arXiv subjects

C. P. Novaes

Publications and source records attributed to C. P. Novaes.

13 recordsLinked to original sources

arXiv2021

The growth rate of cosmic structures in the local Universe with the ALFALFA survey

We investigate the growth rate of structures in the local Universe. For this, we use as a cosmological tracer the HI line extra-galactic sources from the Arecibo Legacy Fast ALFA (ALFALFA) survey to obtain a measurement of the normalized growth rate parameter, $f σ_{8}$, considered a powerful tool to constrain alternative models of gravity. For these analyses, we calculate the Local Group velocity due to the matter structures distribution in the ALFALFA catalogue and compare it with the Local Group velocity relative to the Cosmic Microwave Background frame to obtain the velocity scale parameter, $β$. Using Monte Carlo realizations and log-normal simulations, our methodology quantifies the errors introduced by shot-noise and partial sky coverage of the analysed data. The measurement of the velocity scale parameter $β$, and the calculation of the matter fluctuation of the cosmological tracer, $σ_{8}^{\text{tr}}$, lead us to $f σ_{8} = 0.46 \pm 0.06$ at $\bar{z} = 0.013$, in good agreement (at $1 σ$ level) with the value expected in the $Λ$CDM concordance model. In addition, our analyses of the ALFALFA sample also provide a measurement of the growth rate of structures $f \,=\, 0.56 \pm 0.07$, at $\bar{z} = 0.013$.

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arXiv2021

BAO angular scale at z_eff = 0.11 with the SDSS blue galaxies

We measure the transverse baryon acoustic oscillations (BAO) signal in the local Universe using a sample of blue galaxies from the Sloan Digital Sky Survey (SDSS) survey as a cosmological tracer. The method is weakly dependent on a cosmological model and is suitable for 2D analyses in thin redshift bins to investigate the SDSS data in the interval $z {\in} [0.105, 0.115]$. We detect the transverse BAO signal $θ_{BAO} = 19.8^° {\pm} 1.05^°$ at $z_{eff} = 0.11$, with a statistical significance of $2.2 σ$. Additionally, we perform tests that confirm the robustness of this angular BAO signature. Supported by a large set of log-normal simulations, our error analyses include statistical and systematic contributions. In addition, considering the sound horizon scale calculated by the Planck Collaboration, $r_{s}^{Planck}$, and the $θ_{BAO}$ value obtained here, we obtain a measurement of the angular diameter distance $D_{A}(0.11) = 258.31 {\pm} 13.71 \,Mpc/h$. Moreover, combining this $θ_{BAO}$ measurement at low redshift with other BAO angular scale data reported in the literature, we perform statistical analyses for the cosmological parameters of some Lambda cold dark matter ($Λ$CDM) type models.

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arXiv2020

Baryon acoustic oscillations signature in the three-point angular correlation function from the SDSS-DR12 quasar survey

The clustering properties of the Universe at large-scales are currently being probed at various redshifts through several cosmological tracers and with diverse statistical estimators. Here we use the three-point angular correlation function (3PACF) to probe the baryon acoustic oscillation (BAO) features in the quasars catalogue from the twelfth data release of the Sloan Digital Sky Survey, with mean redshift z = 2.225, detecting the BAO imprint with a statistical significance of 2.9σ, obtained using lognormal mocks. Following a quasi model-independent approach for the 3PACF, we find the BAO transversal signature for triangles with sides $θ_1 = 1.0^\circ$ and $θ_2 = 1.5^\circ$ and the angle between them of $α= 1.59 \pm 0.17$ rad, a value that corresponds to the angular BAO scale $θ_{BAO} = 1.82^\circ \pm 0.21^\circ$ , in excellent agreement with the value found in a recent work ($θ_{BAO} = 1.77^\circ \pm 0.31^\circ$ ) applying the 2PACF to similar data. Moreover, we performed two type of tests: one to confirm the robustness of the BAO signal in the 3PACF through random displacements in the dataset, and the other to verify the suitability of our random samples, a null test that in fact does not show any signature that could bias our results.

