I work at the nexus of cosmology and galaxy formation. The overarching theme of my research is understanding how the basic constituents of our Universe and the physics of gas and star formation shape the formation and evolution of galaxies and the large-scale structure of the Universe. Click on the images below for more information.
Galaxy formation
Cosmology and
large-scale structure
Star formation
GALAXY FORMATION
The ambition of a theory of galaxy formation is to simultaneously describe the large-scale structure of the Universe and the observable properties of galaxies. While cosmological simulations proved crucial for our understanding of galaxy formation, they are still limited by numerical constraints.
The main challenge is the description of sub-galactic "feedback" processes, such as stellar winds and jets from supermassive black holes, which significantly slow down star formation by heating up the surrounding gas. However, an implementation of these mechanisms from first principles would require a resolution that exceeds the typical numerical constraints of cosmological simulations by several orders of magnitude. Feedback processes are therefore included via numerical prescriptions that can vary from code to code.
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Because of the pivotal role of feedback on galaxy formation, it is paramount to find ways to constrain the prescriptions implemented in simulations via observable quantities. With a combination of analytical models and state-of-the-art hydrodynamic cosmological simulation, I investigate the impact of feedback processes on the distribution of dark and baryonic (i.e., "ordinary") matter within and around galaxy-hosting haloes, as well as on the physical state of gas around such haloes and intergalactic space.
Projected gas mass around a halo with mass comparable to the one hosting the Milky Way, in three variants of the SIMBA simulation: (1) no stellar winds nor black-hole-driven jets; (2) stellar winds only; (3) stellar winds and black-hole-driven jets. Darker purple shades show lower mark lower gas densities, whereas brighter yellow patches trace higher gas densities. Different modelling choices for the aforementioned sub-galactic processes affect the spread of gas around the halo.
COSMOLOGY & LARGE-SCALE STRUCTURE
The Universe started off as a quasi-homogeneous distribution of matter, which eventually formed galaxies separated by vast amounts of almost empty space, due to the combined action of gravity and the expansion of the Universe. Dark matter, gas and galaxies do not fill the sky randomly, but they tend to cluster in a "cosmic web" of filaments and knots that constitute the large-scale structure of the universe.
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With cosmological simulations and paper-and-pen models, I study how the astrophysics of sub-galactic processes, such as outflows driven by stars and black holes, affects the large-scale distribution of matter in the Universe. I also study how the statistics of the large-scale structure changes under variations of the relative abundance of the basic constituents of the universe (e.g., "ordinary" matter, dark matter, dark energy, etc.), and what we can learn about the foundations of the standard cosmological model from observations of the large-scale distribution of matter in the Universe.
Projected gas mass in the SIMBA simulation. The figure displays a region with 50 Mpc per side. Darker purple shades show lower mark lower gas densities, whereas brighter yellow patches trace higher gas densities. The gas clearly traces the "cosmic web".
STAR FORMATION
Accurately predicting the observed yearly rate of star formation in the visible universe is a key test of any theory of galaxy formation. I develop first-principles paper-and-pen models of cosmic star formation and compare them with sophisticated cosmological simulations and observed data to unveil the astrophysical processes shaping the build up of stars within galaxies.
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I also study the impact of the cosmological model on star formation history, calculating how star formation would unfold in counterfactual universes, and how that would ultimately favour the generation of intelligent observers such as ourselves. This can shed light on the conundrum behind the observed abundance of "dark energy" in the universe, a mysterious constituent that is responsible for its accelerated expansion.
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Stellar mass formed per year in a reference volume in the Universe, for several variants of the SIMBA simulation with different models for sub-galactic astrophysical processes such as stellar outflows and black-hole-driven jets. The results of the simulations are compared with the predictions of the paper-and-pen model by Sorini & Peacock (2021) and the compilation of observed data collated by Madau & Dickinson (2014). The different predictions of the various models considered enable us to draw conclusions on what determines the observed features of the star formation history (e.g., the peak, the downturn at late times, etc.).
Ref.: Scharré, Sorini and Davé, Monthly Notices of the Royal Astronomical Society, Vol. 534, Issue 1, pp.361-383