Infrared imaging of spiral galaxies: Colors and luminosity profiles

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Abstract

We present surface photometry of 43 S0 and spiral galaxies in the K band with a subset also observed in J. Most of the data are photometrically calibrated. We combine our data with published optical major-axis profiles to construct a set of galaxies with rJK colors, divide the major-axis profiles into bulge-dominated and disk-dominated regions, and compute mean colors and color gradients separately for bulges and disks. Typically the disk colors are measured from 0.8 to 1.8 scale lengths. The colors of the bulge and disk components are strongly correlated, 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] ~ -0.1 to -0.2. Many of the bulges exhibit negative color gradients (bluer outward), which indicate that metallicity gradients of order {DELTA}[Fe/H]~ -0.2 may be common in bulges. Bulges of late-type galaxies are bluer on average than those of early types, probably a consequence of lower metallicity. About 25% of the galaxies have especially red bulge and disk colors, which we interpret as arising from large internal extinction rather than from an enhanced star-formation rate.

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