arXiv subjects

Reinaldo R. Rosa

Publications and source records attributed to Reinaldo R. Rosa.

18 recordsLinked to original sources

arXiv2026

SAGUI: SED-based Segmentation of Multi-band Galaxy Images -- Application to JADES in GOODS-South

We present sagui, a modular framework for the analysis of multi-band imaging data in spatially resolved galaxies, with synergies to integral-field spectroscopy (IFS). Building on the spectro-spatial paradigm introduced by capivara for IFS data, sagui extends this approach to imaging datasets, enabling a coherent, pixel-level treatment of spatial and spectral information across multiple bands. The method follows a two-stage strategy: a starlet-based decomposition is first used to identify and mask spatial structures across multiple scales while suppressing noise, and a spectral-similarity analysis then partitions the image into coherent pixel groups that preserve spectral consistency. In addition to compact and high-contrast structures, the framework incorporates a dedicated statistical treatment, based on a copula transform, to identify and recover faint, diffuse low-surface-brightness components. We demonstrate the method across a diverse range of galaxy morphologies, highlighting its ability to characterize complex spatial structures, including clumps, bars, interacting systems, and low-surface-brightness features. As a case study, we apply it to eleven morphologically diverse galaxies from the James Webb Space Telescope Advanced Deep Extragalactic Survey in the GOODS--South field. sagui is released under an MIT license and is available at https://rafaelsdesouza.github.io/sagui/.

astro-ph.IM↗

arXiv2025

AT2022zod: An Unusual Tidal Disruption Event in an Elliptical Galaxy at Redshift 0.11

Tidal Disruption Events (TDEs) have long been hypothesized as valuable indicators of black holes, offering insight into their demographics and behaviour out to high redshift. TDEs have also enabled the discovery of a few Massive Black Holes (MBHs) with inferred masses of $10^4$--$10^6\,M_\odot$, often associated with the nuclei of dwarf galaxies or ultra-compact dwarf galaxies (UCDs). Here we present AT2022zod, an extreme and short-lived optical flare in an elliptical galaxy at z=0.11, residing within 3kpc of the galaxy's centre. Its luminosity and ~30-day duration make it unlikely to have originated from the host galaxy's central supermassive black hole (SMBH), which estimate to have a mass around $10^8\,M_\odot$. Assuming that the emission mechanism is consistent with known observed TDEs, we find that such a rapidly evolving transient could either be produced by a MBH in the intermediate-mass range or, alternatively, result from the tidal disruption of a star on a non-parabolic orbit around the central SMBH. We suggest that the most plausible origin for AT2022zod is the tidal disruption of a star by a MBH embedded in a UCD. As the Vera C. Rubin Observatory's Legacy Survey of Space and Time comes online, we propose that AT2022zod serves as an important event for refining search strategies and characterization techniques for intermediate-mass black holes.

astro-ph.HE↗

arXiv2024

Regional and Global Collaborations in Astronomy

Policy Brief on "Regional and Global Collaborations in Astronomy", distilled from the corresponding panel that was part of the discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. Astronomy brings together advanced scientific research, state-of-the-art technology, and educational initiatives, all while captivating and stimulating people of all ages. By doing so, it possesses the potential to serve as a powerful catalyst for sustainable global development and the resolution of global societal issues. It attracts a diverse range of scientists and experts from various fields, fostering collaboration and innovation. By leveraging their resources, influence, and diplomatic initiatives, S20 academies can foster an enabling environment for international collaborations in astronomy, facilitate knowledge exchange, and drive scientific advancements that benefit humanity. This policy brief explores the opportunities and challenges presented by regional and global collaborations in astronomy. The policy webinar took place during the G20 presidency in India (2023). A summary based on the seven panels can be found here: arxiv:2401.04623.

astro-ph.IM↗

arXiv2024

AstroInformatics: Recommendations for Global Cooperation

Policy Brief on "AstroInformatics, Recommendations for Global Collaboration", distilled from panel discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. The deliberations encompassed a wide array of topics, including broad astroinformatics, sky surveys, large-scale international initiatives, global data repositories, space-related data, regional and international collaborative efforts, as well as workforce development within the field. These discussions comprehensively addressed the current status, notable achievements, and the manifold challenges that the field of astroinformatics currently confronts. The G20 nations present a unique opportunity due to their abundant human and technological capabilities, coupled with their widespread geographical representation. Leveraging these strengths, significant strides can be made in various domains. These include, but are not limited to, the advancement of STEM education and workforce development, the promotion of equitable resource utilization, and contributions to fields such as Earth Science and Climate Science. We present a concise overview, followed by specific recommendations that pertain to both ground-based and space data initiatives. Our team remains readily available to furnish further elaboration on any of these proposals as required. Furthermore, we anticipate further engagement during the upcoming G20 presidencies in Brazil (2024) and South Africa (2025) to ensure the continued discussion and realization of these objectives. The policy webinar took place during the G20 presidency in India (2023). Notes based on the seven panels will be separately published.