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arXiv2019

The angular scale of homogeneity in the Local Universe with the SDSS blue galaxies

We probe the angular scale of homogeneity in the local Universe using blue galaxies from the SDSS survey as a cosmological tracer. Through the scaled counts in spherical caps, $ \mathcal{N}(<θ) $, and the fractal correlation dimension, $\mathcal{D}_{2}(θ)$, we find an angular scale of transition to homogeneity for this sample of $θ_{\text{H}} = 22.19^{\circ} \pm 1.02^{\circ}$. A comparison of this measurement with another obtained using a different cosmic tracer at a similar redshift range ($z < 0.06$), namely, the HI extragalactic sources from the ALFALFA catalogue, confirms that both results are in excellent agreement (taking into account the corresponding bias correction). We also perform tests to asses the robustness of our results. For instance, we test if the size of the surveyed area is large enough to identify the transition scale we search for, and also we investigate a reduced sample of blue galaxies, obtaining in both cases a similar angular scale for the transition to homogeneity. Our results, besides confirming the existence of an angular scale of transition to homogeneity in different cosmic tracers present in the local Universe, show that the observed angular scale $θ_{\text{H}}$ agrees well with what is expected in the $Λ$CDM scenario. Although we can not prove spatial homogeneity within the approach followed, our results provide one more evidence of it, strengthening the validity of the Cosmological Principle.

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arXiv2018

The scale of homogeneity in the local Universe with the ALFALFA catalogue

We use the scaled counts in spherical caps $\mathcal{N}(<θ)$ and the fractal correlation dimension $ \mathcal{D}_{2}(θ) $ procedures to search for a transition scale to homogeneity in the local universe as given by the ALFALFA catalogue (a sample of extragalactic HI line sources, in the redshift range $0 < z < 0.06$). Our analyses, in the 2-dimensional sky projected data, show a transition to homogeneity at $θ_H = 16.49^{\circ} \pm 0.29^{\circ}$, in remarkable accordance with the angular scale expected from simulations, a result that strengthens the validity of the cosmological principle in the local universe. We test the robustness of our results by analysing the data sample using three versions of the $\mathcal{N}(<θ)$ estimator, which show a well agreement between them. These statistical estimators were validated using mock realizations generated assuming a fractal distribution of points, successfully recovering the input information. In addition, we perform further analyses showing that our approach is also able to indicate the presence of under- and over-densities in the data. Finally, we verify the influence of the sample size to the $θ_H$ estimates by using segment Cox processes of different projected areas, confirming the suitability of the ALFALFA surveyed area for the current analyses.

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arXiv2018

Angular Baryon Acoustic Oscillation measure at z=2.225 from the SDSS quasar survey

Following a quasi model-independent approach we measure the transversal BAO mode at high redshift using the two-point angular correlation function (2PACF). The analyses done here are only possible now with the quasar catalogue from the twelfth data release (DR12Q) from the Sloan Digital Sky Survey, because it is spatially dense enough to allow the measurement of the angular BAO signature with moderate statistical significance and acceptable precision. Our analyses with quasars in the redshift interval z = [2.20,2.25] produce the angular BAO scale theta_BAO = 1.77 +- 0.31 deg with a statistical significance of 2.12 sigma (i.e., 97% confidence level), calculated through a likelihood analysis performed using the theoretical covariance matrix sourced by the analytical power spectra expected in the LCDM concordance model. Additionally, we show that the BAO signal is robust -although with less statistical significance- under diverse bin-size choices and under small displacements of the quasars' angular coordinates. Finally, we also performed cosmological parameter analyses comparing the theta_BAO predictions for wCDM and w(a)CDM models with angular BAO data available in the literature, including the measurement obtained here, jointly with CMB data. The constraints on the parameters Omega_M, w_0 and w_a are in excellent agreement with the LCDM concordance model.

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arXiv2018

The dipole anisotropy of WISE x SuperCOSMOS number counts

We probe the isotropy of the Universe with the largest all-sky photometric redshift dataset currently available, namely WISE~$\times$~SuperCOSMOS. We search for dipole anisotropy of galaxy number counts in multiple redshift shells within the $0.10 < z < 0.35$ range, for two subsamples drawn from the same parent catalogue. Our results show that the dipole directions are in good agreement with most of the previous analyses in the literature, and in most redshift bins the dipole amplitudes are well consistent with $Λ$CDM-based mocks in the cleanest sample of this catalogue. In the $z<0.15$ range, however, we obtain a persistently large anisotropy in both subsamples of our dataset. Overall, we report no significant evidence against the isotropy assumption in this catalogue except for the lowest redshift ranges. The origin of the latter discrepancy is unclear, and improved data may be needed to explain it.

