Only recently have photometric observations of galaxies in the far red and infrared become available which are of sufficient quality to permit accurate construction of stellar synthesis models for these spectral regions (e.g., O'Connell 1974, 1976a, b; Frogel et al. 1975a, b, c, 1977, hereafter Paper I; Whitford 1977; Aaronson, Frogel, and Persson 1977, hereafter Paper II). However, most of these observations have concentrated on the simplest systems to understand, elliptical galaxies.
In this paper we present multiaperture observations at J (1.2 µm), H (1.6 µm), and K (2.2 µm) for a large number of galaxies distributed in morphological type along the Hubble sequence, from early spiral to Magellanic irregular. addition, we present observations of the 2.3 µm CO absorption band and the 1.9 µm H2O absorption band, features which are sensitive measures of luminosity and temperature in late-type stars (Johnson and Mendez 1970; Frogel 1971; Baldwin, Frogel, and Persson 1973; Frogel et al. 1975b; Papers I and II). These data provide valuable constraints on both empirical and evolutionary,population models for composite systems with very different star formation histories.
The observational procedures and data reduction are described in Section II. Using U and V measurements obtained from the literature, the relationships between optical and infrared colors with projected aperture size, morphological type, inclination angle, and absolute magnitude are discussed in Section III. The interrelations among the various colors are also examined. In Section IV qualitative interpretation of the results is given in terms of simple population and metallicity effects. A variety of non-stellar emission mechanisms are considered in Section V in regards to the small subset of galaxies found to have significant 2 µm excesses, and the data is compared with several recently published stellar synthesis models in Section VI. Our results are summarized in Section VII. The system of standard magnitudes and colors are reviewed in Appendix A, a brief description of the InSb detector system used in this work is given in Appendix B, and the calibration of V - K color with mean metallicity is discussed in Appendix C.