astro-ph.IM↗

arXiv2020

Information technology & astronomical data in Brazil: Perspectives and proposals

The Commission on Science and Information Technology (CTCI) of the Brazilian Astronomical Society (SAB) is tasked with assisting the Society on issues of astronomical data management, from its handling and the management of data centres and networks, to technical aspects of the archiving, storage and dissemination of data. In this paper we present a summary of the results of a survey recently conducted by the Commission to diagnose the status of several data-related issues within the Brazilian astronomical community, as well as some proposals derived therefrom.

astro-ph.IM↗

arXiv2020

Stellar Population Properties of ETGs in Compact Groups of Galaxies

We present results on the study of the stellar population in Early-Type galaxies (ETGs) belonging to 151 Compact Groups (CGs). We also selected a field sample composed of 846 ETGs to investigate environmental effects on galaxy evolution. We find that the dependences of mean stellar ages, [Z/H] and [$α$/Fe] on central stellar velocity dispersion are similar, regardless where the ETG resides, CGs or field. When compared to the sample of centrals and satellites from the literature, we find that ETGs in GCs behave similarly to centrals, especially those embedded in low-mass haloes ($M_{h} < 10^ {12.5}M_{\odot}$). Except for the low-mass limit, where field galaxies present a Starforming signature, not seen in CGs, the ionization agent of the gas in CG and field galaxies seem to be similar and due to hot, evolved low-mass stars. However, field ETGs present an excess of H$α$ emission relative to ETGs in CGs. Additionally, we performed a dynamical analysis, which shows that CGs present a bimodality in the group velocity dispersion distribution - a high and low-$σ$ mode. Our results indicate that high-$σ$ groups have a smaller fraction of spirals, shorter crossing times, and a more luminous population of galaxies than the low $σ$ groups. It is important to emphasize that our findings point to a small environmental impact on galaxies located in CGs. The only evidence we find is the change in gas content, suggesting environmentally-driven gas loss.

astro-ph.GA↗

arXiv2019

Spectral fluctuation analysis of ionospheric inhomogeneities over Brazilian territory Part II: E-F valley region plasma instabilities

The turbulent-like process associated with ionospheric instabilities, has been identified as the main nonlinear process that drives the irregularities observed in the different ionospheric regions. In this complementary study, as proposed in the first article of this two-paper series [Fornari et al., Adv. Space Res. 58, 2016], we performed the detrended fluctuation analysis of the equatorial E-F valley region electron density fluctuations measured from an in situ experiment performed over the Brazilian territory. The spectral consistency with the K41 turbulent universality class is analyzed for E-F valley region from the DFA spectra for four electron density time series. A complementary detrended fluctuation analysis for four time series of the F-layer electric field is also presented. Consistent with the results obtained for the F region, the analysis for the E-F valley region also shows a very high spectral variation ($\gg50\%$). Thus, the spectral analysis performed in both parts of the series suggest that a process such as the homogeneous turbulence K41 ($β=-5/3\pm 2\%$) is inappropriate to describe both the fluctuations of electron density and the electric field associated with the main ionospheric instabilities.

