P. J. Outram

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-SDSS LRG and QSO survey: the LRG 2-point correlation function and redshift-space distortions

We present a clustering analysis of luminous red galaxies (LRGs) using nearly 9000 objects from the final, three-year catalogue of the 2dF-SDSS LRG and QSO (2SLAQ) Survey. We measure the redshift-space two-point correlation function, ξ(s) and find that, at the mean LRG redshift of shows the characteristic downturn at small scales (1 h−1 Mpc) expected from line-of-sight velocity dispersion. We fit a double power law to ξ(s) and measure an amplitude and slope of s0 = 17.3+2.5−2.0 h−1 Mpc, γ = 1.03 ± 0.07 at small scales (s 4.5 h−1 Mpc). In the semiprojected correlation function, wp(σ), we find a simple power law with γ = 1.83 ± 0.05 and r0 = 7.30 ± 0.34 h−1 Mpc fits the data in the range 0.4 < σ < 50 h−1 Mpc, although there is evidence of a steeper power law at smaller scales. A single power law also fits the deprojected correlation function ξ(r), with a correlation length of r0 = 7.45 ± 0.35 h−1 Mpc and a power-law slope of γ = 1.72 ± 0.06 in the 0.4 < r < 50 h−1 Mpc range. But it is in the LRG angular correlation function that the strongest evidence for non-power-law features is found where a slope of γ = −2.17 ± 0.07 is seen at 1 < r < 10 h−1 Mpc with a flatter γ = −1.67 ± 0.07 slope apparent at r 1 h−1 Mpc scales. We use the simple power-law fit to the galaxy ξ(r), under the assumption of linear bias, to model the redshift-space distortions in the 2D redshift-space correlation function, ξ(σ, π). We fit for the LRG velocity dispersion, wz, the density parameter, Ωm and β(z), where β(z) = Ω0.6m/b and b is the linear bias parameter. We find values of wz = 330 km s−1, Ωm = 0.10+0.35−0.10 and β = 0.40 ± 0.05. The low values for wz and β reflect the high bias of the LRG sample. These high-redshift results, which incorporate the Alcock–Paczynski effect and the effects of dynamical infall, start to break the degeneracy between Ωm and β found in low-redshift galaxy surveys such as 2dFGRS. This degeneracy is further broken by introducing an additional external constraint, which is the value β(z = 0.1) = 0.45 from 2dFGRS, and then considering the evolution of clustering from z 0 to zLRG 0.55. With these combined methods we find Ωm(z = 0) = 0.30 ± 0.15 and β(z = 0.55) = 0.45 ± 0.05. Assuming these values, we find a value for b(z = 0.55) = 1.66 ± 0.35. We show that this is consistent with a simple ����high-peak’ bias prescription which assumes that LRGs have a constant comoving density and their clustering evolves purely under gravity.

The 2dF-SDSS LRG and QSO (2SLAQ) Luminous Red Galaxy Survey

We present a spectroscopic survey of almost 15 000 candidate intermediate-redshift luminous red galaxies (LRGs) brighter than i = 19.8, observed with 2dF on the Anglo-Australian Telescope. The targets were selected photometrically from the Sloan Digital Sky Survey (SDSS) and lie along two narrow equatorial strips covering 180 deg 2 . Reliable redshifts were obtained for 92 per cent of the targets and the selection is very efficient: over 90 per cent have 0.45 < z < 0.8. More than 80 per cent of the ∼11 000 red galaxies have pure absorption-line spectra consistent with a passively evolving old stellar population. The redshift, photometric and spatial distributions of the LRGs are described. The 2SLAQ data will be released publicly from mid-2006, providing a powerful resource for observational cosmology and the study of galaxy evolution.

