REDSHIFTED MOLECULAR ABSORPTION SYSTEMS TOWARDS PKS 1830 − 211 AND B 0218 + 357 : SUBMILLIMETER CO , C i AND H 2 O DATA

We have detected the J = 4 ← 3 rotational transition of CO in absorption at z = 0.89 towards the quasar PKS 1830−211, but not the CO (5 ← 4) or the P1 ← 3 P0 fine structure line of neutral carbon. The intervening molecular medium thus has a total CO column density of 10 cm ≤ N(CO) ≤ 5×10 cmwith a most likely value of N(CO) ≃ 2×10 cm, which corresponds to the large column density of molecular hydrogen of N(H2)= 2.5 × 10 22 cm and a reddening of Av = 25 magnitudes. The CO excitation temperature is low, below 15 K. Comparison with the molecular absorption results of Wiklind and Combes (1996) shows that the absorbing material has similar molecular abundances to Galactic dark clouds. We find an upper limit for atomic carbon of N(Ci)≤ 10 cm, which again would be the case for most Galactic dark clouds. We also report new observations of the absorbing system towards B 0218+357 at z = 0.68. We have tentatively detected the CO (4 ← 3) line, but for H2O, although a feature is seen at the correct velocity, due to the inadequate signal to noise ratio we report only an upper limit for the fundamental line of ortho water vapor. The tentative detection of the CO J = 4 ← 3 line implies that the CO excitation temperature is lower than 20 K and the column density is fairly large, 4 × 10 cm ≤ N(CO) ≤ 2.2 × 10 cm, with a likely value of N(CO) ≃ 10 cm, giving rise to saturated absorption in the (J = 2 ← 1) transition. The total column density of molecular gas is again large in this source, N(H2)≥ 2× 10 22 cm, which corresponds to a reddening larger than 20 magnitudes. Subject headings: (Galaxies: quasars:) absorption lines — Galaxies: quasars: individual (PKS1830−211,B0218+357) — Galaxies: ISM — ISM: Molecules