SFA I: Galaxy formation

Galaxies are surrounded by vast reservoirs of hot gas, from which cooler clouds condense and "rain" down onto the galaxy, feeding the formation of new stars – a process strikingly similar to rain forming in Earth's atmosphere. These clouds are far too small for cosmological simulations of galaxy formation to capture directly. This project borrows the well-developed multi-fluid approach pioneered at AIP, in which hot and cold gas are treated as separate, interacting fluids and extends it to model gas condensation and applies it to large-scale galaxy simulations. As a highlight, the same computer code will then be used the other way around: to simulate real cloud and rain formation in Earth's atmosphere. The project is multi-scale because it connects cloud physics on scales in the range of light-years to galaxy environments millions of light-years across – over six orders of magnitude – and interdisciplinary because astrophysicists, atmospheric scientists, and applied mathematicians jointly develop one framework serving both fields.

Most of the ordinary matter belonging to a galaxy is not in its stars but in a huge, almost invisible halo of gas around it – the circumgalactic medium. Astronomers study it by analyzing how it absorbs the light of distant bright objects shining through it. Simulations suggest this gas is not smooth: large clouds continuously "shatter" into countless tiny fragments, much like fog forming on Earth. Structures range from roughly the size of the solar system to hundreds of thousands of light-years – nine orders of magnitude. This project uses high-resolution magnetohydrodynamic simulations to determine how this small-scale structure shapes the absorption signals we observe, and thus what telescopes are really telling us about how galaxies get their gas. It is multi-scale by the very nature of the fragmenting gas, and interdisciplinary in bridging computer simulation, plasma physics, and observational astronomy.