arXiv subjects

Felipe Avila

Publications and source records attributed to Felipe Avila.

23 records · Page 2Linked to original sources

arXiv2023

Probing cosmic isotropy in the Local Universe

This is a model-independent analysis that investigates the statistical isotropy in the Local Universe using the ALFALFA survey data ($0 < z < 0.06$). We investigate the angular distribution of HI extra-galactic 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-fit analyses, and determine the statistical significance of the best-fit 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 HI sources of the ALFALFA survey, is in agreement with the hypothesis of statistical isotropy within $2\,σ$ confidence level, for small and large angle analyses, with the only exception of one region -- located near the Dipole Repeller -- which appears slightly outlier ($2.4\,σ$). Interestingly, regarding the large angular distribution of the HI sources, we found 3 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 $δ\simeq -0.7$. 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.

astro-ph.CO↗

arXiv2023

Probing cosmic homogeneity in the Local Universe

We investigate the transition scale to homogeneity, $R_H$, using as cosmic tracer the spectroscopic sample of blue galaxies from the Sloan Digital Sky Survey (SDSS). Considering the spatial distribution of the galaxy sample we compute the two point correlation function $ξ(r)$, the scaled counts in spheres $\mathcal{N}(<r)$, and the fractal dimension $\mathcal{D}_2(r)$ to quantify the homogeneity scale in the Local Universe ($0.04 < z < 0.20$). The sample in analysis is compared with {\it random} and {\it mock} catalogues with the same geometry, and the same number of synthetic cosmic objects as the dataset, to calculate the covariance matrix for the errors determination. The criteria adopted for the transition-to-homogeneity follows the literature, it is attained when $\mathcal{D}_2(r)$ reaches the $1$ per cent level of the limit value $3$ (i.e., where it reaches $2.97$) as the scale increases. We obtain $R_H = 70.33 \pm 10.74$ Mpc$/h$, at the effective redshift $z_{\text{eff}}=0.128$, for a sample containing $150\,302$ SDSS blue galaxies with $0.04 < z < 0.20$. Additionally, we perform robustness tests by analysing the homogeneity scale in sub-volumes of the original one, obtaining coherent results; we also check for a possible artefact in our procedure examining a homogeneous synthetic dataset as a pseudo-data, verifying that such systematic is absent. Because our analyses concentrate in data at low redshifts, $z < 0.20$, we find interesting to use cosmography to calculate the radial comoving distances; therefore in this subject our analyses do not use fiducial cosmological model. For completeness, we evaluate the difference of the comoving distances estimation using cosmography and fiducial cosmology.

astro-ph.CO↗

arXiv2023

The bulk flow motion and the Hubble-Lema\^ıtre law in the Local Universe with the ALFALFA survey

The knowledge of the main features of the bulk flow in the Local Universe is important for a better determination of the relative motions there, an information that would contribute to a precise calculation of the Hubble-Lema\^ıtre law at very low redshifts. We study how to obtain the Hubble-Lema\^ıtre law in two sky regions using the catalog of HI sources of the ALFALFA survey, with data $cz_{\odot} < 6000$ km/s. Our methodology aims to compute $H_0$ in two regions -- located in opposite galactic hemispheres -- mapped by the ALFALFA survey, and look for dependence with distance, direction, and also test for reference frame changes. We calculate the Hubble constant, in the Cosmic Microwave Background reference frame, in opposite galactic hemispheres: $H_0^N = 70.87 \pm 2.38$ and $H_0^S = 66.07 \pm 3.02$, which allows us to measure the bulk flow velocity $V_{BF} = 401.06 \pm 150.55$ km/s at the effective distance $31.3 \pm 6.26$ Mpc, a novel result found analysing the ALFALFA data at low redshift. We confirm the influence of the bulk flow on the structures of the Local Universe which manifests through a dipolar behavior of the Hubble constant in opposite hemispheres.

astro-ph.CO↗

arXiv2022

Inferring $S_8(z)$ and $γ(z)$ with cosmic growth rate measurements using machine learning

Measurements of the cosmological parameter $S_8$ provided by cosmic microwave background and large scale structure data reveal some tension between them, suggesting that the clustering features of matter in these early and late cosmological tracers could be different. In this work, we use a supervised learning method designed to solve Bayesian approach to regression, known as Gaussian Processes regression, to quantify the cosmic evolution of $S_8$ up to $z \sim 1.5$. For this, we propose a novel approach to find firstly the evolution of the function $σ_8(z)$, then we find the function $S_8(z)$. As a sub-product we obtain a minimal cosmological model-dependent $σ_8(z=0)$ and $S_8(z=0)$ estimates. We select independent data measurements of the growth rate $f(z)$ and of $[fσ_8](z)$ according to criteria of non-correlated data, then we perform the Gaussian reconstruction of these data sets to obtain the cosmic evolution of $σ_8(z)$, $S_8(z)$, and the growth index $γ(z)$. Our statistical analyses show that $S_8(z)$ is compatible with Planck $Λ$CDM cosmology; when evaluated at the present time we find $σ_8(z=0) = 0.766 \pm 0.116$ and $S_8(z=0) = 0.732 \pm 0.115$. Applying our methodology to the growth index, we find $γ(z=0) = 0.465 \pm 0.140$. Moreover, we compare our results with others recently obtained in the literature. In none of these functions, i.e. $σ_8(z)$, $S_8(z)$, and $γ(z)$, do we find significant deviations from the standard cosmology predictions.

astro-ph.CO↗

arXiv2021

The homogeneity scale and the growth rate of cosmic structures

We propose a novel approach to obtain the growth rate of cosmic structures, $f(z)$, from the evolution of the cosmic homogeneity scale, $R_{\text{H}}(z)$. Our methodology needs two ingredients in a specific functional form: $R_{\text{H}}(z)$ data and the matter two-point correlation function today, i.e., $ξ(r, z=0)$. We use a Gaussian Process approach to reconstruct the function $R_{\text{H}}$. In the absence of suitable observational information of the matter correlation function in the local Universe, $z \simeq 0$, we assume a fiducial cosmology to obtain $ξ(r, z=0)$. For this reason, our final result turns out to be a consistency test of the cosmological model assumed. Our results show a good agreement between: (i) the growth rate $f^{R_{\text{H}}}(z)$ obtained through our approach, (ii) the $f^{Λ\text{CDM}}(z)$ expected in the fiducial model, and (iii) the best-fit $f(z)$ from data compiled in the literature. Moreover, using this data compilation, we perform a Gaussian Process to reconstruct the growth rate function $f^{\text{data}}(z)$ and compare it with the function $f^{R_{\text{H}}}(z)$ finding a concordance of $< \!2 \,σ$, a good result considering the few data available for both reconstruction processes. With more accurate $R_{\text{H}}(z)$ data, from forthcoming surveys, the homogeneity scale function might be better determined and would have the potential to discriminate between $Λ$CDM and alternative scenarios as a new cosmological observable.

astro-ph.CO↗