Galaxy Clustering Evolution in the UH8K Weak‐Lensing Fields

We present measurements of the two-point galaxy angular correlation function as a function of apparent magnitude, color, and morphology. Our analysis utilizes images taken using the UH8K CCD mosaic camera on the Canada-France-Hawaii Telescope. Six 0 5 × 0 5 fields were observed for a total of 2 hr each in I and V , resulting in catalogs containing ~25,000 galaxies per field. We present new galaxy number counts to limiting magnitudes of I = 24.0 and V = 25.0. We divide each passband sample into intervals of width 1 mag. Within each magnitude interval, we parameterize the angular correlation function by A ω θ -δ and find ω(θ) to be well described by a power law of index δ = 0.8. We find the amplitude of the correlation function, A ω , to decrease monotonically with increasingly faint apparent magnitude. We compare with predictions that utilize redshift distributions based on deep spectroscopic observations. We conclude that simple redshift-dependent models that characterize evolution by means of the parameter inadequately describe the observations. This is because the predictions do not allow for the varying mix of morphologies and absolute luminosities (and hence clustering strengths) of galaxies sampled at different apparent magnitudes. We find a strong clustering dependence on V-I color. This is because galaxies of extreme color lie at similar redshifts and the angular correlation functions for these samples are minimally diluted by chance projections. We find extremely red ( V - I = 3.0) galaxies (likely early-type galaxies at z ~ 1) to have an A ω about 10 times higher, and extremely blue ( V - I = 0.5) galaxies (likely local late types) to have an A ω about 15-20 times higher, than that measured for the full field population. We then present the first attempt to investigate the redshift evolution of clustering, utilizing a population of galaxies of the same morphological type and absolute luminosity. We study the dependence of ω(θ) on redshift for L * early-type galaxies in the redshift range 0.2 < z < 0.9. Although uncertainties are large, we find the evolution in the clustering of these galaxies to be consistent with stable clustering [ = 0 for a redshift dependence of the spatial correlation function, ξ( r ), parameterized as ξ( r , z ) = -γ (1 + z ) -(3+ ) ]. We find L * early-type galaxies to cluster slightly more strongly (physical correlation length r 0 = 5.25 ± 0.28 h -1 Mpc assuming = 0) than the local full field population. This is in good agreement with the correlation length measured by the 2dF Galaxy Redshift Survey for L * early-type galaxies in the local universe.

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