Can Dwarf Galaxies Tell Us How the Milky Way Formed?

Sammanfattning: Dwarf galaxies are a key component in understanding the evolution of galaxies and provide tests on the standard cosmological $\Lambda$ Cold Dark Matter model. According to the formation hierarchy, dwarf galaxies are the pieces that create all galaxies. Our current understanding of dwarf galaxies faces discrepancies between theory and observations. These problems are mostly due to incompleteness in observational data and the low number of simulations available. Simulations are based on the physics that drive the Universe yet they are limited by resolution and our understanding of the Universe. Observations are limited by technology and brightness limitations. The purpose of this project is to study the effect of last major merger modifications on the properties of satellites, such as the satellite luminosity function, the satellite ages and the quenching fraction, around Milky Way-like galaxies. We also show the effect that surface brightness limits have on the number of satellites and the total mass of satellites that a survey might see. To fulfil this, we use 8 cosmological hydrodynamic+N-body zoom-in simulations of Milky Way-mass galaxies. Five of those simulations are from a project called {\footnotesize VINTERGATAN-GM}, where the last major merger mass is modified to create five different simulations of identical final dynamical mass. For this project, these simulations provide an excellent investigation of the effect on the satellite population for the last major merger. In our analysis, we find that the surface brightness limit greatly effects the number of satellite and the masses that surveys would see. Going form a limit of 26 mag/arcsec$^2$, the value of today's surveys, to a limit of 32 mag/arcsec$^2$ the number of satellites increased and the masses of already detected satellites increased. Using the {\footnotesize VINTERGATAN-GM} simulations, we show how the satellite luminosity function evolves. We see that the assembly history of the functions change with the mass of the last major merger, where the galaxy with the smallest merger evolves with a larger number of satellites than the galaxy with the largest merger. By analysing the star formation histories of the simulations, we determined the ages of the satellites. We see an age trend from the smallest merger to the largest, where the oldest are the satellites around the galaxy with the largest merger. We also see the same trend in the quenching fraction where the older satellites are more quenched than the younger. We calculate the quenching fraction for all 8 simulations in order to compare with observations. We use results from two disagreeing large scale surveys, SAGA and ELVES, to compare with our results. Our results lie in between the two surveys with a quenching fraction of 29\%. This does not match with the known quenching fraction of the Milky Way and M31, which is higher than 90\%. This is one of the discrepancies in the studies of satellites, which will benefit from better observations, a larger sample of simulations, and further investigations of quantities such as gas, metallicity, structures, and other galactic effects.