THE NEAR-INFRARED FUNDAMENTAL PLANE OF ELLIPTIC GALAXIES

We present results from a near-infrared K-band imaging survey of 59 el liptical galaxies in five nearby clusters. We measure photometric para meters for each galaxy using surface photometry and draw velocity disp ersions from the literature. Three observables define a near-infrared fundamental plane (FP) of elliptical galaxies with R(e) proportional t o sigma (1.44 +/- 0.04) Sigma(e) (-0.79 +/- 0.04). The scatter in the near-infrared relation is small at 16.5% in distance, which is equival ent to, or less than, the scatter of the optical FP. We suggest that t he small deviation of the near-infrared FP relation from the optical F P is due to the reduction of metallicity effects in the near-infrared bandpass. While the small scatter of the optical FP could be consisten t with compensating effects of age and metallicity, the similarly smal l scatter of the near-infrared FP is nearly independent of metallicity and hence places a strong constraint on possible age spreads among el liptical galaxies at every point along the FP. We suggest that the dep arture of the near-infrared FP from the pure virial form R(e) proporti onal to sigma(2) Sigma(e)(-1), and the corresponding observed relation (M/L) proportional to M(0.16 +/- 0.01), may be explained by slight sy stematic departures of the structure and dynamics of elliptical galaxi es from a homology.