Evolution of Clustering and Bias in a Lambda-CDM Universe

We determine the evolution from z = 3 → 0 of the galaxy and mass correlation functions and bias factor in a 50hMpc ΛCDM hydrodynamic simulation with 10hkpc resolution. The mass correlation function grows with time, but the galaxy correlation function shows little evolution and is well described by a power law. At early times, galaxies are biased traces of mass, with bias being higher on smaller scales. By z = 0, galaxies trace the mass, and the bias shows little scale dependence. The correlation function of galaxies, ξg, is a standard observational measure of structure in the Universe. Understanding the relationship between this observable and the correlation of the underlying mass distribution, ξm, is crucial for relating observations of galaxy clustering to predictions of cosmological models. The relationship between ξg and ξm is usually characterized through the bias parameter b ≡ σg/σm, where σ is the rms fluctuation on some specified scale. Here we investigate the evolution of ξg, ξm and b in a ΛCDM simulation. We simulate a random 50hMpc cube in a ΛCDM universe, with Ωm = 0.4, ΩΛ = 0.6, H0 = 65, n = 0.95, and Ωb = 0.02h . We use Parallel TreeSPH to advance 144 gas and 144 dark matter particles from z = 49 to z = 0. Our spatial resolution is 10h kpc, and our mass resolution per particle is mSPH = 8.5 × 10 M⊙ and mdark = 6.3 × 10 M⊙. Using a 60-particle criterion for our simulated galaxy completeness limit [1] implies that we are resolving most galaxies with Mbaryonic ∼> 5 × 10 M⊙. We include star formation and thermal feedback. Galaxies are identified using Spline Kernel Interpolative DENMAX. At z = 3, 2, 1, and 0, we identify 929, 1781, 4138, and 5264 galaxies, respectively. Note that the majority of galaxies form between z = 2 and z = 1 in this model. We consider the 500 most massive galaxies at each redshift, representing a constant comoving galaxy density of n = 0.004hMpc, comparable to that of Lyman break galaxies and present-day L∗ galaxies. The galaxy correlation