Session 84 - IGM.
Display session, Friday, January 09
Exhibit Hall,

## [84.07] Ly\alpha Forest Cloud Sizes at z \approx 0.6 from a Grouping of Five QSOs

E. Monier, D. Turnshek, C. Hazard (Univ. of Pittsburgh)

Groupings of QSOs closely spaced on the sky provide a way to measure the sizes, shapes, and characteristic clustering lengths of structures responsible for absorption in the Lyman \alpha forest. Recent studies of QSO pairs have suggested large sizes assuming spherical absorbers, while numerical simulations at moderate to high redshift produce filamentary structures that will only be detected through observations of groups of more than two QSOs. We present the results of an analysis of HST-FOS G190H spectra of a unique configuration of five QSOs with pair separations ranging from 1 to 8 arcmin. The redshifts of the four quasars with detected flux in the observed region of 1700 - 2300 Å\ are z_em = 1.10, 1.01, 1.01, and 0.86; the separations between the lines of sight range from 190h^-1 kpc to 1.5h^-1 Mpc at z_abs = 0.4 and from 250h^-1 kpc to 2h^-1 Mpc at z_abs = 0.9 (q_o = 0.5). In the pair with the smallest separation roughly half of the lines are in common, while for the pairs with the largest separations the number of lines in common is consistent with that expected from chance.