UV bright red-sequence galaxies: a comparative study between UV upturn and UV weak systems Maria

• Ano de defesa: 2020
• Autor(a) principal: Dantas, Maria Luiza Linhares
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: análise de dados; data analysis; Early-type galaxies; evolução; evolution; Galáxias elípticas; ultraviolet.; ultravioleta.
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/14/14131/tde-14122020-155924/

Ultraviolet (UV) emission from galaxies is associated with hot components, whether from stellar sources or not. It is an important marker for star-formation rate, yet it can also be associated with evolved and rare stellar evolutionary phases. By making use of colour-colour diagrams, early-type galaxies (ETGs) can be classified in terms of their UV emission in mainly three categories: residual star-formation, UV weak, and UV upturn emission. The UV upturn is a phenomenon characterised by an unexpected rise of the fluxes of quiescent ETGs between the Lyman limit and 2500A. This thesis aims at investigating galaxies presenting UV upturn by comparing them to other systems hosting UV weak emission. This investigation has three fronts: (i) the assessment of the evolution in redshift (z) and stellar mass (logM*) of the fraction of UV bright red-sequence galaxies (RSGs) that host the UV upturn; (ii) the stratification of the aforementioned study in terms of emission lines; (iii) the comparison of stellar population parameters between UV weak and upturn for retired/passive RSGs. A sample of galaxies has been selected from the Galaxy Mass Assembly (GAMA) aperture-matched with the Sloan Digital Sky Survey (SDSS) and the Galaxy Evolution Explorer (GALEX). To tackle the first front, a Bayesian logistic model was applied. The second front expands on the first, dividing the sample into emission line classes by making use of the WHAN diagram. The final front is focused on the study of stellar population properties of UV weak and UV upturn systems, by making use of value-added catalogues from the GAMA collaboration which provide stellar population properties obtained via spectral energy distribution fitting. To analyse both groups of galaxies, the original samples were balanced in terms of z and logM*. With the de-biased samples at hand, three types of comparisons were made: the direct comparison of their stellar population parameters; the estimation of the Spearman correlation rank among these parameters and the differences between both UV classes; and a principal component analysis. The results show that the fraction of UV upturn systems rises up to z~0.25, followed by a decline which remains to be confirmed given the thickness of credible intervals. By stratifying the sample into emission line classes, galaxies with star formation have been identified; the galaxies classified as retired/passive -- the ones associated with evolved stellar phases -- dominate the behaviour with z and logM*. Finally, by analysing the stellar populations of both UV weak and upturn systems, some different characteristics emerge such as median ages, metallicities, and time since last burst of star formation. These results seem to indicate that either UV upturn systems evolve more passively, or settled their stellar population at higher z than their UV weak counterparts. Either way, UV upturn systems have narrower star-formation histories, higher metallicities, and slightly older populations.