No abstract

The FIRST (Faint Images of the Radio Sky at Twenty Centimeters) survey now covers 1550 deg 2 of sky where 07 h 16 < ∼ α < ∼ 17 h 40 and 28 • .3 < ∼ δ < ∼ 42 • . This yields a catalog of 138,665 sources above the survey threshold of 1 mJy, about one third of which are in double-lobed and multi-component sources.We have used these data to obtain the first high-significance measurement of the two-point angular correlation for a deep radio sample. We find that the correlation function between 0.02 • and 2 • is well fitted by a power law of the form Aθ γ where A ≈ 3 × 10 −3 and γ ≈ −1.1. On small scales (θ < 0.2 • ), double and multi-component sources are shown to have a larger clustering amplitude than that of the whole sample. Sources with flux densities below 2 mJy are found to have a shallower slope than that obtained for the whole sample, consistent with there being a significant contribution from starbursting galaxies at these faint fluxes. The cross-correlation of radio sources and Abell clusters is determined. A preliminary approach to inferring spatial information is outlined.

Weak lensing by large‐scale mass inhomogeneities in the Universe induces correlations in the observed ellipticities of distant sources. We first review the harmonic analysis and statistics required of these correlations and discuss calculations for the predicted signal. We consider the ellipticity correlation function, the mean‐square ellipticity, the ellipticity power spectrum and a global maximum‐likelihood analysis to isolate a weak‐lensing signal from the data. Estimates for the sensitivity of a survey of a given area, surface density, and mean intrinsic source ellipticity are presented. We then apply our results to the FIRST radio‐source survey. We predict an rms ellipticity of roughly 0.011 in 1 × 1 deg2 pixels and 0.018 in 20 × 20 arcmin2 pixels if the power spectrum is normalized to σ8 Ω0.53 = 0.6, as indicated by the cluster abundance. The signal is significantly larger in some models if the power spectrum is normalized instead to the COBE anisotropy. The uncertainty in the predictions from imprecise knowledge of the FIRST redshift distribution is about 25 per cent in the rms ellipticity. We show that FIRST should be able to make a statistically significant detection of a weak‐lensing signal for cluster‐abundance‐normalized power spectra.

We present forecasts for constraints on cosmological models that can be obtained using the forthcoming radio continuum surveys: the wide surveys with the Low Frequency Array (LOFAR) for radio astronomy, the Australian Square Kilometre Array Pathfinder (ASKAP) and the Westerbork Observations of the Deep Apertif Northern Sky (WODAN). We use simulated catalogues that are appropriate to the planned surveys in order to predict measurements obtained with the source autocorrelation, the cross‐correlation between radio sources and cosmic microwave background (CMB) maps (the integrated Sachs–Wolfe effect), the cross‐correlation of radio sources with foreground objects resulting from cosmic magnification, and a joint analysis together with the CMB power spectrum and supernovae (SNe). We show that near‐future radio surveys will bring complementary measurements to other experiments, probing different cosmological volumes and having different systematics. Our results show that the unprecedented sky coverage of these surveys combined should provide the most significant measurement yet of the integrated Sachs–Wolfe effect. In addition, we show that the use of the integrated Sachs–Wolfe effect will significantly tighten the constraints on modified gravity parameters, while the best measurements of dark energy models will come from galaxy autocorrelation function analyses. Using a combination of the Evolutionary Map of the Universe (EMU) and WODAN to provide a full‐sky survey, it will be possible to measure the dark energy parameters with an uncertainty of {σ(w0) = 0.05, σ(wa) = 0.12} and the modified gravity parameters {σ(η0) = 0.10, σ(μ0) = 0.05}, assuming Planck CMB+SN (current data) priors. Finally, we show that radio surveys would detect a primordial non‐Gaussianity of fNL= 8 at 1σ, and we briefly discuss other promising probes.