2dF Quasi-stellar Objects Redshift Survey Research Articles

The Evolution QSOs—The Optical Luminosity Function

Using the data of the 2 Degree Field (2dF) QSO Redshift Survey (2QZ) and the associated 6 Degree Field (6dF) QSO Redshift Survey (6QZ) of the Anglo-Australian Telescope, a study of the Optical Luminosity Function of Quasi Stellar Objects (QSOs) has been made to understand the evolutionary scenario of QSOs. Different models for the QSO evolution are studied. The two-power law model of the optical luminosity function with second order polynomial evolution is found to fit best the observed QSO optical luminosity function. We have also determined an improved evolutionary model which fits better than the second order polynomial evolution model. The best fit parameters for the observed optical luminosity function have been determined using the Levenberg-Marquardt algorithm of non-linear least square fit for a flat universe i.e., ΩΛ + Ωm = 1 and Ho = 70 km·s–1·Mpc–1. The observed slope of the log N － m curve i.e., 1.10 ± 0.01 reveals that there were more QSOs at larger distances (or look back times) than there are locally which, in turn, indicates that the QSOs are evolving. The observed value of V/Vmax> is found to be greater than 0.5 for different values of the cosmological constant which also hints strong evolution of the QSOs.

The 2dF-SDSS LRG and QSO survey: QSO clustering and the L-z degeneracy

We combine the quasi-stellar object (QSO) samples from the 2dF QSO Redshift Survey (2QZ) and the 2dF-Sloan Digital Sky Survey luminous red galaxy (LRG) and QSO Survey (2dF-SDSS LRG and QSO, hereafter 2SLAQ) in order to investigate the clustering of z∼ 1.5 QSOs and measure the correlation function (ξ). The clustering signal in redshift-space and projected along the sky direction is similar to that previously obtained from the 2QZ sample alone. By fitting functional forms for ξ(σ, π), the correlation function measured along and across the line of sight, we find, as expected, that β, the dynamical infall parameter and Ω0m , the cosmological density parameter, are degenerate. However, this degeneracy can be lifted by using linear theory predictions under different cosmological scenarios. Using the combination of the 2QZ and 2SLAQ QSO data, we obtain: βQSO(z= 1.5) = 0.60+0.14−0.11, Ω0m= 0.25+0.09−0.07 which imply a value for the QSO bias, b(z= 1.4) = 1.5 ± 0.2 . The combination of the 2QZ with the fainter 2SLAQ QSO sample further reveals that QSO clustering does not depend strongly on luminosity at fixed redshift. This result is inconsistent with the expectation of simple 'high peaks' biasing models where more luminous, rare QSOs are assumed to inhabit higher mass haloes. The data are more consistent with models which predict that QSOs of different luminosities reside in haloes of similar mass. By assuming ellipsoidal models for the collapse of density perturbations, we estimate the mass of the dark matter haloes which the QSOs inhabit as ∼3 × 1012 h−1 M⊙ . We find that this halo mass does not evolve strongly with redshift nor depend on QSO luminosity. Assuming a range of relations which relate halo to black hole mass, we investigate how black hole mass correlates with luminosity and redshift, and ascertain the relation between Eddington efficiency and black hole mass. Our results suggest that QSOs of different luminosities may contain black holes of similar mass.

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 supermassive black holes (M BH ) in quasi-stellar objects (QSOs) and the mass of the dark matter haloes hosting them (M DH ). We measure the widths of broad emission lines (Mg II λ2798, C IV λ1549) 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. based on measurements of QSO clustering. This enables us to trace the M BH -M DH relation over the redshift range z = 0.5-2.5. We calculate the mean zero-point of the M BH -M DH relation to be M BH = 10 8.4±0.2 M ⊙ for an M DH = 10 12.5 M ⊙ . These data are then compared with several models connecting M BH and M DH 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 M BH -M DH relation. The magnitude of this bias depends on the scatter in the M BH -M DH relation, and we re-evaluate 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 M BH between z ∼0.5 and 2.5 for typical, L* QSOs. We also determine the Eddington ratios (L/L Edd ) 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 QSOs. 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 that these evolution results are strongly affected by the virial black hole mass estimators used. Changes to the calibration of these have a significant effect on the evolution results.