physics.space-ph↗

arXiv2017

Bayesian surface photometry analysis for early-type galaxies

We explore the application of Bayesian image analysis to infer the properties of an SDSS early-type galaxy sample including AGN. We use GALPHAT (Yoon et al. 2010) with a Bayes-factor model comparison to photometrically infer an AGN population and verify this using spectroscopic signatures. Our combined posterior sample for the SDSS sample reveals distinct low and high concentration modes after the point-source flux is modeled. This suggests that ETG parameters are intrinsically bimodal. The bimodal signature was weak when analyzed by GALFIT (Peng et al. 2002, 2010). This led us to create several ensembles of synthetic images to investigate the bias of inferred structural parameters and compare with GALFIT. GALPHAT inferences are less biased, especially for high-concentration profiles: GALPHAT Sérsic index $n$, $r_{e}$ and MAG deviate from the true values by $6\%$, $7.6\%$ and $-0.03 \,\mathrm{mag}$, respectively, while GALFIT deviates by $15\%$, $22\%$ and $-0.09$\, mag, respectively. In addition, we explore the reliability for the photometric detection of AGN using Bayes factors. For our SDSS sample with $r_{e}\ge 7.92\,$arcsec, we correctly identify central point sources with $\mathrm{Mag_{PS}}-\mathrm{Mag_{Sersic}}\le 5$ for $n\le6$ and $\mathrm{Mag_{PS}}-\mathrm{Mag_{Sersic}}\le 3$ for $n>6$. The magnitude range increases and classification error decreases with increasing resolution, suggesting that this approach will excel for upcoming high-resolution surveys. Future work will extend this to models that test hypotheses of galaxy evolution through the cosmic time.

astro-ph.GA↗

arXiv2012

A new gravitational N-body simulation algorithm for investigation of cosmological chaotic advection

Recently alternative approaches in cosmology seeks to explain the nature of dark matter as a direct result of the non-linear spacetime curvature due to different types of deformation potentials. In this context, a key test for this hypothesis is to examine the effects of deformation on the evolution of large scales structures. An important requirement for the fine analysis of this pure gravitational signature (without dark matter elements) is to characterize the position of a galaxy during its trajectory to the gravitational collapse of super clusters at low redshifts. In this context, each element in an gravitational N-body simulation behaves as a tracer of collapse governed by the process known as chaotic advection (or lagrangian turbulence). In order to develop a detailed study of this new approach we develop the COsmic LAgrangian TUrbulence Simulator (COLATUS) to perform gravitational N-body simulations based on Compute Unified Device Architecture (CUDA) for graphics processing units (GPUs). In this paper we report the first robust results obtained from COLATUS.

astro-ph.CO↗

arXiv2012

An alternative singularity-free cosmological scenario from cusp geometries

We study an alternative geometrical approach on the problem of classical cosmological singularity. It is based on a generalized function $f (x, y) = x^{2} + y^{2} = (1 - z)z^{n}$ which consists of a cusped coupled isosurface. Such a geometry is computed and discussed into the context of Friedmann singularity-free cosmology where a pre-big bang scenario is considered. Assuming that the mechanism of cusp formation is described by non-linear oscillations of a pre-big bang extended very high energy density field ($> 3 \times 10^{94} kg/m^{3} $), we show that the action under the gravitational field follows a tautochrone of revolution, understood here as the primary projected geometry that alternatively replaces the Friedmann singularity in the standard big bang theory. As shown here this new approach allows us to interpret the nature of both matter and dark energy from first geometric principles.

astro-ph.CO↗

arXiv2008

Evidence of Turbulence-like Universality on the Formation of Galaxy-sized Dark Matter Haloes

Although the theoretical understanding of the nonlinear gravitational clustering has greatly advanced in the last decades, in particular by the outstanding improvement on numerical N-body simulations, the physics behind this process is not fully elucidated. The main goal of this work is the study of the possibility of a turbulent-like physical process in the formation of structures, galaxies and clusters of galaxies, by the action of gravity alone. We use simulation data from the Virgo Consortium, in ten redshift snapshots (from 0 to 10). From this we identify galaxy-sized and cluster-sized dark matter haloes, by using a FoF algorithm and applying a boundedness criteria, and study the gravitational potential energy spectra. We find that the galaxy-sized haloes energy spectrum follows closely a Kolmogorov's power law, similar to the behaviour of dynamically turbulent processes in fluids. This means that the gravitational clustering of dark matter may admit a turbulent-like representation.

astro-ph↗

arXiv2006

Gradient Pattern Analysis of Cosmic Structure Formation: Norm and Phase Statistics

This paper presents the preliminary results of the characterization of pattern evolution in the process of cosmic structure formation. We are applying on N-body cosmological simulations data the technique proposed by Rosa, Sharma & Valdivia (1999) and Ramos et al. (2000) to estimate the time behavior of asymmetries in the gradient field. The gradient pattern analysis is a well tested tool, used to build asymmetrical fragmentation parameters estimated over a gradient field of an image matrix able to quantify a complexity measure of nonlinear extended systems. In this investigation we work with the high resolution cosmological data simulated by the Virgo consortium, in different time steps, in order to obtain a diagnostic of the spatio-temporal disorder in the matter density field. We perform the calculations of the gradient vectors statistics, such as mean, variance, skewness, kurtosis, and correlations on the gradient field. Our main goal is to determine different dynamical regimes through the analysis of complex patterns arising from the evolutionary process of structure formation. The results show that the gradient pattern technique, specially the statistical analysis of second and third gradient moment, may represent a very useful tool to describe the matter clustering in the Universe.

