Description - NGC 4553 is an excellent example of type SA(r)0+. The inner ring is a very bright feature with slight azimuthal surface brightness variations, much of which is likely due to the high inclination. Outside the ring is a bright extended and featureless disk. The lower frame shows that inside the bright center is a very short, weak nuclear bar. The same characteristic has been noted in other galaxies of this type (see, e.g., NGC 7702).
Both the SGC and CSRG interpret the extended outer disk light in terms of an outer ring or ring/lens. The feature has low constrast in any case, and in the image here appears only as an extended envelope.
Multi-Wavelength Morphology - The B-I color index map below reveals weak azimuthal color variations around the inner ring. The ring is slightly bluer along arcs around its major axis.
Interpretation - The presence of the small nuclear bar and the bright inner ring suggests an evolved system that once had a stronger primary bar. The color variations within the inner ring suggest that a low level of star formation may still be occurring in the feature, which was probably more active in the past. From its size relative to the extent of the outer disk, the ring is likely an evolved 4:1 resonant feature that once enveloped a stronger and longer bar. NGC 3081 may be in an earlier phase of this kind of evolution.
