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

Abstract

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 Λ cold dark matter (ΛCDM) 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 Ωbh2= 0.0234+0.0012−0.0014, Ωdmh2= 0.111+0.014−0.016, h= 0.73+0.09−0.05, nS= 0.97+0.06−0.03, 1010AS= 23+7−3 and τ= 0.14+0.14−0.07 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 (nrun=−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 Ωm. 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 fν < 0.087 at 95 per cent confidence, which corresponds to mν < 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.

Extragalactic source contributions to arcminute-scale Cosmic Microwave Background anisotropies

“…New interesting constraints on the CMB angular power spectrum up to ∼ 2500 at 34 GHz should be provided in the near future by the VSA experiment (see, e.g., Rebolo et al 2004). The reduced noise level of the new configuration and an effective cleaning of deep fields down to ∼5 mJy -by dedicated observations with the Ryle Telescope at 15 GHz -will shed new light on the nature of the excess at high multipole and on the point source populations mainly contributing to the number counts at S 34 ∼ a few mJy.…”

Non-linear structure formation in cosmologies with early dark energy

“…According to observations of Supernovae Ia (SNe Ia) (Riess et al 2004), the Cosmic Microwave Background (CMB) (Spergel et al 2003;Readhead et al 2004;Goldstein et al 2003;Rebolo et al 2004), and Large Scale Structure (LSS) (Tegmark et al 2004;Hawkins et al 2003), the expansion of our Universe is accelerating today. A plausible candidate to drive such an acceleration is Dark Energy (DE) which may be described by an effective (Doran & Jäckel 2002) scalar field (Wetterich 1988;Ratra & Peebles 1988;Caldwell et al 1998;Caldwell 2002).…”

“…We select models for which σ 8 is close to 0.8, the optical depth is τ < 0.2, and the spectral indices of initial scalar perturbations are n = 0.99 and n = 1.05, respectively. The data we use for the Monte-Carlo chains are CMB (Spergel et al 2003;Readhead et al 2004;Goldstein et al 2003;Rebolo et al 2004), LSS (Tegmark et al 2004), and SNe Ia (Riess et al 2004) data, thus both models describe current observations well. The parameters for model (I) are: Ω m,0 h 2 = 0.146, Ω b h 2 = 0.026, h = 0.67, n = 1.05, τ = 0.18, w 0 = −0.93, and Ω d,e = 2 × 10 −4 , leading to an effective Dark Energy contribution during structure formation (Doran et al 2001b) of Ω d,sf = 0.04 and σ 8 = 0.82.…”

An analysis method for time ordered data processing of dark matter experiments

“…Evidence for the existence of non-baryonic Dark Matter seems to be well established from the results of recent cosmological observations: CMB anisotropy measurements (Spergel et al 2003;Benoit et al 2003;Rebolo et al 2004;MacTavish et al 2005), large scale structure surveys (Tegmark et al 2004) and type Ia supernova measurements (Perlmutter et al 1999). The leading candidate intended to composed non-baryonic dark matter, is the lightest neutralinoχ proposed by supersymmetric extensions of the standard model of Particle Physics (Jungman et al 1996).…”