Testing density wave theory using multi-wavelength image data and stellar cluster dynamics

Studying galaxy structures from different wavebands enables us to observe a variety of intrinsic galactic features and to test the validity of underlying theories in great detail. Density wave theory, originally proposed by C.C. Lin and F. Shu (Lin & Shu 1964), explains the nature of the spiral arm patterns in spiral galaxies as density waves that propagates through the galactic disk. By focusing on two main implications, the co-rotation radius, and the age gradient, we were able to provide convincing evidence in favor of density wave theory and examples of galaxies which fails to adhere to the classical density wave theory framework. In finding the co-rotation radius twenty nearby galaxies were observed using 3.6µm, 8µm, B-band and FUV images. The co-rotation resonance region creates a radius of localized observable features that can be used to locate and study them. Clear physical offsets are visible when analyzing the images in terms of pitch angles. These pitch angle measurements were used to trace logarithmic spiral arm overlays on each image which were then stacked to observe physical crossing points to locate the co-rotation radius. The results of this study were published in Abdeen et al. 2020. Multiple other methods including arm-inter-arm contrast plots, 2D-fast Fourier transformation plots and 3-D surface intensity plots were also used to identify the co-rotation radius. The search for age gradients is done using star formation history (SFH) maps produced by LIGHTNING (Eufracio et al. 2017) and stellar cluster data. The SFH maps from five non-parametric age bins were analyzed for visible spiral structures using SPIRALITY (Sheilds et al. 2015) and decrement in pitch angle values were observed with increasing age. We have also used azimuthal offsets of spatially resolved stellar clusters in 3 LEGUS galaxies to observe age trends.