

2

3

2

1

2

2

0 1)(

cee yy

For a simple isothermal model

• Typical central value ye0 10-4

• SZE has larger angular size than X-ray image and weaker dependence on


SZ effect and ALMA

1. Simple observables: spectrum

For clusters which aren’t too hot, or at low frequency, the thermal SZE has the Kompaneets spectrum

x is the dimensionless frequency, h/kBTCMB = 0.0186(/GHz)I0 is the specific intensity scale from the thermal SZE


SZ effect and ALMA

1. Simple observables: spectrum

• spectrum related to gradient of CMB spectrum

• zero near peak of CMB spectrum (about 220 GHz)


SZ effect and ALMA

1. Simple observables: kinematic SZE

If the cluster is moving, then in the cluster frame the CMB is anisotropic. Scattering isotropizes it by an amount evz, giving kinematic SZE

Same as spectrum of primordial CMB fluctuations: TCMB change.

ezCMBB

K h

TkchI

3

202


SZ effect and ALMA

1. Simple observables: kinematic SZE

• spectrum related to gradient of CMB spectrum

• no zero• small compared to

thermal effect at low frequency

• confused by primordial structure


SZ effect and ALMA

2. Simple observations

Simplest: single-dish radiometers/radiometer arrays.

Secondary focus:• single on-axis feed• symmetrical dual feeds• array of feeds (large focal plane)

Prime focus:• single on-axis feed• symmetrical dual feeds


SZ effect and ALMA

2. Simple observations: radiometer sensitivity

Always observe with beam-switching + position-switching, or scanning, or some other strategy to reduce systematic errors.Sensitivity expected to be

2sys

A

TNT

(N > 1), but TA doesn’t reduce with time as -1/2 after some limiting time, because gain and Tsys are unsteady.


SZ effect and ALMA

2. Simple observations: z dependence

Angular size and separation of beams leads to redshift dependent efficiency

Shape of curve shows redshift of maximum signal, long plateau


SZ effect and ALMA

2. Simple observations: radiometer results

• 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,

with radiometer arrays

Birkinshaw 1999


SZ effect and ALMA

2. Simple observations: interferometers

OVRO array in compact configuration (old site).


SZ effect and ALMA

2. Simple observations: interferometer sensitivity

Sensitivity of interferometer

synth

source

corr

sys

N

TT

Ncorr = number of antenna-antenna correlations used in making synthesized beam (solid angle synth). source = solid angle of source.


SZ effect and ALMA

2. Simple observations: interferometer baselines

• restricted angular dynamic range set by baseline and antenna size

• good rejection of confusing radio sources (can use long baselines) Abell 665 model, VLA observation

available baselines


SZ effect and ALMA

2. Simple observations: interferometer maps

First interferometric detection of SZE: Ryle telescope, Abell 2218Jones et al. (1993)


SZ effect and ALMA


• restricted angular dynamic range

• high signal/noise (long integration possible)

• clusters easily detectable to z 1

Carlstrom et al. 1999


SZ effect and ALMA


VSA: low-z clustersAbout 100 hours/mapHigh signal/noise detectionApparent noise is confusion from CMB primordial fluctuations – limitation of all single-frequency work

Lancaster et al. (2004; astro-ph/0405582)


SZ effect and ALMA

2. Simple observations: bolometers

A good alternative is bolometric observation using an array: e.g., BOLOCAM on CSO; ACBAR on Viper.Issues to do with the stability of the atmosphere.mm-wave data – good for looking at spectrum.


SZ effect and ALMA

2. Simple observations: bolometer maps

• A 3266: z = 0.06• VIPER +ACBAR• Images at 150, 220, 275

GHz, 5 arcmin FWHM• Remove CMB to leave

thermal SZE (bottom right)

Gómez et al. 2003


SZ effect and ALMA

3. Simple science results

• 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


SZ effect and ALMA

3. Simple science results: integrated SZE

• Total SZ flux density

thermaleeRJ UdzTndS Thermal energy content immediately measured in redshift-independent wayVirial theorem: SZ flux density should be good measure of gravitational potential energy


SZ effect and ALMA

3. Simple science results: integrated SZE

• 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


SZ effect and ALMA

3. Simple science results: SZE structures

• Only crudely measured so far• Relatively more sensitivity to outer parts of

clusters than X-ray data• Angular dynamic range issue: limitation of

array sizes (radiometer, interferometer, bolometer), and CMB confusion

• Will need sensitivity at Jy level on 10 arcsec to 120 arcsec scales


SZ effect and ALMA

3. Simple science results: SZE and lensing

Weak 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/


SZ effect and ALMA

3. Simple science results: total, 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 XMMWorrall & Birkinshaw 2003


SZ effect and ALMA

3. Simple science results: vz

• Kinematic effect separable from thermal SZE by different spectrum

• Confusion with primary CMB fluctuations limits vz accuracy (typically to 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


SZ effect and ALMA

3. Simple science results: vz

Need• good SZ spectrum• X-ray temperature

Confused by CMB structure

Sample vz2

Errors 1000 km s so far

A 2163; figure from LaRoque et al. 2002.


SZ effect and ALMA

3. Simple science results: 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


SZ effect and ALMA

3. Simple science results: cluster Hubble diagram

X-ray surface brightness

SZE intensity change

Eliminate unknown ne to get cluster size L, and hence distance or H0

LTn eeX2/12

LTnI ee

2/320

2/312

eXL

eX

TIH

TIL


SZ effect and ALMA

3. Simple science results: cluster distances

CL 0016+16

DA = 1.36 0.15 Gpc

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

Worrall & Birkinshaw 2003


SZ effect and ALMA

3. Simple science results: cluster Hubble diagram

• poor leverage for other parameters

• need many clusters at z > 0.5

• need reduced random errors

• ad hoc sample • systematic errors

Carlstrom, Holder & Reese 2002


SZ effect and ALMA

3. Simple science results: SZE 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 X-ray/optical surveys– Expect SZ to be better than X-ray at high z


SZ effect and ALMA

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

Primordial fluctuations ignored

Cluster counts strong function of cosmological parameters and cluster formation physics.

