Molecular gas at intermediate redshifts

We present Giant Metrewave Radio Telescope (GMRT) observations of OH absorption in B3 1504+377 (z similar to 0.673) and PKS 1413+135 (z similar to 0.247). OH has now been detected in absorption towards four intermediate redshift systems, viz. the lensing galaxies towards B 0218+357 (z similar to 0.685; Kanekar et al. 2001) and 1830-211 (z similar to 0.886; Chengalur et al. 1999), in addition to the two systems listed above. All four systems also give rise to well studied millimetre wavelength molecular line absorption from a host of molecules, including HCO+. Comparing our OH data with these millimetre line transitions, we find that the linear correlation between N-OH and NHCO+ found in molecular clouds in the Milky Way (Liszt & Lucas 1996) persists out to z similar to 1. It has been suggested (Liszt & Lucas 1999) that OH is a good tracer of H-2, with N-H2/N-OH approximate to 10(7) under a variety of physical conditions. We use this relationship to estimate N-H2 in these absorbers. The estimated N-H2 is greater than or similar to 10(22) in all four cases and substantially different from estimates based on CO observations.