Simulating the chemical enrichment of the intergalactic medium

Abstract

Over the past few decades, it has become evident that the vast amount of space that exists between galaxies contains trace amounts of elements heavier than helium ('metals' in astronomical terms). This is surprising since the baryonic universe is expected to initially be composed of solely hydrogen, helium and very small amounts of lithium and beryllium. Metals are predicted to be exclusively associated with stars, which are extremely rare in the intergalactic medium. The aim is therefore to predict how the metals got there and what is their distribution throughout cosmic time. This work investigates these mechanisms using a suite of over 50 three-dimensional, hydrodynamic, computer simulations. After discussing how metals and background radiation can affect intergalactic gas and in turn galaxy formation/evolution in a significant way, the focus turns to the cosmic distribution of metals. The simulations predict that hot intergalactic gas contains a constant fraction of metals throughout most of the history of the universe, while the metal fraction of the cold phase is increasing. It closes by considering the origin of such metals, finding that low mass galaxies expel metals into the cold phase from early times.