Dissertações de Mestrado PPGA

“O ELO PERDIDO NA EVOLUÇÃO DE RÁDIO-GALÁXIAS: INVESTIGANDO EMISSÕES ESTENDIDAS EM BAIXA FREQUÊNCIA”

Wed, 08 Oct 2025 00:00:00 GMT

“O ELO PERDIDO NA EVOLUÇÃO DE RÁDIO-GALÁXIAS: INVESTIGANDO EMISSÕES ESTENDIDAS EM BAIXA FREQUÊNCIA” Vinícius Sanches Moreira Lima, Vinícius Sanches Moreira Lima Alberto Rodríguez Ardila , Alberto Rodríguez Ardila Active galactic nuclei (AGNs) with jets are morphologically classified according to their evolutionary stage, with Gigahertz Peaked-Spectrum (GPS) and Compact SteepSpectrum (CSS) sources traditionally understood as representing the young and confined phase of jets. However, the paradigm of a linear evolution has been challenged by an abundance of compact sources and the discovery of objects featuring a young nucleus embedded within a structure related to extended and aged emission, indicating multiple episodes of activity (“restarted” jets). This work aims to re-evaluate a sample of 84 sources previously classified as GPS/CSS by leveraging the unparalleled sensitivity of the LOFAR Two-metre Sky Survey (LoTSS) at 144 MHz to detect extended, low-surface-brightness emission undetectable in surveys above 1 GHz. We combined multi-frequency data (from 144 MHz to 4.85 GHz) to perform a comparative morphological analysis and construct Spectral Energy Distributions (SEDs). Our results show that 9 sources (17.3%) display clear morphological evidence of extended emission, being classified as restarted. Another 9 sources (17.3%) are classified as restarted jet candidates, and 28 (53.8%) remain compact. Spectral analysis reveals a diversity of classes (GPS, CSS, HFP, and spectra without peaks or flattened at low frequencies), with a tendency for restarted sources to have steeper (CSS-like) spectra. We conclude that a significant fraction of compact sources are, in fact, restarted jets, suggesting that jet activity is a cyclic and intermittent process. This result has profound implications for evolutionary models of radio galaxies and for the understanding of feedback exerted by multiple episodes of activity Observatorio Nacional Dissertação

“EVALUATION OF THE DYNAMICAL STATE OF THE HIGHREDSHIFT GALAXY CLUSTER SPT-CL J2215-3537”

Tue, 02 Sep 2025 00:00:00 GMT

“EVALUATION OF THE DYNAMICAL STATE OF THE HIGHREDSHIFT GALAXY CLUSTER SPT-CL J2215-3537” VINICIUS DOS SANTOS BESSA RIBEIRO, VINICIUS DOS SANTOS BESSA RIBEIRO Renato de Alencar Dupke, Renato de Alencar Dupke The accurate determination of the dynamical state of galaxy clusters is critical for cluster cosmology, as near-equilibrium processes in the intracluster medium of dynami- cally relaxed systems enable the derivation of the mass distribution and other important scaling relations with minimal uncertainties. Recently the galaxy cluster SPT-CL J2215- 3537 (z = 1.16) has been identified as one of the most distant relaxed cluster using the symmetry–peakiness–alignment (SPA) criterion, which consists in the construction of X-ray morphological statistics to assess the degree of relaxation. However, SPT-CLJ0615- 5746 (z = 0.97), which was previously marked as relaxed by the SPA treatment, showed signs to be in a merging state when analyzed by the intracluster light fraction and tradi- tional X-ray analysis. The present work aims to evaluate the dynamical state of SPT-CL J2215-3537 through X-ray spectral and imaging analyzes. The characterization of the thermodynamical properties of the intracluster medium and its morphological features reveals signatures of sloshing cold fronts in the SE-NW axis. We find a ghost cavity candidate and estimate its mechanical power as log10{Pcav/(10^42 erg/s)} = 2.66+-0.23, indicanting that radiative cooling strongly exceeds AGN feedback heating. The results from our combined analysis suggest that SPT-CL J2215-3537 is mildly disturbed. We use the feedback-regulated precipitation framework to show that the cluster’s core is likely in a transient state towards a stable cooling-feedback cycle within the next ~ 100+-70 Myr. We additionally recalculate traditional X-ray morphological parameters and present a discussion of its limitations for high-redshift clusters. Observatorio Nacional Dissertação

