We report on the first measurement of the average mass and mass-to-light ratio of galaxy groups by analysing the weak lensing signal induced by these systems. The Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2) allows the identification of a large number of groups at intermediate redshifts. For our analysis we use a sample of 50 groups which are selected on the basis of a careful dynamical analysis of group candidates. We detect a signal at the 99% confidence limit. The best fit singular isothermal sphere model yields an Einstein radius rE = 0″.72 ± 0″.29. This corresponds to a velocity dispersion of 〈σ2〉1/2 = 274±+48-59 km/s, which is in good agreement with the dynamical estimate. Under the assumption that the light traces the mass, we find an average mass-to-light ratio of 191 ± 83 h in the restframe B band. Unlike dynamical estimates, this result is insensitive to problems associated with determining group membership. We use the observed mass-to-light ratio to estimate the matter density of the universe, for which we find Ωm = 0.19 ± 0.10 (ΩΛ = 0), in good agreement with other recent estimates. For a closed universe (Ωm + ΩΛ = 1), we obtain Ωm = 0.13 ± 0.07.

We show how estimates of parameters characterizing inflation-based theories of structure formation localized over the past year when large scale structure (LSS) information from galaxy and cluster surveys was combined with the rapidly developing cosmic microwave background (CMB) data, especially from the recent Boomerang and Maxima balloon experiments. All current CMB data plus a relatively weak prior probability on the Hubble constant, age and LSS points to little mean curvature (Ωtot = 1.08±0.06) and nearly scale invariant initial fluctuations (ns = 1.03±0.08), both predictions of (non-baroque) inflation theory. We emphasize the role that degeneracy among parameters in the Lpk = 212 ± 7 position of the (first acoustic) peak plays in defining the Ωtot range upon marginalization over other variables. Though the CDM density is in the expected range (Ωcdmh2 = 0.17 ± 0.02), the baryon density Ωbh2 = 0.030 ± 0.005 is somewhat above the independent 0.019 ± 0.002 nucleosynthesis estimates. CMB+LSS gives independent evidence for dark energy (ΩΛ = 0.66 ± 0.06) at the same level as from supernova (SN1) observations, with a phenomenological quintessence equation of state limited by SN1+CMB+LSS to wQ < −0.7 cf. the wQ=−1 cosmological constant case.

I present a series of diagrams which illustrate why the cosmic microwave background (CMB) data favor certain values for the cosmological parameters. Various methods to extract these parameters from CMB and non-CMB observations are forming an ever-tightening network of interlocking constraints. I review the increasingly precise constraints in the Ωm - ΩΛ plane and show why more cosmologists now prefer ΛCDM cosmologies to any other leading model.

We compare and combine likelihood functions of the cosmological parameters Ωm, h and σ8 from the CMB, type Ia supernovae and from probes of large scale structure. We include the recent results from the CMB experiments BOOMERANG and MAXIMA-1. Our analysis assumes a flat ACDM cosmology with a scale-invariant adiabatic initial power spectrum. First we consider three data sets that directly probe the mass in the Universe, without the need to relate the galaxy distribution to the underlying mass via a “biasing” relation: peculiar velocities, CMB and supernovae. We assume a baryonic fraction as inferred from Big-Bang Nucleosynthesis and find that all three data sets agree well, overlapping significantly at the 2σ level. This therefore justifies a joint analysis, in which we find a joint best fit point and 95% confidence limits of Ωm = 0.28 (0.17, 0.39), h = 0.74 (0.64, 0.86), and σ8 = 1.17 (0.98,1.37). Secondly we extend our earlier work on combining CMB, supernovae, cluster number counts, IRAS galaxy redshift survey data to include BOOMERANG and MAXIMA-1 data and to allow a free Ωbh2. We find that, given our assumption of a scale invariant initial power spectrum (n = 1), we obtain the robust result of Ωbh2 = 0.031 ± 0.03, which is dominated by the CMB constraint.

