NEAR-INFRARED LUMINOSITY FUNCTION AND COLORS OF DWARF GALAXIES IN THECOMA CLUSTER

We present K-band observations of the low-luminosity galaxies in the C oma cluster, which are responsible for the steep upturn in the optical luminosity function at M-R similar to-16, discovered recently. The ma in results of this study are as follows. (i) The optical-near-infrared colours of these galaxies imply that they are dwarf spheroidal galaxi es. The median B-K colour for galaxies with -19.3 < M-K < -16.3 is 3.6 mag. (ii) The K-band luminosity function in the Coma cluster is not w ell constrained, because of the uncertainties due to the field-to-held variance of the background. However, within the estimated large error s, this is consistent with the R-band luminosity function, shifted by similar to 3 mag. (iii) Many of the cluster dwarfs lie in a region of the B - K versus B - R colour-colour diagram where background galaxies are rare (B - K < 5; 1.2 < B - R < 1.6). Local dwarf spheroidal galax ies lie in this region too. This suggests that a better measurement of the K-band cluster luminosity can be made if the field-to-field varia nce of the background can be measured as a function of colour, even if it is large. (iv) If we assume that none of the galaxies in the regio n of the B - K versus B - R plane given in (iii) in our cluster fields are background, and that all the cluster galaxies with 15.5 < K < 18. 5 lie in this region of the plane, then we measure alpha = -1.41-(+0.3 4)(.037) for -19.3 < M-K - 16.3, where alpha is the logarithmic slope of the luminosity function. The uncertainties in this number come from counting statistics.