N. S. Loaring

The 2dF QSO Redshift Survey – XII. The spectroscopic catalogue and luminosity function

We present the final catalogue of the 2dF QSO Redshift Survey (2QZ), based on Anglo-Australian Telescope 2dF spectroscopic observations of 44 576 colour-selected (ub J r) objects with 18.25 < b J < 20.85 selected from automated plate measurement scans of UK Schmidt Telescope (UKST) photographic plates. The 2QZ comprises 23 338 quasi-stellar objects (QSOs), 12 292 galactic stars (including 2071 white dwarfs) and 4558 compact narrow emission-line galaxies. We obtained a reliable spectroscopic identification for 86 per cent of objects observed with 2dF. We also report on the 6dF QSO Redshift Survey (6QZ), based on UKST 6dF observations of 1564 brighter (16 < b J < 18.25) sources selected from the same photographic input catalogue. In total, we identified 322 QSOs spectroscopically in the 6QZ. The completed 2QZ is, by more than a factor of 50, the largest homogeneous QSO catalogue ever constructed at these faint limits (b J < 20.85) and high QSO surface densities (35 QSOs deg -2 ). As such, it represents an important resource in the study of the Universe at moderate-to-high redshifts. As an example of the results possible with the 2QZ, we also present our most recent analysis of the optical QSO luminosity function and its cosmological evolution with redshift. For a flat, Ω m = 0.3 and Ω A = 0.7, universe, we find that a double power law with luminosity evolution that is exponential in look-back time, τ, of the form L* bJ (z) α e 6.15τ , equivalent to an e-folding time of 2 Gyr, provides an acceptable fit to the redshift dependence of the QSO LF over the range 0.4 < z < 2.1 and M bJ < -22.5. Evolution described by a quadratic in redshift is also an acceptable fit, with L* bJ (z) α 10 1.39 z-0.29z 2 .

The 2dF QSO Redshift Survey — I. The optical luminosity function of quasi-stellar objects

We present a determination of the optical QSO luminosity function 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<M_B<-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. The luminosity function is best fit by a two-power-law function of the form. Exponential luminosity evolution models, both as a function of look-back time, and as a general second-order polynomial with redshift, were found to provide acceptable fits to the dataset comprising the 2QZ and the Large Bright Quasar Survey. Exponential evolution with look-back time is prefered for q_0=0.05, while the polynomial evolution model is prefered for q_0=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 2dF QSO 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.

The 2dF QSO Redshift survey - V. : the 10k catalogue.

We present a catalogue comprising over 10 000 QSOs covering an effective area of 289.6 deg2, based on spectroscopic observations with the 2-degree Field (2dF) instrument at the Anglo-Australian Telescope. This catalogue forms the first release of the 2dF QSO Redshift Survey. QSO candidates with 18.25<bJ<20.85 were obtained from a single homogeneous colour-selected catalogue based on APM measurements of UK Schmidt photographic material. The final catalogue will contain approximately 25 000 QSOs and will be released to the public at the end of 2002, one year after the observational phase is concluded.

The correlation of line strength with luminosity and redshift from composite quasi-stellar object spectra

We have generated a series of composite quasi-stellar object (QSO) spectra using over 22 000 individual low-resolution (∼8- ˚

The 2dF QSO Redshift Survey – IX. A measurement of the luminosity dependence of QSO clustering

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 J ≤ (19.80 show a correlation scalelength s 0 = 5.50 ′ 0.79h - 1 Mpc in an Einstein-de Sitter (EdS) universe and s 0 = 8.37 ′ 1.17h - 1 Mpc in a universe with Ω 0 = 0.3 and λ 0 = 0.7 (A), while the best-fitting values for the full magnitude interval (18.25 < b J ≤ 20.85) over the same spatial scales are so = 4.29 + 0 . 3 0 - 0 . 2 9 h - 1 Mpc (EdS) and so = 6.35 + 0 . 4 5 - 0 . 4 4 h - 1 Mpc (A). We can therefore determine that the bias of the brightest subsample is a factor 1.22 ′ 0.15 (EdS) or 1.24 ′ 0.15 (A) 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.

