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A.P.S. Crotts (Columbia U.)
We determine the clustering of metal-line redshift systems using a catalog of published QSO absorption-line spectroscopy, and use this to explore and demonstrate methods by which errors in clustering results can be removed which might otherwise be introduced due to imperfect knowledge of the redshift selection function, which determines the sensitivity of the sample to absorbers as a function of redshift. In particular, we introduce a new expression for constructing the two-point correlation function \xi (or, alternatively, the power spectrum) which removes the effects of such errors in cases where their presence is small and dilute, and concentrate our efforts on cross-correlation between sightlines, which is much less prone to amplifying systematic error than single-sightline approaches. A careful analysis using these data, and comparing them to others, implies a a large value for the scale radius r0 (where \xi (r)=(r/r0)- \gamma, with \gamma assumed to be 1.8) on the order of 10 h-1 Mpc, with the most reliable value once possible systematics are removed being r0 = 13 ±9 h-1 Mpc. While this value is surprisingly large compared to that of galaxies, it is much smaller than those implied by other recent works also using sightline cross-correlation in heterogeneous catalogs. Having a measure of r0 allows us to estimate the extent to which the correlational power might be studied in a larger sample selected in a more homogeneous way. In particular, we evaluate the potential for studies of clustering from an ongoing effort to use QSO spectra from the Sloan Digital Sky Survey to study metal-line absorption.
Additionally, we are performing a similar study for damped Lyman alpha and Lyman limit systems, which should have less severe selection biases. Furthermore, we shall report on our own observational results from a survey of Lyman alpha and metal-line absorbers in a sample of 16 close QSO pairs.
This research was supported by the NSF and the STScI.
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