Calibration of the fundamental plane zero-point in the Leo-I group and an estimate of the Hubble constant

We derive new effective radii and total magnitudes for 5 E and S0 galaxies in the Leo-I group from wide-field CCD images. These are used in conjunction with recent literature velocity data to construct the fundamental plane (FP) of the Leo-I group. The rms scatter that we find is only 6 % in distance. The zero point of this relation provides a calibration of the FP as a distance indicator and directly determines the angular diameter distance ratio between the Leo-I group and more distant clusters. In the language of Jerjen and Tammann (1993) we determine a cosmic velocity of the Leo-I group of 757± 68 km s relative to the Coma cluster, or 796± 57 km s relative to a frame of 9 clusters. Combining this velocity with the Cepheid distance to M96, a member of Leo-I, we find the Hubble constant to be H0 = 67± 8 km s Mpc or H0 = 70± 7 km s Mpc for each case. The distance we obtain for the Coma cluster itself (108± 12 Mpc) is in good agreement with a number of other recent estimates. Subject headings: cosmology: observations — distance scale — galaxies: elliptical and lenticular, cD — galaxies: distances and redshifts — galaxies: fundamental parameters — galaxies: photometry Based on observations made with INT operated on the island of La Palma by the Royal Greenwich Observatory in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrof́ısica de Canarias. Present address: NORDITA, Blegdamsvej 17, DK–2100 Copenhagen Ø, Denmark; [email protected].