Beyond the Bulge: Rethinking Galaxy Structure with High-Resolution IFS Surveys

Understanding how galaxies build up mass and angular momentum is key to understanding their diverse morphology, structure, and dynamics in the present-day Universe. Traditionally, bulge formation has been linked to mergers in galaxies with dispersion-dominated centres with high Sérsic indices, whereas secular processes are thought to shape all other central components. In this talk, I will show how global IFS measurements from the SAMI Galaxy Surveys challenge the traditional view that accretion predominantly drives bulge formation, revealing significant scatter between bulge-to-total ratio, Sérsic index, and V/σ. Additionally, while a correlation exists between a galaxy's global intrinsic thickness and its mean stellar population age, the scatter in this relation points to multiple competing internal and external physical small-scale processes. With the recent advent of high-resolution IFS surveys like TIMER, PHANGS, MAUVE, and GECKOS, we now have the tools to address the complexities of bulge formation with unparalleled precision. Utilising edge-on GECKOS data, I will present a cautionary tale of how different central structures, such as edge-on bars and thick disks, can be misidentified as classical bulges. At the same time, I will show how the diverse GECKOS sample—including the discovery of a counter-rotating stellar thick disk—sheds light on the physical processes driving the observed scatter in bulge properties.