Letter to the Editor
Molecular gas at intermediate redshifts
National Centre for Radio Astrophysics, Post Bag 3, Ganeshkhind, Pune 411 007, India
Accepted: 28 November 2001
We present Giant Metrewave Radio Telescope (GMRT) observations of OH absorption in B3 1504+377 () and PKS 1413+135 (). OH has now been detected in absorption towards four intermediate redshift systems, viz. the lensing galaxies towards B 0218+357 (; Kanekar et al. [CITE]) and 1830-211 (; Chengalur et al. [CITE]), 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 NOH and NHCO^+ found in molecular clouds in the Milky Way (Liszt & Lucas [CITE]) persists out to . It has been suggested (Liszt & Lucas [CITE]) that OH is a good tracer of , with under a variety of physical conditions. We use this relationship to estimate in these absorbers. The estimated is 1022 in all four cases and substantially different from estimates based on CO observations.
Key words: galaxies: evolution: / galaxies: formation: / galaxies: ISM / cosmology: observations / radio lines: galaxies
© ESO, 2002