PhD ceremony Mr. F. Lelli: Starbursts and gas dynamics in low-mass galaxies

PhD ceremony: Mr. F. Lelli

Dissertation: Starbursts and gas dynamics in low-mass galaxies

Promotor(s): prof. M.A.W. Verheijen, prof. F. Fraternali

Faculty: Mathematics and Natural Sciences

During the Universe's lifetime, the process of star formation plays a fundamental role in the growth and shaping of galaxies, and largely determines the different morphologies shown by nearby galaxies in the current cosmic epoch. In my thesis, I investigated the structure and evolution of dwarf galaxies, which are small stellar systems containing less than 1 billion stars and having physical sizes about 20 times smaller than the Milky Way. In particular, I focused on dwarf galaxies that are forming stars at unusually high rates, the so-called starbursting dwarfs. These objects are rare in the current cosmic epoch but were much more common in the early stages of the Universe's life, when the first, small galaxies were forming out of primordial gas. Nearby starbursting dwarfs, therefore, provide key information for understanding the processes that drive intense star formation during different cosmic epochs.

In my thesis, I showed that a close relation exists between the star-formation activity of dwarf galaxies and their internal dynamics, which is determined by the distribution of the luminous matter (mostly made of stars and gas) and of the mysterious dark matter. In starbursting dwarfs, the total mass (luminous and dark) is strongly concentrated towards the galaxy center. When the starbursting phase ends, they likely evolve into a peculiar family of “compact” galaxies, which have a similar central mass concentration. Moreover, the starburst is likely triggered by external mechanisms, such as interactions/mergers between dwarf galaxies. These results shed new light on the overall evolution of dwarf galaxies.