The redshift evolution of the galaxy two-point correlation function is a fundamental cosmological statistic. A key concern is to identify the same underlying galaxy population at different redshifts. Here we examine a strict volume limited sample culled from the CNOC2 catalogues. Our high luminosity subsample, defined as having k corrected and evolution corrected R luminosity of MR ≤ −20 mag (H0 = 100) where M∗ ≃ −20.3 mag, contains about 2300 galaxies distributed between redshifts 0.1 and 0.65 spread over a total of 1.55 square degrees of sky. A similarly defined low redshift sample is drawn from the Las Campanas Redshift survey. We find that the comoving correlation can be described as ξ(r|z) = (r00/r)(1+z) with r00 = 5.08±0.08h−1 Mpc, ǫ = 0.02±0.23 and γ = 1.87 ± 0.07 over the z = 0.03 to 0.65 redshift range, for ΩM = 0.2,Λ = 0. The measured clustering amplitude, and its evolution, are dependent on the adopted cosmology. The evolution rates for ΩM = 1 and flat ΩM = 0.2 background cosmologies are ǫ = 0.9 ± 0.3 and ǫ = −0.5 ± 0.2, respectively, with r00 ≃ 5h−1 Mpc in all cases. The sensitivity of the derived correlations to the evolution corrections and details of the measurements is presented. These slowly evolving correlations are consistent with theories in which galaxies exist only within dark matter halos that are in general biased with respect to the density field; however, they also allow the possibility that “lighttraces-mass” in a low density universe. These results imply that galaxy evolution is not caused by changes in the clustering environment, at least for these high luminosity galaxies at z < 0.7. Subject headings: cosmology: large scale structure, galaxies: evolution Visiting Astronomer, Canada–France–Hawaii Telescope, which is operated by the National Research Council of Canada, le Centre National de Recherche Scientifique, and the University of Hawaii. Department of Astronomy, University of Toronto, Toronto ON, M5S 3H8 Canada Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, , National Research Council of Canada, 5071 West Saanich Road, Victoria, BC, V8X 4M6, Canada Steward Observatory, University of Arizona, Tucson, AZ, 85721 Hubble Fellow Department of Physics & Astronomy, University of Victoria, Victoria, BC, V8W 3P6, Canada Mail Code 320-47, Caltech, Pasadena 91125, USA

The correlation evolution of a high luminosity subsample of the CNOC2 redshift survey is examined. The sample is restricted to galaxies for which the k corrected and evolution corrected R luminosity is MR ≤ −20 mag, where M∗ ≃ −20.3 mag. This subsample contains about 2300 galaxies. In consort with 13000 galaxies in a similarly defined low redshift sample from the Las Campanas Redshift survey we find that the comoving correlation can be described as ξ(r|z) = (r00/r)(1 + z)−(3+ǫ) with r00 = 5.08 ± 0.08h−1 Mpc, ǫ = 0.02 ± 0.23 and γ = 1.81 ± 0.03 over the z = 0.03 to 0.65 redshift range in a cosmology with ΩM = 0.2, Λ = 0. The measured clustering amplitude, and its evolution, are dependent on the adopted cosmology. The evolution rates for ΩM = 1 and flat low density models are ǫ = 0.9 ± 0.3 and ǫ = −0.5 ± 0.2, respectively, with r00 ≃ 5h−1 Mpc in all cases.

We investigate redshift evolution in the galaxy merger and accretion rates, using a well-defined sample of 4184 galaxies with 0.12 less than or equal toz 0.55 and R-C less than or equal to 21.5. We identify 88 galaxies in close (5 less than or equal to r(p) less than or equal to 20 h(-1) kpc) dynamical (Deltav less than or equal to 1500 km s(-1)) pairs. These galaxies are used to compute global pair statistics, after accounting for selection effects resulting from the flux limit, k-corrections, luminosity evolution, and spectroscopic incompleteness. We find that the number of companions per galaxy (for -21 less than or equal to M-B(k,e) less than or equal to -18) is N-c = 0.0321 +/- 0.0077 at z = 0.3. The luminosity in companions, per galaxy, is L-c = 0.0294 +/- 0.0084 x 10(10) h(2) L-circle dot. We assume that is proportional to the galaxy merger rate, while L-c is directly related to the mass accretion rate. After increasing the maximum pair separation to 50 h(-1) kpc and comparing with the low-redshift SSRS2 pair sample, we infer evolution in the galaxy merger and accretion rates of (1+z)(2.3+/-0.7) and (1+z)(2.3+/-0.9), respectively. These are the first such estimates to be made using only confirmed dynamical pairs. When combined with several additional assumptions, this implies that approximately 15% of present epoch galaxies with -21 less than or equal to M-B less than or equal to -18 have undergone a major merger since z = 1.

