Effects on the Nuclear Near-InfraredProperties of Spiral Galaxies

Using JHKL photometric measures available in the literature, we have compared the near-infrared colour indices and central luminosities of samples of relatively isolated spiral galaxies with LINER and H II region-like nuclei (hereafter called L and H) with corresponding samples of interacting galaxies, in order to explore the effects of interactions on their near-infrared properties. We have found that the L galaxies and the isolated H galaxies have, in general, normal near-infrared colours which are fully explainable in terms of emission from late-type evolved stars. On the other hand, the sample of interacting H galaxies displays, on average, somewhat peculiar near-infrared colours (specifically, normal J - H colours, but redward H - K and, especially, K - L excesses), which very probably indicate the presence of thermal emission from hot dust, presumably related to intense star formation activity induced by the interactions. Furthermore, for the same galaxy sample there is some evidence that the emission at λ ~ 2.2 microns is somewhat more centrally concentrated than that at shorter wavelengths. Interestingly, the L galaxies appear to have greater central near-infrared luminosities than the H galaxies, for the same morphological-type interval.