Interferometric Observations of Redshifted Molecular Absorption toward Gravitational Lenses

We have made radioand millimeter-wavelength interferometric observations of a variety of molecular absorption lines toward the gravitational lens systems B0218+357 and PKS 1830−211. The absorption occurs in the lensing galaxies at redshifts of 0.685 and 0.89, respectively. The high spatial resolution of our VLA and VLBA observations allows imaging of the background continuum emission and the absorption distribution. Our multi-transition studies yield estimates of the cosmic microwave background temperature at z = 0.89 and determinations of molecular and isotopic abundance ratios, which allow meaningful comparisons with Galactic molecular clouds.