Galaxy groups likely to be virialized are identified within the CNOC2 intermediate redshift galaxy survey using an iterative method. The number-velocity dispersion relation is in agreement with the low-mass extrapolation of the cluster normalized Press-Schechter function. The two-point group-group correlation function has r_0=6.8+/- 0.3 Mpc, which is larger than the correlations of individual galaxies at the level predicted from n-body calibrated halo clustering. The groups are stacked in velocity and position to create a sample large enough for measurement of a density and velocity dispersion profile. The stacked mean galaxy density profile falls nearly as a power law with r^{-2.5} and has no well-defined core. The projected velocity dispersion is examined for a variety of samples with different methods and found to be either flat or slowly rising outwards. The combination of a steeper-than-isothermal density profile and the outward rising velocity dispersion implies that the mass-to-light ratio of groups rises with radius. The M/L can be kept nearly constant if the galaxy orbits are nearly circular, although such strong tangential anisotropy is not supported by other evidence. The segregation of mass and light is not dependent on galaxy luminosity but is far more prominent in the red galaxies than the blue. The M/L gradient could arise from orbital ``sloshing'' of the galaxies in the group halos, dynamical friction acting on the galaxies in a background of ``classical'' collisionless dark matter, or, more speculatively, the dark matter may have a true core.

We examine how the spatial correlation function of galaxies from the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2) depends on galaxy color, luminosity, and redshift. The projected correlation w(p) function is determined for volume-limited samples of objects with 0.12 less than or equal to z < 0.51 and evolution-compensated R-C-band absolute magnitudes M-R(O) < -20, over the co-moving projected separation range 0.04 h(-1) Mpc < r(p) <10 h(-1) Mpc. Our sample consists of 2937 galaxies that are classified as being either early- or late-type objects according to their spectral energy distribution (SED), as determined from UBVRCIC photometry. For the sake of simplicity, galaxy SEDs are classified independently of redshift : Our classification scheme therefore does not take into account the color evolution of galaxies. Objects with SEDs corresponding to early-type galaxies are found to be more strongly clustered by a factor of 3 and to have a steeper correlation function than those with late-type SEDs. Modeling the spatial correlation function, as a function of comoving separation r, as xi (r) = (r/r(o))(-gamma), we find r(o) = 5.45 +/- 0.28 h(-1) Mpc and gamma = 1.91 +/- 0.06 for early-type objects, and r(o) = 3.95 +/- 0.12 h(-1) Mpc and gamma = 1.59 +/- 0.08 for late-type objects (for Omega (M) = 0.2 Omega (Lambda) = 0). While changing the cutoff between early- and late-type SEDs does affect the correlation amplitudes of the two samples, the ratio of the amplitudes remains constant to within 10%. The redshift dependence of the correlation function also depends on SED type. Modeling the redshift dependence of the comoving correlation amplitude r(o)(gamma) r(o)(gamma)(z) proportional to (1 + z)(gamma -3-epsilon), we find that early-type objects have epsilon = -3.9 +/- 1.0, and late-type objects have epsilon = -7.7 +/- 1.3. Both classes of objects therefore have clustering amplitudes, measured in comoving coordinates, which appear to decrease rapidly with cosmic time. The excess clustering of galaxies with early-type SEDs, relative to late-type objects, is present at all redshifts in our sample. In contrast to the early- and late-type SED samples, the combined sample undergoes little apparent evolution, with epsilon = -2.1 +/- 1.3, which is consistent with earlier results. The apparent increase with redshift of the clustering amplitude in the early- and late-type samples is almost certainly caused by evolution of the galaxies themselves rather than by evolution of the correlation function. If galaxy SEDs have evolved significantly since z similar to 0.5, then our method of classifying SEDs may cause us to overestimate the true evolution of the clustering amplitude for the unevolved counterparts to our early- and late-type samples. However, if color evolution is to explain the apparent clustering evolution, the color evolution experienced by a galaxy must be correlated with the galaxy correlation function. We also investigate the luminosity dependence of the correlation function for volume-limited samples with 0.12 less than or equal to z < 0.40 and M-R(o) < -19.25.We detect a weak luminosity dependence of the correlation amplitude for galaxies with early-type SEDs, d log /dM(R)(o) = -0.35 +/- 0.17, but no significant dependence for late-type objects, d log xi /dM(R)(o) = 0.02 +/- 0.16.

