Constraining the Evolution of Spiral Galaxies over Cosmic Time with Observations and Simulations

Abstract

Spiral structures are observed in approximately two-thirds of massive galaxies in the local Universe, yet their formation mechanisms and impact on gas and stellar distributions remain debated. Theories such as density wave theory, dynamic spiral theory, and tidal-induced spiral theory offer different explanations, each predicting distinct material flows across spiral arms, but observational constraints on the dominant mechanisms remain inconclusive. This thesis aims to bridge this gap by investigating how spiral arms regulate the distribution of gas and stars across different cosmic epochs and environments. Using adaptive optics with the Multi-Unit Spectroscopic Explorer (MUSE) from the Middle Age Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey, I resolve spiral structures in galaxies at z~0.3, achieving 0.6 - 0.8'' spatial resolution. At z~0, I study nearby spiral galaxies from the TYPHOON survey, which provides a large field-of-view covering the entire optical disc. At both redshifts, I compare the star formation rate (SFR) and gas-phase metallicity across the leading edge, spiral arms, and trailing edge. While I find evidence supporting density wave theory in both epochs, this thesis also reveals signatures of dynamic spiral theory, with galaxies lacking clear azimuthal offsets in SFR or metallicity at z~0 and z~ 0.3. Interestingly, an interacting galaxy at z~0 exhibits an azimuthal offset opposite to the prediction of density wave theory, potentially driven by the ongoing merger event. At z~0.3, I further analyse the stellar age distribution using D4000 as a proxy, emphasizing the need for appropriate timescale tracers in studying spiral galaxies.

To interpret these observational results in a broader context of long-term evolution, I use Auriga level 3 cosmological zoom-in simulations to investigate the temporal stellar age distributions. Tracking the stellar age pattern across the past 5 Gyr, I find that the simulated spiral galaxies typically exhibit younger stellar populations on their leading edges, consistent with density wave theory. However, my analysis also shows that mergers and fly-bys can erase the age pattern built by spiral potential, with azimuthal variations recovering within two snapshot (~600 Myr). These results highlight the interplay between external environmental perturbations and internal spiral dynamics in shaping stellar age distributions and propagating star formation over time.

By integrating IFU observations with simulations, this thesis offers new insights into both the short-term dynamics and long-term evolution of spiral arms. While no single theory fully explains the origin of all spiral structures in the low-z Universe, my findings suggest that external perturbations can temporarily erase azimuthal variations imprinted by spiral potentials, helping to reconcile discrepancies between theoretical predictions and observed galaxies. Future work will expand this framework to higher-redshift (z = 1-3) observations and higher temporal-resolution simulations, enabling a statistical test of density wave theory by tracking the evolution of azimuthal variations in gas and stellar populations.