Estimates of galaxy bias and cosmological parameters from galaxy redshift surveys

Abstract

Spectroscopic redshift surveys can map the spatial distribution of galaxy samples. They can be used to analyse galaxy clustering which is one of the most powerful probes to investigate the properties of the Universe and, in particular, the nature of its dark components: the dark matter and the dark energy. In this thesis we work on the largest local all-sky redshift survey to date, the 2MRS (2 MASS Redshift Survey) catalog, consisting of about 40000 objects with measured redshift. Local studies, important per se from an astrophysical point of view, can play an important role also to investigate the origin of some of the systematic errors that a ect the clustering analysis: an ill-constrained bias relation between galaxies and matter, nonlinear e ects, imperfect estimator for galaxy clustering. Futhermore, specific systematic errors can arise from the wide angular coverage of this type of survey, that can be investigated as well. We focus on one of the most common statistical tools to galaxy clustering: the power spectrum. In particular, we consider the "classical" estimator proposed by Feldman , Kaiser and Peacock, with its many advantages (reliability, speed, exibility) and few drawbacks (it is not designed for wide angle surveys). We first focus on the bias parameter and its dependence on galaxy properties. Our results on the luminosity dependence of galaxy bias con rm the qualitative behaviour found in previous works on 2MRS, 2dF and SDSS galaxy catalogs. The bias is con rmed to be a steep function of the luminosity for the brightest galaxies, whereas for fainter objects the dependence is milder or absent altogether. The dependence of the bias on galaxy morphological type is explored as well, for 2MRS galaxies. The result has con rmed that early type objects are more clustered than the late type ones, with a relative bias of 1.228 0.067. Then we focus on the estimate of cosmological parameters by comparing the measured monopole of the 2MRS power spectrum with model predictions. We constrain the matter density parameter M and the bias parameter b with an accuracy 20% and 3%, respectively with best tting values M ' 0:33 and b ' 1:23 in agreement with previous results and theoretical prejudices. Finally, we study the possible dependence of galaxy bias on the scale. Scale dependent bias potentially a ects the results of the clustering analysis of next generation surveys, like Euclid, from which one expects to estimate the cosmological parameters at the level of per-cent. We investigate how scale dependent parametrizations of the bias are constrained by future observations, adopting a Fisher matrix approach. We consider the case of a Euclid-like survey as baseline of future experiments. The results show that allowing for a possible scale dependent bias does not signi cantly increase the errors on the other cosmological parameters except the growth index. The error on this parameter is found to depend on the specific bias model and in the range 5-10 % when a realistic redshift interval is considered. The accuracy on galaxy bias depends on its scale dependence. The scale independent part of the bias, can be determined with high ( 2%) accuracy at various redshifts regardless of the ducial model. The errors on the parameters that quantify the amplitude of the scale dependence are signi cantly larger. Their magnitude depends on the exact type of scale dependence.