Presentation on theme: "Notes… Handouts available for today and yesterday"— Presentation transcript:
1Notes… Handouts available for today and yesterday Some bits might not come out too well, if you want to check against the originals I will put them all on my website:The versions on there currently are so please be careful!
2Suggested Reading… Couple of useful texts (I may add to these): CMB: ‘The Cosmological background Radiation’. Lachieze-Rey and Gunzig. Available in the library.SZ: ‘The Sunyaev Zel’dovich Effect’. A review by Mark Birkinshaw, Physics Reports ‘99, available online (I’ll link it from my website).Many useful papers, websites etc are linked from the ‘4th year seminar’ section on my website.
3Lecture 2Why is SZ useful? Unique property, science we can derive from measurementsReal examples, comparisons between experimentsWhat improvements are required in order to progress with ‘traditional’ aimsScience prospects for the futureObservational IssuesIf I refer generally to SZ, I mean THERMAL!
4A Brief History of SZ Postulated by Sunyaev and Zel’dovich in 1970 Many observational attempts with little success until Birkinshaw trustworthy measurement put the technique on the mapFirst SZ image - Jones 1993.1990s, 2000s - plethora of SZ studies detections, unresolved images2000s onwards - purpose built instruments, surveys, high resolution images, samplesbirkinshaw - single dish. jones - interferometer. mention cambridge and chicago groups in terms of studies. plus others.
5Revision of conceptLow energy CMB photon scatters from high energy cluster electronCMB spectrum shifted to higher energyObserve:Decrement at low frequencyNull at 220GHzIncrement at high frequencyStrength depends on density and temperature of the cluster gasbirkinshaw - single dish. jones - interferometer. mention cambridge and chicago groups in terms of studies. plus others.
6SZ Science BasicsSZ can be exploited alone, or in combination with data from other wavebandsMost astronomy relies on multi-frequency observations (i.e. optical, infrared, X-ray, radio)Can combine SZ with:X-rays (discussed at length here)Strong lensing (total mass)Weak lensingVelocity dispersions from optical spectramulti-freq --> maximise information
7X-ray observationsIn these lectures, we will focus predominantly on how we combine SZ with X-ray dataX-ray surface brightness is given by:More usual to remember that:So the X-ray emission has a different dependence on the cluster temperature and densitymulti-freq --> maximise information
8Redshift Independance Unique property of the SZ effectSZ is a spectral distortion rather than a process of emission. Recall:No redshift dependenceFor central measures, completely independent of redshift. Total flux density depends on angular sizeExtremely useful for surveys - currently detect clusters out to redshift ~1 (optical, IR, X-ray)unique way to map large scale structure
10Scientific Applications We can learn a great deal of science from SZ measurements:Thermal SZ - Cosmology: Angular diameter distance, Hubble’s constant, Hubble diagramsThermal SZ - Cluster properties: Cluster gas fractions, Universal Baryon fractionNumber counts - Test cosmological modelsKinematic SZ - Cluster peculiar velocitiesWe will also look at some major results found in the literature
11Distance EstimatesBack to the equations for SZ and X-ray surface brightness. Approximate the temperature and density distribution as constants:Equate and eliminate the density term:OK to assume \theta is same along l.o.s as in plane of sky as should average out for a big sample.
12Distance EstimatesRelate the size of the cluster on the sky to the line-of-sight distance through itIf spherical, size on sky = l-o-s distanceCould also assume an elliptical modelIn reality: fit a model to the X-ray dataSimplest case:OK to assume \theta is same along l.o.s as in plane of sky as should average out for a big sample.
13Literature....Mason et al. 2001: ‘A measurement of H0 from the S-Z effect’. ~7 clusters,Reese et al 2002: ‘Determing the cosmic distance scale from interferometric measurements of the S-Z Effect’. ~20 clusters,Jones et al. 2005: ‘H0 from an orientation unbiased sample of S-Z and X-ray clusters’, small sample but more sensible selection,mason et al - few clusters, around 7. reese - 18 clusters? note smaller random errors. jones et al - few clusters, but better sample selection - note smaller systematic errors.
14Hubble DiagramAngular diameter distances determined from SZ measurements, plotted against redshiftLines correspond to different cosmologiesClearly need higher redshift data, higher precision measurementsReese et al 2002
15Distance scale - future? Accuracy of distance estimates sensitive to calibration uncertaintiesBest SZ calibration accuracy ~2.5%ROSAT calibration ~10% (XMM and Chandra are better)SYSTEMATICS - uncertain about assumptions of isothermality, substructure, point source contaminationsNeed higher resolution information - purpose built instruments
16Distance scale - future? Also limited by sample size, and incomplete sample selection‘Complete sample’ - e.g. all clusters above some flux limit, regardless of size, shape, radio source population...........believed to more accurately represent the Universe, i.e. less biasSZ Surveys will produce more statistically robust samples, mass limited
17Gas Properties and bHave already seen that we can find the gas density from SZ if we know the temperature - take this from X-ray data.Fit cluster-density model to 2-D SZ signal, e.g. King model:Empirical relation, established for globular clusters (!) but works well here
18..Gas mass, gas fraction..Integrate density distribution out to some radius to find the gas mass:Can find total mass from SZ by assuming hydrostatic equilibrium, otherwise use X-rays / lensing. Then:Compare with findings from e.g. X-rays to test models and assumptionsCompare to findings from X-rays - test models
19Literature....ForGrego et al 2001: ‘Galaxy cluster gas mass fractions from Sunyaev Zel’dovich measurements: Constraints on M.’Lancaster et al 2005: ‘Very Small Array observations of the Sunyaev Zel’dovich effect in nearby galaxy clusters.’Different redshifts - investigate cluster evolution. Both interferometric techniques, but different telescopes with different calibrations.
