A search for atomic hydrogen in clusters of galaxies

Details A search for atomic hydrogen in clusters of galaxies A search for atomic hydrogen in clusters of galaxies

Apr 1978

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978apj...221..414h&link_type=abstract

Astrophysical Journal, Part 1, vol. 221, Apr. 15, 1978, p. 414-421.

Astronomy and Astrophysics

Astronomy

15

Galactic Clusters, Hydrogen Atoms, Hydrogen Clouds, Intergalactic Media, Microwave Spectra, Radio Sources (Astronomy), Astronomical Spectroscopy, Atomic Spectra, Emission Spectra, H Lines, Optical Thickness

Scientific paper

The possibility is investigated that clusters of galaxies are bound by discrete, optically thick clouds of atomic hydrogen. This hypothesis is tested in a search for the 21-cm hydrogen line in absorption in the spectra of radio sources located in the direction of galaxy clusters. No absorption lines were seen in any of the 28 sources searched at the appropriate cluster velocity. From these observations it is inferred that the 21-cm optical depth through the clusters is typically less than 0.1. It is concluded that if H I clouds provide the virial stability for clusters of galaxies, then the mean cloud density must be quite large, greater than 18,000 per cu cm. In order for such clouds to be dynamically stable, they must be rotationally supported against collapse, and hence they will appear as flattened disks; in this case the mean cloud density must be even greater, at least about 100,000 per cu cm. To the extend that such very dense clouds will most likely be molecular H2, not H I, it is concluded that the possibility that clusters of galaxies are bound by isolated clouds of neutral atomic hydrogen is remote. The search for the missing 'binding mass' should be focused on cluster material of another form.

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