200-Mpc-sized structure in the 2dF QSO Redshift survey

The completed 2dF QSO Redshift (2QZ) survey has been used to search for extreme large-scale cosmological structure (∼200 h−1 Mpc) over the redshift range 0 < z < 2.5. We demonstrate that statistically significant overdensities and underdensities do exist and hence represent the detection of cosmological fluctuations on comoving scales that correspond to those presently detected in the cosmic microwave background. However, the fractional overdensities on scales >100 h−1 Mpc are in the linear or only weakly non-linear regime and do not represent collapsed non-linear structures. We compare the measurements with the expectation of the Λ-cold dark matter (ΛCDM) model by measuring the variance of counts in cells and we find that, provided the distribution of quasi-stellar objects (QSOs) on large scales exhibits a mild bias with respect to the distribution of dark matter, the observed fluctuations are found to be in good agreement with the model. There is no evidence on such scales for any extreme structures that might require, for example, departures from the assumption of Gaussian initial perturbations. Thus, the power spectrum derived from the 2QZ survey appears to provide a complete description of the distribution of QSOs. The amount of bias and its redshift dependence that is required is consistent with that found from studying the clustering of 2QZ QSOs on ∼10 h−1 Mpc scales, and may be adequately described by an approximately redshift-invariant power spectrum with normalization σ8≃ 1.0 corresponding to a bias at z= 0 of b≃ 1.1 rising to b≃ 2 at the survey's mean redshift z≃ 1.5.

The 2dF QSO Redshift Survey - XIV. Structure and evolution from the two-point correlation function

In this paper we present a clustering analysis of quasi-stellar objects (QSOs) using over 20000 objects from the final catalogue of the 2dF QSO Redshift Survey (2QZ), measuring the redshift-space two-point correlation function, ξ(s). When averaged over the redshift range 0.3 < z < 2.2 we find that ξ(s) is flat on small scales, steepening on scales above ~25h-1 Mpc. In a WMAP/2dF cosmology (Ωm= 0.27, ΩΛ= 0.73) we find a best-fitting power law with s0= 5.48+0.42-0.48h-1 Mpc and γ= 1.20 +/- 0.10 on scales s= 1 to 25h-1 Mpc. We demonstrate that non-linear redshift-space distortions have a significant effect on the QSO ξ(s) at scales less than ~10h-1 Mpc. A cold dark matter model assuming WMAP/2dF cosmological parameters is a good description of the QSO ξ(s) after accounting for non-linear clustering and redshift-space distortions, and allowing for a linear bias at the mean redshift of bQ(z= 1.35) = 2.02 +/- 0.07. We subdivide the 2QZ into 10 redshift intervals with effective redshifts from z= 0.53 to 2.48. We find a significant increase in clustering amplitude at high redshift in the WMAP/2dF cosmology. The QSO clustering amplitude increases with redshift such that the integrated correlation function, , within 20h-1 Mpc is and . We derive the QSO bias and find it to be a strong function of redshift with bQ(z= 0.53) = 1.13 +/- 0.18 and bQ(z= 2.48) = 4.24 +/- 0.53. We use these bias values to derive the mean dark matter halo (DMH) mass occupied by the QSOs. At all redshifts 2QZ QSOs inhabit approximately the same mass DMHs with MDH= (3.0 +/- 1.6) × 1012h-1 Msolar, which is close to the characteristic mass in the Press-Schechter mass function, M*, at z= 0. These results imply that L*Q QSOs at z~ 0 should be largely unbiased. If the relation between black hole (BH) mass and MDH or host velocity dispersion does not evolve, then we find that the accretion efficiency (L/LEdd) for L*Q QSOs is approximately constant with redshift. Thus the fading of the QSO population from z~ 2 to ~0 appears to be due to less massive BHs being active at low redshift. We apply different methods to estimate, tQ, the active lifetime of QSOs and constrain tQ to be in the range 4 × 106-6 × 108 yr at z~ 2. We test for any luminosity dependence of QSO clustering by measuring ξ(s) as a function of apparent magnitude (equivalent to luminosity relative to L*Q). However, we find no significant evidence of luminosity-dependent clustering from this data set.

