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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]

In this paper we present a clustering analysis of quasi-stellar objects (QSOs) as a function of luminosity over the redshift range z= 0.3–2.9. We use a sample of 10 566 QSOs taken from the preliminary data release catalogue of the 2dF QSO Redshift Survey (2QZ). We analyse QSO clustering as a function of apparent magnitude. The strong luminosity evolution of QSOs means that this is approximately equivalent to analysing the data as a function of absolute magnitude relative to M* over the redshift range that the 2QZ probes. Over the relatively narrow range in apparent magnitude of the 2QZ we find no significant (>2σ) variation in the strength of clustering, however, there is marginal evidence for QSOs with brighter apparent magnitudes having a stronger clustering amplitude. QSOs with 18.25 < b[sub J]≤ 19.80 show a correlation scalelength s[sub 0]= 5.50 ± 0.79h[sup -1] Mpc in an Einstein–de Sitter (EdS) universe and s[sub 0]= 8.37 ± 1.17h[sup -1] Mpc in a universe with Ω[sub 0]= 0.3 and λ[sub 0]= 0.7 (Λ), while the best-fitting values for the full magnitude interval (18.25 < b[sub J]≤ 20.85) over the same spatial scales are s[sub 0]= 4.29[sup +0.30][sub -0.29]h[sup -1] Mpc (EdS) and s[sub 0]= 6.35[sup +0.45][sub -0.44]h[sup -1] Mpc (Λ). We can therefore determine that the bias of the brightest subsample is a factor 1.22 ± 0.15 (EdS) or 1.24 ± 0.15 (Λ) larger than that of the full data set. An increase in clustering with luminosity, if confirmed, would be in qualitative agreement with models in which the luminosity of a QSO is correlated to the mass of the dark halo in which it resides, implying that the mass of the host plays at least some part in determining the formation of a QSO and evolution. These models predict that the clustering in brighter QSO data sets, such as the Sloan Digital Sky Survey QSO sample or the bright extension of the 2QZ, should show a higher clustering amplitude than the 2QZ. [ABSTRACT FROM AUTHOR]

We have optically identified a sample of 56 featureless continuum objects without significant proper motion from the 2dF quasi-stellar object (QSO) redshift survey (2QZ). The steep number–magnitude relation of the sample, n(b[sub J]) ∝ 10[sup 0.7b[sub J]], is similar to that derived for QSOs in the 2QZ and inconsistent with any population of Galactic objects. Follow-up high-resolution, high signal-to-noise spectroscopy of five randomly selected objects confirms the featureless nature of these sources. Assuming the objects in the sample to be largely featureless active galactic nuclei (AGN), and using the QSO evolution model derived for the 2QZ, we predict the median redshift of the sample to be z= 1.1. This model also reproduces the observed number–magnitude relation of the sample using a renormalization of the QSO luminosity function, O[sup *]=O[sup *][sub QSO]/66 ≃ 1.65 x 10[sup –10] mag[sup –1] MPC[sup –3]. Only ∼20 per cent of the objects have a radio flux density of S[sub 1.4] > 3 mJy, and further Very Large Array observations at 8.4 GHz place a 5σ limit of S[sub 8.4] < 0.2 mJy on the bulk of the sample. We postulate that these objects could form a population of radio-weak AGN with weak or absent emission lines, whose optical spectra are indistinguishable from those of BL Lac objects. [ABSTRACT FROM AUTHOR]

