Probing large-scale structures with the two-point function and the power spectrum: insights into cosmic clustering evolution

TL;DR

The paper investigates the evolution of cosmic clustering in the Local Universe by analyzing SDSS blue galaxies in two tomographic shells with model-independent statistics. It combines the two-point angular correlation function and the angular power spectrum, using log-normal mocks and Bayesian inference to test $\Lambda$CDM against observations. The results show stronger clustering in the older shell and clear signatures of large-scale structures, with non-linear power becoming important at small scales in the nearby Universe. Overall, the analyses serve as consistency tests of the $\Lambda$CDM model and demonstrate the value of multi-estimator, tomographic approaches for probing cosmic structure growth.

Abstract

Understanding the large-scale structure of the Universe requires analyses of cosmic clustering and its evolution over time. In this work, we investigate the clustering properties of SDSS blue galaxies, which are excellent tracers of dark matter, along two distinct epochs of the Universe, utilizing estimators like the two-point angular correlation function (2PACF), the angular power spectra, among others. Considering a model-independent approach, we perform analyses in two disjoint redshift shells, $0 \leq z < 0.06$ and $0.06 \leq z < 0.12$, to investigate the distribution of large cosmic structures. Using Bayesian inference methods, we constrain the parameter that quantifies the galaxy clustering in the 2PACF, enabling us to perform comparisons among different regions on the sky and between different epochs in the Universe regarding the gravitational action on matter structures. Our analyses complement previous efforts to map large-scale structures in the Local Universe. In addition, this study reveals differences regarding the clustering of large cosmic structures comparing two epochs of the Universe, analyses done with diverse estimators. Results reveal, clearly, distinct evolutionary signatures between the two redshift shells. Moreover, we had the opportunity to test the concordance cosmological model under extreme conditions in the highly non-linear Local Universe, computing the amplitude of the angular power spectrum at very small scales. Ultimately, all our analyses serve as a set of consistency tests of the concordance cosmological model, the $Λ$CDM.

Figures (21)

• Figure 1: SDSS footprint in equatorial coordinates. The Northern Galactic Hemisphere (NGH), shown in blue, is the central region of the projection, while the Southern Galactic Hemisphere (SGH), in dark blue, is located at the edges. Both regions have irregular boundaries, with the NGH exhibiting higher density of observations compared to the SGH.
• Figure 2: Redshift distribution of the SDSS blue galaxies selected sample compared to the total sample.
• Figure 3: Footprint of the selected sample, located in the NGH. We divided each shell into $12$ Areas. Upper panel: Shell 1 ($0 \leq z < 0.06$) contains $62,495$ galaxies; Bottom panel: Shell 2 ($0.06 \leq z < 0.12$) contains $96,712$ galaxies.
• Figure 4: 2PACF for small-angle analyses in Shell 1. Angular distribution of the $12$ regions illustrated in Figure \ref{['fig:footprint_shells']} within the angular range $0^{\circ} < \theta \leq 10^{\circ}$.
• Figure 5: 2PACF for small-angle analyses in Shell 2. Angular distribution of the $12$ regions illustrated in Figure \ref{['fig:footprint_shells']} within the angular range $0^{\circ} < \theta \leq 10^{\circ}$.