Study of the origin of DLA and SBLA using cosmological simulations

In the spectra of quasars at high redshift, we observe the Lyman 𝛼 forest, a series of absorptions by the Lyman 𝛼  hydrogen line . In a relatively small fraction of  the spectra we also observe absorption systems called DLAs (Damped Lyman 𝛼 Absorbers). These objects are observed when the line of sight crosses gas clouds with a column density of at least 10^20cm^-2 and have been associated with late-type galaxies. These galaxies are at a redshift greater than 2 and, in general, cannot be directly observed, although we do have indications that they can be detected in absorption as SBLAs (Pieri et al. 2014, Pérez-Ràfols et al. 2023). Detecting these galaxies is critical to better understand when and how the peak of star formation occurred, which occurred around a redshift of 2. Furthermore, these galaxies could be used as tracers to measure the expansion of the Universe using the technique of BAO (Baryon Acoustic oscillations).

 

In astrophysics, as in many other fields of science, simulations have started to play a very important role in comparing theoretical models with observations. These become essential in cases where the observations are incomplete or of low quality, as occurs for galactic systems at an intermediate redshift. In recent years, the techniques for simulating the formation of galaxies at high redshift have greatly improved, both increasing the simulated physical processes and the spatial, temporal, and mass resolutions. In this context, simulations can be very useful to study the properties of the gas clouds that cause DLAs.

 

The project proposed here consists of studying the effect of the circumgalactic medium and its properties on the generation of DLAs and SBLAs. To do this we will analyze the spectra obtained by tracing many lines of sight that cross several simulated galactic systems covering a wide range of distances and angles. The results obtained will allow us to compare the predictions of the simulations with the observations already available. Depending on the student's preferences, the project may focus on the measurement of typical metallicity in DLAs and/or SBLAs, on the detailed study of the simulated Lyman alpha forest or on the distribution of these objects, among others.

 

The Advisors Ignasi and Santi are experts in the study of the Lyman forest 𝛼 and of the DLAs and SBLAs (the first) and in galaxy simulations (the second).