The line-of-sight analysis of spatial distribution of galaxies in the COSMOS2015 catalogue

TL;DR

This paper analyzes the large-scale distribution of galaxies along the line of sight using the COSMOS2015 catalogue, estimating the sizes of cosmic structures and their deviations from homogeneity within the $ ext{Lambda}$CDM model.

Contribution

It introduces a new line-of-sight analysis method for galaxy distribution and provides estimates of cosmic structure sizes and variances based on the latest galaxy catalogue.

Findings

Average structure size is approximately 790 Mpc in $ ext{Lambda}$CDM.

Standard deviation of structures from homogeneity is about 0.09 in $ ext{Lambda}$CDM.

Empirical homogeneity estimates yield a structure size of around 640 Mpc.

Abstract

New observations of high-redshift objects are crucial for the improvement of the standard $\Lambda$CDM cosmological model and our understanding of the Universe. One of the main directions of modern observational cosmology is the analysis of the large-scale structure of Universe, in particular, in deep fields. We study the large-scale structure of the Universe along the line of sight using the latest version of the COSMOS2015 catalogue, which contains 518,404 high quality photometric redshifts of galaxies selected in the optical range of the COSMOS field ($2\times 2$ deg$^2$), with depth up to the redshift $z \sim 6$. We analyze large-scale fluctuations in the number of galaxies along the line of sight and provide an estimate of the average linear sizes of the self-correlating fluctuations (structures) in independent redshift bins of $ \Delta z = 0.1 $ along with the estimate of the standard deviation from homogeneity (the observed cosmic variance). We suggest a new method of the line-of-sight analysis based on previous works and formulate further prospects of method development. For the case of the theoretical form of approximation of homogeneity in the $\Lambda$CDM framework, the average standard deviation of detected structures from homogeneity is $ \sigma_\text{mean}^{\Lambda \text{CDM}} = 0.09 \pm 0.02 $, and the average characteristic size of structures is $ R_\text{mean}^{\Lambda \text{CDM}} = 790 \pm 150 $ Mpc. For the case of the empirical approximation of homogeneity, the average standard deviation of detected structures from homogeneity is $ \sigma_\text{mean}^\text{empiric} = 0.08 \pm 0.01 $, and the average characteristic size of structures is $ R_\text{mean}^\text{empiric} = 640 \pm 140 $ Mpc.