arXiv subjects

Camila Franco

Publications and source records attributed to Camila Franco.

8 recordsLinked to original sources

arXiv2025

The homogeneity scale in the Local Universe: model-independent estimate from S-PLUS DR4 blue galaxies

We present a model-independent estimate of the angular homogeneity scale in the Local Universe by analysing data from the Southern Photometric Local Universe Survey (S-PLUS). Two complementary estimators are employed: (i) a parametric approach fitting the power-law of the two-point angular correlation function, which yields the homogeneity scale $θ_H = 9.01_{-3.61}^{+8.43}\;{\rm deg}$; and (ii) a non-parametric fractal correlation dimension method, computing $\mathcal{D}_2(θ)$ directly from the correlation function, which results in $θ_H = 6.28_{-4.43}^{+8.72}\;{\rm deg}$. From the mock catalogues generated with the GLASS algorithm, we find that the estimates from both methods are within $1 σ$ of the median values obtained by applying both methodologies to the mocks. The transition scale to homogeneity, according to the $Λ$CDM model, is defined for matter, i.e. $b = 1$. Measurements of this scale with observational data clearly depends on the cosmic tracer analysed, and a calibration is necessary. Our study with blue galaxies, with bias $b \simeq 1$, provides a suitable estimate for comparison. Indeed, the results obtained in both approaches are compared with the value expected in the $Λ$CDM model, obtaining a good concordance.

astro-ph.CO↗

arXiv2025

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

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.

astro-ph.CO↗

arXiv2025

Probing the Cosmic Distance Duality Relation via Non-Parametric Reconstruction for High Redshifts

We test the validity of the cosmic distance duality relation (CDDR) by combining angular diameter distance and luminosity distance measurements from recent cosmological observations. For the angular diameter distance, we use data from transverse baryon acoustic oscillations and galaxy clusters. On the other hand, the luminosity distance is obtained from Type Ia supernovae in the Pantheon+ sample and from quasar catalogs. To reduce the large dispersion in quasar luminosity distances, we apply a selection criterion based on their deviation from the $Λ$CDM model and implement a binning procedure to suppress statistical noise. We reconstruct the CDDR using Gaussian Processes, a non-parametric supervised machine learning method. Our results show no significant deviation from the CDDR within the $2σ$ confidence level across the redshift range explored, supporting its validity even at high redshifts.

astro-ph.CO↗

arXiv2025

Is $ω_0 ω_a$CDM a good model for the clumpy Universe?

The DESI collaboration just obtained a set of precise BAO measurements, that combined with CMB and SNIa datasets show that the $ω_0 ω_a$CDM model is preferred over $Λ$CDM, at more than $4\,σ$, to describe the dynamics of the expanding Universe. This raises the question whether this model also suitably describes the clumpy Universe. Also lately, detailed analyses of diverse cosmic tracers resulted in a new dataset of measurements of an observable from the clumpy Universe: $σ_8(z)$, spanning a high-redshift data $z \in [0.013, 3.8]$. In this work we use this dataset of 15 $σ_8(z_i)$ measurements to study the viability of the $ω_0 ω_a$CDM cosmological model to explain the clustered Universe. Our analyses compare the $ω_0 ω_a$CDM model with the $σ_8(z)$ function reconstructed from the data points using Gaussian Process. Moreover, we perform a similar evaluation of the $Λ$CDM model considering Planck and~DESI best-fit parameters. In addition, we implemented robustness tests regarding Gaussian Process reconstruction to support our results.

astro-ph.CO↗

arXiv2025

Dipolar fluence distribution of statistically isotropic FERMI gamma-ray bursts

We investigated the large-angle distribution of the gamma-ray bursts (GRBs) from the updated FERMI/GBM catalog to probe the statistical isotropy of these astrophysical transient events. We also studied the angular distribution of the GRB fluence as a way to explore whether this radiative feature shows some preferred direction on the sky that suggest their origin. Our model-independent approach performed a directional analysis of the updated FERMI/GBM catalog. The statistical significance of our results is obtained by comparison with a large set of statistically isotropic samples of cosmic objects, with the same features of the FERMI data. Our analyses confirm that the angular distribution of the FERMIGRB is statistically isotropic on the celestial sphere. Moreover, analyzing the directional distribution of the FERMIGRB fluence, that is, the median GRB fluence in a set of directions that scans the celestial sphere, we found that this astrophysical property exhibits a net dipolar structure with a directional preference for latitudes near the Galactic plane. However, additional studies show that this directional preference is not correlated with the Milky Way Galactic plane, which suggests that the GRB dataset, and its fluence dipolar structure, are extra-Galactic in origin. Interestingly, the analyses of the BATSE Channel 4 fluence data, that is, those GRBs from BATSE with energy $>$ 300 keV, reveal that its dipole direction is very well aligned with the cosmic microwave background dipole.

