IMAGE:

The circumgalactic medium across 5 billion years

Galaxies are part of a complex cosmic ecosystem in which gas is continuously exchanged between the inner galactic regions where stars form and the diffuse intergalactic medium that pervades the Universe. A pressing and critical goal of modern cosmology is to obtain a comprehensive view of how galaxies acquire the fresh fuel needed for the formation of new stars, and how they disperse gas enriched with heavy elements produced in stars back into the cosmos. Members of the IMAGE group at Durham University are using the world's largest telescopes in synergy with state-of-the-art simulations to advance our current understanding of gas is exchanged by galaxies across over 5 billion years of cosmic history.

To study gas flows, members of the IMAGE group are exploiting quasars as a flashlight to probe and illuminate the tenuous gas near galaxies. As part of this study, they are focusing on serendipitous alignments of multiple closeby quasars to map the extended morphology of gas near galaxies and gain a novel vantage point on inflows and outflows. The IMAGE group is also leading major programmes using the Very Large Telescope and the Hubble Space Telescope to connect the properties of inflows and outflows as seen in absorption to the physical properties of the galaxies as seen in emission across over 5 billion years of cosmic history.

The origin of the first elements

The first elements were created just minutes after the Big Bang, during a process that is commonly referred to as Big Bang Nucleosynthesis. During this time, only the lightest elements of the periodic table were created, including hydrogen, helium, and trace amounts of lithium. The relative abundances of these primordial elements are determined by a competition between the early expansion rate of the Universe and a small handful of nuclear reaction rates. Deviations from the so called Standard Model of cosmology and particle physics would manifest itself in changes to the relative abundances of primordial H, He, and Li nuclides. Members of the IMAGE group are developing new techniques and analysis strategies to measure the abundance of the primordial elements to high precision using near-pristine environments. These measurements currently provide the earliest probe of physics beyond the Standard Model.

The remaining elements of the periodic table - referred to generally as 'metals' - were first created by the first generation of stars. These first stars (also called Population III, or Pop III stars) were responsible for some of the most important physical and chemical transformations of the Universe; Not only did they create the first metals, but they are also believed to have triggered the reionization of the intergalactic medium, and heralded the end of the Dark Ages. However, despite the importance of the first stars during this Cosmic Dawn, we are still in the dark about many of their properties. Some of the key characteristics of the first stars (including their mass and supernova explosion energy) can be inferred by measuring the relative abundances of the elements they made. In particular, the first elements in the chain of stellar nucleosynthesis (carbon, nitrogen and oxygen) provide a sensitive probe of the first stars' properties. Members of the IMAGE group at Durham University have developed state of the art techniques to identify environments that may have been solely polluted by the first metals.

The physics of the intergalactic medium

Members of the IMAGE group are active in both observational and theoretical projects designed to understand the physical properties of the intergalactic medium, and particularly its thermal history, the evolution of metal enrichment, and the properties of the extragalactic ultraviolet background.