We generalise the procedure for joint estimation of cosmological parameters to allow freedom in the relative weights of various probes. This is done by including in the joint Likelihood function a set of ‘Hyper-Parameters’, which are dealt with using Bayesian considerations. The resulting algorithm is simple to implement. We illustrate the method by estimating the Hubble constant H0 from the recent Cosmic Microwave Background experiments Boomerang and Maxima. For an assumed flat Λ-CDM model with fixed parameters (n = 1, Ωm = 1 - Δ = 0.3, Ωbh2 = 0.03, Qrms = 18μK) we solve for a single parameter, H0 = 79 ± 4 km/sec/Mpc (95 % CL, random errors only), slightly higher but still consistent with recent results from Cepheids. We discuss how the ‘Hyper-Parameters’ approach can be generalised for a combination of cosmic probes, and for other priors on the Hyper-Parameters.

Estimates of the curvature parameters Ω0 (density parameter) and Δ0 (cosmological constant) can be made geometrically by use of either a standard candle or a standard ruler. Just as supernovae of Type Ia appear to provide a good empirical standard candle, it now appears observationally justified to use the peak in the power spectrum of density perturbations at L ≍ 130±10h-1 Mpc as an empirical standard rod. It will be shown that voids of this size are traced by quasars in a homogeneous catalogue near the South Galactic Pole at z ˜ 2 and that the large scale structure peak of the catalogue constrains the value of Ω0 to 0.1 < Ω0 < 0.45 (68% confidence), independently of Δ0. Combination with the supernovae Ia data is sufficient to show that the observable Universe is almost flat. In other words, the combination of a standard ruler and a standard candle detected in two presently available data sets is sufficient to show that the Universe is nearly flat, independently of any microwave background data or any other data analyses.

Prospects for future satellite missions, operating in the FIR-mm wavelength region, to study the polarisation of the cosmic background radiation (CBR) and to carry out imaging and spectroscopy of high-redshift galaxies, are discussed. Full characterisation of the CBR polarisation offers the possibility of determining the energy scale of inflation and constraining the form of the inflaton potential. Current technology in FIR imaging and spectroscopy falls well short of matching capabilities in the optical/UV and the mm regions. Filling this gap is important to allow detailed examination of the physics and evolution of high-redshift galaxies, and will be possible with future FIR observatories which are now being studied.

We review the use of the X-ray background (XRB) as a cosmological tool with emphasis on three techniques: multipole analysis, autocorrelation functions and excess fluctuations. Although these methods of analysis of XRB fluctuations, and in particular the excess fluctuations method, are quite sensitive to cosmological parameters, the poor knowledge of a possibly redshift dependent bias parameter for the sources that dominate the X-ray background prevents the derivation of firm conclusions at present. Conversely, knowledge of the cosmological parameters could be used together with XRB fluctuations to assess the clustering properties of AGN as the dominant XRB sources.

The goal of the Sky Polarisation Observatory (SPOrt) Program is the measurement of the sky linearly polarised emission in the 22-90 GHz frequency range from the International Space Station (2003-2004). The instrument configuration together with most relevant ground support activities are presented. In particular, the development of hardware solutions for high sensitive polarimetric measurements has been addressed by the SPOrt team to match the experiment requirements.

This meeting has covered a broad agenda. This contribution to the concluding session offers comments on some current controversies, and on the prospects for cosmology in the coming decade.

I review the reason for considering the prime purpose of the program of measurements of the fundamental parameters of cosmology to be the tests of cosmological models. I comment on the philosophy by which we are approaching this goal, offer an assessment of where we stand, and present some thoughts on where the tests may be headed.

A recent comprehensive photometric survey of 45 low-z X-ray selected Abell clusters (López-Cruz 1997) has measured significant variations in the faint end slope of the luminosity function (LF). This result indicates that dwarf galaxies (dGs) comprise a different fraction of the cluster population as a function cluster environment. Clusters having a central “cD-like” galaxy have a flatter faint end slope than non-cD clusters. Also, cD clusters were found to have a dwarf-to-giant ratio (D/ G) which was smaller than non-cD clusters. López-Cruz et al. (1997) has suggested that the light contained in cD envelopes can be accounted for by assuming that it is produced from stars that originally formed dGs. In this simple model, the D/ G would be expected to increase with radial distance from the cluster centre due to the decrease in the disruptive forces.

