Mathematics – Logic
Scientific paper
Jul 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004hst..prop10151h&link_type=abstract
HST Proposal ID #10151
Mathematics
Logic
Hst Proposal Id #10151 Quasar Absorption Lines/Igm
Scientific paper
Cosmological hydrodynamical simulations predict that 30%-40% of the low-redshift baryons reside in a collisionally ionized phase {log T 5 to 7} of the intergalactic medium {IGM} associated with large-scale, unvirialized filaments of galaxies. Recent surveys of O VI gas have lent some support to the presence of this warm-hot intergalactic medium {WHIM}, but the results are significantly limited by uncertainties in the ionization mechanism {photo- vs. collisionally ionized} and metallicity of the gas. We are pursuing a large program to test predictions of the WHIM and to improve existing measurements of the OVI absorbers. The primary goals are {i} to increase the redshift path for detection of the hottest IGM, previously only accessible through X-ray absorption studies, using EUV absorption from Ne VIII and Mg X, and {ii} to constrain the IGM physics using UV absorption from H I Ly-alpha, C III, C IV, and O VI. Our team has been awarded a FUSE Legacy program to probe the moderate-redshift WHIM using unique ionization diagnostics in the restframe EUV waveband, including O V, Ne VIII and Mg X. Here we propose to complement our FUSE Legacy program with STIS intermediate-resolution echelle-mode observations of five moderate-redshift {0.45 < z < 0.98} AGNs. The unique combination of FUSE EUV and STIS UV spectra will allow us {1} to test the current models of the WHIM by studying the ionization mechanisms responsible for producing highly-ionized metals in the IGM and determining the frequency of genuine high-temperature metal absorbers in the low-redshift IGM; {2} to investigate the relationship between WHIM and large-scale galaxy structures using galaxy redshift measurements obtained with DEIMOS on Keck and IMACS at Las Campanas Observatory; and {3} to determine the ionization state and metallicity of O VI absorbers in order to accurately assess their contribution to the total baryon budget. Finally, we will make high-level science products derived from these data freely available to the general astronomical community.
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