Using Lyα to illuminate the circumgalactic medium and the Epoch of Reionization—Lessons from low redshift

During recent years the Lyα emission line has come to the fore as a potentially very powerful astrophysical tool and is now routinely used to find galaxies at the very highest redshifts. However, using Lyα is complicated by the fact that it is a resonant line, which means that it undergoes radiative transfer in neutral hydrogen. This makes Lyα observations very difficult to interpret, but it also means that Lyα can provide information about the neutral hydrogen in the universe, giving it the potential to, for instance, map the progression of the Epoch of Reionization.
Even though Lyα is relatively easy to detect at high redshift we cannot study the details of the escape process there, due to the lack of additional information about the emitting galaxies.  In order to understand Lyα in detail, we need to observe galaxies at much lower redshift where we can get more information. This is the main driver of the projects included in my thesis which I will present and which focuses on furthering our understanding of Lyα using local universe observations.
Studying both spectral and spatial distributions of Lyα, and comparing high and low redshift observations, we find that Lyα properties of galaxies seem remarkably unchanged as a function of cosmic time strongly supporting the notion that we can use low-z as a way to understand processes occurring at high-z.   We use our low-z observations to give some of the first indications of the source of spatially extended Lyα emission which is ubiquitous at high-z, showing that it may in fact partially be produced by in-situ recombination. 
Additionally I will present results demonstrating that that Lyα escape is a strongly multivariate issue and that using simple machine learning techniques can both help us predict Lyα and determine what the main drivers of Lyα emission are, and discuss how we can use this to learn more about, for instance, the Epoch of Reionization.