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This presentation reports on first evidence for a low-mass-density/positive-cosmological-constant universe that will expand forever, based on observations of a set of 40 high-redshift supernovae. The experimental strategy, data sets, and analysis techniques are described.

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]

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 describe a method from which cosmology may be constrained from the 2dF QSO Redshift Survey (2QZ). By comparing clustering properties parallel and perpendicular to the line of sight and by modelling the effects of redshift-space distortions, we are able to study geometric distortions in the clustering pattern which occur if a wrong cosmology is assumed when translating redshifts into comoving distances. Alcock & Paczyński pointed out that this technique was particularly sensitive as a test for a large cosmological constant, Λ. Using mock 2QZ catalogues, drawn from the Hubble Volume simulation, we find that there is a degeneracy between the geometric distortions and the redshift-space distortions, parametrized by β[sub QSO](z), that makes it difficult to obtain an unambiguous estimate of Ω[sub m](0), the matter density parameter, from the geometric tests alone. This is in agreement with the conclusions of Ballinger et al. However, we demonstrate that by combining results from the above geometric test with those from a second test based on the evolution of the QSO clustering amplitude, which has a different dependence on β[sub QSO](z) and Ω[sub m](0), we are able to place stronger constraints on cosmology. In the analysis of the Hubble Volume mock catalogues we find that we are able to break the degeneracy between Ω[sub m](0) and β[sub QSO](z) and that independent constraints to ±20 per cent (1σ) accuracy on Ω[sub m](0) and ±10 per cent (1σ) accuracy on β[sub QSO](z) should be possible in the full 2QZ survey. Finally we apply the method to the 10k catalogue of 2QZ QSOs. The smaller number of QSOs and the current status of the survey mean that a strong result on cosmology is not possible but we do constrain β[sub QSO](z) to 0.35±0.2. By combining this constraint with the further constraint available from the amplitude of QSO clustering, we find tentative evidence favouring a model with non-zero Ω[sub Λ](0), although an Ω[sub m](0)=1 model provides only a marginally less good fit. A model with Ω[sub Λ](0)=1 is ruled out. The results are in agreement with those found by Outram et al. using a similar analysis in Fourier space. [ABSTRACT FROM AUTHOR]

Focuses on the availability of the geometrical test for cosmological constant upon the completion of 2dF QSO Redshift Survey. Effects of peculiar velocities and bulk motions in redshift space; Shapes of the redshift-space and geometric distortions; Excess of ultraviolet rays.

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.

In this paper we present a clustering analysis of QSOs over the redshift range z=0.3–2.9. We use a sample of 10 558 QSOs taken from the preliminary data release catalogue of the 2dF QSO Redshift Survey (2QZ). The two-point redshift-space correlation function of QSOs, ξ[sub Q](s), is shown to follow a power law on scales s≃1–35 h[sup -1] Mpc. Fitting a power law of the form ξ[sub Q](s)=(s/s[sub 0])[sup -γ] to the QSO clustering averaged over the redshift interval 0.399 per cent confidence level). A redshift-dependent bias is required to reconcile QSO clustering observations with theory. A simple biasing model, in which QSOs have cosmologically long lifetimes (or alternatively form in peaks above a constant threshold in the density field), is acceptable in an Ω[sub 0]=1 cosmology, but is only marginally acceptable if Ω[sub 0]=0.3 and λ[sub 0]=0.7. Biasing models in which QSOs are assumed to form over a range in redshift, based on the Press–Schechter formalism, are consistent with QSO clustering evolution for a minimum halo mass of ∼10[sup 12] and ∼10[sup 13] M[sub ⊙] in an Einstein–de Sitter and cosmological constant dominated universe, respectively. However, until an accurate, physically motivated model of QSO formation and evolution is developed, we should be cautious in interpreting the fits to. [ABSTRACT FROM AUTHOR]

We present a determination of the optical luminosity function of quasi-stellar objects (QSOs) and its cosmological evolution with redshift for a sample of over 6000 QSOs identified primarily from the first observations of the 2dF QSO Redshift Survey (2QZ). For QSOs with -26< MB< -23 and 0.35< z< 2.3, we find that pure luminosity evolution (PLE) models provide an acceptable fit to the observed redshift dependence of the luminosity function (LF). The LF is best fitted by a two-power-law function of the form Φ(LB ∝ [(LB/L*B)α + (LB/L*B)β]-1 Exponential luminosity evolution models, both as a function of look-back time, L*B(z) = L*B(0)ek1τ] and as a general second-order polynomial, L*B(z) ∝ 10k1z+k2z2] were found to provide acceptable fits to the data set comprising the 2QZ and the Large Bright Quasar Survey. Exponential evolution with look-back time is preferred for q0=0.05, while the polynomial evolution model is preferred for q0=0.5. The shape and evolution of the LF at low redshifts (z<0.5) and/or high luminosities, not currently well sampled by the 2QZ survey, may show departures from pure luminosity evolution, but the results presented here show that, over a significant range of redshift, PLE is a good description of QSO evolution. [ABSTRACT FROM AUTHOR]

