Implications of Spikes in the Redshift Distribution ofz∼ 3 Galaxies

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Abstract
We address the high peaks found by Steidel and coworkers in the redshift distribution of "Lyman-break" objects (LBOs) at redshift z 3. The highest spike represents a relative overdensity of 2.6 in the distribution of LBOs in pixels of comoving size ~10 h-1 Mpc. We examine the likelihood of such a spike in the redshift distribution within a suite of models for the evolution of structure in the universe, including models with Ω = 1 (a standard cold dark matter [SCDM] and a cold plus hot dark matter model [CHDM]) and with Ω0 = 0.4-0.5 (a flat cold dark matter model with a nonzero cosmological constant Λ [ΛCDM] and an open cold dark matter model [OCDM]). Using high-resolution dissipationless N-body simulations, we analyze deep pencil-beam surveys from these models in the same way that they are actually observed, identifying LBOs with the most massive dark matter halos. We find that all the models (with SCDM as a marginal exception) have a substantial probability of producing spikes similar to those observed, because the massive halos are much more clumped than the underlying matter; i.e., they are biased. Therefore, the likelihood of such a spike is not a good discriminator among these models. We find in these models that the mean biasing parameter b of LBOs with respect to dark matter varies within a range b 2-5 on a scale of ~10 h-1 Mpc. However, all models show considerable dispersion in their biasing, with the local biasing parameter reaching values as high as ten. We also compute the two-body correlation functions of LBOs predicted in these models. The LBO correlation functions are less steep than galaxies today (γ ≈ -1.4) but show similar or slightly longer correlation lengths.

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