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
URL http://adsabs.org/2013hst.prop13444W
Library Catalog adslabs.org
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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