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We study the spatial distribution and colours of galaxies within the region covered by the cold spot in the cosmic microwave background recently detected by the Very Small Array interpherometer (VSA) towards the Corona Borealis supercluster (CrB-SC). The spot is in the northern part of a region with a radius at the redshift of CrB-SC) enclosing the clusters Abell 2056, 2065, 2059 and 2073, and where the density of galaxies, excluding the contribution from those clusters, is approximately two times higher than the mean value in typical intercluster regions of the CrB-SC. Two of such clusters (Abell 2056 and 2065) are members of the CrB-SC, while the other two are in the background. This high-density intercluster region is quite inhomogeneous, being the most remarkable feature a large concentration of galaxies in a narrow filament running from Abell 2065 with a length of ∼35 arcmin ( at the redshift of CrB-SC) in the SW–NE direction. This intercluster population of galaxies probably results from the interaction of clusters Abell 2065 and 2056. The area subtended by the VSA cold spot shows an excess of faint and red galaxies as compared with typical values within the CrB-SC intercluster regions. This overdensity of galaxies shows a radial dependence and extends out to ∼15 arcmin. This could be the signature of a previously unnoted cluster in the background. [ABSTRACT FROM AUTHOR]

Accurate calibration of data is essential for the current generation of cosmic microwave background (CMB) experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 per cent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. At 30 GHz the careful correction for atmospheric emission and absorption is shown to be essential for achieving 1 per cent precision. The sources for which a 1 per cent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC 7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ∼30 GHz is given for each. Cas A, Tau A, NGC 7027 and Venus were examined for variability. Cas A was found to be decreasing at 0.394 ± 0.019 per cent yr−1 over the period 2001 March to 2004 August. In the same period Tau A was decreasing at 0.22 ± 0.07 per cent yr−1. A survey of the published data showed that the planetary nebula NGC 7027 decreased at 0.16 ± 0.04 per cent yr−1 over the period 1967–2003. Venus showed an insignificant (1.5 ± 1.3 per cent) variation with Venusian illumination. The integrated polarization of Tau A at 33 GHz was found to be 7.8 ± 0.6 per cent at position angle =148°± 3°. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the constraints on basic cosmological parameters set by the first compact-configuration observations of the Very Small Array (VSA), and other cosmological data sets, in the standard inflationary ΛCDM model. Using the weak priors 40 < H[sub 0] < 90 km s[sup -1] Mpc[sup -1] and 0 < τ < 0.5 , we find that the VSA and COBE-DMR data alone produce the constraints Ω[sub tot]= 1.03[sup +0.12][sub -0.12], Ω[sub b]h[sup 2]= 0.029[sup +0.009][sub -0.009], Ω[sub cdm]h[sup 2]= 0.13[sup +0.08][sub -0.05] and n[sub s]= 1.04[sup +0.11][sub -0.08] at the 68 per cent confidence level. Adding in the Type Ia supernova constraints, we additionally find Ω[sub m]= 0.32[sup +0.09][sub -0.06] and Ω[sub Λ]= 0.71[sup +0.07][sub -0.07] . These constraints are consistent with those found by the BOOMERanG, DASI and MAXIMA experiments. We also find that, by combining all these cosmic microwave background experiments and assuming the Hubble Space Telescope Key Project limits for H[sub 0] (for which the X-ray plus Sunyaev–Zel'dovich route gives a similar result), we obtain the tight constraints Ω[sub m]= 0.28[sup +0.14][sub -0.07] and Ω[sub Λ]= 0.72[sup +0.07][sub -0.13] , which are consistent with, but independent of, those obtained using the supernova data. [ABSTRACT FROM AUTHOR]

ABSTRACT 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. [ABSTRACT FROM AUTHOR]

ABSTRACT 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. [ABSTRACT FROM AUTHOR]

ABSTRACT We have observed the cosmic microwave background (CMB) 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 of (equivalent to angular multipoles ℓ= 150–900 ). We describe the field selection and observing strategy for these observations. In the full-resolution images (with synthesized beam of FWHM ≃17 arcmin) the thermal noise is typically 45 μK and the CMB signal typically 55 μK. 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 arising from unsubtracted radio sources is less than 14 mJy beam[sup -1] (15 μK in the full-resolution images), which added in quadrature to the thermal noise increases the noise level by 6 per cent. We estimate that the rms contribution to the images from diffuse Galactic emission is less than 6 μK. We also present images that are convolved to maximize the signal-to-noise ratio of the CMB features and are co-added in overlapping areas, in which the signal-to-noise ratio of some individual CMB features exceeds 8. [ABSTRACT FROM AUTHOR]

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° 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 and 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. [ABSTRACT FROM AUTHOR]