Fernando Hidalgo Pineda *     (Spain)

fernando @ mpa-garching.mpg.de    //    fehidalgo @ mpia.de

Gas flows in galactic ecosystems

Galaxy formation theory predicts that gas accreting into dark matter halos shock-heats to virial temperatures before cooling and forming stars in galactic centers. Because this phase occurs in diffuse, faint regions of the Universe, it has historically been constrained primarily by analytic theory and numerical simulations. Recent advances in observational capabilities have fundamentally changed this picture. Direct probes of the circumgalactic medium now reveal substantial reservoirs of cold (∼10⁴ K) gas in galaxy halos, including under-pressured gas, compact cold structures, and gas at intermediate temperatures that should be thermally unstable. These discoveries are in strong tension with theoretical expectations of hydrostatic equilibrium, pressure balance, and thermal stability, calling into question the physical assumptions underlying current models of halo gas and, by extension, galaxy formation.

My research seeks to understand the physical origin, evolution, and fate of cold gas in galaxy halos and its role in the baryon cycle. I address a range of interconnected questions, including how stellar and AGN feedback interact with cold gas embedded in a realistic, fractal interstellar medium, extending existing theories that are largely based on idealized, spherical clouds in hot backgrounds. I also investigate how gas driven out by galactic winds can cool, survive, and reaccrete to fuel future star formation, and how theoretical criteria derived from simplified setups apply in a dynamically evolving, multiphase ISM. I pursue these problems using targeted, high-resolution MHD simulations combined with analytic theory to isolate the governing physical mechanisms in highly non-linear regimes, and to develop theoretical estimates that can be used in larger-scale simulations or by observers.

Supervisor:    Max Gronke   (ARI)