The Canadian Network for Observational Cosmology (CNOC2) Field Galaxy Redshift Survey is a spectroscopic/photometric survey of faint galaxies over 1.5 square degrees of sky with a nominal spectroscopic limit of Rc ∼ 21.5 mag. The primary goals of the survey are to investigate the evolution of galaxy clustering and galaxy populations over the redshift range of ∼ 0.1 to ∼ 0.6. The survey area contains four widely separated patches on the sky with a total sample of over 6000 redshifts, representing a sampling rate of about 45%. In addition, 5-color photometry (in Ic, Rc, V , B, and U) for a complete sample of approximately 40,000 galaxies to Rc ∼ 23.0 mag is also available. We describe the survey and observational strategies, multi-object spectroscopy mask design procedure, and data reduction techniques for creating the spectroscopic-photometric catalogs. We also discuss the derivations of statistical weights, including corrections for the effects of limited spectral bandwidth, for the redshift sample which allow it to be used as a complete sample. As the initial release of the survey data, we present the full data set and some statistics for the Patch CNOC 0223+00. Subject headings: galaxies: redshifts — galaxies: photometry — galaxies: general — surveys — techniques: photometric — techniques: spectroscopic Department of Astronomy, University of Toronto, Toronto, Ontario M5S 3H8, Canada. Email: hyee, carlberg, hall, patton, and shepherd @astro.utoronto.ca Visiting Astronomer, Canada-France-Hawaii Telescope, which is operated by the National Research Council of Canada, Le Centre National de Recherche Scientifique, and the University of Hawaii. Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, 5071 W. Sannich Rd, Victoria, BC, V8X 4M6, Canada. Email: Simon.Morris@hia.nrc.ca Present address: Steward Observatory, University of Arizona, Tucson, AZ 85721. Email: hlin@as.arizona.edu Hubble Fellow Present address: CalTech, Mail Code 320–47, Pasadena, CA 91125. Email: sawicki@pirx.caltech.edu Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 3P6 Present address: Keck Observatory, Waimea, HI 96743. Email: wirth@keck.hawaii.edu CASA, University of Colorado, Boulder, CO 80309. Email: e.elling@casa.colorado.edu

The redshift evolution of the galaxy two-point correlation function is a fundamental cosmological statistic. To identify similar galaxy populations at different redshifts, we select a strict volume-limited sample culled from the 6100 cataloged Canadian Network for Observational Cosmology field galaxy redshift survey (CNOC2) galaxies. Our high-luminosity subsample selects galaxies having k-corrected and evolution-compensated R luminosities, M, above -20 mag (H0 = 100 km s-1 Mpc-1 ), where M(R) ≃ -20.3 mag. This subsample contains about 2300 galaxies distributed between redshifts 0.1 and 0.65 spread over a total of 1.55 deg2 of sky. A similarly defined low-redshift sample is drawn from the Las Campanas Redshift Survey. We find that the comoving two-point correlation function can be described as ξ(r|z) = (r00/r)γ(1 + z)-(3+ϵ-γ), with r00 = 5.03 ± 0.08 h-1 Mpc, ϵ = -0.17 ± 0.18, and γ = 1.87 ± 0.07 over the z = 0.03-0.65 redshift range, for ΩM = 0.2 and Λ = 0. The measured clustering amplitude and its evolution are dependent on the adopted cosmology. The measured evolution rates for ΩM = 1 and flat ΩM = 0.2 background cosmologies are ϵ = 0.80 ± 0.22 and ϵ = -0.81 ± 0.19, respectively, with r00 = 5.30 ± 0.1 and 4.85 ± 0.1 h-1 Mpc, respectively. The sensitivity of the derived correlations to the evolution corrections and details of the measurements is presented. The analytic prediction of biased clustering evolution for only the low-density, ΛCDM cosmology is readily consistent with the observations, with biased clustering in an open cosmology somewhat marginally excluded and a biased ΩM = 1 model predicting clustering evolution that is more than 6 standard deviations from the measured value.

