Stationary Density Wave Theory predicts the existence of an age gradient across the spiral arms with a phase crossing at the co-rotation radius. Using star formation history (SFH) maps of 12 nearby spiral galaxies derived from textsc{LIGHTNING} citep{Eufracio:2017}, a spectral energy distribution (SED) fitting procedure, and by using textsc{Spirality} citep{Shield:2015} a textsc{MATLAB}-based code which plots synthetic spiral arms over textsc{FITS} images, we have found a gradual decrement in pitch angles with increasing age, thus providing us with evidence in favour of the Stationary Density Wave Theory. We have also used azimuthal offsets of spatially resolved stellar clusters in 3 LEGUS galaxies to observe age trends.
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