Mathematics – Logic
Scientific paper
Jul 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999hst..prop.8165j&link_type=abstract
HST Proposal ID #8165
Mathematics
Logic
Hst Proposal Id #8165 Quasar Absorption Lines
Scientific paper
We propose to use STIS to search for hidden and pervasive hot gas in the intracluster media of groups of galaxies. Cosmological simulations predict that at z 0, most groups of galaxies should be embedded in large filaments and sheets of shock heated gas at 10^5 - 10^6 ^degreesK. This hot gas may contain a substantial fraction of the baryons in the universe at the present epoch, but its quantity and existence is not firmly established because gas in this temperature range is difficult to detect in x-ray emission. However, it can easily be detected via absorption lines of highly ionized species such as O VI. We propose to observe H1821+643 and PG1116+215 to search for O VI and broad H I LyAlpha absorption due to the intracluster media of thirteen known galaxy groups pierced by the sight lines. Toward H1821+643, we have already discovered O VI absorption associated with a galaxy group at z = 0.225 using low resolution HST GHRS spectra, but we could not determine if the O VI absorber is collisionally ionized or photoionized. With the vastly improved resolution and sensitivity provided by STIS, we will be able to identify the ionization mechanism in this absorber by {1} searching for broad H I absorption in collisionally ionized gas or narrow H I indicative of photionized gas, {2} measuring C II/C III/C IV and Si II/Si III/Si IV, and {3} examining the velocity widths of low and high ionization stages.
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