On the Clustering of Lyα Clouds, High‐Redshift Galaxies, and Underlying Mass
We examine the correlation property of Lya forest (along the line of sight) utilizing a hydrodynamic simulation of Lya clouds in a cold dark matter universe with a cosmological constant, and compare it to the correlation of underlying mass and galaxies. A consistent picture seems to emerge : the correlation strength for a given set of objects is positively correlated with their characteristic global density and the di †erences among the correlations of galaxies, Lya clouds, and mass reÑect the
... nd mass reÑect the di †erences in density that each trace. We Ðnd that the galaxies are strongly biased (nearly independent of scales) over mass by a factor of D3.0, in accord with recent observations of high-redshift galaxies. The correlation strength of Lya clouds with column densities of 1013È1014 cm~2 is comparable to that of total mass. Positive correlations with a strength of 0.1È1.0 are found for Lya clouds in the velocity range 50È300 km s~1. The correlation is less than 0.3 at *v [ 300 km s~1, but here our simulated box is too small to give a reliable measure. Among the correlational measures examined, an optical depth correlation function proposed (eq. ) here may serve as the best correlational measure. It faithfully represents the true correlation of the underlying matter, enabling a better indication of the relationship between galaxies, Lya clouds, and underlying mass. Furthermore, it appears to be a better alternative to the conventional line-line correlation function, because it does not require ambiguous postobservation Ðtting procedures such as those commonly employed in the conventional line-Ðtting methods. Neither does it depend sensitively on the observational resolution (e.g., FWHM), insofar as the clouds are resolved (i.e., the FWHM is smaller than the line width). Conveniently, it can be easily measured with the current observational sensitivity without being contaminated signiÐcantly by the presence of noise.