Abstract
In this thesis I investigated the chemical evolution of r-process elements (traced by Europium) generated by neutron star-neutron star (NS-NS) mergers using the cosmological zoom-in simulation of a Milky Way analogue, Eris.
This study focuses on understanding the contributions of dwarf galaxies in the Eu abundances of stars in the host galaxy as well as satellite galaxies at z = 0. The chemical evolution model follows the fiducial model in Shen et al. (2015) for delay time distribution (power law of t-1), minimum delay time (100 Myr) and Eu yields. In the analysis the information of which galaxy the merger events belong to is recorded for all snapshots. I then compute the fraction of Eu coming from dwarf galaxies for each stellar particle. I also looked at the spacial distribution of Eu in the host and the satellite galaxies. I found that:
- Eu from dwarf galaxies at early times can contribute significantly to the Eu abundance in the host galaxy, resulting in a high [Eu/Fe] abundance ratio for metal poor stars;
- at later times and for the higher metallicity stars in the host galaxy, the relative contribution from dwarf galaxies decreases, possibly due to the fact that the ISM is continually being enriched by later episodes of star formation (and mergers) in the host galaxy;
- the satellite galaxies’ Eu abundance are overall similar to that of the host galaxy, and also show a decreased dwarf galaxy contribution towards higher metallicity, indicating that a significant amount of the Eu enrichment in today’s satellites are from the host galaxy because of the large-scale baryonic cycles;
- the enrichment pattern of Eu in satellite galaxies that are not effected by the host galaxy shows an extremely large enhancement [Eu/Fe] (~ 3-4 in one galaxy), and an increasing trend of [Eu/Fe] with metallicity, which is drastically different from that of the Milky Way.
Ongoing and future observations of r-process enhanced metal-poor halo stars will provide a good test to this model.
Veileder: Førsteamanuensis Sijing Shen, Institutt for teoretisk astrofysikk, UiO
Intern sensor: Professor Øystein Elgarøy, Instiutt for teoretisk astrofysikk, UiO
Ekstern sensor: Ryan Cooke, Durham University