We present five candidate gravitational lenses discovered spectroscopically in the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2), along with one found in follow-up observations. Each has a secure redshift based on several features, plus a discrepant emission line that does not match any known or plausible feature and is visible in multiple direct spectral images. We identify these lines as Lyα λ1216 or [O II] λ3727 emission from galaxies lensed by or projected onto the CNOC2 target galaxies. Einstein radii estimated from the candidate deflector galaxy luminosities indicate that for two candidates the lines are probably [O II] from projected z < 1 galaxies (consistent with the detection of Hβ as well as [O II] in one of them), but that in the remaining four cases the lines could be Lyα from lensed z < 3 galaxies. We estimate that only 1.9 ± 0.7 [O II]–emitting galaxies are expected to project onto target galaxies in the original CNOC2 sample, consistent with three or four of the six candidates being true gravitational lenses.

The Canadian Network for Observational Cosmology (CNOC2) Field Galaxy Redshift Survey is a spectroscopic/photometric survey of faint galaxies over 1.5 deg(2) of sky with a nominal spectroscopic limit of R-C similar to 21.5 mag. The primary goals of the survey are to investigate the evolution of galaxy clustering and galaxy populations over the redshift range of similar to0.1-0.6. The survey area contains four widely separated patches on the sky with a total sample of over 6000 redshifts, representing a sampling rate of about 45%. In addition, five-color photometry (in I-C, R-C, V, B, and U) for a complete sample of approximately 40,000 galaxies to R-C similar to 23.0 mag is also available. We describe the survey and observational strategies, multiobject spectroscopy mask design procedure, and data reduction techniques for creating the spectroscopic-photometric catalogs. We also discuss the derivations of statistical weights, including corrections for the effects of limited spectral bandwidth, for the redshift sample, which allow it to be used as a complete sample. As the initial release of the survey data, we present the full data set and some statistics for the patch CNOC 0223 + 00.

We examine the evolution of the galaxy luminosity function (LF) using a sample of over 2000 galaxies, with 0.12 < z < 0.55 and 17.0 < R-c < 21.5, drawn from the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2), at present the largest such sample at intermediate redshifts. We use UBVR,I, photometry and the spectral energy distributions (SEDs) of Coleman, Wu, and Weedman to classify our galaxies into early, intermediate, and late types, for which we compute LFs in the rest-frame B, R-c, and U bandpasses. In particular, we adopt a convenient parameterization of LF evolution including luminosity and number density evolution and take care to quantify correlations among our LF evolution parameters. We also carefully measure and account for sample selection effects as functions of galaxy magnitude and color.Our principal result is a clear quantitative separation of luminosity and density evolution for different galaxy populations and the finding that the character of the LF evolution is strongly dependent on galaxy type. Specifically, we find that the early- and intermediate-type LFs show primarily brightening at higher redshifts and only modest density evolution, whereas the late-type LF is best fit by strong number density increases at higher z with little luminosity evolution. We also confirm the trend seen in previous smaller z less than or similar to 1 samples of the contrast between the strongly increasing luminosity density of late-type galaxies and the relatively constant luminosity density of early-type objects. Specific comparisons against the Canada-France and Autofib redshift surveys show general agreement among our LF evolution results, although there remain some detailed discrepancies. In addition, we use our number count and color distribution data to further confirm the validity of our LF evolution models to z similar to 0.75, and we also show that our results are not significantly affected by potential systematic effects such as surface brightness selection, photometric errors, or redshift incompleteness.