nlin.PS↗

arXiv2005

Generalized Thermostatistics and Wavelet Analysis of the Solar Wind and Proton Density Variability

In this paper, we analyze the probability density function (PDF) of solar wind velocity and proton density, based on generalized thermostatistics (GT) approach, comparing theoretical results with observational data. The time series analyzed were obtained from the SOHO satellite mission where measurements were sampled every hour. We present in the investigations data for two years of different solar activity: (a) moderate activity (MA) period (1997) and (b) high activity (HA) period (2000). For the MA period, the results show good agreement between experimental data and GT model. For the HA period, the agreement between experimental and theoretical PDFs was fairly good, but some distortions were observed, probably due to intermittent characteristics of turbulent processes. As a complementary analysis, the Global Wavelet Spectrum (GWS) was obtained allowing the characterization of the predominant temporal variability scales for both the periods and the stochastics aspects of the nonlinear solar wind variability are discussed.

physics.geo-ph↗

arXiv2004

Nonextensivity and Galaxy Clustering in the Universe

We investigate two important questions about the use of the nonextensive thermostatistics (NETS) formalism in the context of nonlinear galaxy clustering in the Universe. Firstly, we define a quantitative criterion for justifying nonextensivity at different physical scales. Then, we discuss the physics behind the ansatz of the entropic parameter $q(r)$. Our results suggest the approximate range where nonextensivity can be justified and, hence, give some support to the applicability of NETS to the study of large scale structures.

astro-ph↗

arXiv2004

Value-at-Risk and Tsallis statistics: risk analysis of the aerospace sector

In this study, we analyze the aerospace stocks prices in order to characterize the sector behavior. The data analyzed cover the period from January 1987 to April 1999. We present a new index for the aerospace sector and we investigate the statistical characteristics of this index. Our results show that this index is well described by Tsallis distribution. We explore this result and modify the standard Value-at-Risk (VaR), financial risk assessment methodology in order to reflect an asset which obeys Tsallis non-extensive statistics.

cond-mat.stat-mech↗

arXiv2004

Nonextensive Thermostatistics and the $H$-Theorem Revisited

In this paper we present a new derivation of the $H$-theorem and the corresponding collisional equilibrium velocity distributions, within the framework of Tsallis' nonextensive thermostatistics. Unlike previous works, in our derivation we do not assume any modification on the functional form of Boltzmann's original "molecular chaos hypothesis". Rather, we explicitly introduce into the collision scenario, the existence of statistical dependence between the molecules before the collision has taken place, through a conditional distribution $f(\vec{v}_2|\vec{v}_1)$. In this approach, different equilibrium scenarios emerge depending on the value of the nonextensive entropic parameter.

cond-mat.stat-mech↗

arXiv2004

Atmospheric turbulence within and above an Amazon forest

In this paper, we discuss the impact of a rain forest canopy on the statistical characteristics of atmospheric turbulence. This issue is of particular interest for understanding on how the Amazon terrestrial biosphere interact with the atmosphere. For this, we used a probability density function model of velocity and temperature differences based on Tsallis' non-extensive thermostatistics. We compared theoretical results with experimental data measured in a 66 m micrometeorological tower, during the wet-season campaign of the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA). Particularly, we investigated how the value of the entropic parameter is affected when one moves into the canopy, or when one passes from day/unstable to night/stable conditions. We show that this new approach provides interesting insights on turbulence in a complex environment such as the Amazon forest.

physics.ao-ph↗

arXiv2000

Complex Entropic Forms for Gradient Pattern Analysis of Spatio-temporal Dynamics

In this paper we describe two new computational operators, called complex entropic form (CEF) and generalized complex entropic form (GEF), for pattern characterization of spatially extended systems. Besides of being a measure of regularity, both operators permit to quantify the degree of phase disorder associated with a given gradient field. An application of CEF and GEF to the analysis of the gradient pattern dynamics of a logistic Coupled Map Lattice is presented. Simulations using a Gaussian and random initial condition, provide interesting insights on the the system gradual transition from order/symmetry to disorder/randomness.

cond-mat↗