Gravitational lensing by galaxy groups in the Hubble Deep Field

We investigate strong lensing of galaxies in the Hubble Deep Field by foreground groups and clusters of galaxies with masses from 10(13) to 10(15) M-.. Over this mass range, groups with the Navarro, Frenk, & White profile are less efficient than singular isothermal spheres at producing multiple images of galaxies, by factors of 5 x 10(-2) to 10(-3). This difference highlights the sensitivity of the lensing cross section to the central density profile. Nonetheless, with either profile we find that the expected number of galaxies lensed by groups in the Hubble Deep Field is at most less than or similar to1, consistent with the lack of clearly identiDed group lens systems.