The Canadian Network for Observational Cosmology cluster data are used to constrain the ΩM-ΩΛ pair to the region ΩM 0.24e± 0.3(1-0.4ΩΛ) for 0≤ΩΛ ≤ 1. The constraint is based on estimating the apparent mass density of the universe, Ωe(z), as the product of cluster mass-to-light ratios, M/L, with the field luminosity density at the same redshift. The luminosity density contains a volume element, which for measurements at z > 0 causes Ωe(z) to depend on both the density parameter ΩM and the cosmological constant, ΩΛ. The ΩΛ-dependence of the Ωe(z) measurement is about 25% less than the volume-redshift relation but about 50% greater than the luminosity-redshift relation. Most usefully this constraint is approximately orthogonal to the luminosity-redshift relation in the ΩM-ΩΛ plane. The practical application to measuring cosmological parameters has the considerable benefit that all quantities are used in a differential sense, so that common selection effects and galaxy evolution effects will cancel. The residual differential galaxy evolution between field, and the clustered galaxies can be estimated from the sample data. The inferred ΩM has an inverse correlation with ΩΛ, giving a constraint complementary to both the cosmic microwave background and the supernovae distances. Monte Carlo simulations, calibrated with observational data, show that 100 clusters spread over the 0-1 redshift range, each having M/L values of about 25% accuracy, will measure ΩΛ to about 7% statistical error.

The Canadian Network for Observational Cosmology cluster data are used to constrain the Omega(M)-Omega(Lambda) pair to the region Omega(M) similar or equal to 0.24e(+/-0.3)(1 - 0.4 Omega(Lambda)) for 0 less than or equal to Omega(Lambda) less than or equal to 1. The constraint is based on estimating the apparent mass density of the universe, Omega(e)(z), as the product of cluster mass-to-light ratios, M/L, with the field luminosity density at the same redshift. The luminosity density contains a volume element, which for measurements at z > 0 causes Omega(e)(z) to depend on both the density parameter Omega(M) and the cosmological constant, Omega(Lambda). The Omega(Lambda)-dependence of the Omega(e)(z) measurement is about 25% less than the volume-redshift relation but about 50% greater than the luminosity-redshift relation. Most usefully this constraint is approximately orthogonal to the luminosity-redshift relation in the Omega(M)-Omega(Lambda) plane. The practical application to measuring cosmological parameters has the considerable benefit that all quantities are used in a differential sense, so that common selection effects and galaxy evolution effects will cancel. The residual differential galaxy evolution between field, and the clustered galaxies can be estimated from the sample data. The inferred Omega(M) has an inverse correlation with Omega(Lambda), giving a constraint complementary to both the cosmic microwave background and the supernovae distances. Monte Carlo simulations, calibrated with observational data, show that 100 clusters spread over the 0-1 redshift range, each having M/L values of about 25% accuracy, will measure Omega(Lambda) to about 7% statistical error.

The CNOC1 cluster survey measures Omega_M via Oort's method, Omega_M= M/L x j/rho_c, where M/L is the field mass-to-light ratio, j is the field luminosity density and rho_c is the closure density. A wide range of potential systematic effects are explicitly controlled by independently deriving the mean cluster mass profile (finding good agreement with theoretical predictions), the cluster light profile, the redshift evolution of both cluster and field galaxies, the differential evolution between the two, and the field and cluster efficiencies for the conversion of baryons into galaxies. We conclude that Omega_M=0.19+/-0.06 where the errors are objectively evaluated via resampling methods. The redshift evolution of the numbers of clusters per unit co-moving volume over the 0< z < 0.6 range is found to be very slow, as is required for consistency with a low density universe. The evolution of galaxy clustering in the field is compatible with a low density universe, and strongly disfavors models of galaxy evolution that associate low density halos with individual galaxies.

The CNOC2 Field Galaxy Redshift Survey presently contains some 5000 galaxy redshifts, plus extensive UBgRI photometry, and is the largest galaxy sample at moderate redshifts 0.1 < z < 0.6. Here we present some preliminary results on the galaxy luminosity function (LF) and its redshift evolution, using a sample of R < 21.5 CNOC2 galaxies, subdivided into early, intermediate, and late types based on their B − R colors relative to non-evolving galaxy models. We find a significant steepening in the faint-end slope α of the LF as one proceeds from early to late types. Also, for all galaxy types we find a rate of M∗ evolution consistent with that from passively evolving galaxy models. Finally, late-type galaxies show positive density evolution with redshift, in contrast to negative or no density evolution for earlier types.