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Ultraviolet (UV) emission from galaxies is associated with hot components,whether from stellar sources or not. By making use of colour-colour diagrams,early-type galaxies (ETGs) can be classified in terms of their UV emission inmainly three categories: residual star-formation, UV weak, and UV upturn. Thisthesis aims at investigating galaxies presenting UV upturn by comparing them toUV weak systems. This investigation has three fronts: (i) the assessment of theevolution in redshift (z) and stellar mass (logM*) of the fraction of UV upturnsystems in terms of the total of UV bright ETGs; (ii) the stratification of thefirst study in terms of emission lines; (iii) the comparison between UV weakand upturn for passive RSGs in terms of their stellar populations. To tacklethe first front, a Bayesian logistic model was applied. The second frontexpands on the first, dividing the sample into emission line classes. The finalfront is focused on the study of stellar population properties of UV weak andupturn systems, by making use of catalogues from GAMA-DR3. The results showthat the fraction of UV upturn systems rises up to z~0.25, followed by adecline which remains to be confirmed. By stratifying the sample into emissionline classes, the galaxies classified as retired/passive -- the ones associatedwith evolved stellar phases -- dominate the behaviour with z and logM*. Byanalysing the stellar populations of both types of systems, differentcharacteristics emerge such as median ages, metallicities, and time since lastburst of star formation. These results seem to indicate that UV upturn systemshave narrower star-formation histories, higher metallicities, and slightlyolder populations.

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