3. Simple science results: SZE sky


SZ effect and ALMA

See talks of

Stefano Borgani Scott Kay

Antonio da Silva Lauro Moscardini

Jim Bartlett Joseph Silk

3. Simple science results: SZE sky


SZ effect and ALMA

3. Simple science results: fB

SRJ Ne Te

Total SZ flux total electron count total baryon content.Compare with total mass (from X-ray or gravitational lensing) baryon mass fraction

Figure from Carlstrom et al. 1999.

b/m


SZ effect and ALMA

4. More complicated observables• Detailed structures

– Gross mass model– Clumping– Shocks and cluster substructures

• Detailed spectra– Temperature-dependent/other deviations from

Kompaneets spectrum– CMB temperature

• Polarization– Multiple scatterings– Velocity term


SZ effect and ALMA

4. More complicated observables: detailed structures

Clumping induced by galaxy motions, minor mergers, etc. affects the SZE/X-ray relationship

More extreme structures caused by major mergers, associated with shocks, cold fronts

Further SZE (density/temperature-dominated) structures associated with radio sources (local heating likely), cooling flows, large-scale gas motions (kinematic effect).


SZ effect and ALMA


J0717.5+3745

z = 0.548

Clearly disturbed, shock-like substructure, filament

What will SZ image look like?


SZ effect and ALMA


See talks by

Monique Arnaud Doris Neumann

Steen Hansen Tetsu Kitayama

Christoph Pfrommer Andrea Lapi


SZ effect and ALMA

4. More complicated observables: detailed spectra

• 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 TCMB (1 + z)

Battistelli et al. (2002)


SZ effect and ALMA

• for low-Te gas effect is independent of Te

• Te > 5 keV, spectrum is noticeable function of Te

• non-thermal effect (high energies) gives distortion

• multiple scatterings give another distortion

5 keV15 keV

4. More complicated observables: detailed

spectra


SZ effect and ALMA

4. More complicated observables: detailed spectra

See talks by

Francesco Melchiorri Björn Schaeffer

Diego Herranz Sergio Colafrancesco

Jens Chluba


SZ effect and ALMA

4. More complicated observables: polarization

Polarization signals are O(z) or O(e) smaller than the total intensity signals: this makes them extremely hard to measure

Interferometers help by rejecting much of the resolved signal, since some of the polarization signal has smaller angular size than I


SZ effect and ALMA

4. More complicated observables: polarization

See talks by

Doris Neumann Asantha Cooray

Jens Chluba


SZ effect and ALMA

5. Requirements on observations

Use Size (mK) Critical issues

Energetics 0.50 Absolute calibration

Baryon count 0.50 Absolute calibration; isothermal/spherical cluster; gross model

Gas structure 0.50 Beamshape; confusion

Mass distribution 0.50 Absolute calibration; isothermal/spherical cluster

Hubble diagram 0.50 Absolute calibration; gross model; clumping; axial ratio selection bias


SZ effect and ALMA



Blind surveys 0.10 Gross model; confusion

Baryon fraction evolution

0.10 Absolute calibration; isothermal/spherical cluster; gross model

CMB temperature

0.10 Absolute calibration; substructure

Radial velocity 0.05 Absolute calibration; gross model; bandpass calibration; velocity substructure


SZ effect and ALMA



Cluster formation 0.02 Absolute calibration

Transverse velocity

0.01 Confusion; polarization calibration


SZ effect and ALMA

6. Status at the time of ALMA: 2005

Current status• About 100 cluster detections

– high significance (> 10) detections– multi-telescope confirmations– interferometer maps, structures usually from X-rays

• Spectral measurements still rudimentary – no kinematic effect detections

• Preliminary blind and semi-blind surveys– a few detections


SZ effect and ALMA

6. Status at the time of ALMA: 2005-2010

See talks byRüdiger Kneissl Guo-Chin Liu

Katy Lancaster Pierre Cox

Frank Bertoldi John Carlstrom

Björn Schaefer

… and other SZ instrumentation projects


SZ effect and ALMA

6. Status at the time of ALMA: 2010

• About 5000 cluster detections– Most from Planck catalogue, low-z– 10% from high-resolution surveys (AMiBA, SZA,

BOLOCAM, etc.)

• About 100 images with > 100 resolution elements– Mostly interferometric, tailored arrays, 10 arcsec FWHM– Some bolometric maps, 15 arcsec FWHM

• About 50 integrated spectral measurements – Still confusion limited– Still problems with absolute calibration


SZ effect and ALMA

6. Status at the time of ALMA: ALMA, 2010

• ALMA band 1 suitable for SZE– 1 microJy in 10 arcsec FWHM over 145 arcsec primary

beam in 12 hours– Cluster substructure mapping (loses largest scales)– Quality of mosaics still uncertain

• Band 1 is not likely to be available in 2010• Blind surveys using ALMA band-1 not likely – wrong

angular scales

See talks by Robert Laing, Steve Myers


SZ effect and ALMA

6. Status at the time of ALMA: X-ray context: 2010

• No XMM or Chandra• Constellation-X/XEUS not available

• Working with archival X-ray surveys• X-ray spectra of high-z clusters of relatively poor

quality

Optical/IR survey follow-up in SZE, or order of follow-ups reversed: SZE before X-ray.

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The Sunyaev-Zel’dovich effect: background and issues