Galaxy Dark Matter: Galaxy-Galaxy Lensing in the Hubble Deep Field

Abstract

In this Letter we present calibrated observations of the average mass of galaxies with 22 < I < 25 in the Hubble Deep Field. We measure the mean mass profile using the statistical gravitational lens distortion of faint blue background galaxies, based on 2221 foreground-background pairs. The observed weak lensing distortion is calibrated via full three-dimensional simulations and other Hubble Space Telescope data on a foreground cluster of known mass. Inside a projected radius of 5" we find a 3 sigma detection of shear. Fitting to an isothermal mass distribution, we find a distortion of 0.066 ^{+0.018}_{-0.019} at a radius of 2" (~8 h-1 kpc). The (1 sigma ) limits on the parameters for the truncated isothermal model are sigma _{{v}} = 185 ^{+30}_{-35} km s-1, router >= 15 h-1 kpc, and rcore = 0.6 ^{+1.3}_{-0.6} h-1 kpc. This corresponds to an average galaxy mass interior to 20 h-1 kpc of 5.9 ^{+2.5}_{-2.7} x 1011 h-1 Msolar. Inside 10 h-1 kpc, we find an average rest-frame V-band mass-to-light ratio of 11.4 ^{+6.0}_{-6.7} h (M/LV)solar.