“CARACTERIZANDO ESTRELAS GIGANTES VERMELHAS NO AGLOMERADO ABERTO IC 2714: UM ESTUDO ECTROSCÓPICO E ASTROMÉTRICO”

Wed, 12 Mar 2025 00:00:00 GMT

“CARACTERIZANDO ESTRELAS GIGANTES VERMELHAS NO AGLOMERADO ABERTO IC 2714: UM ESTUDO ECTROSCÓPICO E ASTROMÉTRICO” Thiago Flaulhabe Xavier Gomes, Thiago Flaulhabe Xavier Gomes José Nacizo Holanda Junior, José Nacizo Holanda Junior In this work, our objective is to conduct a comprehensive study of a sample of eight red giants previously reported as members of the open cluster IC 2714. Using high-resolution spectra, we have performed a chemical analysis by determining atmospheric parameters, projected rotational velocities, and chemical abundances for 21 species in the sample, employing equivalent width measurements and spectral synthesis as techniques. Further- more, using robust algorithms from recent literature, we have conducted a membership study using astrometric data and estimated the physical parameters of the cluster through isochrone fitting. Our astrometric study allows us to classify 898 stars as cluster members, and due to their discrepant astrometric results, two stars in our sample were classified as non-members. The chemical abundances of all the red giants classified as members in our sample agree with literature results for dwarfs and giants in the solar neighbor- hood. Moreover, three stars in our sample exhibit anomalous rotation, and among them, we report a lithium-rich giant candidate. To explain this chemically peculiar nature, we suggest that this star underwent accretion of a planet or substellar companion, which possibly triggered a self-enrichment lithium process. Finally, we discuss our results for the open cluster IC 2714 in the context of chemical gradients in the Galaxy and the study of cosmic chronometers. The results of this work can contribute to the study of stellar nucleosynthesis models and Galactic chemical evolution models, in addition to guiding possible more in-depth studies. Observatorio Nacional Dissertação

“Caracterização Instrumental e do Céu no Observatório Astronômico do Sertão de Itaparica (OASI)”

Fri, 26 Sep 2025 00:00:00 GMT

“Caracterização Instrumental e do Céu no Observatório Astronômico do Sertão de Itaparica (OASI)” Tatiane Corrêa da Costa e Silva, Tatiane Corrêa da Costa e Silva Eduardo de Jesús Rondón Briceño, Eduardo de Jesús Rondón Briceño The instrumental and night-sky characterization of an astronomical observatory are essential for efficient observation planning, appropriate of new instrument selection, and the application of photometric corrections, thereby enabling more accurate determination of the physical parameters of observed objects. This work presents a detailed description of the instrumentation currently available at the Observatório Astronômico do Sertão de Itaparica (OASI), with comments on recent acquisitions, planned equipment, identified operational limitations, and proposed mitigation strategies. On the other hand, the characterization of the sky was carried out, determining the seeing distribution for 30- and 40-second exposures, both peaking at a mode of $1.35''$. The mean seeing was $1.48''$ (30 s) and $1.36''$ (40 s), with standard deviations of $0.55''$ and $0.47''$, respectively. The annual analysis showed no apparent correlation between seeing and seasonality, indicating the presence of photometric nights throughout most of the year. No correlation were found between seeing and meteorological parameters such as humidity, atmospheric pressure, and temperature. Nevertheless, the possibility of a correlation in multivariate analyses that consider combinations of meteorological parameters cannot be ruled out. Another parameter studied was the atmospheric extinction coefficient in the R filter, using data from 2011 to 2018. The distribution of this parameter showed a mode at $0.318$, median of $0.236$, and mean of $0.261$. These values are consistent with OASI’s local characteristics, including its low elevation, proximity to a river, and the presence of dust, which contribute to increased aerosol scattering. Finally, an analysis of light pollution was conducted using All-Sky camera images. A progressive increase in light pollution was observed up to 2018, followed by a reduction during the COVID-19 pandemic, and a sharp rise from 2021 onward, linked to urban infrastructure projects and the replacement of sodium lamps with LEDs. The main emission sources were identified in nearby cities, with a newly detected hotspot located in in Coité, only 5.5 km from OASI. Light pollution imposes significant observational constraints, especially for low-altitude targets ($<20^\circ$), such as Atira-type asteroids and Sungrazers, primarily affecting the western sky. In contrast, the eastern sky remains with low light pollution, providing more favorable conditions for observing these objects at sunrise. Observatorio Nacional Dissertação