A Morphological Method to Determine Co-Rotation Radii in Spiral Galaxies

Shock induced star formation in a stellar density wave scenario produces an azimuthal gradient of ages across the spiral arms which has opposite 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 spiral galaxies. Basically, we compare the behavior of the phase angle of the two-armed spiral in blue and infrared colors which pick out respectively young and older disk stellar population. We illustrate the method using theoretical leading and trailing, spirals. We have also applied 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 and three CRs respectively.Comment: 9 pages, accepted for publication in ApJL, figures 4 and 6 avaliables at ftp://ftp.inaoep.mx/pub/salida/puerari, full paper also avaliable at http://www.inaoep.mx/~puerar

Trends for Outer Disk Profiles

The surface-brightness profiles of galaxy disks fall into three main classes, based on whether they are simple exponentials (Type I), bend down at large radii (Type II, "truncations") or bend up at large radii (Type III, "antitruncations"). Here, we discuss how the frequency of these different profiles depends on Hubble type, environment, and the presence or absence of bars; these trends may herald important new tests for disk formation models.Comment: LaTeX, 2 pages, 1 EPS figure, uses modified newpasp.sty (included). To appear in Formation and Evlution of Galaxy Disks, eds. J.G. Funes and E.M. Corsin