Abstract
We have used the Green Bank Telescope (GBT) and Berkeley-Illinois-Maryland Association (BIMA) array to search for redshifted millimetre absorption in a sample of damped Lymanalpha absorption systems (DLAs). This brings the number of published systems searched from 18 to 30. In 17 cases we reach 3σ limits of τ 6 0.1, which is a significant improvement over the previous searches and more than sufficient to detect the 4 known redshifted millimetre absorbers (τ > 1). While the CO rotational (millimetre) column density limits obtained are weaker than the electronic (optical) limits, they may provide useful limits below the atmospheric cut-off for the Lyman and Werner H2-bands in the UV (zabs < 1.8). Using a model for the DLA metallicity evolution combined with assumed HCO + /H2 and CO/H2 conversion ratios, we use the molecular column density limits to calculate plausible H2 molecular fraction limits. Finally, we use these results to discuss the fea sibility of detecting rotational CO transitions in DLAs with the next generation of large radio telescopes.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
