6.2 Global NIR Colors

The mean near-infrared H-Ks and J-Ks isophotal colors (per morphological type) are shown in Figure 20. Early-type spirals (S0/Sa/Sb) show little color variation, with a mean J-Ks ~ 1.0 and H-Ks ~ 0.27 mag. Late-type spirals show a significant blue trend in both measures, peaking with Sdm types, J-Ks ~ 0.7 mag. Irregular/peculiar galaxies have redder colors, J-K ~ 1.1, although the scatter is much larger, indicative of their complex and dust reddened structures. Also note that ellipticals/spheroids have blue colors compared to early-type spirals (e.g., J-K = 0.9 vs 1.0), probably indicative of the low metallicity and lack of significant amounts of gas and dust in ellipticals. Finally, "barred" galaxies do not show color differences with normal galaxies. There is a hint, however, of a difference in color for the S0/Sa vs. SB0/SBa types. This weak trend is not surprising given that the colors are derived from large isophotal apertures, and hence the contrast between bar colors and nuclear or bulge colors is somewhat diluted. A better contrast would be realized through separation of the colors of the nucleus, bulge and bar components.

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