astro-ph.HE↗

arXiv2025

Measuring the matter fluctuations in the Local Universe with the ALFALFA catalog

The standard model of cosmology describes the matter fluctuations through the matter power spectrum, where $σ_{8} \equiv σ_{8,0} \equiv σ_{8}(z = 0)$, defined at the scale of $8 h^{-1}$ Mpc, acts as a normalisation parameter. Currently, the literature reports measurements of $σ_{8}$ analysing different cosmic tracers, where some of these results were obtained assuming a fiducial cosmology. In this study we measure, in a model-independent approach, the matter fluctuations in the Local Universe using HI extragalactic sources mapped by the ALFALFA survey. Our analyses allow us to test the standard cosmological model under extreme conditions in the highly non-linear Local Universe, quantifying the amplitude of the matter fluctuations there. Our work directly measures $σ_{8}$ using the 3-dimensional distances of the HI sources determined by the ALFALFA survey without assuming a fiducial cosmology, resulting in a robust model-independent measurement of $σ_{8}$. Our methodology involves the construction of suitable mock catalogues to simulate the large scale structure features observed in the data, applying the 2-point correlation function, and making use of Markov Chain Monte Carlo methods to estimate the parameters. Analysing these data we measure $σ_8 = 0.78 \pm 0.04$ for $h = 0.6727$, $σ_8 = 0.80 \pm 0.05$ for $h = 0.698$, and $σ_8 = 0.83 \pm 0.05$ for $h = 0.7304$. Considering the data pairs $(σ_8, H_0)$ from the Planck CMB and Atacama Cosmology Telescope (ACT) CMB-lensing analyses, our measurement agrees with them within $1\,σ$ confidence level. From a model-independent perspective, we find that the scale where the matter fluctuation is $1$ is $R = 7.2 \pm 1.5~\text{Mpc}$.

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arXiv2024

Bulk Flow Motion Detection in the Local Universe with Pantheon$+$ Type Ia Supernovae

The {\em bulk flow} in the Local Universe is a collective phenomenon due to the peculiar motions of matter structures, which, instead of moving in random directions, appears to follow an approximate dipole velocity flow. We apply a directional analysis to investigate, through the Hubble-Lema\^ıtre diagram, the angular dependence of the Hubble constant $H_0$ of a sample of Type Ia Supernovae from the Pantheon+ catalog in the Local Universe ($0.015 \le z \le 0.06$). We perform a directional analysis that reveals a statistically significant dipole variation of $H_0$, at more than $99.9\%$ confidence level, showing that matter structures follow a dipole bulk flow motion towards $(l,b) = (326.^\circ1 \pm 11.^\circ2,27.^\circ8 \pm 11.^\circ2)$, close to the Shapley supercluster $(l_{\scalebox{0.6}{Shapley}},b_{\scalebox{0.6}{Shapley}}) = (311.^\circ5, 32.^\circ3)$, with velocity $132.14 \pm 109.3$ km s$^{-1}$ at the effective distance $102.83 \pm 10.2$~Mpc. Interestingly, the antipodal direction of this dipole points close to the Dipole Repeller structure. Our analyses confirm that the gravitational dipole system Shapley-Dipole Repeller explains well the observed bulk flow velocity field in the Local Universe. Furthermore, we performed robustness tests that support our results. Additionally, our approach provides a measurement of the Hubble constant $H_0 = 70.39 \pm 1.4$~\text{km s$^{-1}$ Mpc$^{-1}$}, at the effective distance $102.8$~Mpc, $z \simeq 0.025$. Note that this value was obtained using the first order approximation of the Hubble law because our methodology is model-independent. If one assumes, for instance, cosmography at second order with the $Λ$CDM value $q_0 = -0.55$, which is a model-dependent hypothesis, then $H_0 = 72.6 \pm 1.5$ km s$^{-1}$ Mpc$^{-1}$, but our results: bulk flow velocity, dipole direction and its statistical significance remain the same.

astro-ph.CO↗

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.

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