THE DISTANCE TO THE COMA CLUSTER FROM SURFACE BRIGHTNESS FLUCTUATIONS

We report on the first determination of the distance to the Coma Clust er from surface brightness fluctuation (SBF) measurements obtained fro m Hobble Space Telescope WFPC2 observations of the bright E0 galaxy NG C 4881 in the Coma Cluster and ground-based observations of the ''stan dard'' E1 galaxy NGC 3379 in the Leo-I group. Relative distances based on the I-band fluctuation magnitude, (m) over bar(I), are strongly de pendent on the metallicity and age of the stellar population. However, the radial changes in the stellar populations of the two giant ellipt icals NGC 3379 and NGC 4881 are well described by published Mg-2 gradi ents, and the ground-based measurements of (m) over bar(I) at several radial points in NGC 3379 are used to calibrate (m) over bar(I) in ter ms of the Mg-2 index. The distance to NGC 3379, assumed to be identica l to the average SBF distance of the Leo-I group, is combined with the new SBF measurements of NGC 4881 to obtain a Coma Cluster distance of 102 +/- 14 Mpc. Combining this distance with the cosmic recession vel ocity of the Coma Cluster (7186 +/- 428 km s(-1)), we find the Hubble constant to be H-0 = 71 +/- 11 km s(-1) Mpc(-1).