Galaxy clustering and large-scale structure from z=0.2 to z=0.5 in two Norris redshift surveys

We present a study of the nature and evolution of large-scale structure based on two independent redshift surveys of faint held galaxies conducted with the 176 fiber Norris Spectrograph on the Palomar 200 inch telescope. The two surveys sparsely cover similar to 20 deg(2) and contain 835 r less than or equal to 21 mag galaxies with redshifts 0.2 < z < 0.5. Both surveys have a median redshift of z(med) approximate to 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 (q(0) = 0.5) at z(med) = 0.30, with a power-law slope gamma = 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] lambda 3727, are more strongly clustered than galaxies with significant ongoing star formation. The rest frame pairwise velocity dispersion of the sample is 326(-52)(+67) km s(-l), similar to 25% lower than typical values measured locally. Our sample is still too small to obtain useful constraints on mean hows. 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 less than or similar to 0.5. A friends-of-friends analysis of the galaxy distribution supports the visual impression that greater than or similar to 90% of all galaxies at z less than or similar to 0.5 are part of larger structures with overdensities of greater than or similar to 5, although these numbers are sensitive to the precise parameters chosen for the friends-of-friends algorithm.