NOAO >   Observing Info >   Approved Programs >   2003B-0291

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Proposal Information for 2003B-0291


PI: Arlin Crotts, Columbia U., arlin@astro.columbia.edu
Address: Department of Astronomy, 550 W.~120th St., New York, NY 10027, U.S.A.

CoI: David Tytler,David Kirkman, University of California, San Diego

Title: Ly(alpha) Forest Clustering and the Cosmological Constant

Abstract: Having used absorption spectroscopy of close groups of QSOs to measure the properties of Ly(alpha) forest absorbers e.g. their size and mass, we are poised to use them to set cosmologically interesting constraints. For instance, comparing the radial versus transverse clustering in the forest can provide a local measurement, \it free of population evolution, of the cosmological constant (Lambda), perhaps sensitive to (Lambda)'s redshift dependence, if any. Also, sightline groups provide a valuable test of the flattening of Ly(alpha) absorbers, key in determining their contribution to the baryonic mass density. Finally, transverse structure in the forest, as probed by close sightlines, tests different numerical models of hydrodynamical/gravitational evolution of structure at high redshift, versus single sightline data, which match models with a wide range of inputs. Having amassed (primarily through NOAO) spectra of 16 QSO pairs including two triplets on the verge of realizing these tests, we propose to augment them with several dozen more in a collaboration involving Keck/LRIS. These will serve to make decisive the results in the previously mentioned tests, and most dramatically, provide a measure of the cosmological constant (Lambda) in a way independent of type Ia supernovae and the cosmic microwave background (at other redshifts). This will take advantage of the Alcock-Paczynski effect, nearly purely due to (Lambda) rather than mass density \Omega, which measures the apparent distortion due to viewing through cosmological spacetime of an otherwise spherical object e.g., the three-dimensional two-point correlation function \xi, which measured radially versus transversely, is much more distorted by the A-P effect than anisotropic distortion (caused by nonlinear, large scale structure) of \xi in velocity space. The sample of QSO pairs we will amass will suffice, along with Keck/LRIS spectroscopy, to determine (Lambda) to an accuracy currently implied by SNe Ia results, thereby providing a direct cross-check on (Lambda) and the radically strange cosmology of our Universe that it implies.


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