Exploring bending waves through stars of different ages

Abstract

This dissertation investigates the complex role of bending waves’ vertical oscillations in galactic disks in shaping the structure and internal dynamics of disk galaxies. The focus is on understanding how these waves influence the interaction between stellar and gaseous components within the disk, particularly in regions near the galactic midplane where such interactions are most dynamically active. Bending waves, often triggered by tidal interactions, satellite perturbations, or instabilities within the disk, propagate through the galaxy and can lead to significant vertical displacements of matter. These vertical motions are not purely random, and their influence may vary depending on the properties of the affected populations, such as stellar age and gas density. A high-resolution simulated galaxy, developed and analyzed using the Pynbody framework, serves as the primary platform for studying the emergence and propagation of bending waves. The simulation allows for a detailed exploration of the kinematic and spatial behaviour of both stars and gas, enabling a direct comparison of their responses to the same vertical perturbations. Special attention is given to the differential impact on stellar populations of varying ages, revealing that younger stars tend to exhibit a stronger coupling with the gas component. This age-dependent sensitivity suggests that younger stars, likely born in the thin disk and more dynamically cold, are more readily influenced by the wave-induced motions of the surrounding gas, whereas older stars, which have had time to heat and scatter kinematically, show a weaker response. The analysis further explores the degree of alignment between the vertical displacements of stars and gas. Statistical tools and a probabilistic framework are employed to evaluate the likelihood of such alignments occurring by chance. The results indicate that the observed coherence between stars and gas is significantly higher than would be expected from random fluctuations, thereby implying a physically meaningful correlation. This correlation is attributed to the shared response of both components to the same bending wave dynamics, reinforcing the idea that such waves act as a unifying vertical influence within the disk. These findings suggest that similar effects could be present in real galaxies, where vertical structures such as warps, flaring, and phase-space spirals are commonly observed. The results therefore emphasize the importance of stellar age as a controlling factor in the star-gas interaction within bending wave structures, and highlight the broader role of vertical dynamical processes in the evolution and morphology of galaxies.