This material was presented to the American Astronomical Society meeting in Austin, TX on January 6, 1999. Each figure above is a link to a higher-resolution version of the image. Spiral galaxy morphology is a strong function of wavelength. In the figures above, we show three-color images of six galaxies. The nomenclature is not related to the age of the galaxies.
Galaxy classification is based on B-band images.
However, the blue light is dominated by hot, young stars, and is strongly effected by obscuration due to interstellar dust. The near-IR light is dominated by emission from the old, cool stars, and is much less effected by dust obscuration. Thus it gives a much better picture of the underlying mass distribution of spirals. We have prepared a plot of the H-band vs. optical morphological types for our full sample. While the level of agreement is generally good, there are examples of gross deviation that reflect the real differences in the optical and IR morphologies of galaxies.