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Title

Molecular fraction limits in damped Lyman alpha absorption systems

Author(s)

Curran, Stephen J.;  Murphy, Michael T.;  Pihlstrom, Ylva M.;  Webb, J. K.;  Bolatto, A. D.;  Bower, Geoffrey C.

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 Lyman alpha absorption systems (DLAs). This increases the number of published systems searched from 18 to 30. In 17 cases we reach 3sigma limits of tau less than or equal to 0.1, which is a significant improvement over the previous searches and more than sufficient to detect the four known redshifted millimetre absorbers (tau greater than or similar to 1). Although 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 H-2 bands in the UV (z(abs) less than or similar to 1.8). Using a model for the DLA metallicity evolution combined with assumed HCO+/H-2 and CO/H-2 conversion ratios, we use the molecular column density limits to calculate plausible H-2 molecular fraction limits. Finally, we use these results to discuss the feasibility of detecting rotational CO transitions in DLAs with the next generation of large radio telescopes.

Publication type

Journal article

Source

Monthly Notices of the Royal Astronomical Society, Vol. 352, no. 2 (Aug 2004), pp. 563-570

Publication year

2004

Keyword(s)

CO absorption;  Continuum galaxies;  Early epochs;  Early universe;  Einstein a-coefficients;  Galaxies;  Gravitational lens;  High-redshift;  ISM;  Lines;  Neutral gas;  Physical constants;  Quasar absorption lines;  Radio;  Radio-sources;  Vib-rotational transitions

Publisher

Wiley-Blackwell Publishing

ISSN

0035-8711

Publisher URL

http://dx.doi.org/10.1111/j.1365-2966.2004.07945.x

Copyright

Copyright © 2004 the authors. Journal compilation copyright © 2004 Royal Astronomical Society. The accepted manuscript of the paper is reproduced here in accordance with the copyright policy of the publisher. The definitive publication is available at www.interscience.wiley.com.

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