joint analysis of weak lensing and sze data from the arcminute microkelvin imager natasha...
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Joint Analysis of Weak Lensing and SZE data from the Arcminute
Microkelvin Imager
Natasha Hurley-Walkerin collaboration with
Farhan Feroz, Jonathan Zwart,and the AMI Team
17th March 2008Rencontres de Moriond: Cosmology
Talk Outline
AMIScience Goals with AMICluster Samples
pointed sampleweak lensing sample
Lensing AnalysisBayesian AnalysisResultsProspects
AMI Small Array
AMI Large Array
Science Goals
Cluster SurveyEvolution of cluster population: N(m,z) → σ8
CMB power spectrum at high angular scales (ℓ > 3000)Other non-Gaussian features, e.g. cosmic strings, ionization regions
Pointed cluster observations (Zwart et al 2008, in prep)Known clusters → H
0, q
0, f
g
Cluster scaling relations, Lx–T, M, z, etcGalactic Objects (see Anna Scaife’s talk on Thursday)Source Counts (→ Planck etc)Joint Lensing Analysis
AMI Pointed Cluster Sample
Ryle Telescope source survey (2004–6)4 days for each of ~ 80 ‘lucky’ targets
Refined sample of 31 clustersFavourable 15-GHz source environments
Sub-sample of 8 (Zwart et al, in prep.)Range of L
X, z
6 SA maps:
SA Cluster Maps
Lensing Sample
22 clusters observed with MegaCam on CFHTSelection above 10º declination leaves 16Currently can only subtract point sources of less than 20mJy some distance from pointing centre: leaves 8 clusters:
A115, A611, A851, A1914, A2111, A2218, Zw1358+62, A2259
MegaCam Images
2 hour exposuresseeing of 0.7”r magnitude limit 25.9 in AB1º x 1º field of view
2.2' square section of r-band map of A115
Lensing Analysis
SExtract sourcesSelect stars from FWHM - magnitude diagramRun im2shape (Bridle et al 2002)Discard outliers
Interpolate e1, e
2 at each galaxy position to
create PSF over map
Point-Spread Function
Ellipticity varies 0-0.1 over the mapAmplitude by about 5%Lensing signal 2-3 orders of magnitude smallerCareful interpolation and deconvolution needed
Lensing Analysis (2)
Run im2shape on background galaxies, deconvolving with the interpolated PSF
Extract catalogue of positions, ellipticities, position angles
Bayesian Analysis of Galaxy Clusters
Parameter estimationModel comparison (evidence)
MCADAMSee Marshall et al 2003, Lancaster et al 2005Improved MCMC engine: nested sampler
Faster; copes well with multimodal distributions and degeneracies
Parametric SZ & strong/weak lensing analysis
Cluster Models
Geometry: Spherical/ellipticalTemperature: Isothermal/PolytropicMass: Singular Isothermal Sphere, NFW, Cored Power-LawGas: Beta Model, Hydrostatic Equilibrium
All model parameters including point source positions, fluxes and spectra have priors
Different number of parameters for each model; evidence values allow you to compare models
SZ Data
2/1
2
2
2e1
Cπ=Z
χ
Z=θ|DataPr=L
visNL
LSZ
Generate mock visibilities given model parameters and compare with χ2
Likelihood function gives you probability of model, given the data
Covariance matrices C model other contributions
Noise Modelling
Noise on the SZ observation can be described by the covariance matrix
C = Csystem + CCMB + Cconfusion
Csystem: diagonal matrix with elements
CCMB: contains significant off diagonal elements and can be calculated from a given CMB power spectrum following Hobson & Maisinger (2002).
Cconfusion: Scheuer expression for confusion
iji δσ 2
SZ Posteriors
Combining SZ & Lensing Data
Covariance matrix for lensing is diagonal for Gaussian distribution of ellipticitiesGenerate reduced shear given the model at each galaxy position and compare to data using χ2 Add likelihoods from SZ and lensing for joint analysis
LensingSZ L+L=L logloglog
Results so farImages are lensing-quality:
Decrements ~5-10 σ in radio data
Prospects
SZ/Lensing reduction pipeline in placeSA observing programme in progressPapers in preparation on Galactic objects, pointed cluster observations, source countsLA in final calibration stagesSZ survey begins soon
LA map of A1914:
References
Scheuer, P. A. G. “A statistical method for analysing observations of faint radio stars” 1957; Proceedings of the Cambridge Philisophical Society, vol. 53, pp. 764-773Bridle, S.; Kneib, J.-P.; Bardeau, S.; Gull, S. “Bayesian galaxy shape estimation” 2002; Proceedings of the Yale Cosmology Workshop "The Shapes of Galaxies and Their Dark Matter Halos"Hobson, M. P.; Maisinger, Klaus “Maximum-likelihood estimation of the cosmic microwave background power spectrum from interferometer observations” 2002; MNRAS 334, 3, 569Marshall, P.J.; Hobson, M. P.; Slosar, A. “Bayesian joint analysis of cluster weak lensing and Sunyaev-Zel'dovich effect data” 2003; MNRAS 346, 489Lancaster et al “Very Small Array observations of the Sunyaev-Zel'dovich effect in nearby galaxy clusters” 2005; MNRAS 359, 16LScaife, A. M. M.; Hurley-Walker, N.; Green, D.; “AMI limits on 15 GHz excess emission in northern HII regions” 2007; MNRAS (accepted)