Thesis Topic: The Cosmic Evolution of Baryons


Thesis Supervisor: Celine Peroux


Spectacular measurements of the Cosmic Microwave Background (CMB) provide an understanding of the initial conditions that are at the origin of the cosmic structures we see today. We now know the basic constituents of the present Universe: 73% dark energy, 23% dark matter, 4% in baryons of which only 0.4% is in stars. Only a minority of the baryons can be probed by observations of starlight from galaxies. The project will study the remaining 90% of the baryons, as traced by the intergalactic gas. A powerful tool to study this low density gas is offered by absorption lines in the spectra of background quasars.

The project will use a dataset from the Very Large Telescope in Chile which is more than twice larger than any previously available at optical wavelengths by searching for cold and hot gas seen in absorption in high-resolution quasar spectra. Data mining and advanced analysis techniques will be used to search and characterise the appropriate absorption features in the large quasar spectra sample. By estimating the number and strength of the absorbers in a given volume, we will measure of the cosmic volume density of different phases of the gas. Accurate abundance determinations will provide new measurements of the metal and dust content of the Universe and its evolution over a large look-back time. Thus, by examining the statistical properties of gas probed in absorption, the spatial distribution of matter can be inferred.

The project is part of a team effort to study the cosmic baryon cycle through multi-wavelength observations and simulations of galaxies. The student will be part of a large team of scientists with a huge accumulated experience on studies of galaxy evolution.