Generation of magnetic fields on galactic scale

Sammanfattning: In these pages we will go through the topic of astrophysical magnetic fields, focusing on galactic fields, their observation and the theories that have been developed for a proper understanding of the these physical phenomena.We review the main work in the study of galactic magnetic fields, often seeing how it is important to deal with problems of general validity in order to be able to point out the right elements needed for a correct interpretation of specific situations. We also aim to summarize some of the conflicts that arise using different theoretical approaches to be proficient in future choices of our research guidelines.This thesis consists in an introductory text and three papers dealing with some specific topics that are introduced in the first three chapters.In the first chapter we will talk about the state of the art of the observations of galactic fields. We review current techniques and observations.In the second chapter we describe the current theories that best describe the generation of magnetic fields. We also mention here two of the three works presented in this licentiate thesis. We will then deal with the possibility to have a proper measure of the $\alpha$ effect in numerical simulationsof dynamo action.Then we consider a particular aspect of magnetic helicity, that is, its connection with the topology of the magnetic field in a given system.In the third chapter we focus on theories related to galactic fields and their validity.We also present our work on the generation of vorticity in the interstellar medium as well as a study ofturbulent diffusivity in a system presenting spherical expansion waves.