We report measurements of the mass density, Ω M , and cosmological-constant energy density, Ω Λ , of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these supernovae, at redshifts between 0.18 and 0.83, are fit jointly with a set of supernovae from the Calán/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All supernova peak magnitudes are standardized using a SN Ia lightcurve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8 Ω M − 0.6 Ω Λ ≈ −0.2 ± 0.1 in the region of interest (Ω M ∼ < 1.5). For a flat (Ω M + Ω Λ = 1) cosmology we find Ω flat M = 0.28 +0.09 −0.08 (1σ statistical) +0.05 −0.04 (identified systematics). The data are strongly inconsistent with a Λ = 0 flat cosmology, the simplest inflationary universe model. An open, Λ = 0 cosmology also does not fit the data well: the data indicate that the cosmological constant is non-zero and positive, with a confidence of P(Λ > 0) = 99%, including the identified systematic uncertainties. The best-fit age of the universe relative to the Hubble time is t flat 0 = 14.9 +1.4 −1.1 (0.63/h) Gyr for a flat cosmology. The size of our sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We find no significant differences in either the host reddening distribution or Malmquist bias between the low-redshift Calán/Tololo sample and our high-redshift sample. Excluding those few supernovae which are outliers in color excess or fit residual does not significantly change the results. The conclusions are also robust whether or not a width-luminosity relation is used to standardize the supernova peak magnitudes. We discuss, and constrain where possible, hypothetical alternatives to a cosmological constant.

A B S T R A C TThe 2dF Galaxy Redshift Survey (2dFGRS) is designed to measure redshifts for approximately 250 000 galaxies. This paper describes the survey design, the spectroscopic observations, the redshift measurements and the survey data base. The 2dFGRS uses the 2dF multifibre spectrograph on the Anglo-Australian Telescope, which is capable of observing 400 objects simultaneously over a 28 diameter field. The source catalogue for the survey is a revised and extended version of the APM galaxy catalogue, and the targets are galaxies with extinction-corrected magnitudes brighter than b J ¼ 19:45. The main survey regions are two declination strips, one in the southern Galactic hemisphere spanning 808 Â 158 around the SGP, and the other in the northern Galactic hemisphere spanning 758 Â 108 along the celestial equator; in addition, there are 99 fields spread over the southern Galactic cap. The survey covers 2000 deg 2 and has a median depth of z ¼ 0:11. Adaptive tiling is used to give a highly uniform sampling rate of 93 per cent over the whole survey region. Redshifts are measured from spectra covering 3600-8000A at a two-pixel resolution of 9.0 Å and a median S/N of 13 pixel 21 . All redshift identifications are visually checked and assigned a quality parameter Q in the range 1-5; Q $ 3 redshifts are 98.4 per cent reliable and have an rms uncertainty of 85 km s 21 . The overall redshift completeness for Q $ 3 redshifts is 91.8 per cent, but this varies with magnitude from 99 per cent for the brightest galaxies to 90 per cent for objects at the survey limit. The 2dFGRS data base is available on the World Wide Web at http://www. mso.anu.edu.au/2dFGRS.

Using traditional morphological classifications of galaxies in 10 intermediate-redshift (z ∼ 0.5) clusters observed with WFPC-2 on the Hubble Space Telescope, we derive relations between morphology and local galaxy density similar to that found by Dressler for low-redshift clusters. Taken collectively, the "morphology-density" relationship, T − Σ , for these more distant, presumably younger clusters is qualitatively similar to that found for the local sample, but a detailed comparison shows two substantial differences: (1) For the clusters in our sample, the T − Σ relation is strong in centrally concentrated "regular" clusters, those with a strong correlation of radius and surface density, but nearly absent for clusters that are less concentrated and irregular, in contrast to the situation for low redshift clusters where a strong relation has been found for both. (2) In every cluster the fraction of elliptical galaxies is as large or larger than in low-redshift clusters, but the S0 fraction is 2-3 times smaller, with a proportional increase of the spiral fraction.Straightforward, though probably not unique, interpretations of these observations are (1) morphological segregation proceeds hierarchically, affecting richer, denser groups of galaxies earlier, and (2) the formation of elliptical galaxies predates the formation of rich clusters, and occurs instead in the loose-group phase or even earlier, but S0's are generated in large numbers only after cluster virialization.

We present a detailed analysis of the spectroscopic catalog of galaxies in 10 distant clusters from Dressler et al. (1999, D99). We investigate the nature of the different spectral classes defined by D99 including star forming, post-starburst and passive galaxy populations, and reproduce their basic properties using our spectral synthesis model. We attempt to identify the evolutionary pathways between the various spectral classes in order to search for the progenitors of the numerous post-starburst galaxies. The comparison of the spectra of the distant galaxy populations with samples drawn from the local Universe leads us to identify a significant population of dust-enshrouded starburst galaxies, showing both strong Balmer absorption and relatively modest [OII] emission, that we believe are the most likely progenitors of the post-starburst population. We present the differences between the field and cluster galaxies at z=0.4-0.5. We then compare the spectral and the morphological properties of the distant cluster galaxies, exploring the connection between the quenching of star formation inferred from the spectra and the strong evolution of the S0 population discussed by Dressler et al. (1997). We conclude that either two different timescales and/or two different physical processes are responsible for the spectral and the morphological transformation.Comment: 15 pages, LaTeX, 10 figures, uses emulateapj.sty, ApJ in pres

We present a power-spectrum analysis of the final 2dF Galaxy Redshift Survey (2dFGRS), employing a direct Fourier method. The sample used comprises 221 414 galaxies with measured redshifts. We investigate in detail the modelling of the sample selection, improving on previous treatments in a number of respects. A new angular mask is derived, based on revisions to the photometric calibration. The redshift selection function is determined by dividing the survey according to rest-frame colour, and deducing a self-consistent treatment of k-corrections and evolution for each population. The covariance matrix for the power-spectrum estimates is determined using two different approaches to the construction of mock surveys, which are used to demonstrate that the input cosmological model can be correctly recovered. We discuss in detail the possible differences between the galaxy and mass power spectra, and treat these using simulations, analytic models and a hybrid empirical approach. Based on these investigations, we are confident that the 2dFGRS power spectrum can be used to infer the matter content of the universe. On large scales, our estimated power spectrum shows evidence for the 'baryon oscillations' that are predicted in cold dark matter (CDM) models. Fitting to a CDM model, assuming a primordial n s = 1 spectrum, h = 0.72 and negligible neutrino mass, the preferred parameters are m h = 0.168 ± 0.016 and a baryon fraction b / m = 0.185 ± 0.046 (1σ errors). The value of m h is 1σ lower than the 0.20 ± 0.03 in our 2001 analysis of the partially E-mail: shaun.cole@durham.ac.uk C 2005 RAS 506 S. Cole et al.complete 2dFGRS. This shift is largely due to the signal from the newly sampled regions of space, rather than the refinements in the treatment of observational selection. This analysis therefore implies a density significantly below the standard m = 0.3: in combination with cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy Probe (WMAP), we infer m = 0.231 ± 0.021.