Klaus Maisinger

High-sensitivity measurements of the cosmic microwave background power spectrum with the extended Very Small Array

We present deep Ka-band (ν ≈ 33 GHz) observations of the cosmic microwave background (CMB) made with the extended Very Small Array (VSA). This configuration produces a naturally weighted synthesized FWHM beamwidth of ∼11 arcmin, which covers anrange of 300 to 1500. On these scales, foreground extragalactic sources can be a major source of contamination to the CMB anisotropy. This problem has been alleviated by identifying sources at 15 GHz with the Ryle Telescope and then monitoring these sources at 33 GHz using a single-baseline interferometer collocated with the VSA. Sources with flux densities20 mJy at 33 GHz are subtracted from the data. In addition, we calculate a statistical correction for the small residual contribution from weaker sources that are below the detection limit of the survey. The CMB power spectrum corrected for Galactic foregrounds and extragalactic point sources is presented. A totalrange of 150-1500 is achieved by combining the complete extended array data with earlier VSA data in a compact configuration. Our resolution of �� ≈ 60 allows the first three acoustic peaks to be clearly delineated. This is achieved by using mosaiced observations in seven regions covering a total area of 82 deg 2 . There is good agreement with the Wilkinson Microwave Anisotropy Probe (WMAP) data up to � = 700 where WMAP data run out of resolution. For highervalues out to � = 1500, the agreement in power spectrum amplitudes with other experiments is also very good despite differences in frequency and observing technique.

The cosmic microwave background power spectrum out to ℓ= 1400 measured by the Very Small Array

We have observed the cosmic microwave background (CMB) in three regions of sky using the Very Small Array (VSA) in an extended configuration with antennas of beamwidth 2 degrees at 34 GHz. Combined with data from previous VSA observations using a more compact array with larger beamwidth, we measure the power spectrum of the primordial CMB anisotropies between angular multipoles l = 160 - 1400. Such measurements at high l are vital for breaking degeneracies in parameter estimation from the CMB power spectrum and other cosmological data. The power spectrum clearly resolves the first three acoustic peaks, shows the expected fall off in power at high l and starts to constrain the position and height of a fourth peak.

First results from the Very Small Array — I. Observational methods

The Very Small Array (VSA) is a synthesis telescope designed to image faint structures in the cosmic microwave background on degree and sub-degree angular scales. The VSA has key differences from other CMB interferometers with the result that different systematic errors are expected. We have tested the operation of the VSA with a variety of blank-field and calibrator observations, and cross-checked its calibration scale against independent measurements. We find that systematic effects can be suppressed below the thermal noise level in long observations; the overall calibration accuracy of the flux density scale is 3.5 per cent and is limited by the external absolute calibration scale.

First results from the Very Small array: III. The cosmic microwave background power spectrum

We present the power spectrum of the fluctuations in the cosmic microwave background detected by the Very Small Array (VSA) in its first season of observations in its compact configuration. We find clear detections of first and second acoustic peaks at l≈ 200 and ≈550, plus detection of power on scales up to l= 800. The VSA power spectrum is in very good agreement with the results of the BOOMERanG, DASI and MAXIMA telescopes despite the differing potential systematic errors.

Maximum-likelihood estimation of the cosmic microwave background power spectrum from interferometer observations

A maximum-likelihood method is presented for estimating the power spectrum of anisotropies in the cosmic microwave background (CMB) from interferometer observations. The method calculates flat band-power estimates in separate bins in l-space, together with confidence intervals on the power in each bin. For multifrequency data, the power spectrum of the other foreground components may also be recovered. Advantage is taken of several characteristic properties of interferometer data, which together allow the fast calculation of the likelihood function. The method may be applied to single-field or mosaicked observations, and proper account can be taken of non-coplanar baselines. The method is illustrated by application to simulated data from the Very Small Array.

Cosmological parameter estimation using Very Small Array data out to ℓ = 1500

We estimate cosmological parameters using data obtained by the Very Small Array (VSA) in its extended configuration, in conjunction with a variety of other cosmic microwave background (CMB) data and external priors. Within the flat A cold dark matter (ACDM) model, we find that the inclusion of high-resolution data from the VSA modifies the limits on the cosmological parameters as compared to those suggested by the Wilkinson Microwave Anisotropy Probe (WMAP) alone, while still remaining compatible with their estimates. We find that Omega(b)h(2) = 0.0234(-0.0014)(+0.0012), Omegadmh2 = 0.111(-0.016)(+0.014), h = 0.73(-0.05)(+0.09), n(S) = 0.97(-0.03)(+0.06), 10(10) A(S) = 23(-3)(+7) and tau = 0.14(-0.07)(+0.14) for WMAP and VSA when no external prior is included. On extending the model to include a running spectral index of density fluctuations, we find that the inclusion of VSA data leads to a negative running at a level of more than 95 per cent confidence (n(run) = -0.069 +/- 0.032), something that is not significantly changed by the inclusion of a stringent prior on the Hubble constant. Inclusion of prior information from the 2dF galaxy redshift survey reduces the significance of the result by constraining the value of Omega(m). We discuss the veracity of this result in the context of various systematic effects and also a broken spectral index model. We also constrain the fraction of neutrinos and find that f(v) < 0.087 at 95 per cent confidence, which corresponds to m(v) <0.32 eV when all neutrino masses are equal. Finally, we consider the global best fit within a general cosmological model with 12 parameters and find consistency with other analyses available in the literature. The evidence for nrun < 0 is only marginal within this model.

