The impact of stellar feedback on the circumstellar medium and galaxy evolution

Abstract

The formation and evolution of galaxies is an interesting field of study that has attracted considerable interest. One process that affects galaxies is the feedback from stars. It has effects not only in the stellar vicinity, but also globally in the galaxy and beyond as it can alter the star formation rate, morphology or outflows of galaxies. Due to the importance of stellar feedback, it is included in simulations of galaxies. As stars and their evolution are below the resolution achievable in these simulations, sub-grid models must be employed. However, these models are based on simplifying assumptions. <br/> This thesis examines some of these assumptions with the aim of improving sub-grid models of stellar feedback. Special emphasis is given to early stellar feedback that occurs before the first supernovae (SNe), also known as pre-SN feedback. The early feedback was initially neglected in simulations, but is now included more frequently in some form. While also incorporating SN feedback, this thesis investigates two types of early feedback, stellar winds and, in the later projects, also photoionisation feedback.<br/> In the first project, we derive the feedback of stellar winds from a grid of massive stellar models for a range of metallicities. To account for their effect on the feedback, the grid includes single stars with different stellar rotation velocities and, in addition, binary systems with different orbital periods. In comparison to the case of non-rotating single stars, which are commonly assumed, accounting for stellar rotation and binarity can strongly increase the feedback energy from stellar winds, especially at low metallicity. The inclusion of stellar winds in a cosmological simulation reduces the stellar mass, the outflows and the fluctuation of the star formation rate of the simulated galaxy compared to a scenario of only SN feedback. Accounting for stellar rotation and binarity in the feedback lead to similar results for the galaxy compared to the non-rotating single star case, despite the high differences in the stellar wind energy. <br/> In the second project, we investigate how the circumstellar medium, which is below the resolution in galaxy simulations, influences the stellar feedback available at resolved scales. We perform a grid of 1D simulations of the circumstellar medium, affected by stellar winds, photoionisation and SN feedback. We calculate the cumulative energy in the ambient gas that flows through different distances from the stellar source. We find that the circumstellar medium can alter the feedback through energy dissipation and changing kinetic energy ratios. Furthermore, the arrival of energy can be delayed with respect to the stellar ejection. These effects are stronger at a large distance from the stellar source. Like in the first project, we see the importance of the early feedback, together with the low relevance of the enhance energy from populations of rotating and binary stars. <br/> In a third project, a first attempt of a sub-grid feedback model accounting for the circumstellar medium is presented for a galaxy simulation code. Through a simple test - the evolution of an isolated feedback bubble - we reveal and discuss challenges the model faces.<br/> In this thesis, we investigate early stellar feedback, stellar models beyond non-rotating single stars and the effect of the circumstellar medium. The findings of the thesis can improve sub-grid models of stellar feedback and advance the modelling of galaxies.