A MORPHOLOGICAL METHOD TO DETERMINE COROTATION RADII IN SPIRAL GALAXIES

Shock-induced star formation in a stellar density wave scenario produc es an azimuthal gradient of ages across the spiral arms that has oppos ite signs on either side of the corotation resonance (CR). We present a method based on the Fourier analysis of azimuthal profiles to locate the CR and determine the arm character (trailing or leading) in spira l galaxies. Basically, we compare the behavior of the phase angle of t he two-armed spiral in blue and infrared colors that pick out, respect ively, young and older disk stellar population. We illustrate the meth od using theoretical leading and trailing spirals. We have also applie d the method to the spiral galaxies NGC 7479, for which we confirm the reported leading arms, and NGC 1832. In these galaxies, we find two a nd three CRs, respectively.