The evolution of host mass and black hole mass in quasi-stellar objects from the 2dF QSO Redshift Survey

We investigate the relation between the mass of super-massive black holes (MBH) in QSOs and the mass of the dark matter halos hosting them (MDH). We measure the widths of broad emission lines (Mg ii �2798, C iv �1549) from QSO composite spectra as a function of redshift. These widths are then used to determine virial black hole mass estimates. We compare our virial black hole mass estimates to dark matter halo masses for QSO hosts derived by Croom et al. (2005) based on measurements of QSO clustering. This enables us to trace the MBH MDH relation over the redshift range z = 0.5 to 2.5. We calculate the mean zero-point of the MBH MDH relation to be MBH = 10 8.4±0.2 M⊙ for an MDH = 10 12.5 M⊙. These data are then compared with several models connecting MBH and MDH as well as recent hydrodynamical simulations of galaxy evolution. We note that the flux limited nature of QSO samples can cause a Malmquist-type bias in the measured zero-point of the MBH MDH relation. The magnitude of this bias depends on the scatter in the MBH MDH relation, and we reevaluate the zero-point assuming three published values for this scatter. We create a subsample of our data defined by a constant magnitude interval around L ∗ and find (1 + z) 3.3±1.3 evolution in MBH between z � 0.5 and 2.5 for typical, L ∗ QSOs. We also determine the Eddington ratios (L/LEdd) for the same subsample and find no significant evolution: (1 + z) −0.4±1.1 . Taken at face value, our data suggest that a decrease in active black hole mass since z � 2.5 is the driving force behind luminosity evolution of typical, L ∗ , optically selected AGN. However, we note that our data are also consistent with a picture in which reductions in both black hole mass and accretion rate contribute equally to luminosity evolution. In addition we find these evolution results are strongly affected by the virial black hole mass estimators used. Changes to the calibration of these has a significant effect on the evolution results.

The 2dF QSO Redshift Survey – X. Lensing of background QSOs by galaxy groups

We cross-correlate quasi-stellar objects (QSOs) from the 2dF QSO Redshift Survey with groups of galaxies. In the southern region of the 2dF we utilize galaxies from the APM Survey. In the northern strip, galaxies are taken from the recent Sloan Digital Sky Survey Early Data Release. Both galaxy samples are limited to a depth B < 20.5. We use an objective clustering algorithm to detect groups in these galaxy catalogues. A 3a anticorrelation is observed between 2dF QSOs and galaxy groups, confirming the effect found by Boyle, Fong & Shanks in an independent data set. This paucity of faint QSOs around groups cannot be readily attributed to a selection effect and is not due to restrictions on the placement of 2dF fibres. By observing the colours of QSOs on the scales of the anticorrelation, we limit the influence intervening dust in galaxy groups can have on background QSO flux, finding a maximum reddening on the scale of the anticorrelation of E(b j - r) ≤ 0.012 at the 95 per cent level. The small amount of dust inferred from the QSO colours would be insufficient to account for the anticorrelation, supporting the suggestion by Croom & Shanks that the signal is likely to be caused by weak gravitational lensing. The possibility remains that tailored dust models involving grey dust, heavy patches of dust or a combination of dust and lensing, could explain the anticorrelation. Under the assumption that the signal is caused by lensing rather than dust, we measure the average velocity dispersion of a singular isothermal sphere that would cause the anticorrelation, finding a ∼ 1150 km s - 1 . Simple simulations reject σ ∼ 600 km s - 1 at the 5 per cent significance level. We also suppose that the foreground mass distribution consists of dark matter haloes with an Navarro-Frenk-White (NFW) profile and measure the typical mass within 1.5 h - 1 Mpc of the halo centre as M 1 . 5 = 1.2 ′ 0.9 × 10 1 5 h - 1 M O .. Regardless of whether we utilize a singular isothermal sphere or NFW dark matter profile, our simple lensing model favours more mass in groups of galaxies than is accounted for in a universe with density parameter Ω m = 0.3. Detailed simulations and galaxy group redshift information will significantly reduce the current systematic uncertainties in these Ω m estimates. Reducing the remaining statistical uncertainty in this result will require larger QSO and galaxy group surveys.

