The star formation & chemical evolution timescales of two nearby dwarf spheroidal galaxies

PhD ceremony: Mr. T.J.L. de Boer, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: The star formation & chemical evolution timescales of two nearby dwarf spheroidal galaxies

Promotor(s): prof. E. Tolstoy

Faculty: Mathematics and Natural Sciences

The study of the detailed properties of individual stars in nearby galaxies allows us unprecedented accuracy in understanding the build up of stellar populations and chemical elements in galaxies, from the earliest times to the present day. These properties and how they change over time make galaxies what they are today. During my PhD I have developed a new and innovative approach to combine large spectroscopic data sets of detailed abundances with photometric Colour-Magnitude Diagrams. This technique was applied to two nearby dwarf galaxies in the Local Group, which are excellent places to study the formation and evolution of galaxies. I constructed accurate star formation histories of the Sculptor and Fornax dwarf galaxies, which tell us when each generation of stars was formed, and with which metallicity. This information is used to obtain the age of individual stars, for which we know detailed abundances from observations. Thus, for the first time, we now have the ability to analyse the chemical abundances directly as a function of time. This allowed me to obtain a detailed picture of how and especially when different processes built up the galaxy as we see it today. It also allowed me to constrain the timescale of important processes of galaxy evolution, such as the age at which different supernovae types start to contribute to the chemical enrichment. Furthermore, the detailed analysis of the Sculptor dwarf galaxy was also used to test the outcome of galaxy evolution models, and constrain the physics used in simulations.