First Detection of Hydrogen 21-cm Emission
in a Galaxy at Cosmological Distance.

Martin Zwaan, Peter van Dokkum, Marc Verheijen

The purple contours show the distribution of the neutral hydrogen gas. (ps-version) This gas has been detected in our deep survey with the Westerbork Synthesis Radio Telescope and is at a distance of approximately three billion light-years. The underlying colour image shows that the hydrogen gas coincides with a spiral galaxy in the outskirts of galaxy cluster Abell 2218. One of the galaxy's spiral arms seems to be connected with a smaller companion galaxy.
(Optical image taken with the Keck Telescope on Hawaii.)

This Hubble Space Telescope image shows the center of cluster Abell 2218. (Click here for a larger version.) Our detection of neutral hydrogen is approximately 6 million light years to the west of this dense centre. (picture credit: Hubble Space Telescope, NASA)

The paper will be published in the 7 September edition of Science.