Kinematic bulges and discs: implications for galaxy evolution

Abstract: 

Galaxies are among the most fascinating and rich objects in our Universe, whose evolution is regulated by a complex interplay between internal and external processes. In the current evolutionary paradigm, galaxies evolve in two phases: an early stage of gas collapse and mergers leading to bulge formation, followed by secular evolution and in situ star formation related to the disc build-up. Quantifying the contribution of these structures is crucial for identifying the key physical mechanisms driving galaxy evolution. However, verifying this evolutionary framework is challenging, primarily due to the difficulties in determining the relative content of bulges and disks. 

In this talk, we present a new technique (BAyesian modelliNg of Galaxies, BANG) that extends bulge+disc decomposition to galactic dynamics and the results obtained from its application on the MaNGA survey. Our methodology, simultaneously fitting galaxy photometry and kinematics for Integral Field Spectroscopy data, encompasses standard approaches. In the context of the two-phase scenario, our analysis revealed key insights: (1) bulges and disks are not well-defined classes when looked at through kinematic; (2) structures with the same light content can have different individual dynamical properties, resulting in different global galactic dynamics; (3) major merger relics dominates only at high (higher than what previously thought) masses; and (4) the presence of large bulges does not necessarily suppress star formation, indicating that morphological quenching is not a dominant evolutionary pathway.