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SZ – overview

SZ – overview

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SZ – overview

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  1. SZ – overview Mark Birkinshaw University of Bristol

  2. Thermal SZ effect Photons gain energy, spectrum depressed at low  I  Mark Birkinshaw, U. Bristol

  3. tSZ effect – Kompaneets spectrum • for non-relativistic electrons, effect is independent of Te • at Te > 5 keV enough electrons relativistic that spectrum varies at high : relativistic corrections measure mass-weighted Te • Kompaneets form useful approximation at low  for all Te 5 keV 15 keV Mark Birkinshaw, U. Bristol

  4. The yeparameter The Comptonization parameter At low frequency the tSZ effect has amplitudeΔTRJ = -2ye  10-4 for the centre of a rich cluster. CMB photons are far from equilibrium with cluster gas after scattering. ye defines the angular shape of the cluster SZ effect – it is a function of position on the sky, measures line-of-sight averaged pressure, and is redshift independent. Mark Birkinshaw, U. Bristol

  5. The Yeparameter A survey usually measures an integrated tSZE flux density, proportional to the integrated Comptonization in the survey beam An observation will measure only some fraction of the integrated flux density because of the implicit spatial filtering. Ye is redshift dependent but a strong indicator of cluster binding energy (mass). Mark Birkinshaw, U. Bristol

  6. Angular structure X-ray (L), SZ effect (R) ellipsoidal models for Abell 665: note difference in angular structures – tSZ effect is far more extended. Mark Birkinshaw, U. Bristol

  7. The kSZ effect If the cluster is moving along the line of sight, then in the cluster frame the CMB is anisotropic. Scattering isotropizes it by an amount  evz, giving kinematic SZE This makes the kinematic effect hard to see against the brighter thermal effect – it’s necessary to use spectral differences to separate the effects. Even then, the kinematic effect is heavily confused by primordial CMB structures – has same spectrum. Mark Birkinshaw, U. Bristol

  8. kSZ effect • kinematic spectrum related to temperature gradient of CMB spectrum • no zero • small compared to thermal effect at low frequency • confused by primordial structure Mark Birkinshaw, U. Bristol

  9. Polarization effects There are three contributions to the polarization signal • scattering the quadrupole in the primordial CMB, effect ~ 0.1 K in either the E or B modes and coherent shape across the cluster • multiple scatterings inside the cluster, effect ~ 0.1 K in a ring about the cluster centre • transverse velocity of the cluster, effect ~ 10× smaller (easier to measure through transverse lensing effect in intensity, ~ 0.1 K) These effects are confused by the cluster lensing the primordial CMB polarization, causing a signal ~ 3 K Spectral and spatial structures of these effects differ, may allow separation, though lensing effect dominates. All effects beyond current capabilities. Mark Birkinshaw, U. Bristol

  10. Levels of study of SZ effect • First level: detection of integrated effect • Complete since mid 1980s • 200+ clusters well detected • Narrow band of cluster properties (selection effect imposed by sensitivity, resolution) • Cluster energy contents, mass measurements, baryon mass fractions, Hubble constant Mark Birkinshaw, U. Bristol

  11. tSZE distribution: X-ray selected clusters Lancaster et al., in prep. Mark Birkinshaw, U. Bristol

  12. Scaling relations: tSZ/kTe Close to self-similar slope. Cluster scaling relation at z ~ 0.2. Mass probe to z > Lancaster et al., in prep. Mark Birkinshaw, U. Bristol

  13. Cluster energy content Total SZ flux density Thermal energy content immediately measured in redshift-independent way Virial theorem then suggests SZ flux density is direct measure of gravitational potential energy Flux density indicates mass and degree of organization of cluster atmosphere. Mark Birkinshaw, U. Bristol

  14. Cluster energy content Useful measurement requires absolute calibration of flux density scale – still an issue in radio astronomy at 5% level. Comparisons with galaxy kinematics at 5% level valuable but little work so far. Requires integration over entire cluster – high level of confusion for low-z clusters unless the cluster is mapped and point sources (AGN at cm , star-forming or dusty galaxies at mm ) and primordial CMB are removed Mark Birkinshaw, U. Bristol

  15. Cluster baryonic content Total SZ flux density 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 Redshift-independence of ye should allow baryon content to be measured to large z. Mark Birkinshaw, U. Bristol

  16. Cluster baryonic content • Effective measurement of electron number in cluster requires • absolute calibration of SZ data and • adequacy of isothermal model over full SZ extent • accurate electron temperature from X-ray • Technique avoids assumptions on cluster shape, or hydrostatic equilibrium. Compare with X-ray data to test cluster model. • Integral over cluster, subject to confusion problems at low z. • Much of SZ effect comes from outer gas where Teis poorly measured in the X-ray. Mark Birkinshaw, U. Bristol

