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Register a new userThe 2dF QSO Redshift Survey - XV. Correlation analysis of redshift-Space distortions
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J. da Angela
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We analyse the redshift-space (z-space) distortions of QSO clustering in the 2dF QSO Redshift Survey (2QZ). To interpret the z-space correlation function, xi(sigma,pi), we require an accurate model for the QSO real-space correlation function, xi(r). Although a single power-law xi(r) model fits the projected correlation function (wp(sigma)) at small scales, it implies somewhat too shallow a slope for both wp(sigma) and the z-space correlation function, xi(s), at larger scales > 20 h^(-1) Mpc. Motivated by the form for xi(r) seen in the 2dF Galaxy Redshift Survey (2dFGRS) and in standard LCDM predictions, we use a double power-law model for xi(r) which gives a good fit to xi(s) and wp(sigma). The model is parametrized by a slope of gamma=1.45 for 1<r<10 h^(-1) Mpc and gamma=2.30 for 10<r<40 h^(-1) Mpc. As found for 2dFGRS, the value of beta determined from the ratio of xi(s)/xi(r) depends sensitively on the form of xi(r) assumed. With our double power-law form for xi(r), we measure beta(z=1.4)=0.32(+0.09)(-0.11). Assuming the same model for xi(r) we then analyse the z-space distortions in the 2QZ xi(sigma,pi) and put constraints on the values of Omega m and beta(z=1.4), using an improved version of the method of Hoyle et al. The constraints we derive are Omega m=0.35(+0.19)(-0.13), beta(z=1.4)=0.50(+0.13)(-0.15), in agreement with our xi(s)/xi(r) results at the ~1 sigma level.
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We present a clustering analysis of Luminous Red Galaxies (LRGs) using nearly 9 000 objects from the final catalogue of the 2dF-SDSS LRG And QSO (2SLAQ) Survey. We measure the redshift-space two-point correlation function, xi(s), at the mean LRG redshift of z=0.55. A single power-law fits the deprojected correlation function, xi(r), with a correlation length of r_0=7.45+-0.35 Mpc and a power-law slope of gamma=1.72+-0.06 in the 0.4<r<50 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 gamma=-2.17+-0.07 is seen at 1<r<10 Mpc with a flatter gamma=-1.67+-0.03 slope apparent at r<~1 Mpc scales. We use the simple power-law fit to the galaxy xi(r) to model the redshift space distortions in the 2-D redshift-space correlation function, xi(sigma,pi). We fit for the LRG velocity dispersion, w_z, Omega_m and beta, where beta=Omega_m^0.6/b and b is the linear bias parameter. We find values of w_z=330kms^-1, Omega_m= 0.10+0.35-0.10 and beta=0.40+-0.05. These high redshift results, which incorporate the Alcock-Paczynski effect and the effects of dynamical infall, start to break the degeneracy between Omega_m and beta found in low-redshift galaxy surveys. This degeneracy is further broken by introducing an additional external constraint, the value of beta(z=0.1)=0.45 from 2dFGRS, and then considering the evolution of clustering from z~0 to z_LRG~0.55. With these combined methods we find Omega_m(z=0)=0.30+-0.15 and beta(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 peaks bias prescription which assumes that LRGs have a constant co-moving density and their clustering evolves purely under gravity. [ABRIDGED]
We present clustering results from the 2dF QSO Redshift Survey (2QZ) which currently contains over 20,000 QSOs at z<3. The two-point correlation function of QSOs averaged over the entire survey (<z>~1.5) is found to be similar to that of local galaxies. When sub-dividing the sample as a function of redshift, we find that for an Einstein-de Sitter universe QSO clustering is constant (in comoving coordinates) over the entire redshift range probed by the 2QZ, while in a universe with Omega_0=0.3 and Lambda_0=0.7 there is a marginal increase in clustering with redshift. Sub-dividing the 2QZ on the basis of apparent magnitude we find only a slight difference between the clustering of QSOs of different apparent brightness, with the brightest QSOs having marginally stronger clustering. We have made a first measurement of the redshift space distortion of QSO clustering, with the goal of determining the value of cosmological parameters (in partcular Lambda_0) from geometric distortions. The current data do not allow us to discriminate between models, however, in combination with constraints from the evolution of mass clustering we find Omega_0=1-Lambda_0=0.23 +0.44-0.13 and beta(z~1.4)=0.39 +0.18-0.17. The full 2QZ data set will provide further cosmological constraints.
With ~10000 QSO redshifts, the 2dF QSO Redshift Survey (2QZ) is already the biggest individual QSO survey. The aim for the survey is to have ~25000 QSO redshifts, providing an order of magnitude increase in QSO clustering statistics. We first describe the observational parameters of the 2dF QSO survey. We then describe several highlights of the survey so far; we present new estimates of the QSO luminosity function and the QSO correlation function. We also present the first estimate of the QSO power spectrum from the 2QZ catalogue, probing the form of the fluctuation power-spectrum out to the ~1000h-1Mpc scales only previously probed by COBE. We find a power spectrum which is steeper than the prediction of standard CDM and more consistent with the prediction of Lambda-CDM. The best-fit value for the power spectrum shape parameter for a range of cosmologies is Gamma=0.1+-0.1. Finally, we discuss how the complete QSO survey will be able to constrain the value of Omega_Lambda by combining results from the evolution of QSO clustering and from a geometric test of clustering isotropy.
We present a power spectrum analysis of the final 2dF QSO Redshift Survey catalogue containing 22652 QSOs. Utilising the huge volume probed by the QSOs, we can accurately measure power out to scales of ~500Mpc and derive new constraints, at z~1.4, on the matter and baryonic contents of the Universe. Importantly, these new cosmological constraints are derived at an intermediate epoch between the CMB observations at z~1000, and local (z~0) studies of large-scale structure; the average QSO redshift corresponds to a look-back time of approximately two-thirds of the age of the Universe. We find that the amplitude of clustering of the QSOs at z~1.4 is similar to that of present day galaxies. The power spectra of the QSOs at high and low redshift are compared and we find little evidence for any evolution in the amplitude. Assuming a lambda cosmology to derive the comoving distances, r(z), to the QSOs, the power spectrum derived can be well described by a model with shape parameter Gamma=0.13+-0.02. If an Einstein-de Sitter model r(z) is instead assumed, a slightly higher value of Gamma=0.16+-0.03 is obtained. A comparison with the Hubble Volume LCDM simulation shows very good agreement over the whole range of scales considered. A standard (Omega_m=1) CDM model, however, predicts a much higher value of Gamma than is observed, and it is difficult to reconcile such a model with these data. We fit CDM model power spectra (assuming scale-invariant initial fluctuations), convolved with the survey window function, and corrected for redshift space distortions, and find that models with baryon oscillations are slightly preferred, with the baryon fraction Omega_b/Omega_m=0.18+-0.10. The overall shape of the power spectrum provides a strong constraint on Omega_m*h (where h is the Hubble parameter), with Omega_m*h=0.19+-0.05.
We present a catalogue comprising over 10000 QSOs covering an effective area of 289.6 sq. degrees, based on spectroscopic observations with the 2-degree Field instrument at the Anglo-Australian Telescope. This catalogue forms the first release of the 2-degree Field QSO Redshift Survey. QSO candidates with 18.25<b_J<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 25000 QSOs and will be released to the public at the end of 2002, one year after the observational phase is concluded.
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