Redshifted Molecular Absorption Systems toward PKS 1830−211 and B0218+357: Submillimeter CO, C [CSC]i[/CSC], and H[TINF]2[/TINF]O Data

Abstract

We have detected the J=4←3 rotational transition of 12CO in absorption at z = 0.89 toward the quasar PKS 1830-211, but not the 12CO (5←4) or the 3P1←3P0 fine-structure line of neutral carbon. The intervening molecular medium thus has a total 12CO column density of 1018 cm−2≤N(CO)≤5×1018 cm-2 with a most likely value of N(CO)≃2×1018 cm-2, which corresponds to the large column density of molecular hydrogen of N(H2)=2.5×1022 cm-2 and a reddening of Av = 25 mag. The 12CO excitation temperature is low, below 15 K. Comparison with existing molecular absorption results shows that the absorbing material has molecular abundances similar to Galactic dark clouds. We find an upper limit for atomic carbon of N(C I)≤1018 cm-2, which again would be the case for most Galactic dark clouds.