First results from the Very Small Array – II. Observations of the cosmic microwave background

We have observed the cosmic microwave background temperature fluctuations in eight fields covering three separated areas of sky with the Very Small Array at 34 GHz. A total area of 101 square degrees has been imaged, with sensitivity on angular scales 3. ◦ 6–0. ◦ 4 (equivalent to angular multipoles l=150–900). We describe the field selection and observing strategy for these observations. In the full-resolution images (with synthesised beam of FWHM ≃ 17 arcmin) the thermal noise is typically 45 � K and the CMB signal typically 55 � k. The noise levels in each field agree well with the expected thermal noise level of the telescope, and there is no evidence of any residual systematic features. The same CMB features are detected in separate, overlapping observations. Discrete radio sources have been detected using a separate 15 GHz survey and their effects removed using pointed follow-up observations at 34 GHz. We estimate that the residual confusion noise due to unsubtracted radio sources is less than 14 mJy beam −1 (15 � K in the full-resolution images), which added in quadrature to the thermal noise increases the noise level by 6 %. We estimate that the rms contribution to the images from diffuse Galactic emission is less than 6 � K. We also present images which are convolved to maximise the signal-to-noise of the CMB features and are co-added in overlapping areas, in which the signal-to-noise of some individual CMB features exceeds 8.

High sensitivity measurements of the CMB power spectrum with the extended Very Small Array

We present deep Ka-band (ν ≈ 33 GHz) observations of the cosmic microwave background (CMB) made with the extended Very Small Array (VSA). This configuration produces a naturally weighted synthesized FWHM beamwidth of ∼11 arcmin, which covers anrange of 300 to 1500. On these scales, foreground extragalactic sources can be a major source of contamination to the CMB anisotropy. This problem has been alleviated by identifying sources at 15 GHz with the Ryle Telescope and then monitoring these sources at 33 GHz using a single-baseline interferometer collocated with the VSA. Sources with flux densities20 mJy at 33 GHz are subtracted from the data. In addition, we calculate a statistical correction for the small residual contribution from weaker sources that are below the detection limit of the survey. The CMB power spectrum corrected for Galactic foregrounds and extragalactic point sources is presented. A totalrange of 150-1500 is achieved by combining the complete extended array data with earlier VSA data in a compact configuration. Our resolution of �� ≈ 60 allows the first three acoustic peaks to be clearly delineated. This is achieved by using mosaiced observations in seven regions covering a total area of 82 deg 2 . There is good agreement with the Wilkinson Microwave Anisotropy Probe (WMAP) data up to � = 700 where WMAP data run out of resolution. For highervalues out to � = 1500, the agreement in power spectrum amplitudes with other experiments is also very good despite differences in frequency and observing technique.

Cosmological parameter estimation and Bayesian model comparison using Very Small Array data

We constrain the basic cosmological parameters using the first observations by the Very Small Array (VSA) in its extended configuration, together with existing cosmic microwave background data and other cosmological observations. We estimate cosmological parameters for four different models of increasing complexity. In each case, careful consideration is given to implied priors and the Bayesian evidence is calculated in order to perform model selection. We find that the data are most convincingly explained by a simple flat ACDM cosmology without tensor modes. In this case, combining just the VSA and COBE data sets yields the 68 per cent confidence intervals Ω b h 2 = 0.034 + 0 . 0 0 7 - 0 . 0 0 7 , Ω d m h 2 = 0.18 + 0 . 0 6 - 0 . 0 4 , h = 0.72 + 0 . 1 5 - 0 . 1 3 , n s = 1.07 + 0 . 0 6 - 0 . 0 6 and σ 8 = 1.17 + 0 . 2 5 - 0 . 2 0 . The most general model considered includes spatial curvature, tensor modes, massive neutrinos and a parametrized equation of state for the dark energy. In this case, by combining all recent cosmological data, we find, in particular, a 95 per cent limit on the tensor-to-scalar ratio R < 0.63 and on the fraction of massive neutrinos f v < 0.11; we also obtain the 68 per cent confidence interval w = -1.06 + 0 . 2 0 - 0 . 2 5 on the equation of state of dark energy.

Maximum-entropy image reconstruction using wavelets

The maximum-entropy method (MEM) is often used for enhancing astronomical images and, in particular, has recently been applied to cosmic microwave background (CMB) observations. Wavelet functions are also now used widely in astronomy, since they allow the sparse and efficient representation of a signal at different scales, and the application of wavelets to the denoising of CMB maps has been investigated. In this paper, we give a systematic discussion of how to combine these two approaches by the use of the MEM in wavelet bases for the denoising and deconvolution of general images and, in particular, CMB maps. We find that the MEM in the a trous wavelet basis has lower reconstruction residuals than conventional pixel-basis MEM in the case when the signal-to-noise ratio is low and the point spread function is narrow. Furthermore, the Bayesian evidence for the wavelet MEM reconstructions is generally higher for a wide range of images. From a Bayesian point of view, the wavelet basis thus provides a better model of the image.