Fluctuations of the spatial galaxy distribution in the COSMOS deep survey at gigaparsec scales

Abstract

We analyse the radial galaxy distribution of the deep survey COSMOS. The value of “cosmic variance” is estimated by using large red shift bins (Δz =0.1 ÷ 0.3) that contain a suffi ciently large number of galaxies for the Poisson noise(~ 1/N ^{1 / 2})to be small(σP ~ 0.01).The accuracy of photometric red shifts (δz ~ 0.012(1+z))allows the study of spatial in homogeneities with sizes larger than the bin size Δz ≥ 0.1, i.e.,ΔR ≥ 300 Mpc/h. The LCDM model predicts for the COSMOS survey the value of cosmic variance of dark matter σ(z)dm =0.039 forz =1.7 and Δz =0.2 (Moster etal.,Astrophys.J.,731,113(2011)). Our analysis of the COSMOS survey shows that at z =1.7, with redshift bins Δz =0.2, the amplitude of the galaxy number fluctuations is σ(z)obs =0.37, i.e., an order of magnitude larger than LCDM prediction for non-baryonic dark matter. In order to reconcile the observed amplitude with the LCDM model, the biasfactor shouldbe b ≈ 10.Observed radial sizes of detected in homogeneities extend to1500Mpc, while the predicted LCDM correlation function ξdm =0 on a scale of r = 174 Mpc, independent of bias. Our results are consistent with recent observations of the COSMOS field by ALHAMBRA, as well as X-ray and sub-millimetresurveys (SPT,ALMA).

Keywords:

cosmology, large scale structure of the Universe, deep galaxy surveys, COSMOS, ALHAMBRA, SPT, ALMA