The 2QZ BL Lac survey

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(bj) oc 10 0 . 7 b 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, Φ* = Φ* Q S O / 6 6 ≃ 1.65 x 10 - 8 mag - 1 Mpc - 3 . Only ∼20 per cent of the objects have a radio flux density of S 1 . 4 > 3 mJy, and further Very Large Array observations at 8.4 GHz place a 5σ limit of S 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.

The 2dF QSO Redshift Survey - IV. The QSO Power Spectrum from the 10k Catalogue

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 func- tion, we use the Virgo Consortiums Hubble Volume simulation to demonstrate that we are able to make a useful first measurement of the power spectrum over more than a decade in scale. We compare the redshift-space power spectra of QSOs to those measured for galaxies and Abell clusters at low redshift and find that they show similar shapes in their overlap range, 50-150h 1 Mpc, with PQSO(k) / k 1.4 . The amplitude of the QSO power spectrum at z � 1.4 is almost comparable to that of galaxies at the present day if m=0.3 and �=0.7 (thecosmology), and a factor of � 3 lower if m=1 (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 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 m �0.1 this represents evidence for a QSO-mass bias that evolves as a function of time. The QSO power spectrum may show a spike feature at � 90h 1 Mpc assuming thecosmology or � 65h 1 Mpc assuming an EdS cosmology. Although the spike appears to reproduce in both the North and South strips and in two independent redshift ranges, its statistical significance is still marginal and more data is needed to test further its reality. We compare the QSO power spectra to CDM models to obtain a constraint on the shape parameter, . For two choices of cosmology ( m=1, �=0 and m=0.3, �=0.7), we find the best fit model has � 0.1 ± 0.1. In addition, we have shown that a power spectrum analysis of the Hubble VolumeCDM mock QSO catalogues with = 0 .17 as input, produces a result which is statistically consistent with the data. The analysis of the mock catalogues also indicates that the above results for are unlikely to be dominated by systematic effects due 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.

The 2dF QSO Redshift Survey — VI. Measuring α and β from redshift-space distortions in the power spectrum

When the 2dF QSO Redshift Survey (2QZ) is complete, a powerful geometric test for the cosmological constant will be available. By comparing the clustering along and across the line of sight and modelling the effects of peculiar velocities and bulk motions in redshift space, geometric distortions, which occur if the wrong cosmology is assumed, can be detected. n n n nIn this paper we investigate the effect of geometric and redshift-space distortions in the power spectrum parallel and perpendicular to the observers line of sight, . Ballinger et al. developed a model to estimate the cosmological constant, Λ, and the important parameter from these distortions. We apply this model to a detailed simulation of the final 25k 2QZ, produced using the Virgo Consortiums huge Hubble Volume N-body ΛCDM (cold dark matter) light-cone simulation. We confirm the conclusions of Ballinger et al.: the shapes of the redshift-space and geometric distortions are very similar, and discriminating between the two to produce a purely geometric constraint on Λ is difficult. When all the uncertainties in measuring for the 2QZ are taken into account, we find that only a joint constraint is possible. n n n nBy combining this result with a second constraint based on mass clustering evolution, however, we can make significant progress. We predict that this method should allow us to constrain β to approximately ±0.1, and Ωm to ±0.25, using the final catalogue. We apply the method to the 2QZ catalogue of 10xa0000 quasars (QSOs) and find that this incomplete catalogue marginally favours a Λ cosmology, obtaining best-fitting values of and . However, Einstein–de Sitter , models are only rejected at the 1.4σ level in the current survey. The rejection of lambda-dominated , models is stronger at ∼2σ.