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Session 95 - Cosmological Parameters and Large Scale Structure Formation.
Oral session, Friday, January 09
International Ballroom Center,
Lyman-alpha absorption features in the spectra of QSOs allow us to detect clouds of atomic hydrogen that exist between the QSOs and us. This information about the location of hydrogen clouds in a single QSO spectra is clearly one dimensional, but we can use it to recover information about the 3-D structure of the clouds. Consider the clouds located using three spectra with small angular separations. We can easily imagine that if the clouds are large and flat, we will often find that all three lines of sight will intersect a single cloud. This is detected as an absorption feature at nearly the same redshift in each of the three lines of sight. If the clouds are filamentary, we imagine it possible to detect one of them in two of the lines of sight, but not the third; or if they are more point-like, we do not expect any coincident signals in the three lines.
An adapted (to fit the data format) form of the reduced three-point correlation function is used to look at the strength of three-point clustering in several models. We begin with the hypothesis that an enhanced three-point function picks out sheet-like structures. Three toy models are filled with mass in the form of disks, filaments, or points. The parameters are adjusted so that the two-point correlation is nearly the same in all models. The reduced three-point function is calculated and shown to distinguish the disks from the filaments and points. The same statistics are then applied to three different n-body simulations (in redshift space) with initial power spectra P(k) \propto k^n, n = -2, -1, +1. The n = -2 model is strongly characterized by sheets and filaments and is found to have an enhanced three-point correlation, demonstrating that the reduced three-point correlation function is picking out the sheet-like structures.
