A Self-Consistent Theoretical Framework for Estimating Outflow Rates, Lyman Alpha Escape, and Lyman Continuum Escape

Abstract

Over the past two decades, both theory and observations have made tremendous progress revealing the inner workings of galaxy formation. In the current paradigm, theory predicts pristine inflows of gas, left over from the Big Bang and captured in the gravitational potential wells of dark matter halos, to be constantly feeding star formation and super massive black holes. This in turn leads to various forms of feedback (e.g., supernovae, stellar winds, radiation pressure, relativistic jets, cosmic rays, etc.) which then drive massive outflows of processed gas back out of the galaxy. In this way, feedback acts to regulate star formation. While we have drawn back the curtain to reveal the big picture behind galaxy formation, many open questions remain. We don’t yet know which sources of feedback are the primary drivers of outflows, the efficiency at which they operate, or how they influence their surroundings. Making precise measurements of the properties of flows will be essential to answering these questions. Traditionally, the properties of flows are measured from absorption and emission lines imprinted on the spectra of background sources, which encodes information about the density and velocity of the intervening gas. Extracting flow properties from absorption lines is easier said than done, however. The difficulty reflects the complex physics governing the radiation transfer underlying the lines and early attempts at modeling the lines have been limited. In this thesis, we present novel semi-analytical line transfer (SALT) models designed to predict the spectra of galactic flows to reveal their properties. The models are based on the transport of radiation through an extended moving medium and represent a major improvement to prior models. We demonstrate the model’s effectiveness by showcasing various comparison tests between SALT predictions and those of idealized numerical radiation transfer codes as well as numerical simulations of galaxy formation. In doing so, we develop a self-consistent theoretical framework linking simulations to observations. After demonstrating the effectiveness of the model, we show results from various applications including constraints on outflow rates and predictions of the ionizing escape fraction from star forming galaxies.