Dissertações de Mestrado PPGA

“MAPPING THE 2D MATTER DISTRIBUTION IN THE LOCAL UNIVERSE USING BLUE GALAXIES FROM SDSS DR12”

Fri, 24 Jul 2026 00:00:00 GMT

“MAPPING THE 2D MATTER DISTRIBUTION IN THE LOCAL UNIVERSE USING BLUE GALAXIES FROM SDSS DR12” Maria Vitoria Lazarin, Maria Vitoria Lazarin Armando Bartolome Bernui Leo , Armando Bartolome Bernui Leo Baryon Acoustic Oscillations (BAO), a preferred scale of approximately 150 Mpc im- printed on the large-scale matter distribution by acoustic waves in the primordial plasma, constitute one of the most robust standard rulers in cosmology. In contrast to the more common angular approach, based on the angular correlation function ω(θ), in this work the BAO are measured through the angular power spectrum Cℓ, in harmonic space, using a sample of star-forming blue galaxies at low redshift from the twelfth data release of the Sloan Digital Sky Survey (SDSS). The aim is to validate a pipeline for the angular analysis of BAO in harmonic space and to apply it to this unconventional sample. The methodology is only weakly dependent on the assumed cosmological model: by working in transverse harmonic space, it does not require the conversion of redshifts into radial dis- tances, so that the information on the acoustic scale follows exclusively from the position of the oscillatory feature in multipole space. For the analysis, the sample was divided into two redshift bins: 0.15 < z < 0.25 (the main measurement) and 0.05 < z < 0.15 (pipeline validation). The angular power spectrum of both samples is estimated with the pseudo-Cℓ formalism, and the covariance is built from 1000 lognormal catalogs generated with the GLASS code and iteratively recalibrated. The shift parameter α is determined by two independent methods: the profile likelihood and Markov Chain Monte Carlo (MCMC). For the main bin, we obtain α = 1.034+0.155-0.162 and α = 0.974+0.247-0.194, respectively, both consistent, within the uncertainties, with the value <α> = 1 expected in the ΛCDM model. The preference for the oscillatory model is marginal (∆χ2 = 1.38; 1.17σ), consistent with the accuracy allowed by the volume and sky coverage of the survey (f_sky ~ 0.18); in the low-redshift bin no significant preference is found (∆χ2 < 0.1), as expected in the absence of a detectable signal. The measured scale corresponds to a ratio between the transverse comoving distance and the sound horizon of D_M / r_d = 5.606 +/- 1.276 at z_eff = 0.20, without being able to discriminate between the predictions of Planck (2018) and DESI (2025), and to an acoustic angular scale θ_BAO = (10.21 +/- 2.326)deg. Combined with angular compilations from the literature, it yields Ωm,0 = 0.269+0.018-0.017 and h*r_d = 103.11+0.98-0.99 Mpc. Although the low significance reflects the intrinsic difficulty of the measurement in this regime, the results suggest the viability of blue galaxies as BAO tracers and validate the analysis framework for application to future surveys. Observatorio Nacional Dissertação

COSMOGRAFIA COM ONDAS GRAVITACIONAIS”

Fri, 31 Jul 2026 00:00:00 GMT

COSMOGRAFIA COM ONDAS GRAVITACIONAIS” Jonathan Silva de Morais, Jonathan Silva de Morais Jailson Souza de Alcaniz , Jailson Souza de Alcaniz In this work, we investigate the potential of gravitational-wave standard sirens to constrain cosmographic parameters independently of a specific cosmological model. We consider simulated catalogs of \textit{bright sirens}, assuming the identification of electromagnetic counterparts and, therefore, an independent determination of the source redshifts. The analysis is performed for three observational configurations: Advanced LIGO, Einstein Telescope, and DECIGO, allowing us to compare the performance of current and future detectors in reconstructing the luminosity distance--redshift relation. To describe the cosmic expansion, we use the Taylor cosmographic expansion up to $\mathcal{O}(z^3)$ and the Padé approximants $P_{2,1}$ and $P_{3,2}$, evaluating their convergence properties and their impact on the constraints of the parameters $H_0$, $q_0$, and $j_0$, as well as the higher-order parameters $s_0$ and $l_0$ in the case of Padé $P_{3,2}$. We study two complementary scenarios: an analysis as a function of the signal-to-noise ratio of the events and an analysis as a function of the total number of detections. The results show that Advanced LIGO is mainly sensitive to the determination of $H_0$, reaching relative precisions of about $2\%$ in the SNR-based analysis and approximately $1.1\%$ in the most optimistic scenarios based on the number of events. The Einstein Telescope significantly improves the constraints, reaching subpercent precision for $H_0$, of about $0.5\%$--$0.6\%$, and constraining $q_0$ with relative precision of approximately $16\%$--$19\%$. DECIGO provides the best overall performance, reaching precisions of about $0.25\%$--$0.30\%$ for $H_0$, $6\%$--$10\%$ for $q_0$, and making the jerk parameter $j_0$ observationally informative, with relative precision of approximately $16\%$ in the most favorable scenario. In general, the Taylor expansion provides the best precision for the common set of parameters within its domain of validity, while the Padé approximants are important for assessing the stability of the cosmographic reconstruction over wider redshift intervals. We conclude that gravitational-wave standard sirens constitute a promising and complementary tool for investigating the expansion history of the Universe and testing possible deviations from the standard cosmological model. Observatorio Nacional Dissertação

