A Lower Limit on Omega-Lambda Using Gravitational Lensing in the Hubble Deep Field

Abstract

We calculate the expected number of multiply-imaged galaxies in the Hubble Deep Field (HDF), using photometric redshift information for galaxies with $m_I < 27$ that were detected in all four HDF passbands. A comparison of these expectations with the observed number of strongly lensed galaxies places a lower limit on the current value of $Ω_m-Ω_Λ$, where $Ω_m$ is the cosmological mass density of the universe and $Ω_Λ$ is the normalized cosmological constant. Based on current estimates of the HDF luminosity function and associated uncertainties in individual parameters, our 95% confidence lower limit on $Ω_m-Ω_Λ$ is between -0.44, if there are no strongly lensed galaxies in the HDF, and -0.73, if there are two strongly lensed galaxies in the HDF. If the only lensed galaxy in the HDF is the one presently viable candidate, then, in a flat universe ($Ω_m+Ω_Λ=1$), $Ω_Λ < 0.79$ (95% C.L.). These lower limits are compatible with estimates based on high-redshift supernovae and with previous limits based on gravitational lensing.