R. T. Génova-Santos

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.

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.

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.

Very Small Array observations of the anomalous microwave emission in the Perseus region

The dust complex G159.6-18.5 in the Perseus region has previously been observed with the {COSMOSOMAS} experiment on angular scales of {\textasciitilde}1??,and was found to exhibit anomalous microwave emission. We present thefirst high angular resolution observations of this dust complex,performed with the Very Small Array ({VSA}) at 33GHz, to help increase theunderstanding of the nature of this anomalous emission.On the angular scales observed with the {VSA} ({\textasciitilde}10-40arcmin), G159.6-18.5consists of five distinct components, all of which are found to exhibitan excess of emission at 33GHz that is highly correlated withfar-infrared emission. Within the region, we find a range of physicalconditions: one of the features, which is associated with the reflectionnebula {IC} 348, has a dust emissivity comparable to that of {HII} regions,while the other four features have values in agreement with previousobservations of intermediate Galactic latitudes. We provide evidencethat all of these compact components have anomalous emission that isconsistent with electric dipole emission from very small, rapidlyrotating dust grains. We find that these five components contribute {\textasciitilde}10per cent to the flux density of the diffuse extended emission detectedby {COSMOSOMAS}, implying that the bulk of the anomalous emission inPerseus is diffuse and not concentrated in these compact components.

Source subtraction for the extended Very Small Array and 33-GHz source count estimates

We describe the source subtraction strategy and observations for the extended Very Small Array (VSA), a cosmic microwave background interferometer operating at 33 GHz. A total of 453 sources were monitored at 33 GHz using a dedicated source subtraction baseline. 131 sources brighter than 20 mJy were directly subtracted from the VSA visibility data. Some characteristics of the subtracted sources, such as spectra and variability, are discussed. The 33-GHz source counts are estimated from a sample selected at 15 GHz. The selection of VSA fields in order to avoid bright sources introduces a bias into the observed counts. This bias is corrected and the resulting source count is estimated to be complete in the flux-density range 20‐114 mJy. The 33-GHz source counts are used to calculate a correction to the VSA power spectrum for sources below the subtraction limit. Ke yw ords: surveys ‐ cosmic microwave background ‐ radio continuum: galaxies.

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.

CONSTRAINTS ON THE POLARIZATION OF THE ANOMALOUS MICROWAVE EMISSION IN THE PERSEUS MOLECULAR COMPLEX FROM SEVEN-YEAR WMAP DATA

We have used the seven-year Wilkinson Microwave Anisotropy Probe (WMAP) data in order to update the measurements of the intensity signal in the G159.6-18.5 region within the Perseus molecular complex and to set constraints on the polarization level of the anomalous microwave emission in the frequency range where this emission is dominant. At 23, 33, and 41 GHz, we obtain upper limits on the fractional linear polarization of 1.0%, 1.8%, and 2.7%, respectively (with a 95% confidence level). These measurements rule out a significant number of models based on magnetic dipole emission of grains that consist of a simple domain as responsible for the anomalous emission. When combining our results with the measurement obtained with the COSMOSOMAS experiment at 11 GHz, we find consistency with the predictions of the electric dipole and resonance relaxation theory at this frequency range.

Constraints on spinning dust towards Galactic targets with the Very Small Array: a tentative detection of excess microwave emission towards 3C396

We present results from observations made at 33 GHz with the Very Small Array (VSA) telescope towards potential candidates in the Galactic plane for spinning dust emission. In the cases of the diffuse H II regions LPH96 and NRAO591 we find no evidence for anomalous emission and, in combination with Effelsberg data at 1.4 and 2.7 GHz, confirm that their spectra are consistent with optically thin free‐free emission. In the case of the infrared bright supernova remnant 3C396 we find emission inconsistent with a purely non-thermal spectrum and discuss the possibility of this excess arising from either a spinning dust component or a shallow spectrum pulsar wind nebula, although we conclude that the second case is unlikely given the strong constraints available from lower-frequency radio images.

The Quijote CMB Experiment

We present the current status of the QUIJOTE (Q-U-I JOint TEnerife) CMB Experiment, a new instrument which will start operations early in 2009 at Teide Observatory with the aim of characterizing the polarization of the CMB and other processes of galactic and extragalactic emission in the frequency range 10–30GHz and at large angular scales. QUIJOTE will be a valuable complement at low frequencies for the PLANCK mission, and will have the required sensitivity to detect a primordial gravitational-wave component if the tensor-to-scalar ratio is larger than r = 0.05.