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J. Darling (University of Colorado), T. Wiklind (STScI)
We report the detection of the ground state transition 110 - 111 of ortho-formaldehyde (H2CO) in absorption toward the Einstein ring B0218+357 at z=0.68. Combined with the 211 - 212 transition detected by Menten & Reid (1996), we obtain measurements of the excitation and column density of H2CO, estimate n(H2), and compare these to determinations made from other molecular transitions such as ammonia and CO. The excitation temperature of H2CO appears to be significantly below the local microwave background temperature, TCMB = (1+z) 2.73 K = 4.60 K, mimicking the behavior of formaldehyde in Galactic molecular clouds. We also report upper limits on the J=1/2 2Pi1/2 and J=5/2 2Pi3/2 lambda-doubled OH and CH transitions and the 51 - 60 A+ CH3OH (methanol) rotation transition toward B0218+357, B3 1504+377, and PKS 1413+135. The 110 - 111 transition of ortho-H2CO has also not been detected toward the latter two systems.
Support for this work was provided by NASA through Hubble Fellowship grant HF-01183.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.