  17. Baryon mass fraction Inside 250 kpc: XMM +SZ Mtot = (2.0  0.1)1014 M Mgas = (2.6  0.2)  1013 M Combine results: fb = 0.13 ± 0.02 (distance-independent) WMAP: fb = 0.12 ± 0.02 CL 0016+16 with XMM Worrall & Birkinshaw 2003 Mark Birkinshaw, U. Bristol

  18. Baryon mass fraction evolution 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

  19. Cluster Hubble diagram X-ray surface brightness SZE intensity change Eliminate unknown ne to get cluster size L, and hence distance or H0 Mark Birkinshaw, U. Bristol

  20. Cluster Hubble diagram CL 0016+16 DA = 1.36  0.15 Gpc H0 = 68  8  18 km s-1 Mpc-1 Worrall & Birkinshaw 2003 Mark Birkinshaw, U. Bristol

  21. Cluster Hubble diagram • poor leverage for other parameters • need many clusters at z > 0.5 • need reduced random errors • ad hoc sample • systematic errors • cluster evolution should not affect method, can extend to higher z From Carlstrom, Holder & Reese 2002 Mark Birkinshaw, U. Bristol

  22. Levels of study • First level: detection of integrated effect • Second level: structure of integrated effect • Still rudimentary (compare X-ray images) • Low dynamic range of data in contrast (20:1 about best) • Low dynamic range of data in angular scale (5:1 about best) • Astrophysics of cluster structure formation, thermalization of gas, cluster mergers Mark Birkinshaw, U. Bristol

  23. Cluster gas structures Better measured in the X-ray, since higher signal/noise. But in principle the ne dependence of the SZ effect gives higher sensitivity to cluster edges than ne2. Gas structure poorly sampled by current tSZ data: few map points (radiometer arrays), poor angular dynamic range (interferometers). New bolometer data (MUSTANG, APEX-SZ) better. Aim: go beyond global models to astrophysics of gas structures – atmosphere assembly physics, feedback. NFW  Mark Birkinshaw, U. Bristol

  24. Cluster gas structures Effective use of SZ to get gas structures requires • high sensitivity (long integrations/low systematic errors) • good beamshape knowledge (hard for arrays) • excellent angular dynamic range (hard for interferometers) • good avoidance of confusion and cluster AGN Variety of cluster substructures (shocks, etc.) will also affect interpretation of large-scale structure. Future of SZ effect may be in finding pressure substructures. Mark Birkinshaw, U. Bristol

  25. Lensing and SZ effect Weak lensing measures ellipticity field e, and so surface mass density Surface mass density map combined with SZ effect map gives a map of fb SRJ/, and shows distribution of baryons relative to dark matter in clusters. Integrated over solid angle gives measure of fb. Mark Birkinshaw, U. Bristol

  26. Lensing and SZ effect 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 2003 Mark Birkinshaw, U. Bristol

  27. z=0.68 z=0.68 z=0.58 z=0.14 z=0.25 z=0.73 z=0.29 z=0.14 z=0.25 Lensing and the tSZ effect pixel data from simulations 4.25 clusters identified in simulations × Noise dominated region 4.5 Mark Birkinshaw, U. Bristol

  28. Levels of study • First level: detection of integrated effect • Second level: structure of integrated effect • Third level: use of integrated effect to find clusters • Focus of most new instruments: SZA, SPT, APEX/LABOCA, AMI, OCRA-F, AMiBA, … • Extensive low-z sample from Planck • Emphasis on cosmology via cluster counts: redshift distribution sensitive to σ8 (or Λ) • Generally rely on multi-band separation of SZ and primary CMB signals Mark Birkinshaw, U. Bristol

  29. Cluster surveys: X-ray XMM-LSS field Contains many cluster candidates at z > 1 Mark Birkinshaw, U. Bristol

  30. Cluster counts • SZ-selected samples • almost mass limited and orientation independent • potentially more sensitive than X-ray at high z • 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 • First large survey results starting to emerge (Bonn meeting, last week) Mark Birkinshaw, U. Bristol

  31. Cluster counts dN/dz Cluster counts and redshift distribution provide strong constraints on 8, m, and cluster heating. Wm=1.0 WL=0 s8=0.52 Wm=0.3 WL=0.7 s8=0.93 Wm=0.3 WL=0 s8=0.87 z Figure from Fan & Chiueh 2001 Mark Birkinshaw, U. Bristol

