Constraining the size of intergalactic clouds with QSO pairs

Type Journal Article
Names Bart Wakker
Publication HST Proposal
Pages 13444
Journal Abbreviation HST Proposal
Date October 1, 2013
Library Catalog
Abstract This proposal aims at a geometric estimate of the size of intergalactic absorbers {clouds} near redshift 0, which make up the 10^4 K photoionized phase of the intergalactic medium {IGM}. Theoretically the size of these clouds is expected to be 170 kpc at log N{HI}=13.3 and 20 kpc at log N{HI}=16. So far, this has only be tested observationally for a few rare systems in which metal-line absorption allows photoionization modeling. We propose to observe 4 QSO pairs {7 new QSOs and 1 archival dataset} separated by 2 to 5 arcmin {corresponding to 20 kpc at cz=1500 km/s}. Using these data we can set a completely independent, geometrical, constraint on the cloud sizes, even if no metal lines are seen. The data will further allow determining velocity gradients in single clouds.
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