Multiaperture J (1.2 µm), H (1.6 µm), and K (2.2 µm) photometric observations are presented for the central regions of 91 galaxies distributed along the Hubble sequence, ranging in morphological type from early spiral to Magellanic irregular. In addition, multiaperture measurements of the luminosity-sensitive 2.3 µm CO absorption feature, and the temperature-sensitive 1.9 µm H2O absorption feature, are presented for about half the sample.
The main results of this work are: 1) galaxies whose nuclear regions are dominated in the optical by a stellar population with mean spectral type ranging from near K to near F have similar stellar compositions in the infrared; and 2) this red stellar component is compatible only with synthesis models characterized by giant branches rich late M stars, flat main-sequence luminosity functions, values of M / LV < 10.
The correlation of the data with parameters - including projected aperture magnitude, and inclination angle - is examined. The relation between U - V and V - K color is discussed and interpreted in terms of simple population and/or metallicity changes. Several non-stellar emission mechanisms are considered in regards to the small subset of galaxies found to have significant 2 µm excesses. Detailed comparison is made with recently published synthesis models of Turnrose and of Williams; the latter author's models are incompatible with the infrared data.