LYMAN-ALPHA FOREST CORRELATIONS USING NEIGHBOR COUNTS

Abstract

We present a novel technique for calculating the two-point autocorrelation function of the Lyman-alpha forest based on the relation between the two-point correlation function and the Neighbor Probability Distribution Functions. The technique appears to reduce the scatter in estimates of the correlation function by a factor of about two from the traditional pair-counting method. We apply the technique to the Lyman-alpha forest line lists determined from the spectra of seven z > 2 QSOs observed at high resolution ( < 25 km/s ). Of these, only two spectra, those of Q0055-259 and Q0014+813, appear to be sufficiently free of systematics to obtain meaningful estimates of the correlation function. We find positive correlations, with a maximum amplitude of 0.5 - 1, on the scale of 0.5 - 3 h^{-1} Mpc (comoving), or 100 - 600 km/s, in the forests of both QSOs. The technique also finds strong evidence for anticorrelation on the scale of 3 - 6 h^{-1} Mpc. The strength of the positive correlations is comparable to that predicted from the primordial power spectrum inferred from optically-selected galaxy redshift surveys. If the anticorrelations are physical, it becomes unclear whether the detected clustering is consistent with current models of structure formation with a homogeneous photoionizing UV metagalactic background. Instead, the anti-clustering may require inhomogeneity in the UV background, and possibly in the process of reionization itself.

18 pages, uuencoded, compressed, postscript, figures included. To appear in the Astrophysical Journal Letters

References in corpus (5)

• Gravitational Collapse of Small-Scale Structure as the Origin of the Lyman Alpha Forest
• Physically Detached "Compact Groups"
• The Power Spectrum of Galaxies in the Nearby Universe
• The Structure and Evolution of Lyman-alpha Forest Clouds in the Minihalo Model
• Lick Optical Spectra of Quasar HS 1946+7658 at 10 km/sec Resolution: Lyman-Alpha Forest and Metal Absorption Systems

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• Evidence for Large Scale Structure in the Lyman alpha Forest at z>2.6
• Is Deuterium in High Redshift Lyman Limit Systems Primordial?
• Contribution of Bremsstrahlung Emission from Lyman-alpha Clouds to the Microwave Background Fluctuations
• One-point Statistics of the Cosmic Density Field in Real and Redshift Spaces with A Multiresolutional Decomposition