Showing papers by "Risa H. Wechsler published in 1998"

Implications of spikes in the redshift distribution of z ~ 3 galaxies

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.

The nature of Lyman-break galaxies

Abstract: Using semi-analytic models of galaxy formation, we investigate the properties of $z\sim3$ galaxies and compare them with the observed population of Lyman-break galaxies (LBGs). In addition to the usual quiescent mode of star formation, we introduce a physical model for starbursts triggered by galaxy-galaxy interactions. We find that with the merger rate that arises naturally in the CDM-based merging hierarchy, a significant fraction of bright galaxies identified at high redshift ($z \ga 2$) are likely to be low-mass, bursting satellite galaxies. The abundance of LBGs as a function of redshift and the luminosity function of LBGs both appear to be in better agreement with the data when the starburst mode is included, especially when effects of dust extinction are considered. The objects that we identify as LBGs have observable properties including low velocity dispersions that are in good agreement with the available data. In this ``Bursting Satellite'' scenario, quiescent star formation at $z\ga2$ is relatively inefficient and most of the observed LBGs are starbursts triggered by satellite mergers within massive halos. In high-resolution N-body simulations, we find that the most massive dark matter halos cluster at redshift $z\sim 3$ much as the LBGs are observed to do. This is true for both the $\Omega=1$ CHDM model and low-$\Omega$ \LCDM and OCDM models, all of which have fluctuation power spectra $P(k)$ consistent with the distribution of low-redshift galaxies. The Bursting Satellite scenario can resolve the apparent paradox of LBGs that cluster like massive dark matter halos but have narrow linewidths and small stellar masses.