What is the Nature of the Cold Medium in Cooling Flow Clusters? Clues from L-alpha

Details What is the Nature of the Cold Medium in Cooling Flow Clusters? Clues from L-alpha What is the Nature of the Cold Medium in Cooling Flow Clusters? Clues from L-alpha

Jul 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999hst..prop.8107o&link_type=abstract

HST Proposal ID #8107

Physics

Hst Proposal Id #8107 Clusters Of Galaxies And Lensing

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, and for molecular gas traced by CO yielded null results at the required levels. The LyAlpha absorption cross section is >= 10^7 times larger than for the 21 cm line, and it can therefore be used as a much more sensitive probe of H I in clusters. This method was applied to the Perseus CF cluster using a medium resolution { 250 km s^-1} HST spectrum, yielding an upper limit on the H I column about three orders of magnitude smaller than implied by X-ray spectra. We propose to obtain higher resolution { 40 km s^-1}, spatially extended spectra of the Ly-alpha emission line filaments in three CF clusters with the brightest known LyAlpha fluxes. These spectra will allow us to probe H I columns about 10^7 smaller than deduced from the excess X-ray absorption in these clusters {>= 10^20 cm^-2}, and thus put very strong constraints on the nature of the cold absorbing medium and its covering factor. If substantial amounts of cold gas do exist in the ICM, this would have important implications for our understanding of cooling flows, the physics of the ICM, galaxy formation and evolution, and LyAlpha forest systems.

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