INFRARED IMAGING OF SPIRAL GALAXIES - COLORS AND LUMINOSITY PROFILES

We present surface photometry of 43 SO and spiral galaxies in the K ba nd with a subset also observed in J. Most of the data are photometrica lly calibrated. We combine our data with published optical major-axis profiles to construct a set of galaxies with rJK colors, divide the ma jor-axis profiles into bulge-dominated and disk-dominated regions, and compute mean colors and color gradients separately for bulges and dis ks. Typically the disk colors are measured from 0.8 to 1.8 scale lengt hs. The colors of the bulge and disk components are strongly correlate d, indicating that both components have a red stellar content that is similar in both age and metallicity. In the mean the disks are 0.1 mag bluer in r - K than bulges; this color difference would arise if the disks are 2-4 x 10(9) yr younger or have lower metallicities by Delta[ Fe/H] approximate to -0.1 to -0.2. Many of the bulges exhibit negative color gradients (bluer outward), which indicate that metallicity grad ients of order Delta[Fe/H] similar to -0.2 may be common in bulges. Bu lges of late-type galaxies are bluer on average than those of early ty pes, probably a consequence of lower metallicity. About 25% of the gal axies have especially red bulge and disk colors, which we interpret as arising from large internal extinction rather than from an enhanced s tar-formation rate.