RESONANCES AND EXTENT OF SPIRAL ARMS IN DISK GALAXIES

The distribution of visual matter in 84 spiral galaxies was estimated from NIR Kband maps observed with SOFI/NTT, ESO. Decomposing the maps into standard axisymmetric components (e.g. disk and bulge) and using HI line width data with a maximum disk assumption for the halo, synthetic rotation curves were estimated for each galaxy. The extent of the main spiral pattern measured on the K maps of galaxies was compared with the distance between major resonances (i.e. ILR, 4:1, CR and OLR) as obtained from the synthetic rotation curves assuming that the start of the spiral corresponded to either ILR or CR. The first preliminary analysis indicated that 1/3 of the disk galaxies have a main, symmetric spiral structure with a radial extent consistent with that of the ILR-4:1 distance in a maximum disk, rotation curve model. Another 1/3 of the sample show better agreement with the CR-OLR resonances. The extent of the spirals does not agree with distances estimated for neither ILR-CR nor ILROLR. Sub-maximum disk rotation curve models (e.g. 60%) show larger scatter.