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- ˚

Emission linewidths and QSO black hole mass estimates from the 2dF QSO Redshift Survey

We have used composite spectra generated from more than 22 000 quasi-stellar objects (QSOs) observed during the course of the 2dF and 6dF QSO Redshift Surveys to investigate the relationship between the velocity width of emission lines and QSO luminosity. We find that the velocity widths of the broad emission lines Hβ, Hy, Mg II, C III] and C IV are correlated with the continuum luminosity, with a significance of more than 99 per cent. Of the major narrow emission lines ([O III] λ5007, [O II] λ3727, [Ne III] λ3870 and [Ne V] λ3426) only [O III] exhibits a significant correlation between linewidth and luminosity. Assuming that the gas is moving in Keplerian orbits and that the radius of the broad line region is related to the QSO continuum luminosity, we use the velocity widths of the broad lines to derive average black hole masses for the QSOs contributing to the composite spectra. The resultant QSO mass-luminosity relationship is consistent with M α L 0 . 9 7 ′ 0 . 1 6 . We find that the correlation between linewidth and redshift, if present, must be weak, and only C IV shows significant evidence of evolution. This enables us to constrain the redshift evolution of the black hole mass-luminosity ratio to be ∼(1 + z) β with β ≤ 1, much less than the ∼(1 + z) 3 evolution seen in QSO luminosity evolution. Assuming that the motion of the broad line region gas is Keplerian and that its radius depends on the QSO luminosity, our models indicate that the observed weak redshift dependence is too small for the observed QSO luminosity function to be due to the evolution of a single long-lived population of sources.

The 2dF QSO Redshift Survey- XV. Correlation analysis of redshift-space distortions

We analyse the redshift-space (z-space) distortions of quasi-stellar object (QSO) clustering in the 2-degree field instrument (2dF) QSO Redshift Survey (2QZ). To interpret the z-space correlation function, ξ(σ, π), we require an accurate model for the QSO real-space correlation function, ξ(r). Although a single power-law ξ(r) oc r -γ model fits the projected correlation function [ω p (σ)] at small scales, it implies somewhat too shallow a slope for both w p (σ) and the z-space correlation function, ξ(s), at larger scales (?20 h -1 Mpc). Motivated by the form for ξ(r) seen in the 2dF Galaxy Redshift Survey (2dFGRS) and in standard A cold dark matter (CDM) predictions, we use a double power-law model for ξ(r), which gives a good fit to ξ(s) and w p (σ). The model is parametrized by a slope of y = 1.45 for 1 < r < 10 h -1 Mpc and y = 2.30 for 10 < r < 40 h -1 Mpc. As found for the 2dFGRS, the value of β determined from the ratio of ξ(s)/ξ(r) depends sensitively on the form of ξ(r) assumed. With our double power-law form for ξ(r), we measure β(z = 1.4) = 0.32 +0.09 -0.11 . Assuming the same model for ξ(r), we then analyse the z-space distortions in the 2QZ ξ(σ, π) and put constraints on the values of Ω 0 m and β(z = 1.4), using an improved version of the method of Hoyle et al. The constraints we derive are Ω 0 m = 0.35 +0.19 -0.13 , β(z = 1.4) = 0.50 +0.13 -0.15 , in agreement with our ξ(s)/ξ(r) results at the ∼ 1σ level.

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 – XIII. A measurement of Λ from the quasi‐stellar object power spectrum, PS(k∥, k⊥)

We report on measurements of the cosmological constant, Lambda, and the redshift space distortion parameter beta=Omega_m^0.6/b, based on an analysis of the QSO power spectrum parallel and perpendicular to the observers line of sight, from the final catalogue of the 2dF QSO Redshift Survey. We derive a joint Lambda - beta 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 Lambda cosmology r(z) function to convert from redshift into comoving distance, we find best fit values of Omega_Lambda=0.71^{+0.09}_{-0.17} and beta(z~1.4)=0.45^{+0.09}_{-0.11}. Assuming instead an EdS cosmology r(z) we find that the best fit model obtained, with Omega_Lambda=0.64^{+0.11}_{-0.16} and beta(z~1.4)=0.40^{+0.09}_{-0.09}, is consistent with the Lambda r(z) results, and inconsistent with a Lambda=0 flat cosmology at over 95 per cent confidence.

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.