Ly alpha Constraints on the Nature of the X-Ray--absorbing Medium in Cooling Flow Clusters

Details Ly alpha Constraints on the Nature of the X-Ray--absorbing Medium in Cooling Flow Clusters Ly alpha Constraints on the Nature of the X-Ray--absorbing Medium in Cooling Flow Clusters

Jul 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...483l.103l&link_type=abstract

Astrophysical Journal Letters v.483, p.L103

Astronomy and Astrophysics

Astronomy

4

Galaxies: Cooling Flows, Galaxies: Individual Ngc Number: Ngc 1275

Scientific paper

X-ray spectra of a significant fraction of cooling flow (CF) clusters of galaxies indicate the presence of large columns of "cold" absorbing material. The physical nature of the absorbing medium remains a mystery. Searches for H I in this medium using the 21 cm hyperfine structure line yielded null results in most cases. The Ly alpha absorption cross section is >=107 times larger than that for the 21 cm line, and it can therefore be used as a much more sensitive probe of H I in clusters. This method is applied to the Perseus CF cluster, where a medium resolution (~250 km s-1) UV spectrum is available. The upper limit on the H I column obtained using Ly alpha is at least ~2000 smaller than implied by X-ray spectra, indicating that the X-ray absorber is exceedingly devoid of H I. Higher resolution UV spectra with the Hubble Space Telescope may improve the H I column limits by an additional factor of up to ~4000 and thus put severe constraints on the nature of the X-ray--absorbing medium. Most CF clusters have emission-line nebulae at their center, and this method can therefore be applied in a significant number of CF clusters.

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