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arXiv2017

Isotropy analyses of the Planck convergence map

The presence of matter in the path of relic photons causes distortions in the angular pattern of the cosmic microwave background (CMB) temperature fluctuations, modifying their properties in a slight but measurable way. Recently, the Planck Collaboration released the estimated convergence map, an integrated measure of the large-scale matter distribution that produced the weak gravitational lensing (WL) phenomenon observed in Planck CMB data. We perform exhaustive analyses of this convergence map calculating the variance in small and large regions of the sky, but excluding the area masked due to galactic contaminations, and compare them with the features expected in the set of simulated convergence maps, also released by the Planck collaboration. Our goal is to search for sky directions or regions where the WL imprints anomalous signatures to the variance estimator revealed through a $χ^2$ analyses at a statistically significant level. In the local analysis of the Planck convergence map we identified 8 patches of the sky in disagreement, in more than 2$σ$, with what is observed in the average of the simulations. In contrast, in the large regions analysis we found no statistically significant discrepancies, but, interestingly, the regions with the highest $χ^2$ values are surrounding the ecliptic poles. Thus, our results show a good agreement with the features expected by the $Λ$CDM concordance model, as given by the simulations. Yet, the outliers regions found here could suggest that the data still contain residual contamination, like noise, due to over- or under-estimation of systematic effects in the simulation data set.

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arXiv2017

Is there evidence for anomalous dipole anisotropy in the large-scale structure?

We probe the anisotropy of the large-scale structure (LSS) with the WISE-2MASS catalogue. This analysis is performed by a directional comparison of the galaxy number counts through the entire celestial sphere once systematic effects, such as star-galaxy separation and foregrounds contamination, are properly taken into account. We find a maximal hemispherical asymmetry whose dipolar component is $A = 0.0507 \pm 0.0014$ toward the $(l,b) = (323^{\circ},-5^{\circ})$ direction, whose result is consistent with previous estimations of our proper motion in low and intermediate redshifts, as those carried out with Type Ia Supernovae and similar LSS catalogues. Furthermore, this dipole amplitude is statistically consistent ($p$-value = $0.061$) with mock catalogues simulated according to the expected $Λ$CDM matter density fluctuations, in addition to observational biases such as the incomplete celestial coverage and anisotropic sky exposure. Our results suggest, therefore, that there is no strong evidence for anomalous anisotropy in the LSS, given the limitations and systematics of current data, in the concordance model scenario.

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arXiv2016

A Bayesian estimate of the CMB-large-scale structure cross-correlation

Evidences for late-time acceleration of the Universe are provided by multiple probes, such as Type Ia supernovae, the cosmic microwave background (CMB) and large-scale structure (LSS). In this work, we focus on the integrated Sachs--Wolfe (ISW) effect, i.e., secondary CMB fluctuations generated by evolving gravitational potentials due to the transition between, e.g., the matter and dark energy (DE) dominated phases. Therefore, assuming a flat universe, DE properties can be inferred from ISW detections. We present a Bayesian approach to compute the CMB--LSS cross-correlation signal. The method is based on the estimate of the likelihood for measuring a combined set consisting of a CMB temperature and a galaxy contrast maps, provided that we have some information on the statistical properties of the fluctuations affecting these maps. The likelihood is estimated by a sampling algorithm, therefore avoiding the computationally demanding techniques of direct evaluation in either pixel or harmonic space. As local tracers of the matter distribution at large scales, we used the Two Micron All Sky Survey (2MASS) galaxy catalog and, for the CMB temperature fluctuations, the ninth-year data release of the Wilkinson Microwave Anisotropy Probe (WMAP9). The results show a dominance of cosmic variance over the weak recovered signal, due mainly to the shallowness of the catalog used, with systematics associated with the sampling algorithm playing a secondary role as sources of uncertainty. When combined with other complementary probes, the method presented in this paper is expected to be a useful tool to late-time acceleration studies in cosmology.