We apply gravitational lensing statistics to: (1) place a limit on the cosmological constant (ΩΛ); (2) place a limit on the average red-shift (< z >) of gamma-ray bursters (GRBs); (3) investigate models of galaxy evolution to see how compatible these models are with lensing statistics. We also point out the sources of uncertainty in lensing statistics, leading to uncertainty in the results.

The recently completed I-band SBF Survey of Galaxy Distances contains about 300 galaxy distances within cz ≲ 4000 km/s. These data allow for good constraints on the local mass density and velocity fields. The mass density parameter βI ≡ Ω0.6/bI, where bI is the biasing factor of the IRAS redshift survey galaxies, is found to be βI ≍ 0.45.

We present radial velocities for 144 globular clusters (GCs) around the Virgo gE NGC 4472 (M49), and ages and metallicities for 131 GCs. We confirm our earlier finding that the metal-poor GCs have a significantly higher velocity dispersion than the metal-rich GCs, and we find little or no rotation in the metal-rich GCs. The velocity dispersion profile is consistent with isotropic GC orbits and the mass distribution inferred from X-ray data. Our sample of GCs spans a metallicity range of −1.6 ≤ [Fe/H] ≤ 0 dex. The metal-poor and metal-rich GCs are coeval within the errors, and all GCs older than 6 Gyr at 95% confidence.

To exploit gravitational lensing for cosmology large, reliable and statistically complete surveys are required. With the Cosmic Lens All-Sky Survey (CLASS) we have set out to achieve these goals. We pre-select targets to be flat spectrum radio sources and map every source with the VLA at 200mas resolution. Candidates having multiple compact components with flux density ratios ≤10:1 and separation in the range 0.3 to 15 arcsec are followed up with high resolution MERLIN and VLBA observations, eliminating those candidates which do not match strictly defined surface brightness and morphological criteria. A complete sample of 11685 sources have been surveyed and nineteen lens systems have been found.

Compton scattering of photons from ionised gas in galaxy clusters along the line of sight leaves an imprint in the polarization of the cosmic microwave background. We investigate this process taking account of the effects of relativistic electron velocity dispersion and primordial anisotropy on the frequency spectrum of the generated polarization. We also discuss the prospects of detecting such effects with the Planck survey.

Observations of the Sunyaev-Zeldovich (S-Z) effect offer the possibility of both investigating evolution of clusters and of determining cosmological parameters when combined with X-ray observations. We describe a dedicated instrument (MITO) consisting of a 2.6-m in diameter telescope operating at 3500 m a.s.l. in the 2.1, 1.4, 1.1 and 0.8 mm channels with ˜ 10% bandwidths. Here we briefly report the results of MITO measurements towards the Coma cluster.

Subsamples of galaxies with different morphological types have been sorted out from Stromlo-APM redshift survey. Two-point correlation function for each subsample has been calculated. The two-point correlation functions for all subsamples show very large scale fluctuation. We show that the two-point correlation function with fluctuation could be fitted by a modified power spectrum with power excess at wave number comparable to the scale of the fluctuation.

An analysis of primordial nucleosynthesis is made in the perspective of transition in the early universe from quark gluon to a hadronic phase in a CP violating vacuum. The universe opaque to color, quarks and anti quarks binds into globally colorless hadrons. u, d and s quarks are considered in a sea of degenerate neutrinos for the case of μve = μvμ = μvτ. The nn/np ratio is calculated for a transition temperature ˜ 100 − 200MeV for various values of neutrino degeneracy ξve = μve/T, μve being the chemical potential of electron type neutrino. The limiting value of ξve is found to be 2.38, if the upper bound of fractional helium abundance Yp is 0.26.