Spatially resolved millimeter spectroscopy of the gravitational lens PKS 1830-211

This paper presents data from the BIMA interferometer showing spatially res olved absorption spectra of the gravitationally lensed quasar PKS 183-211. High-resolution (1.2 km s(-1)) spectra were taken in two spectral windows c entered on the redshifted frequencies of the HCO+(2 <-- 1) and HCN(2 <-- 1) molecular transitions. There is no molecular absorption in the northeast i mage, but the southwest image reveals optically thick absorbing gas at thes e transition frequencies. Further analyses conclude that the spectra are co nsistent with completely saturated absorption in the southwest image, and t he line profiles suggest that the absorbing medium is complex, perhaps cont aining multiple components and small-scale structure. The absorption occurs along a pencil beam through the lensing galaxy which is thought to be a la te-type spiral oriented almost face-on. However, the spectra show absorptio n spanning more than 60 km s(-1), which is difficult to explain for this sc enario.