Mass and Light in the Universe

Abstract

We present a weak lensing and photometric study of six half by half degree fields observed at the CFHT using the UH8K CCD mosaic camera. The fields were observed for a total of 2 hours each in I and V, resulting in catalogs containing ~ 20 000 galaxies per passband per field. We use V-I color and I magnitude to select bright early type galaxies at redshifts 0.1 < z < 0.9. We measure the gravitational shear from faint galaxies in the range 21 < m_I < 25 from a composite catalog and find a strong correlation with that predicted from the early types if they trace the mass with mass-to-light ratio 300\pm75 h (in solar units) for a flat (Omega_m0 = 0.3, Omega_l0 = 0.7) lambda cosmology and 400\pm100 h for Einstein-de Sitter. We make two-dimensional reconstructions of the mass surface density. Cross-correlation of the measured mass surface density with that predicted from the early type galaxy distribution shows a strong peak at zero lag (significant at the 5.2-sigma level). We azimuthally average the cross- and auto-correlation functions. We conclude that the profiles are consistent with early type galaxies tracing mass on scales of > 45 arcsec (> 200 kpc at z = 0.5). We sub-divide our bright early type galaxies by redshift and obtain similar conclusions. These mass-to-light ratios imply Omega_m0 = 0.10\pm0.02 (Omega_m0 = 0.13\pm0.03 for Einstein-de Sitter) of closure density.