The conversion of gas into stars tells us about how galaxies in general and our Milky Way in particular form and assemble. The diversity of physical processes (gravitation, hydrodynamics, cooling, radiation etc.), their non-linear coupling and the wide range of scales involved make this topic complicated to understand. In the Milky Way, and more specifically in the solar neighbourhood where star formation is slow and inefficient, observations can resolve the star forming sites and tell us about the 'quiet regime' of star formation.
However, along their formation in the early Universe, galaxies experience much more violent episodes like interactions and mergers, making star formation more rapid and more efficient. Such events are observed in distant galaxies, but cannot be resolved even with modern telescopes with sufficient details to probe the mechanisms at stake. Therefore, we do not fully understand how the stimuli from galaxy evolution are convoyed from the large, cosmological scales down to that of the star forming cocoons, which hinders our understanding of galaxy formation and evolution as a whole. One solution consists in exploring extreme environments and analysing the differences in the physical processes (and their coupling) involved in star formation with that found in quiescent galaxies. Numerical simulations are the best tool to conduct such experiments.
The proposed project will focus on interactions between gas rich galaxies during which a boost of the star formation rate is observed. The simulations will reproduce such a boost and will allow us to explore the mechanisms driving it. Among others, we will focus on the interstellar turbulence, both globally mixing and locally compressing the interstellar medium. From our previous works, we suspect turbulence to be the main actor in shaping the galactic gas into the dense clumps that will in turn host the formation of stars.
We will conduct two simulations of galaxy mergers varying the initial conditions of the interstellar medium, that we will compare to two reference runs of isolated galaxy progenitors. In a second phase, we will set galaxies in the environment of a compact group, where they experience repeated collisions. We will then monitor how repeated events further increase the boost of star formation, or rather lead to a saturation effect. Intensive comparison with published observations (in term of star formation rate, the location and duration of the boosts) will be made. By exploring these extremes phases in the evolution of galaxies, we will get new insights on how they assemble, and thus on the origins of our Milky Way home.