Searching for fossil fragments into the galactic bulge

The exact mechanism that drove the formation of the bulge in the Milky Way and in analogous galaxies is still largely debated. Two main formation channels are currently invoked to reproduce the observed chemo-dynamical properties of the MW inner region: a dynamical secular evolution of the disk, and the merging at high redshift of massive clumps formedfrom the fragmentation of the primordial gas-rich disk. The global picture emerging from the photometric and spectroscopic analyses presented in this Thesis is that two peculiar Bulge stellar clusters, Terzan 5 and Liller 1, at odds with their appearance, did not undergo the same formation and evolution path of globular clusters (GCs). Conversely, they experienced a prolonged, multi-episode star formation history fueled by iron-enriched gas that had been deposited in the central region of the clusters. This is more likely explainable by invoking a self-enrichment process. These evidences make them strong candidate present-day remnants of the massive clumps observed in high-redshift galaxies, opening a new line of investigation: these peculiar stellar systems could represent the first observational proof of the hierarchical assembling process predicted by the clump-origin scenario, shedding new light on the formation of our bulge and galaxies’ bulges in a more general cosmological picture.