Near-Infrared Fundamental Plane of Elliptical Galaxies

Near-infrared (2.2 \mu m) observations of a sample of 48 elliptical galaxies in the Coma cluster have been carried out and used to study the near-ir fundamental plane (FP) of ellipticals in this cluster. An rms scatter of 0.076 dex was found for this relation. This corresponds to an uncertainty of 19% in distances to individual galaxies derived from this relation. The sensitivity of the near-infrared FP to the star formation or changes in metallicity and stellar population among the ellipticals was explored and found to be small. Therefore, a likely source of scatter in this relation for ellipticals in the Coma cluster is contributions from the Asymptotic Giant Branch (AGB) population to their near-infrared light. The cluster galaxies presented here, provide the zero-point for the peculiar velocity studies, using the near-infrared FP. Changes in the slopes of the $D-\sigma$ and $L-\sigma$ relations of ellipticals between the optical and near-infrared wavelengths were investigated and found to be due to variations in metallicity or age (or a combination of them). However, it was not possible to disentangle the effects of age and metallicity in these relations. We find $M/L\propto M^{\alpha}$ with $\alpha=0.14\pm 0.01$ at the near-ir and $\alpha=0.24\pm 0.01$ at the optical wavelengths, This is interpreted as due to a mass-metallicity effect or changes in age or the IMF slope with mass. Using evolutionary population synthesis models, we find that the effects of age and metallicity decouple on the (M/L)_K vs. Mg_2 and (M/L)_K vs. (V-K) diagrams. The observed trends on these relations are found to be due to an age sequence while metallicity mainly contributing to the scatter