Letter to the Editor

Molecular gas at intermediate redshifts

National Centre for Radio Astrophysics, Post Bag 3, Ganeshkhind, Pune 411 007, India

Corresponding authors: N. Kanekar, nissim@ncra.tifr.res.in chengalu@ncra.tifr.res.in

Received: 8 November 2001
Accepted: 28 November 2001

Abstract

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 N_OH and N_HCO^+ 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.