Weak‐Lensing Determination of the Mass in Galaxy Halos

Abstract

We detect the weak gravitational lensing distortion of 450,000 background galaxies (20 < R < 23) by 790 foreground galaxies (R < 18) selected from the Las Campanas Redshift Survey (LCRS). This is the first detection of weak lensing by field galaxies of known redshift, and as such permits us to reconstruct the shear profile of the typical field galaxy halo in absolute physical units (modulo H0), 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 redshift distribution and the seeing correction are negligible. Within a projected radius of 200 h-1 kpc, the shear profile is consistent with an isothermal profile with circular velocity vc = 164 ± 20 km s-1 for an L* galaxy, consistent with the typical circular velocity for the disks of spirals at this luminosity. This halo mass normalization, combined with the halo profile derived by Fischer and coworkers from a galaxy-galaxy lensing analysis of the Sloan Digital Sky Survey, places a lower limit of (2.7 ± 0.6) × 1012 h-1 M☉ on the mass of an L* galaxy halo, in good agreement with the satellite galaxy studies of Zaritsky et al. Given the known luminosity function of LCRS galaxies, and assuming that M ∝ Lβ for galaxies, we determine that the mass within 260 h-1 kpc of normal galaxies contributes Ω = 0.16 ± 0.03 to the density of the universe (for β = 1) or Ω = 0.24 ± 0.06 for β = 0.5. These lensing data suggest that 0.6 < β < 2.4 (95% confidence level), only marginally in agreement with the usual β ≈ 0.5 Faber-Jackson or Tully-Fisher scaling. This is the most complete direct inventory of the matter content of the universe to date.