Todd A. Small

The Norris Survey of the Corona Borealis Supercluster. II. Galaxy Evolution with Redshift and Environment

We measure the field galaxy luminosity function (LF) as a function of color and redshift from z = 0 to z = 0.5 using galaxies from the Norris Survey of the Corona Borealis Supercluster. The data set consists of 603 field galaxies with 0 < z ? 0.5 and spans a wide range in apparent magnitude (14.0 r 21.5), although our field galaxy LF analysis is limited to 493 galaxies with r ? 20.0 mag. We use the observed g-r colors of the galaxies to compute accurate corrections to the rest BAB and r bands. We find that our local r-band LF, when normalized to counts in high galactic latitude fields, agrees well with the local LF measured in the Las Campanas Redshift Survey. Our BAB-band local LF, however, does not match the bj-band LF from the Stromlo/APM survey, having a normalization 1.6 times higher. We see compelling evidence that the BAB-band field galaxy LF evolves with redshift. The evolution is strongest for the population of star-forming galaxies with [O II] ?3727 rest-frame equivalent widths greater than 10 ?. The population of red, quiescent galaxies shows no sign of evolution to z = 0.5. The evolution of the LF that we observe is consistent with the findings of other faint galaxy redshift surveys. The fraction of galaxies with [O II] emission increases rapidly with redshift, but the fraction of galaxies with strong H? absorption, a signature of a burst of star formation, does not. We thus conclude that the star formation in distant galaxies is primarily long-lived. We also compute the LFs of the Corona Borealis supercluster (z ? 0.07, 419 galaxies with 14.1 ? r ? 20.0 mag) and the Abell 2069 supercluster (z ? 0.11, 318 galaxies with 15.1 ? r ? 20.0 mag). The shapes of the two supercluster luminosity functions are broadly similar to the shape of the local luminosity function. However, there are important differences. Both supercluster LFs have an excess of very bright galaxies. In addition, the characteristic magnitude of the Corona Borealis supercluster LF is roughly half a magnitude brighter than that of the local field galaxy LF, and there is a suggestion of an upturn in the LF for galaxies fainter than M(BAB) ~ -17 + 5 log10 h mag, where h is the Hubble constant in units of 100 km s-1 Mpc-1.

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 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.

Results from the Norris Survey of the Corona Borealis Supercluster

We present results from our redshift survey of the Corona Borealis Supercluster. Using the Norris Multifiber Spectrograph on the Palomar 200-inch telescope, we have obtained redshifts for 528 galaxies in the supercluster and for 726 field galaxies with redshifts extending to z ~ 0.7. In this contribution, we discuss the structure and dynamics of the supercluster and the luminosity functions of the local field and of the supercluster.