Evidence in favour of density wave theory through star formation history
  maps and spatially resolved stellar clusters
  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.
