http://hdl.handle.net/11422/50 Thu, 30 Jul 2026 08:38:29 GMT 2026-07-30T08:38:29Z http://hdl.handle.net/11422/29406 Title: Towards forecasting cosmological constraints from velocity angular power spectrum of type Ia supernovae Author(s)/Inventor(s): Bonifácio, João Pedro Monteiro Advisor: Gonçalves, Thiago Signorini Abstract: Galaxies’ peculiar velocities provide a powerful probe of cosmic structure growth through their correlations. However, measuring these velocities requires distance indicators. Type Ia supernovae (SNe Ia) serve as fundamental distance indicators due to their nature as standardizable candles, offering superior distance estimates compared to galaxy scaling relations, which have traditionally been used due to the limited number of detected SNe Ia. With the upcoming Rubin Observatory Legacy Survey of Space and Time (Rubin LSST) set to detect one million of SNe Ia, we have an opportunity to leverage them for peculiar velocity studies. Yet, current methods rely on 3D statistical estimators, which are ill-suited for Rubin LSST’s photometric data. Without a robust alternative, we risk failing to fully exploit Rubin LSST’s vast dataset for cosmic structure studies. To address this challenge, we investigate the application of angular power spectrum analysis to velocity fields. We examine the velocity-density field relationship, compute the velocity angular power spectrum, and compare it with existing literature. Due to computational challenges posed by highly oscillatory functions, we implement the Limber approximation—a calculation not previously applied to velocity fields. We find that while efficient at small angular scales, this approximation introduces significant errors at large scales, as expected. Additionally, we assess whether LSST’s large photometric sample could compensate for photometric redshift imprecision. Through the signal-to noise analysis, we demonstrate that precise redshift measurements are important to PV studies. This work represents a critical step toward enabling cosmological parameter forecasts using SNe Ia peculiar velocities in the Rubin LSST era. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação Thu, 27 Feb 2025 00:00:00 GMT http://hdl.handle.net/11422/29406 2025-02-27T00:00:00Z http://hdl.handle.net/11422/6082 Title: Fotodestruição do benzeno em ambientes interestelares Author(s)/Inventor(s): Neves, Rosicler da Silva Advisor: Boechat-Roberty, Heloísa Maria Abstract: The abundance of interstellar molecules depends on their dissociation and destruction rate, and those depend on the photodissociation cross section which is function of the photon energy. We had experimentally study photoionization and photodissociation processes of the benzene (C6H6), and the deuterated benzene (C6D6). Benzene is an essential intermediate in the formation pathways of polycyclic aromatic hydrocarbons (PAHs), which are thought to be responsible for unidentified infrared bands (UIR), observed in differents astronomical environments. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), using soft X-ray and UV photons. The experimental set-up consists of a high vacuum chamber with a Time-Of-Flight Mass Spectrometer (TOF-MS). Kinetic energy distributions, abundances for each ionic fragment and dissociative and non-dissociative photoionization cross sections were determined by using PhotoElectron PhotoIon Coincidence techniques. We have observed that C6H6 is extremely resistant to UV photons, confirming that PAHs absorb the UV photons and after some internal energetic rearrangements, they can emit in the IR range. However, this molecule is destroyed by soft X-rays photons producing several ionic fragments. We also observed that C6D6 is more resistant than benzene. Stable doubly-charged species were observed. From the photodissociation and cross sections we have determined the photodissociation rate and the half-life of C6H6 and C6D6 in differents astrophysical environments. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação Wed, 04 Apr 2007 00:00:00 GMT http://hdl.handle.net/11422/6082 2007-04-04T00:00:00Z http://hdl.handle.net/11422/6070 Title: Perturbações das equações de Einstein-Boltzmann e suas aplicações à radiação cósmica de fundo Author(s)/Inventor(s): Barros, Gustavo de Advisor: Calvão, Maurício Ortiz Abstract: Study aimed at understanding the basics of the new and growing topic of cosmic microwave background (CMB) physics. We present the fundamental concepts, principles and results related with this problem. Since the relevant equations are essentially the Einstein-Boltzmann perturbed equations, a great part of this work is dedicated to these linearized equations, in the conformal Newtonian gauge, with vanishing tri-curvature, for scalar perturbations only. The initial conditions are also touched on. Another part of paramount importance is the application to the description of the power spectrum of temperature anisotropies. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação Mon, 08 May 2006 00:00:00 GMT http://hdl.handle.net/11422/6070 2006-05-08T00:00:00Z http://hdl.handle.net/11422/5943 Title: Homogeneidades espacial e observacional da distribuição de galáxias Author(s)/Inventor(s): Lemos, Luis Juracy Rangel Advisor: Ribeiro, Marcelo Byrro Abstract: In this work we propose a second way of analysing the homogeneity of the matter distribution in the Universe, called here as observational homogeneity (OH), and which is carried out along the past light cone null type hypersurface. The usual type of homogeneity is given by the Cosmological Principle, called here as spatial homogeneity (SH), and which is defined along space-like hypersurfaces of the spacetime. In this work we adopted the Einstein-de Sitter cosmological model. All discussion regarding homogeneity were done by means of four cosmological distances, namely, the area distance dA, the galaxy area distance dG, the luminosity distance dL and the redshift distance dz. Simulations of various types of counting of cosmological sources were carried out and in the case of an universe model with SH we used the number counting obtained from the Einsteinde Sitter (EdS) model (NEdS), since it assumes the Cosmological Principle. In order to simulate an universe with OH, we adopted the number counts expression advanced by Wertz (1970) and Pietronero (1987) for the galaxy distribution. Starting from two radial density functions defined in Ribeiro (2005), namely the differential density γi and the integral differential density γ ∗ i , we carried out an analysis of spatial and observational homogeneities of the galaxy distribution, were the latter (OH) was defined by the constant value of γ ∗ i . Various plots were presented showing the central role played by the cosmological distance choice. It was also clearly observed that in order to characterize whether or not the large-scale galaxy distribution in the Universe has, or has not, OH, it is necessary to know not only the general mass-energy distribution, which is determined by the count Ni of cosmological sources, but also the geometrical volume which defines the density and, by itself, depends on the cosmological distance. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação Mon, 16 Oct 2006 00:00:00 GMT http://hdl.handle.net/11422/5943 2006-10-16T00:00:00Z