Spatial density fluctuations and selection effects in galaxy redshift surveys

Abstract

One of the main problems of observational cosmology is to determine the range in which a reliable measurement of galaxy correlations is possible. This corresponds to determine the shape of the correlation function, its possible evolution with redshift and the size and amplitude of large scale structures. Different selection effects, inevitably entering in any observation, introduce important constraints in the measurement of correlations. In the context of galaxy redshift surveys selection effects can be caused by observational techniques and strategies and by implicit assumptions used in the data analysis. Generally all these effects are taken into account by using pair-counting algorithms to measure two-point correlations. We review these methods stressing that they are based on the a-priori assumption that galaxy distribution is spatially homogeneous inside a given sample. We show that, when this assumption is not satisfied by the data, results of the correlation analysis are affected by finite size effects.In order to quantify these effects, we introduce a new method based on the computation of the gradient of galaxy counts along tiny cylinders. We show, by using artificial homogeneous and inhomogeneous point distributions, that this method is to identify redshift dependent selection effects and to disentangle them from the presence of large scale density fluctuations. We then apply this new method to several redshift catalogs and we find evidences that galaxy distribution, in those samples where selection effects are small enough, is characterized by power-law correlations with exponent $\gamma =0.9$ up to $20$ Mpc/h followed by a change of slope that, in the range [20,100] Mpc/h, corresponds to a power-law exponent $\gamma =0.25$. Whether a crossover to spatial unformity occurs at $\sim 100$ Mpc/h cannot be clarified by the present data.

35 pages, Journal of Cosmology and Astroparticle Physics in the press

References in corpus (39)

• The Sloan Digital Sky Survey: Technical Summary
• The many lives of active galactic nuclei: cooling flows, black holes and the luminosities and colours of galaxies
• The 2dF Galaxy Redshift Survey: Spectra and redshifts
• Spectroscopic Target Selection in the Sloan Digital Sky Survey: The Main Galaxy Sample
• The Sixth Data Release of the Sloan Digital Sky Survey
• The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
• Spectroscopic Target Selection for the Sloan Digital Sky Survey: The Luminous Red Galaxy Sample
• The Sloan Digital Sky Survey Quasar Catalog V. Seventh Data Release
• Power Spectrum Analysis of Three-Dimensional Redshift Surveys
• The Luminosity and Color Dependence of the Galaxy Correlation Function
• The 2MASS Redshift Survey - Description and Data Release
• The WiggleZ Dark Energy Survey: Survey Design and First Data Release
• Statistical Analysis of Galaxy Surveys - I. Robust error estimation for 2-point clustering statistics
• Cosmic homogeneity demonstrated with luminous red galaxies
• Scale-invariance of galaxy clustering
• Clustering of Low-Redshift (z <= 2.2) Quasars from the Sloan Digital Sky Survey
• Quasar Clustering from SDSS DR5: Dependences on Physical Properties
• A comparison of estimators for the two-point correlation function
• The Baryonic Acoustic Feature and Large-Scale Clustering in the SDSS LRG Sample
• The WiggleZ Dark Energy Survey: the transition to large-scale cosmic homogeneity
• A structure in the early universe at z ~ 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology
• The Large-Scale Smoothness of the Universe
• The Sloan Great Wall. Morphology and galaxy content
• Basic properties of galaxy clustering in the light of recent results from the Sloan Digital Sky Survey
• Seeing patterns in noise: Gigaparsec-scale `structures' that do not violate homogeneity
• Absence of self-averaging and of homogeneity in the large scale galaxy distribution
• Inhomogeneities in the universe
• Absence of anti-correlations and of baryon acoustic oscillations in the galaxy correlation function from the Sloan Digital Sky Survey DR7
• Fractal Dimensions of a Weakly Clustered Distribution and the Scale of Homogeneity
• Breaking the self-averaging properties of spatial galaxy fluctuations in the Sloan Digital Sky Survey - Data Release Six
• Power law correlations in galaxy distribution and finite volume effects from the Sloan Digital Sky Survey Data Release Four
• Large-scale fluctuations in the distribution of galaxies from the Two Degree Field Galaxy Redshift Survey
• Galaxy distribution and extreme value statistics
• Persistent fluctuations in the distribution of galaxies from the Two degree Field Galaxy Redshift Survey
• Evolution of the Galaxy Luminosity Function at z < 0.3
• Extension and estimation of correlations in Cold Dark Matter models
• Testing the Copernican and Cosmological Principles in the local universe with galaxy surveys
• Method for analyzing the spatial distribution of galaxies on gigaparsec scales. II. application to a grid of the HUDF-FDF-COSMOS-HDF surveys
• Method of analysis of the spatial galaxy distribution at gigaparsec scales. I. Initial principles

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