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Register a new userCosmology with Galaxy Clusters in the XMM Large-Scale Structure Survey
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Added by
Alexandre Refregier
Publication date
2001
fields
Physics
and research's language is
English
Authors
Alexandre Refregier Cambridge
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The upcoming XMM Large Scale Structure Survey (XMM-LSS) will ultimately provide a unique mapping of the distribution of X-ray sources in a contiguous 64 sq. deg. region. In particular, it will provide the 3-dimensional location of about 900 galaxy clusters out to a redshift of about 1. We study the prospects that this cluster catalogue offers for measuring cosmological parameters. We use the Press-Schechter formalism to predict the counts of clusters and their X-ray properties in several CDM models. We compute the detection efficiency of clusters, using realistic simulations of XMM X-ray images, and study how it differs from a conventional flux limit. We compute the expected correlation function of clusters using the extended halo model, and show that it is expected to evolve very little out to z~2, once the selection function of the survey is taken into account. The shape and the amplitude of the correlation function can be used to brake degeneracies present when cluster counts alone are considered. Ignoring systematic uncertainties, the combination of cluster counts evolution and of the correlation function yields measurements of Omega_m, sigma_8 and Gamma with a precision of about 15%, 10% and 35%, respectively, in a LCDM model. This combination will also provide a consistency check for the LCDM model, and a discrimination between this model and the OCDM model. The XMM-LSS will therefore provide important constraints on cosmological parameters, complementing that from other methods such as the Cosmic Microwave Background. We discuss how these constraints are affected by instrumental systematics and by the uncertainties in the scaling relations of clusters.
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The Large Scale Structure (LSS) in the galaxy distribution is investigated using the Sloan Digital Sky Survey Early Data Release (SDSS EDR). Using the Minimal Spanning Tree technique we have extracted sets of filaments, of wall-like structures, of galaxy groups, and of rich clusters from this unique sample. The physical properties of these structures were then measured and compared with the expectations from Zeldovich theory. The measured characteristics of galaxy walls were found to be consistent with those for a spatially flat $Lambda$CDM cosmological model with $Omega_mapprox$ 0.3 and $Omega_Lambda approx$ 0.7, and for Gaussian initial perturbations with a Harrison -- Zeldovich power spectrum. Furthermore, we found that the mass functions of groups and of unrelaxed structure elements generally fit well with the expectations from Zeldovich theory, although there was some discrepancy for lower mass groups which may be due to incompleteness in the selected sample of groups. We also note that both groups and rich clusters tend to prefer the environments of walls, which tend to be of higher density, rather than the environments of filaments, which tend to be of lower density. Finally, we note evidence of systematic differences in the properties of the LSS between the Northern Galactic Cap stripe and the Southern Galactic Cap stripe -- in particular, in the physical properties of the walls, their spatial distribution, and the relative numbers of clusters embedded in walls. Because the mean separation of walls is $approx$ 60 -- 70$h^{-1}$ Mpc, each stripe only intersects a few tens of walls. Thus, small number statistics and cosmic variance are the likely drivers of these systematic differences.
We present X-ray and optical spectroscopic observations of twelve galaxy groups and clusters identified within the XMM Large-Scale Structure (LSS) survey. Groups and clusters are selected as extended X-ray sources from a 3.5 deg2 XMM image mosaic above a flux limit 8e-15 ergs/s/cm2 in the [0.5-2] keV energy band. Deep BVRI images and multi-object spectroscopy confirm each source as a galaxy concentration located within the redshift interval 0.29<z<0.56. We combine line-of-sight velocity dispersions with the X-ray properties of each structure computed from a two-dimensional surface brightness model and a single temperature fit to the XMM spectral data. The resulting distribution of X-ray luminosity, temperature and velocity dispersion indicate that the XMM-LSS survey is detecting low-mass clusters and galaxy groups to redshifts z < 0.6. Confirmed systems display little or no evidence for X-ray luminosity evolution at a given X-ray temperature compared to lower redshift X-ray group and cluster samples. A more complete understanding of these trends will be possible with the compilation of a statistically complete sample of galaxy groups and clusters anticipated within the continuing XMM-LSS survey.
The 2dF Galaxy Redshift Survey is the first to measure more than 100,000 redshifts. This allows precise measurements of many of the key statistical measures of galaxy clustering, in particular redshift-space distortions and the large-scale power spectrum. This paper presents the current 2dFGRS results in these areas. Redshift-space distortions are detected with a high degree of significance, confirming the detailed Kaiser distortion from large-scale infall velocities, and measuring the distortion parameter beta = 0.43 +/- 0.07. The power spectrum is measured to < 10% accuracy for k > 0.02 h Mpc^-1, and is well fitted by a CDM model with Omega_m h = 0.20 +/- 0.03 and a baryon fraction of 0.15 +/- 0.07.
Published galaxy power spectra from the 2dFGRS and SDSS are not in good agreement. We revisit this issue by analyzing both the 2dFGRS and SDSS DR5 catalogues using essentially identical techniques. We confirm that the 2dFGRS exhibits relatively more large scale power than the SDSS, or, equivalently, SDSS has more small scale power. We demonstrate that this difference is due to the r-band selected SDSS catalogue being dominated by more strongly clustered red galaxies, which have a stronger scale dependent bias. The power spectra of galaxies of the same rest frame colours from the two surveys match well. If not accounted for, the difference between the SDSS and 2dFGRS power spectra causes a bias in the obtained constraints on cosmological parameters which is larger than the uncertainty with which they are determined. We also found that the correction developed by Cole et al.(2005) to model the distortion in the shape of the power spectrum due to non-linear evolution and scale dependent bias is not able to reconcile the constraints obtained from the 2dFGRS and SDSS power spectra. Intriguingly, the model is able to describe the differences between the 2dFGRS and the much more strongly clustered LRG sample, which exhibits greater nonlinearities. This shows that more work is needed to understand the relation between the galaxy power spectrum and the linear perturbation theory prediction for the power spectrum of matter fluctuations. It is therefore important to accurately model these effects to get precise estimates of cosmological parameters from these power spectra and from future galaxy surveys like Pan-STARRS, or the Dark Energy Survey, which will use selection criteria similar to the one of SDSS.
Thanks to its unrivalled sensitivity and large field of view, XMM potentially occupies a leading position as a survey instrument. We present cosmological arguments in favour of a medium-sensitivity, large-scale structure survey with XMM, using galaxy clusters as tracers of the cosmic network. We show how this has motivated the definition of a concrete survey, the XMM Large-Scale Structure Survey (XMM-LSS), which will cover 64 square degrees with a sensitivity about 1000 times better than that of the ROSAT All-Sky Survey. We present our predictions for cluster counts based on the Press-Schechter formalism and detailed X-ray image simulations, and show how they agree with the cluster statistics from recent ROSAT cluster surveys. We also present the extensive multi-wavelength follow-up associated with XMM-LSS, as well as the first observations from the programme.
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