Cosmic evolution of quasar clustering: implications for the host haloes

We present detailed clustering measurements from the 2dF Quasi-Stellar Object Redshift Survey (2QZ) in the redshift range 0.8 < z < 2.1. Using a flux-limited sample of ∼14 000 objects with effective redshift z eff = 1.47, we estimate the quasar projected correlation function for separations 1 < r/ h −1 Mpc < 20. We find that the two-point correlation function in real space is well approximated by a power law with slope γ = 1.5 ± 0.2 and comoving correlation length r 0 = 4.8 +0.9 h −1 Mpc. Splitting the sample into three subsets based on redshift, we find evidence for an increase of the clustering amplitude with look-back time. For a fixed γ ,e v olution of r0 is detected at the 3.6σ confidence level. The ratio between the quasar correlation function and the mass autocorrelation function (derived adopting the concordance cosmological model) is found to be scale-independent. For a linear mass-clustering amplitude σ 8 = 0.8, the ‘bias parameter’ decreases from b � 3.9 at z eff = 1.89 to b � 1.8 at z eff = 1.06. From the observed abundance and clustering, we infer how quasars populate dark matter

The 2dF QSO Redshift Survey - XIII. A measurement of Λ from the quasi-stellar object power spectrum,PS(k∥,k⊥)

We report on measurements of the cosmological constant, A, and the redshift space distortion parameter β = Ω 0.6 m/b, based on an analysis of the quasi-stellar object (QSO) power spectrum parallel and perpendicular to the observer's line of sight, P S (k∥, k⊥), from the final catalogue of the Two-Degree Field (2dF) QSO Redshift Survey. We derive a joint Λ - β 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 (Ω m + Ω Λ = 1) cosmology and a A cosmology r(z) function to convert from redshift into comoving distance, we find best-fitting values of Ω Λ = 0.71 +0.09 -0.17 and β q (z ∼ 1.4) = 0.45 +0.09 -0.11. Assuming instead an Einstein-de Sitter cosmology r(z) we find that the best-fitting model obtained, with Ω Λ = 0.64 +0.11 -0.16 and β q (z ∼ 1.4) = 0.40 +0.09 -0.09, is consistent with the A r(z) results, and inconsistent with a Ω Λ = 0 flat cosmology at over 95 per cent confidence.

The detection of periodicity in QSO data sets

The issue of periodicity in quasi-stellar object (QSO) data sets is re-examined in the light of the failure to detect a periodicity in the 2dF QSO Redshift Survey, and of a recent claim that edge effects might have generated a spurious periodicity of 0.089 in log 1 0 (1 + z) in earlier data sets. A new methodology is described by which the contribution of edge effects may be assessed. It is shown that they have not in fact induced a spurious periodicity in the earlier data sets. Several possible factors are discussed which may tend to mask the periodicity in the 2dF Survey. Thus the earlier evidence for the periodicity in QSO redshifts is unaffected, although new constraints on astrophysical models may be imposed.

No periodicities in 2dF Redshift Survey data

We have used the publicly available data from the 2dF Galaxy Redshift Survey and the 2dF QSO Redshift Survey to test the hypothesis that there is a periodicity in the redshift distribution of quasi-stellar objects (QSOs) found projected close to foreground galaxies. These data provide by far the largest and most homogeneous sample for such a study, yielding 1647 QSO-galaxy pairs. There is no evidence for a periodicity at the predicted frequency in log(1 + z), or at any other frequency.

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.

Cosmological constraint from the 2dF QSO spatial power spectrum

We obtain constraints on the cosmological density parameters, Ωm and Ωb, by comparing the preliminary measurement of the quasi-stellar object (QSO) power spectrum from the Two-Degree Field (2dF) QSO Redshift (2QZ) survey with results from an analytic technique of power spectrum estimation, described herein. We demonstrate the validity of the analytic approach by comparing the results with the power spectrum of an N-body simulation. We find a better fit to the shape of the QSO power spectrum for low-density models with Ωm= 0.1–0.4. We show that a finite baryon fraction Ωb/Ωm= 0.2, consistent with observations of the cosmic microwave background anisotropies and nucleosynthesis, fits the observational result of the 2QZ survey better, though the constraint is not very tight. By using the Fisher matrix technique, we investigate just how large a survey would be required before a significant constraint on the density parameters could be obtained. We demonstrate that the constraint could be significantly improved if the survey was four times larger.