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We report on measurements of the cosmological constant, Λ, and the redshift space distortion parameter , based on an analysis of the quasi-stellar object (QSO) power spectrum parallel and perpendicular to the observer's line of sight, , from the final catalogue of the Two-Degree Field (2dF) QSO Redshift Survey. We derive a joint constraint from the geometric and redshift-space distortions in the power spectrum. By combining this result with a second constraint based on mass clustering evolution, we break this degeneracy and obtain strong constraints on both parameters. Assuming a flat cosmology and a Λ cosmology r( z) function to convert from redshift into comoving distance, we find best-fitting values of and . Assuming instead an Einstein–de Sitter cosmology r( z) we find that the best-fitting model obtained, with and , is consistent with the Λ r( z) results, and inconsistent with a flat cosmology at over 95 per cent confidence. [ABSTRACT FROM AUTHOR]

We report the possible discovery of multiple gravitationally lensed images of quasi-stellar objects (QSOs) with angular separations on arcmin scales. The QSOs were selected from the completed 2dF QSO Survey as having redshifts and optical colours which are statistically consistent. In this paper we present higher-quality optical spectra of the candidates and discuss the likelihood that they genuinely are systems lensed by massive clusters of galaxies. From a comparison of the spectra it appears that up to six pairs of QSOs may be lensed multiple images, although the true number may be less than that and further observations should be undertaken to amass more evidence and to detect the lensing clusters. Two of the candidates may be associated with low-redshift clusters of galaxies. [ABSTRACT FROM AUTHOR]

This paper explores the X-ray properties of normal galaxies using a shallow (2-10 ks) XMM-Newton survey covering an area of &ap;1.5 deg[SUP2]. The X-ray survey overlaps with the 2dF Galaxy Redshift Survey. Compared with previous studies this has the advantage that high- quality spectra and spectral classifications (early-, late-type) exist for all galaxies to b[SUBj] = 19.4. Moreover, sources with optical spectra revealing powerful active galactic nuclei (AGN) can easily be discarded from the normal galaxy sample used here. In particular, we present stacking analysis results for about 200 galaxies from the 2dF Galaxy Redshift Survey at a mean redshift of z &ap; 0.1. We detect a strong signal for the whole sample (&ap;6σ) in the soft 0.5-2 keV band corresponding to a flux of &ap;7 × 10[SUP6] erg s[SUP-1] cm[SUP2] and a luminosity of &ap;2 × 10[SUP40] erg s[SUP-1]. A statistically significant signal is also detected for both the early and late galaxy subsamples with X-ray luminosities of &ap;3 × 10[SUP40] and &ap;5 × 10[SUP39] erg s[SUP-1], respectively. In contrast, no signal is detected in the hard 2-8 keV band for any of the above samples. The mean L[SUBX]/L[SUBB] ratio of the spiral galaxy sample is found to be consistent with both local (<100 Mpc) and distant (z &ap; 1) samples (after accounting for differences in L[SUBB]), suggesting little or no evolution of the X-ray emission mechanisms relative to the optical. The 0.5-2 keV X-ray background (XRB) contribution of the spiral galaxy subsample at z &ap; 0.1 is estimated to be 0.4 per cent, in broad agreement with the XRB fractions estimated in previous studies. Assuming that star-forming galaxies evolve with redshift as (1 + z)[SUPk], the present data combined with previous studies suggest k < 3. [ABSTRACT FROM AUTHOR]

We report on measurements of the cosmological constant, Λ, and the redshift space distortion parameter , based on an analysis of the quasi-stellar object (QSO) power spectrum parallel and perpendicular to the observer's line of sight, , from the final catalogue of the Two-Degree Field (2dF) QSO Redshift Survey. We derive a joint constraint from the geometric and redshift-space distortions in the power spectrum. By combining this result with a second constraint based on mass clustering evolution, we break this degeneracy and obtain strong constraints on both parameters. Assuming a flat cosmology and a Λ cosmology r( z) function to convert from redshift into comoving distance, we find best-fitting values of and . Assuming instead an Einstein–de Sitter cosmology r( z) we find that the best-fitting model obtained, with and , is consistent with the Λ r( z) results, and inconsistent with a flat cosmology at over 95 per cent confidence. [ABSTRACT FROM AUTHOR]