Galaxy Clustering and Large-Scale Structure from z = 0.2 to z = 0.5 in Two Norris Redshift Surveys

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Abstract
We present a study of the nature and evolution of large-scale structure based on two independent redshift surveys of faint field galaxies conducted with the 176 fiber Norris Spectrograph on the Palomar 200 inch telescope. The two surveys sparsely cover ~20 deg2 and contain 835 r ≤ 21 mag galaxies with redshifts 0.2 < z < 0.5. Both surveys have a median redshift of zmed ≈ 0.30. To obtain a rough estimate of the cosmic variance, we analyze the two surveys independently. We have measured the two-point spatial correlation function and the pairwise velocity dispersion for galaxies with 0.2 < z < 0.5. We measure the comoving correlation length to be 3.70 ± 0.13 h-1 Mpc (q0 = 0.5) at zmed = 0.30, with a power-law slope γ = 1.77 ± 0.05. Dividing the sample into low (0.2 < z < 0.3) and high (0.3 < z < 0.5) redshift intervals, we find no evidence for a change in the comoving correlation length over the redshift range 0.2 < z < 0.5. Similar to the well-established results in the local universe, we find that intrinsically bright galaxies are more strongly clustered than intrinsically faint galaxies and that galaxies with little ongoing star formation, as judged from the rest frame equivalent width of [O II] λ3727, are more strongly clustered than galaxies with significant ongoing star formation. The rest frame pairwise velocity dispersion of the sample is 326 km s-1, ~25% lower than typical values measured locally. Our sample is still too small to obtain useful constraints on mean flows. The appearance of the galaxy distribution, particularly in the more densely sampled Abell 104 field, is quite striking. The pattern of sheets and voids that has been observed locally continues at least to z 0.5. A friends-of-friends analysis of the galaxy distribution supports the visual impression that 90% of all galaxies at z 0.5 are part of larger structures with overdensities of 5, although these numbers are sensitive to the precise parameters chosen for the friends-of-friends algorithm.

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