Joshua Wallace, University of Utah
Physical Sciences
We study the effect of the circum-galactic gas environment on the observed Lyman-alpha emission from Lyman-alpha emitting galaxies. These galaxies are primarily high-redshift star-forming galaxies that are important in understanding both galaxy and universe evolution. The Lyman-alpha photons emitted from these galaxies should hold valuable clues about the general environmental properties (such as gas velocity, density, and distribution) around galaxies, since the photons can be strongly affected and scattered by the neutral hydrogen atoms that make up the majority of the gas. However, explaining exactly how a galaxy’s environment affects its Lyman-alpha emission is very complex and currently cannot be predicted with complete certainty — every time a Lyman-alpha photon interacts with a hydrogen atom, its direction and frequency are changed, which in turn affects how far it will travel before the next interaction. We study the environmental effects on Lyman-alpha emission properties by applying Monte Carlo Lyman-alpha radiative transfer modeling to simple analytic models and find an important role of the anisotropic distribution of gas in determining the observed photometric and spectral properties of Lyman-alpha emission. We further perform a detailed investigation by applying the radiative transfer modeling to realistic star-forming galaxies in high-resolution cosmological galaxy formation simulation. From our analysis so far, we find the Lyman-alpha emission from the models shows a strong dependence on viewing angle, as well as correlations between observed spectral features and environmental conditions. We plan to model and analyze a large sample of simulated galaxies to better describe and statistically quantify the above dependence and correlations. Our study will lead to a better understanding of the effects galaxy environment on the observed Lyman-alpha emission and in turn provide a theoretical guide on how to use observed Lyman-alpha emission to learn about the environments of star-forming galaxies and hence galaxy formation and evolution.