Paul Frederic Robert
Hi, my name is Fred. I am a PhD candidate at the centre for Astrophysics and Supercomputing (CAS), under the supervision of Prof. Michael Murphy, Dr. Glenn Kacprzak, and Dr. Neil Crighton.
My main interests are Galaxy Formation and Evolution, and the Intergalactic Medium (IGM). The IGM is the gas between galaxies. It is supposed to be the principal reservoir of normal matter: baryons. Therefore, it plays a crucial part for the formation of the first stars and consequently the first galaxies. It is then very important to probe its properties. However, it doesnâ€™t emit much light. To detect it, we have to rely on the quasar absorption line technique. Quasars are very bright objects that can be seen even at a relatively large distance from us. They shine through the IGM and intervening gas interacts with their emitted light. That process will leave absorption patterns in the quasarâ€™s spectrum collected by a spectrograph. By studying these features, we can infer which elements compose the absorbing gas in the line of sight, physical properties such as velocity distribution, density, temperature, metallicity, ionization state, etcâ€¦
My project is oriented toward a particular class of absorbers: the Lyman limit systems (LLS). They are defined by a neutral hydrogen column density, N(HI), such that 17.2 < log(N(HI)/cm2) < 20.3. In the past five years, very metal-poor LLSs, i.e. with almost no metal lines, have been detected (metals here refer elements heavier than helium). The existence of such metal poor, or near-pristine, environments in the vicinity of the IGM is exciting as it could bring more information about the first stars (Pop III stars), and the gas cycle in early structure formation. Pop III stars supposedly appeared in metal-free gas clouds, and their death as supernovae polluted the IGM with metals. Near-pristine absorbers could be remnants of this primordial gas. My aims are to:
I. Identify more of these extremely low metallicity absorbers, either with existing data or future observations.
II. Find explanations for their origin.
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