  32. Cluster counts • SZ-selected samples limited by changing cluster linear size (and temperature) and coherence at high z since selection is by thermal energy content • maximum detectable redshift probably  2 • evolution little constrained by SZ data – observations over a wide range of redshift, but insufficient angular dynamic range; need ye distribution at several z • need for good follow-up SZ imaging of cluster samples, including multi-band removal of CMB (10 arcsec or better angular resolution; 10 μK or better noise; μJy sensitivities) • beware Malmquist bias – flux density surveys Mark Birkinshaw, U. Bristol

  33. Levels of study • First level: detection of integrated effect • Second level: structure of integrated effect • Third level: use of integrated effect to find clusters • Fourth level: spectral studies • Extend cluster surveys to lower temperatures • Few attempts at cluster velocities, cluster velocity evolution • No serious work on multi-phase plasmas and non-thermal SZ effect Mark Birkinshaw, U. Bristol

  34. Cluster radial velocity • kinematic effect z-independent in I() • separable from thermal SZ effect by spectrum • confusion with primary CMB 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 from cluster samples Mark Birkinshaw, U. Bristol

  35. Cluster radial velocity Need • good SZ spectrum • X-ray temperature Confused by CMB structure Sample  vz2 Few clusters so far, vz  1000 km s A 2163; figure from LaRoque et al. 2002. Mark Birkinshaw, U. Bristol

  36. Cluster radial velocity Extracting the kinematic SZ effect requires spectral separation, so • absolute calibration to high precision over range of wavelengths • excellent bandpass calibration to fit spectrum well • knowledge of cluster thermal structure – also requires precision calculation of spectrum including relativistic and multiple-scattering effects Expect velocity substructure in cluster gas from mergers and infall – might be observable in future If can detect statistically in samples of clusters at different redshifts, can get measure of kinematic evolution of clustering (new datum for cluster formation studies) Mark Birkinshaw, U. Bristol

  37. Cluster radial velocity J0717.5+3745 at z = 0.548 Particularly interesting in mergers such as this. Clearly disturbed, shock-like structure, filament. Hot! Structure on few arcsec scale, large field map needed. Mark Birkinshaw, U. Bristol

  38. SZ effect confusion on CMB Figure from Molnar & Birkinshaw 2000 thermal SZ kinematic SZ RS effect Mark Birkinshaw, U. Bristol

  39. SZ effect confusion on CMB 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. Need new technology to perform surveys to low-mass, high-z clusters. Mark Birkinshaw, U. Bristol

  40. CMB properties • Ratio of SZ effects at two ν is a function of TCMB (some dependence on Te and cluster velocity) • Use SZ effect spectrum to measure CMB temperature at distant locations and over range of redshifts • Test Trad  (1 + z) • SZ results plus molecular excitation Battistelli et al. (2002) Mark Birkinshaw, U. Bristol

  41. Levels of study • First level: detection of integrated effect • Second level: structure of integrated effect • Third level: use of integrated effect to find clusters • Fourth level: spectral studies • Fifth level: polarization • No useful work to date • Access to 3-D velocity field, remote measure of Q Mark Birkinshaw, U. Bristol

  42. CMB properties • CMB power spectrum shows low quadrupolar power r • Measure quadrupole at other places in Universe • SZ effect polarization, important term is conversion of CMB quadrupole to linear polarization • Polarization signal small, confused by larger effect of cluster lensing CMB polarization Mark Birkinshaw, U. Bristol

  43. Requirements on observations Mark Birkinshaw, U. Bristol

  44. Requirements on observations Mark Birkinshaw, U. Bristol

  45. Requirements on observations Mark Birkinshaw, U. Bristol

  46. Things to shoot for • First level: detection of integrated effect. • Simple for high-temperature clusters • Second level: structure of integrated effects. • Depends on noise characteristics, sensitivity, CMB removal • Third level: use integrated effect to find clusters. • Similar requirements to structure, but on large sky areas • Fourth level: spectral studies. • Essentially new contribution of current and next generation • Velocity information requires significant cluster sample • Multi-component study requires high signal/noise • Fifth level: polarization. • Would be completely new Mark Birkinshaw, U. Bristol

  47. Possible SZ unique studies • Fast hot outflows around ionizing objects at recombination (or later) may show kinematic SZ with little thermal SZ. • Information on multiple components in cluster atmospheres via spectral studies. Inversion of spectrum into electron distribution function. • Information on developing cluster velocity field. • Non-thermal SZ effect in large-scale radio sources to test equipartition (c.f., X-ray inverse-Compton studies). Also issue of non-standard electron populations seen in hot spots and jets. Mark Birkinshaw, U. Bristol