Foto del docente

Federico Marinacci

Senior assistant professor (fixed-term)

Department of Physics and Astronomy "Augusto Righi"

Academic discipline: FIS/05 Astronomy and Astrophysics

Research

Keywords: Numerical simulations Cosmlogical simulations Galaxy formation and evolution Gas dynamics in galaxies Feedback processes Circumgalactic medium Gas accretion Magnetic fields

I am an expert in hydrodynamical simulations of galaxy formation from small-scale simulations, designed to investigate processes that are at the core of galactic evolution, to large-scale cosmological simulations modelling a large patch of the Universe. I am also part of large international collaborations (such as the Auriga and the IllustrisTNG projects) that are at the forefront of the field of numerical galaxy formation and evolution in a full cosmological context. Finally, I am an expert in designing and developing sophisticated codes for astrophysical applications. Below you can find some more details on some of my research highlights.

 

Disc-halo connection in star-forming galaxies

My work on the disc-halo connection in galaxies like the Milky Way aims at answering the question: how do galaxies get their gas? To investigate this key issue I have explored the mass and momentum exchange between the hot cosmological corona and cold gas clouds outside the plane in disc galaxies (extra-planar gas) generated by the galactic fountain. I studied the interaction between the two phases with idealized simulations modeling the evolution of a cloud of cool gas traveling through a more tenuous and hotter medium representing the galactic corona. These simulations have shown that the condensation of the coronal gas prevails over the evaporation of the clouds, if the metallicity and the pressure of the corona are high enough. The rate at which the gas condenses out of the corona is remarkably close to the value of 1 Msunyr-1 , which is necessary to feed star-formation in a galaxy like the Milky Way. For what concerns the transfer of momentum, the simulations have indicated that this process is strongly influenced by the radiative cooling of the gas, the net effect being a reduction of the transferred momentum from the cold to the hot gas when the cooling is switched on. These results have provided a theoretical framework to interpret the dynamical state of the cold phase of the extra-planar gas in the Milky Way and external galaxies, and are at the core of a model that makes successful predictions for the kinematics of the warm-hot absorbers observed in the Milky Way lower corona. Finally, a PhD student under my supervision has extended these results to systems different from the Milky Way by including thermal conduction. Thermal conduction makes the condensation of the corona more difficult for massive systems, with major implications for galaxy evolution.

 

Formation of disc galaxies

The formation of Milky Way-like galaxies is a major challenge in cosmological simulations. My main contribution to this area is the first successful application of the moving-mesh code Arepo to this complex problem. Arepo is a a cosmological hydrodynamic code that solves the Euler equations on an unstructured Voronoi tessellation of the space. The distinctive feature of Arepo is that the mesh is free to move and to change its topology according to the flow. This allows the code to automatically adapt to density changes, in a way similar to what Lagrangian (SPH) codes do, while retaining the accuracy advantages of a grid-based approach in solving hydrodynamics equations. With Arepo I have performed a series of cosmological hydrodynamic simulations of Milky Way-size halos, which have demonstrated the ability of the code in producing simulated disc galaxies in agreement with observations. With these simulations, I have also investigated the properties of the circum-galactic medium (CGM) that surrounds the simulated galaxies. I pay special attention to the metal content of the CGM, which can have an important impact on the cooling rate of this gas and, ultimately, on regulating the gas supply that is provided to the star-forming disc. I am currently part of the core team of the Auriga project, which extends these results with more sophisticated simulations to a larger sample size. In Auriga, I have analysed the neutral hydrogen content of the simulated galaxies. This is a crucial stepping stone to study in detail the kinematics of simulated disc galaxies through the creation of synthetic HI interferometric observations.

 

Magnetic fields in the Universe

One of the lines of research that I am currently pursuing is the study of the co-evolution between magnetic fields in the Universe and the structures that host them. In particular, I have focused on the amplification of primordial magnetic fields due to the assembly of cosmological structures. I started this investigation with cosmological simulations of Milky Way-type galaxies, for which my collaborators and I found that it is possible to form a realistic late-type galaxy with the typical magnetic field intensities and morphologies of these systems. More recently, I extended this study to large-scale cosmological MHD simulations. In these calculations I show that radiative cooling and gas turbulence driven by stellar and AGN feedback processes play a key role in the amplification of a small magnetic seed field to the present-day intensities observed in galaxy and galaxy clusters, and give rise to a magnetic field topology in agreement with Faraday rotation observations. With these simulations I have also explored the potential influence that magnetic fields might have on the global properties of the galaxy population and the large-scale distribution of the extra-galactic gas. Finally, I am part of the IllustrisTNG project, the successor of the Illustris simulations, that aims at understanding the physical processes that drive galaxy evolution. In IllustrisTNG, other than studying the amplification of magnetic fields in the Universe, I have also predicted and analysed the diffuse synchrotron radio emission of simulated galaxy clusters, further exploring the link between magnetic fields and cosmic structures.

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