We present measurements of the angular correlation function of galaxies selected from a B[sub J]∼23.5 multicolour survey of two 5°×5° fields located at high galactic latitudes. The galaxy catalogue of ∼4×10[sup 5] galaxies is comparable in size to catalogues used to determine the galaxy correlation function at low redshift. Measurements of the z∼0.4 correlation function at large angular scales show no evidence for a break from a power law, although our results are not inconsistent with a break at &gsim;15 h[sup -1] Mpc. Despite the large fields-of-view, there are large discrepancies between the measurements of the correlation function in each field, possibly caused by dwarf galaxies within z∼0.11 clusters near the South Galactic Pole. Colour selection is used to study the clustering of galaxies from z∼0 to z∼0.4. The galaxy correlation function is found to depend strongly on colour, with red galaxies more strongly clustered than blue galaxies by a factor of &gsim;5 at small scales. The slope of the correlation function is also found to vary with colour, with γ∼1.8 for red galaxies and γ∼1.5 for blue galaxies. The clustering of red galaxies is consistently strong over the entire magnitude range studied, although there are large variations between the two fields. The clustering of blue galaxies is extremely weak over the observed magnitude range, with clustering consistent with r[sub 0]∼2 h[sup -1] Mpc. This is weaker than the clustering of late-type galaxies in the local Universe, and suggests that galaxy clustering is more strongly correlated with colour than morphology. This may also be the first detection of a substantial low-redshift galaxy population with clustering properties similar to faint blue galaxies. [ABSTRACT FROM AUTHOR]

We report on the initial results of a comprehensive Hubble Space Telescope (HST) snapshot imaging survey of 76 low-redshift (z<0.15) X-ray-selected active galactic nuclei (AGN) in the Einstein Extended Medium Sensitivity Survey. This survey is expected to show no bias with respect to host galaxy types, and so is arguably one of the best available samples with HST imaging for the study of the host galaxies. The HST observations in the F814W band are complemented by deeper ground-based observations in the B and R bands for most AGN. The absolute magnitudes for AGN in this sample lie in the range -24

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]

Supernova 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supernovae and probably the first supernova associated with a γ-ray burst. In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the Anglo-Australian Telescope, the UK Schmidt Telescope and the Siding Springs Observatories 2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94 d after V-band maximum in comparison with well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event. Though the early spectra differ greatly from observations of classical Ic supernovae (SNe), we find that the evolution from the photospheric to nebular phases is slow but otherwise typical. The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta. We find that by day 19, the absorption line minima blueshifts are 10–50 per cent higher than other SNe and on day 94 emission lines are 45 per cent broader, as expected if the progenitor had a massive envelope. However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that an additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope. [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]

An angular correlation of low significance (2σ) is observed between 0.30.5 QSOs. After converting to an excess of galaxies physically associated with the QSO, this lack of strong correlation is shown to be consistent with the clustering of normal galaxies at the same moderate redshifts. Combined with previous observations, these results imply that the environments of radio-quiet QSOs do not undergo significant evolution with respect to the galaxy population over a wide range of redshifts (0

Determines the nature of infrared and X-ray observations of an obscured high-redshift quasi-stellar objects. Discrepancy in the absorbing column; Evidence of an active galactic nucleus; Presentation of high ionization lines.

We present results from a continuing campaign to secure deep multi-colour CCD sequences for photometric calibration in UK Schmidt fields with galactic latitudes |b|>50°. In this paper we present UBVR photometry in 12 fields and BR photometry in a further 14 fields observed within UK Schmidt survey fields centred at δ=-30°. Photometric errors are at the 0.05 level at 20.2, 21, 20.5 and 20 mag for UBVR sequences respectively. Our observations were carried out with the 0.9-m telescope at the Cerro-Tololo Inter-American Observatory. These data are not intended for use as highly accurate individual photometric standards, but rather for use as sequences, using a large number of stars to calibrate wide-area data such as photographic plates. The data are available electronically at http://icstar5.ph.ic.ac.uk/~scroom/phot/photom.html. [ABSTRACT FROM AUTHOR]

We present the results of an intermediate-resolution (1.5\AA) spectroscopic study of 17 X-ray luminous narrow emission-line galaxies previously identified in the Cambridge-Cambridge {\it ROSAT} Serendipity Survey and the {\it Einstein} Extended Medium Sensitivity Survey. Emission-line ratios reveal that the sample is composed of ten Seyfert and seven starburst galaxies. Measured linewidths for the narrow Hα emission lines lie in the range 170−460kms−1. Five of the objects show clear evidence for asymmetry in the [OIII]λ5007 emission-line profile. Broad Hα emission is detected in six of the Seyfert galaxies, which range in type from Seyfert 1.5 to 2. Broad Hβ emission is only detected in one Seyfert galaxy. The mean full width at half maximum for the broad lines in the Seyfert galaxies is FWHM=3900±1750kms−1. Broad (FWHM=2200±600kms−1) Hα emission is also detected in three of the starburst galaxies, which could originate from stellar winds or supernovae remnants. The mean Balmer decrement for the sample is Hα/Hβ=3, consistent with little or no reddening for the bulk of the sample. There is no evidence for any trend with X-ray luminosity in the ratio of starburst galaxies to Seyfert galaxies. Based on our previous observations, it is therefore likely that both classes of object comprise ∼10per cent of the 2keV X-ray background., Astronomy

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]