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arXiv2016

Local analyses of Planck maps with Minkowski Functionals

Minkowski Functionals (MF) are excellent tools to investigate the statistical properties of the cosmic background radiation (CMB) maps. Between their notorious advantages is the possibility to use them efficiently in patches of the CMB sphere, which allow studies in masked skies, inclusive analyses of small sky regions. Then, possible deviations from Gaussianity are investigated by comparison with MF obtained from a set of Gaussian isotropic simulated CMB maps to which are applied the same cut-sky masks. These analyses are sensitive enough to detect contaminations of small intensity like primary and secondary CMB anisotropies. Our methodology uses the MF, widely employed to study non-Gaussianities in CMB data, and asserts Gaussian deviations only when all of them points out an exceptional $χ^2$ value, at more than $2.2 σ$ confidence level, in a given sky patch. Following this rigorous procedure, we find 13 regions in the foreground-cleaned Planck maps that evince such high levels of non-Gaussian deviations. According to our results, these non-Gaussian contributions show signatures that can be associated to the presence of hot or cold spots in such regions. Moreover, some of these non-Gaussian deviations signals suggest the presence of foreground residuals in those regions located near the galactic plane. Additionally, we confirm that most of the regions revealed in our analyses, but not all, have been recently reported in studies done by the Planck collaboration. Furthermore, we also investigate whether these non-Gaussian deviations can be possibly sourced by systematics, like inhomogeneous noise and beam effect in the released Planck data, or perhaps due to residual galactic foregrounds.

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arXiv2015

A Neural-Network based estimator to search for primordial non-Gaussianity in Planck CMB maps

We present an upgraded combined estimator, based on Minkowski Functionals and Neural Networks, with excellent performance in detecting primordial non-Gaussianity in simulated maps that also contain a weighted mixture of Galactic contaminations, besides real pixel's noise from Planck cosmic microwave background radiation data. We rigorously test the efficiency of our estimator considering several plausible scenarios for residual non-Gaussianities in the foreground-cleaned Planck maps, with the intuition to optimize the training procedure of the Neural Network to discriminate between contaminations with primordial and secondary non-Gaussian signatures. We look for constraints of primordial local non-Gaussianity at large angular scales in the foreground-cleaned Planck maps. For the $\mathtt{SMICA}$ map we found ${f}_{\rm \,NL} = 33 \pm 23$, at $1σ$ confidence level, in excellent agreement with the WMAP-9yr and Planck results. In addition, for the other three Planck maps we obtain similar constraints with values in the interval ${f}_{\rm \,NL} \in [33, 41]$, concomitant with the fact that these maps manifest distinct features in reported analyses, like having different pixel's noise intensities.

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arXiv2013

Searching for primordial non-Gaussianity in Planck CMB maps using a combined estimator

The extensive search for deviations from Gaussianity in cosmic microwave background radiation (CMB) data is very important due to the information about the very early moments of the universe encoded there. Recent analyses from Planck CMB data do not exclude the presence of non-Gaussianity of small amplitude, although they are consistent with the Gaussian hypothesis. The use of different techniques is essential to provide information about types and amplitudes of non-Gaussianities in the CMB data. In particular, we find interesting to construct an estimator based upon the combination of two powerful statistical tools that appears to be sensitive enough to detect tiny deviations from Gaussianity in CMB maps. This estimator combines the Minkowski functionals with a Neural Network, maximizing a tool widely used to study non-Gaussian signals with a reinforcement of another tool designed to identify patterns in a data set. We test our estimator by analyzing simulated CMB maps contaminated with different amounts of local primordial non-Gaussianity quantified by the dimensionless parameter fNL. We apply it to these sets of CMB maps and find \gtrsim 98% of chance of positive detection, even for small intensity local non-Gaussianity like fNL = 38 +/- 18, the current limit from Planck data for large angular scales. Additionally, we test the suitability to distinguish between primary and secondary non-Gaussianities and find out that our method successfully classifies ~ 95% of the tested maps. Furthermore, we analyze the foreground-cleaned Planck maps obtaining constraints for non-Gaussianity at large-angles that are in good agreement with recent constraints. Finally, we also test the robustness of our estimator including cut-sky masks and realistic noise maps measured by Planck, obtaining successful results as well.

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