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

TL;DR

This study compares UV upturn and UV weak early-type galaxies, revealing differences in their stellar populations, evolution with redshift, and emission line properties, advancing understanding of their origins and evolution.

Contribution

It provides a comparative analysis of UV upturn and UV weak systems, including their evolution, emission line stratification, and stellar population characteristics, using Bayesian modeling and GAMA data.

Findings

UV upturn fraction peaks at z~0.25

UV upturn systems have higher metallicities

UV upturn galaxies are slightly older

Abstract

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 in mainly three categories: residual star-formation, UV weak, and UV upturn. This thesis aims at investigating galaxies presenting UV upturn by comparing them to UV weak systems. This investigation has three fronts: (i) the assessment of the evolution in redshift (z) and stellar mass (logM*) of the fraction of UV upturn systems in terms of the total of UV bright ETGs; (ii) the stratification of the first study in terms of emission lines; (iii) the comparison between UV weak and upturn for passive RSGs in terms of their stellar populations. 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. The final front is focused on the study of stellar population properties of UV weak and upturn systems, by making use of catalogues from GAMA-DR3. 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. By stratifying the sample into emission line classes, the galaxies classified as retired/passive -- the ones associated with evolved stellar phases -- dominate the behaviour with z and logM*. By analysing the stellar populations of both types of systems, different characteristics emerge such as median ages, metallicities, and time since last burst of star formation. These results seem to indicate that UV upturn systems have narrower star-formation histories, higher metallicities, and slightly older populations.