We present a power spectrum analysis of the 10k catalogue from the 2dF QSO Redshift Survey. Although the Survey currently has a patchy angular selection function, we use the Virgo Consortium's Hubble Volume simulation to demonstrate that we are able to make a useful first measurement of the power spectrum over a wide range of scales. We compare the redshift-space power spectra of QSOs with those measured for galaxies and Abell clusters at low redshift and find that they show similar shapes in their overlap range, , with . The amplitude of the QSO power spectrum at is almost comparable to that of galaxies at the present day if and (the Λ cosmology), and a factor of ≈ 3 lower if (the EdS cosmology) is assumed. The amplitude of the QSO power spectrum is a factor of ≈ 10 lower than that measured for Abell clusters at the present day. At larger scales, the QSO power spectra continue to rise robustly to ≈ 400 h[sup -1] Mpc, implying more power at large scales than in the APM galaxy power spectrum measured by Baugh & Efstathiou. We split the QSO sample into two redshift bins and find little evolution in the amplitude of the power spectrum, consistent with the result for the QSO correlation function. In models with this represents evidence for a QSO-mass bias that evolves as a function of time. We compare the QSO power spectra with cold dark matter (CDM) models to obtain a constraint on the shape parameter, Γ. For two choices of cosmology , and , , we find that the best-fitting model has . In addition, we have shown that a power spectrum analysis of the Hubble Volume ΛCDM mock QSO catalogues with as input produces a result that is statistically consistent with the data. The analysis of the mock catalogues also indicates that the above results for Γ are unlikely to be dominated by systematic effects, owing to the current catalogue window. We conclude that the form of the QSO power spectrum shows large-scale power significantly in excess of the standard CDM prediction, similar to that seen in local galaxy surveys at intermediate scales. [ABSTRACT FROM AUTHOR]

Investigates the 2dF quasars (QSO) redshift survey in the power spectrum. Comparison of clusters on the line of sight; Model on the effects of peculiar velocities and bulk motions in redshift space and geometric distortions; Estimation of the cosmological constant.

Analyzes the ROSAT and ASCA spectra of active galactic nuclei (AGN) quasi-stellar objects (QSO). Association of AGN with normal blue QSO; Calculation of power law of ASCA band; Observation of concave spectra of QSO.

We present an analysis of X-ray variability in a flux-limited sample of quasi-stellar objects (QSOs). Selected from our deep ROSAT survey, these QSOs span a wide range in redshift (0.10.5) do not show the anticorrelation with luminosity seen in local AGN. We speculate on the implications of these results for physical models of AGN and their evolution. Finally, we find evidence for X-ray variability in an object classified as a narrow-emission-line galaxy, suggesting the presence of an AGN. [ABSTRACT FROM AUTHOR]

Using a sample of 165 X-ray selected QSOs from seven deep ROSAT fields f[sub (0.5–2.0 keV)]&gsim;4×10[sup -15] erg cm[sup -2] s[sup -1]], we investigate the X-ray spectral properties of an ‘average’ radio-quiet broad-line QSO as a function of redshift. The QSO stacked spectra, in the observer’s 0.1–2 keV band, in five redshift bins over the range 0.1&les;z&les;3.2, apparently harden from an equivalent photon index of Γ∼2.6 at z=0.4 to Γ∼2.1 at z=2.4 as seen in other QSO samples. In contrast, the spectra in the 0.5–2 keV band show no significant variation in spectral index with redshift. This suggests the presence of a spectral upturn at low energies (<0.5 keV). Indeed, while at high redshifts (z>1.0) the single power-law model gives an acceptable fit to the data over the full energy band, at lower redshifts the spectra need a second component at low energies, a ‘soft excess’. Inclusion of a simple model for the soft excess, i.e. a blackbody component (kT∼100 eV), results in a significant improvement to the model fit, and yields power-law slopes of Γ∼1.8–1.9, for all redshift bins. This power law is not inconsistent, within the error bars, with those of nearby active galactic nuclei (AGN) in the 2–10 keV band, suggesting that the same intrinsic power-law slope may continue from 10 keV down to below ∼0.5 keV. We caution that there is a possibility that the spectral upturn observed may not represent a real physical component, but could be caused by co-adding spectra with a large dispersion in spectral indices. Regardless of the origin of the soft excess, the average QSO spectrum has important consequences for the origin of the X-ray background: the average spectra of a typical, faint, high-redshift QSO are significantly steeper than the spectrum of the X-ray background, extending the spectral paradox into the soft 0.1–2 keV X-ray band. [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]