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

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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. We also report new observations of the absorbing system toward B0218+357 at z = 0.68. We have tentatively detected the 13CO (4←3) line, but for H2O, although a feature is seen at the correct velocity, because of 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 13CO J=4←3 line implies that the 13CO excitation temperature is lower than 20 K and the column density is fairly large, 4×1016 cm−2≤N(CO13)≤2.2×1017 cm-2, with a likely value of N(CO13)1017 cm-2, 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)≥2×1022 cm-2, which corresponds to a reddening larger than 20 mag.
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