Precision photometry of early-type galaxies in the Coma and Virgo clusters: a test of the universality of the colour-magnitude relation - I. The data

We have undertaken a comprehensive study of a large sample of early-type galaxies in the Virgo and Coma clusters. In the first of two papers, we present accurate UVJK photometry for a total of 94 elliptical and S0 galaxies. All U- and V-band measurements are based on CCD observations made with the 2. 5-m Isaac Newton Telescope. J- and K-band observations for the Coma cluster were made with a chopping photometer at the United Kingdom Infrared Telescope (UKIRT). Virgo J- and K-band measurements have been taken from Persson, Frogel 0. 030, 0. 021, 0. 026 and 0. 027 mag for Coma U, V (13-arcsec aperture), J and K (17-arcsec aperture) measurements. We have been careful to ensure that the data set is internally homogeneous. We estimate that the photometric zero-points in the two clusters agree to better than 0. 01 mag for U and V and 0. 02 mag for J and K. these measurements, we have derived U – V, V – K and J – K colours corrected for redshift, galactic extinction and aperture effects. After allowing for the systematic uncertainties in these corrections, we estimate that the U – V, V – K and J – K colour systems in both clusters are matched to better than 0. 02, 0. 03 and 0. 04 mag respectively. This data set is completed by photometric diameter parameters derived from our own V-band data, total V-band magnitudes derived from a combination of our measurements and those of Godwin & Peach and Michard, and velocity dispersions and morphological types taken from the literature. A detailed analysis of colour–magnitude correlations of these galaxies will be presented in Paper II (this issue).