Other
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.5816t&link_type=abstract
HST Proposal ID #5816
Other
Hst Proposal Id #5816 Quasars
Scientific paper
QSO Lyman-alpha forest absorption systems have traditionally been considered intergalactic primordial gas clouds, but new data suggest that many of them at high redshift contain metals with abundances of C/H eq -3, which means 10^-3 solar. We propose to search for metals in HST spectra of LyAlpha forest systems at low redshift. The search has two parts: first we look for 2 Sigma metal lines at the expected positions of known LyAlpha lines, and we estimate the number of chance identifications. Second, we align and coadd spectra at the expected positions of the metal lines in each LyAlpha systems. We will look for the strong metal lines {C IV, O VI, N V, C III, Mg X and Ne VIII} in this composite. There are five reasons why we expect to find metals. {1} We are finding C IV in LyAlpha clouds at high z. {2} The number of C IV systems increases with decreasing redshift. {3} In general, abundances should be higher at low z. {4} We are now identifying many low redshift LyAlpha lines with the outer regions of galaxies. {5} O VI should be stronger than C IV. O VI is not easily seen at high z because of confusion in the LyAlpha forest, but it will be accessible in HST data. With 100 LyAlpha systems from the HST spectra of 167 QSOs we should reach a limit of C/H <= -2.3 for C IV, and worse for other ions. If we find metals, we begin to determine if they are more common in LyAlpha clouds which are associated with galaxies, and especially whether they occur in clouds which are intergalactic.
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