Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe 2dF QSO Redshift Survey - XI. The QSO Power Spectrum
338
0
0.0
(
0
)
Authors
P. J. Outram
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
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.
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 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.
The technique of estimating redshifts using photometric rather than spectroscopic observations has recently received great attention due to its simplicity and the accuracy of the results obtained. In this work, we estimate photometric redshifts for an X-ray selected QSO sample. This is the first time this technique is applied on such a sample. We first calculate the accuracy of the results obtained by comparing photometric to spectroscopic redshifts for a sub-sample of our QSO sample: for the majority (~67%) of the objects in this sub-sample, photometric redshift estimates are correct within Dz<0.3. We then derive the photometric redshift distribution for the whole QSO sample. In the future, we expect to use the photometric redshift distribution in order to derive the distributions of properties such as the Hardness Ratio and hence the hydrogen column density, the luminosity function etc. As an example, we estimate here the dependence of the Hardness Ratio of the QSO sample on photometric redshift.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
