부산대학교 도서관

Thin stellar discs are ubiquitous in galaxies, both on galactic and nuclear scales. These fragile structures are thought to be easily destroyed in major mergers, making the age-dating of their stellar populations a useful diagnostic for the assembly history of galaxies. My study aims to investigate the fragility of these discs in intermediate-mass-ratio encounters. To achieve this, I use high-resolution N-body simulations of galaxy models that are tailored to match the structural and kinematic properties of observed galaxies. My first step is to create a dynamical model of NGC 1381 (FCC 170), a nearly edge-on galaxy in the Fornax cluster, which includes both a kpc-scale disc and a nuclear stellar disc (NSD). I use detailed kinematic data from the Multi-Unit Spectroscopic Explorer and a novel method for constructing distribution function-based self-consistent galaxy models to create this model. I then generate N-body realisations of this model and demonstrate that it remains in equilibrium and preserves its properties over many Gyr when evolved with a sufficiently high particle number. However, my simulations reveal that the NSD is more susceptible to numerical heating, leading to a gradual increase in thickness by up to 22 per cent over ∼10 Gyr, even in my highest-resolution runs. Then, I investigate the vulnerability of thin-disc structures, including both galactic scale and nuclear discs, to intermediate mergers in parabolic orbits consistent with cosmological simulations. My simulations reveal that the kinematics and structure of the thin galactic disc are significantly altered by such mergers, whereas the NSD demonstrates remarkable resilience, showing only a gradual increase in size when compared to the model evolved in isolation. Based on my results, I suggest that thin galactic discs are better indicators for intermediate-mass-ratio mergers, while NSDs may provide more insight into major encounters. By combining my simulations with previous analyses of the stellar populations, I conclude that FCC 170 has not experienced any intermediate-mass-ratio dry encounters for at least ∼10 Gyr, as indicated by the age of its thin-disc stellar populations. Last, I analyse the evolution of kinematically-defined stellar discs in 10 Fornax-like clusters identified in the TNG50 run from the IllustrisTNG suite of cosmological simulations. My sample includes disc galaxies with present-day stellar mass M⋆ ≥ 3 x 10⁸ M⊙, and I track their evolution since first entering their host cluster. My results show that very few stellar discs survive in such dense environments, with survival rates ranging from 40 per cent to complete disruption, consistent with earlier reports for the two more massive Virgo-like clusters in TNG50. However, the low number of present-day disc galaxies in Fornax-like clusters may be at odds with the presence of three edge-on disc galaxies in the actual Fornax cluster, as indicated by the Fornax3D survey. I investigate this by randomly selecting Fornax analogues from various directions and applying the same selection function as Fornax3D. I find that the probability of finding three edge-on disc galaxies in any one Fornax-like cluster in TNG50 is rather low, though not impossible. Moreover, I compare the stellar-population properties near the equatorial plane derived from integral-field spectroscopy for the three edge-on disc galaxies in Fornax to similar line-of-sight integrated values for present-day disc galaxies in TNG50. My analysis shows that for one of these galaxies, the very old and metal-rich stellar population of its disc cannot be matched by any of the disc galaxies in TNG50, including those in the field. I discuss possible interpretations of these findings, pointing to the need for future studies on passive cluster spirals as a way to further test state-of-the-art cosmological simulations.