“IDENTIFICAÇÃO E CARACTERIZAÇÃO DE EXOPLANETAS ROCHOSOS ASTROBIOLOGICAMENTE INTERESSANTES”

Thu, 13 Aug 2026 00:00:00 GMT

“IDENTIFICAÇÃO E CARACTERIZAÇÃO DE EXOPLANETAS ROCHOSOS ASTROBIOLOGICAMENTE INTERESSANTES” Fábio Calabrio Evangelista da Silva, Fábio Calabrio Evangelista da Silva Marcelo Borges Fernandes, Marcelo Borges Fernandes The primary objective of this dissertation is the search for astrobiologically interesting rocky exoplanets through the characterization of their physical and orbital parameters, as well as their positions within the Habitable Zone (HZ) of their host stars. Physical parameters and the HZ were calculated for a sample of more than 6,000 exoplanets available in the NASA database (NASA Exoplanet Archive). The calculations were performed using codes developed by the author of this research together with a one-dimensional radiative-convective climate model (ATMOS). By combining the climate model with the orbital distances of the planets, it is possible to infer their likely atmospheric composition, as well as assume their surface temperature and surface pressure. These parameters make it possible to rank exoplanets according to their Earth Similarity Index (ESI). Two samples with distinct limiting physical parameters were analyzed: Rocky Planets Including Super-Earths/Hycean Planets and Small Rocky Planets. A total of 1,447 Small Rocky Exoplanets (0.1 M⊕ < Mp < 4.37 M⊕ or 0.1 R⊕ < RP < 1.64 R⊕) were compiled. Of these, 44 are located within the Optimistic Habitable Zone, and 26 within the Conservative Habitable Zone. By following the ATMOS model, 25 of these exoplanets were classified within the Conservative Habitable Zone, of which 20 are consistent with a possible Earth-like atmosphere and 15 exhibit an ESI > 0.8. Further, a total of 1,161 Rocky Super-Earth/Hycean Exoplanets (4.37 M⊕ < MP < 10 M⊕ or 1.64 R⊕ < RP < 2.5 R⊕) were compiled. Of these, 31 are located within the Optimistic Habitable Zone, and 14 within the Conservative Habitable Zone. By following the ATMOS model, 14 of these exoplanets were classified within the Conservative Habitable Zone, of which 15 are consistent with a possible Earth-like atmosphere and 9 exhibit an ESI > 0.8. The analysis identifies eight exoplanets with surface temperatures capable of sustaining liquid water: GJ 1002b, GJ 180c, GJ 433d, Kepler-1652b, Kepler-22b, Kepler-442b, Kepler-443b, and TOI-700d. Only two of these are classified as Super-Earth/Hycean planets: Kepler-22b and Kepler-443b. Nearly all exhibit an ESI > 0.8, with the sole exception of Kepler-443b. Among them, GJ 1002b stands out as the most promising candidate because of its strong similarity to Earth across the four parameters used in the ESI calculation. The results reinforce the potential of rocky planets located within habitable zones as priority targets for future observations with instruments such as the JWST (James Webb Space Telescope) and high-resolution spectrographs. At the same time, they highlight methodological limitations that should be addressed, including the need for a broader range of atmospheric models and more accurate mass-radius relationships. Observatorio Nacional Dissertação

“CONSTRUINDO UMA ABRANGENTE LISTA DE LINHAS ESPECTRAIS PARA ESPECTROSCOPIA NO INFRAVERMELHO PRÓXIMO DE λ 1–5 μM”

Fri, 20 Mar 2026 00:00:00 GMT

“CONSTRUINDO UMA ABRANGENTE LISTA DE LINHAS ESPECTRAIS PARA ESPECTROSCOPIA NO INFRAVERMELHO PRÓXIMO DE λ 1–5 μM” Gabriela Neves Lima, Gabriela Neves Lima Katia Maria Leite da Cunha , Katia Maria Leite da Cunha Spectral line lists constitute the foundation for spectral synthesis calculations and the determination of chemical abundances, including those derived from large spectroscopic surveys such as SDSS–APOGEE. This project extended beyond the APOGEE spectral region (between λ 1.5 and 1.7, μm) and produced a new and comprehensive atomic and molecular line list covering the wavelength range λ 1 to 5, μm. Currently available atomic and molecular data were critically reviewed and consolidated into an updated line list, spanning a spectral range compatible with several combinations of ground-based telescopes and spectrographs, as well as with the NIRSpec spectrograph aboard the James Webb Space Telescope. The line list was constructed in the format accepted by the spectral synthesis code Turbospectrum, which was used to generate the synthetic spectra employed for comparison with the observed spectra. The atomic and molecular data were evaluated through comparisons with the benchmark stars the Sun, Arcturus, and an M dwarf with previously determined parameters, using high-quality, high-resolution near-infrared spectra. The inclusion of an M-type dwarf star in the fitting and validation processes is essential, as these stars exhibit a high molecular concentration in the spectral region λ = 1 to 5μm, producing a pseudo-continuum strongly dominated by molecular features, such as those of H2O and FeH. Once the line list was completed, we focused on the analysis of spectra of Barnard’s Star, determining its effective temperature, surface gravity, metallicity, and chemical abundances using the BACCHUS code, and subsequently employing this star to validate the line list developed in this work. Observatorio Nacional Dissertação