The Chemical and Dynamical Evolution of Simulated Late-Type Galaxies

Abstract

In this thesis I discuss two projects that have been a major part of my postgraduate studies. The aim of these projects is to study the dynamics and chemodynamics of simulated Milky Way analogues. Specifically, I investigate chemical abundances in the solar-neighbourhood and of the outflow rates of gas of Milky Way analogue discs.
In the first project, I describe a galaxy simulated with the code RAMSES-CH and compare this with chemical abundance data from the Gaia-ESO survey and the RAVE survey. The aim of this work is to improve matching the chemical abundances in stars within the galaxy to those in observational surveys. This is done by sampling our simulation to best match what an observer does in observational surveys. In addition to carrying out an observationally-motivated spatial selection within the simulation and thus comparing like for like, we take into account observational uncertainty and the selection effects (photometric, effective temperature and surface gravity). Incorporating these factors within the simulation data, we find that simply taking a spatial cut alone within a simulation model is not sufficient to match simulated abundances like for like with observational surveys. For complete observational selection functions, like that in the Gaia-ESO survey, the selection function has a minimal impact on the ages and metal abundances. However for a narrower selection function like in the RAVE survey, the impact becomes more noticeable. The method that improves simulation abundance patterns with observations however is the inclusion of an observationally motivated scatter based on the uncertainties of the observational survey you are studying.

In my second project I study the outflow abundances of gas from the disc of Milky Way-like galaxy in isolation along with inflow from a hot gas halo. I generate a galaxy model from the initial conditions generator code GalactICS and run the simulation with the meshless Lagrangian Godunov-type code GIZMO. The simulation's aim is to investigate gravity driven turbulence of a gas disc in the absence of more commonly considered sources of feedback such as supernovae. Our goal is to place a lower limit on this effect in Milky-Way analogues, which from initial investigations conducted without full self-gravity is admittedly anticipated to be small. We present a study the outflow of gas and its relation to the surface density and radius of the disc. In comparison to more idealised parameter studies, we find that the outflows of gas from high surface density regions are suppressed by the cooling flow of the gas halo. This contradicts results from small box simulations, but is reflective of the physics in a full disc model. Nonetheless, outflows up to 1.5 kpc in height are found, and vertical velocity dispersions are in broad agreement with other work that includes additional sources of feedback.