Description
Lyman limit systems (LLSs) are high-density clouds in the intergalactic medium, characterised by strong absorption features in quasar spectra due to their substantial neutral hydrogen content. As their density increases, self-shielding becomes significant, reducing photoheating while increasing cooling efficiency through various mechanisms. Meanwhile, they are also affected by additional heating mechanisms, such as shocks, galactic outflows, or local ionisation effects. These competing processes lead to significant temperature scatter at a given density, making LLSs thermally diverse environments and posing challenges of constraining their temperatures observationally.
Deuterium systems, which trace the hydrogen content in these clouds, provide an alternative method for probing the temperature of LLSs. As relics of Big Bang nucleosynthesis, deuterium has been largely destroyed by stellar processes, making these systems exceptionally rare. In this talk, we will present our search for Lyman limit deuterium systems using archival data from VLT/UVES and Keck/HIRES, facilitated by our developed deep learning pipeline. Additionally, we will discuss our interpretation of these findings combined with insights from EAGLE simulations, with a focus on the temperature-density relation of hydrogen content.