20Unable to constrain this well at the moment! Cluster Evolution?Grego et al 2001Unable to constrain this well at the moment!
21Constraining MExpect ~90% of cluster baryons to exist as ICM. Remaining ~10% in galaxies.Gas fraction is lower limit on Universal baryon fractionSo, measure baryon fraction from SZ, take baryon fraction from eg BBN or primordial CMB, leads directly to an estimate of the matter density:VSA ⇒
22ICM properties - future? Again, larger SZ samples will enable better determination of parameters for individual clustersHigh resolution observations will allow us to fit sophisticated models to the cluster gas - substructureSZ imaging needs to progress in order to keep up with developments in X-rays
25Peculiar Velocities Can only be derived from the kinematic SZ effect Observe at the thermal null, or use multi- frequency dataSpectrally the same as primordial CMB - difficult to measure peculiar velocity for individual objects.Samples more promising - uncertainties average outMeasure velocity fields at high redshift by finding peculiar velocities for many clusters
26Literature... Thermal + Kinematic SZ for Abell 2163 SuZIE Diabolo + SuZIEBIMAThermal + Kinematic SZ for Abell 2163Always measure thermal + kinematic. At low frequency, the KSZE is negligible. Need multi-freq / thermal null in order to separate the two. Striking agreement between different instruments (ie all points fit on line)Best-fit ThermalBest-fit KinematicBest-fit Combined
27Literature... Thermal + Kinematic SZ for Abell 2163 SuZIE Diabolo + SuZIEBIMAThermal + Kinematic SZ for Abell 2163Always measure thermal + kinematic. At low frequency, the KSZE is negligible. Need multi-freq / thermal null in order to separate the two.
28Why are peculiar velocities useful? Measure for a number of clusters in a particular redshift ‘bin’ and minimise errorsRepeat for a range of redshift binsCan derive something about the formation of large scale structure - i.e. how quickly things are moving around at different redshiftsClusters move under gravity - learn about distribution of matter at different epochs
29Surveys: New ScienceSZ selected samples will allow us to improve on ‘traditional’ SZ applications (Hubble const. etc)New frontier - cluster number density and its evolution with timeThe potential of this application will be realised with the release of cluster catalogues from SZ surveysOne aim is simply to record how many clusters are found in e.g. different redshift binsExamine cluster evolution (e.g. mass functions) and the geometry of the Universe
30Cluster Abundance Distinguish between cosmological models Carlstrom et al 2002
31SZ-selected samplesPrevious SZ samples are often chosen somewhat arbitrarily - i.e. clusters picked because they are easy to observeSome attempts to select representative samples from X-ray catalogues (e.g. Jones et al 2005, Lancaster et al 2005)Still subject to ‘selection effects’ (i.e. X- rays point preferentially to dense clusters)SZ catalogues will be mass-limited only
32SZ-selected samplesX-ray catalogues are limited in numbers due to rapid fall off of detectable flux with distanceSZ catalogues do not suffer from this limitation - will yield large numbers of new clusters, enabling studies of large scale structure via methods currently applied to galaxy catalogues e.g. 2DFWill also provide the first picture of the high-redshift Universe
34SZ Science to date Distance estimates to reasonable precision Good agreement between different experimentsICM properties e.g. gas fractionsLarge errors but consistent between experiements
35Future Science Prospects Detailed images - physics of clusters as individuals, and Universal populationLarge samples - more statistically robust estimates of cosmological parametersBlind surveys - direct view of the growth of large-scale structure over entire redshift range
36SZ PracticalitiesSZ is a tiny signal - requires sophisticated observing techniquesVarious sources of contamination and confusion, which observing techniques deal with in different waysRadio sources (galaxies, planets)Atmospheric emission, ground emissionPrimordial CMB fluctuationsToday, a few details. We will discuss the various observing techniques and how they cope with these issues tomorrow
37Radio SourcesIf a radio source is present in the field of a galaxy cluster, it will ‘fill in’ the SZ decrementThis could be true for sources in front of / behind the cluster, or indeed member galaxiesProblem greater at low frequency: most sources are ‘steep spectrum’Can choose to observe clusters with no sources - introduce biasBetter to ‘subtract’ effectsNo high-freq. radio surveys - further complication
38Atmosphere, Ground Atmosphere is ‘warm’ - radiates. Time variable emissionGround also a source of thermal emissionVaries with pointing angle or telescopeCan minimise this using a ‘ground shield’Various ways exist of dealing with these contaminant signals
39Primordial CMBPrimordial anisotropies look remarkably similar to the SZ effect on large angular scales (tens of arcminutes)Seem unsurprising that telescopes such as the VSA and CBI (built to observe the primordial CMB) suffer drastically from this type of contamination.........We were still surprised!