Weak-lensing determination of the mass in galaxy halos

We detect the weak gravitational lensing distortion of 450,000 background g alaxies (20 < R < 23) by 790 foreground galaxies (R < 18) selected from the Las Campanas Redshift Survey (LCRS). This is the first detection of weak l ensing by field galaxies of known redshift, and as such permits us to recon struct the shear profile of the typical field galaxy halo in absolute physi cal units (modulo H-o), and to investigate the dependence of halo mass upon galaxy luminosity. This is also the first galaxy-galaxy lensing study for which the calibration errors due to uncertainty in the background galaxy re dshift distribution and the seeing correction are negligible. Within a proj ected radius of 200 h(-1) kpc, the shear profile is consistent with an isot hermal profile with circular velocity v(c) = 164 +/- 20 km s(-1) for an L-* galaxy, consistent with the typical circular velocity for the disks of spi rals at this luminosity. This halo mass normalization, combined with the ha lo profile derived by Fischer and coworkers from a galaxy-galaxy lensing an alysis of the Sloan Digital Sky Survey, places a lower limit of (2.7 +/- 0. 6) x 10(12) h(-1) on M. on the mass of an L-* galaxy halo, in good agreemen t with the satellite galaxy studies of Zaritsky et al. Given the known lumi nosity function of LCRS galaxies, and assuming that M <proportional to> L-b eta for galaxies, we determine that the mass within 260 h(-1) kpc of normal galaxies contributes Omega = 0.16 +/- 0.03 to the density of the universe (for beta = 1) or Omega = 0.24 +/- 0.06 for beta = 0.5. These lensing data suggest that 0.6 < <beta> < 2.4 (95% confidence level), only marginally in agreement with the usual <beta> approximate to 0.5 Faber-Jackson or Tully-F isher scaling. This is the most complete direct inventory of the matter con tent of the universe to date.