2023/11/23 by Camila Franco, Felipe Avila, Armando Bernui · 1 voice
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Cosmology and Gravitation Theories #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.1093/mnras/stad3616
openalex publication_date 2023/11/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
ABSTRACT This is a model-independent analysis that investigates the statistical isotropy in the Local Universe using the Arecibo Legacy Fast ALFA (ALFALFA) survey data (0 < z < 0.06). We investigate the angular distribution of H i extragalactic sources from the ALFALFA catalogue and study whether they are compatible with the statistical isotropy hypothesis using the two-point angular correlation function (2PACF). Aware that the Local Universe is plenty of clustered structures and large voids, we compute the 2PACF with the Landy–Szalay estimator performing directional analyses to inspect 10 sky regions. We investigate these 2PACF using power-law best-fitting analyses, and determine the statistical significance of the best-fitting parameters for the 10 ALFALFA regions by comparison with the ones obtained through the same procedure applied to a set of mock catalogues produced under the homogeneity and isotropy hypotheses. Our conclusion is that the Local Universe, as mapped by the H i sources of the ALFALFA survey, is in agreement with the hypothesis of statistical isotropy within 2σ confidence level, for small- and large-angle analyses, with the only exception of one region – located near the Dipole Repeller – that appears slightly outlier (2.4σ). Interestingly, regarding the large angular distribution of the H i sources, we found three regions where the presence of cosmic voids reported in the literature left their signature in our 2PACF, suggesting projected large underdensities there, with number-density contrast δ ≃ −0.7. According to the current literature, these regions correspond, partially, to the sky position of the void structures known as Local Cosmic Void and Dipole Repeller.