C. W. Shepherd

The CNOC2 Field Galaxy Luminosity Function. I. A Description of Luminosity Function Evolution

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 < RC < 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 UBVRCIC 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, RC, 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 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 ~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.

Dynamically Close Galaxy Pairs and Merger Rate Evolution in the CNOC2 Redshift Survey

We investigate redshift evolution in the galaxy merger and accretion rates, using a well-defined sample of 4184 galaxies with 0.12 ≤ z ≤ 0.55 and RC ≤ 21.5. We identify 88 galaxies in close (5 ≤ rp ≤ 20 h-1 kpc) dynamical (Δv ≤ 500 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 ≤ M ≤ -18) is Nc = 0.0321 ± 0.0077 at z = 0.3. The luminosity in companions, per galaxy, is Lc = 0.0294 ± 0.0084 × 1010 h2 L☉. We assume that Nc is proportional to the galaxy merger rate, while Lc 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 ≤ MB ≤ -18 have undergone a major merger since z = 1.

The CNOC2 Field Galaxy Redshift Survey. I. The Survey and the Catalog for the Patch CNOC 0223+00

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 R_c=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 approximately 0.1 to 0.6. The survey area contains four widely separated patches on the sky with a total spectroscopic sample of over 6000 redshifts and a photometric sample of over 40,000 galaxies with 5-color photometry. 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 various statistical weights 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 data set and some statistics for the Patch CNOC0223+00.

The Galaxy Correlation Function in the CNOC2 Redshift Survey: Dependence on Color, Luminosity, and Redshift

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 function wp is determined for volume-limited samples of objects with 0.12 ≤ z < 0.51 and evolution-compensated RC-band absolute magnitudes M < -20, over the comoving projected separation range 0.04 h-1 Mpc < rp < 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 ξ(r) = -γ, we find r0 = 5.45 ± 0.28 h-1 Mpc and γ = 1.91 ± 0.06 for early-type objects, and r0 = 3.95 ± 0.12 h-1 Mpc and γ = 1.59 ± 0.08 for late-type objects (for ΩM = 0.2, ΩΛ = 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 as r(z) (1 + z)γ-3-, we find that early-type objects have = -3.9 ± 1.0, and late-type objects have = -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 = -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 ~ 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 ≤ z < 0.40 and M < -19.25. We detect a weak luminosity dependence of the correlation amplitude for galaxies with early-type SEDs, d log ξ/dM = -0.35 ± 0.17, but no significant dependence for late-type objects, d log ξ/dM = 0.02 ± 0.16.

The Real Space and Redshift Space Correlation Functions at Redshift z = 1/3

We present the results of a study of the two-point correlation function for a sample of field galaxies taken from the Canadian Network for Observational Cosmology cluster survey. The sample consists of 183 galaxies within a contiguous region of sky covering 216 square arcminutes. The objects have r-band magnitudes 17.0 ≤ r ≤ 21.7 and redshifts 0.21 ≤ z ≤ 0.53. The median redshift of the sample is 0.37. We fit the real space correlation function to a power law ξ(r) = (r/r0)-1.7, finding r0=1.9−0.4+0.4 h-1 Mpc (Ω0 = 1), or r0=2.2−0.4+0.5 h−1 Mpc (Ω0 = 0.2); uncertainties are estimated using the bias-corrected bootstrap resampling method, with 300 resamplings. This low correlation length implies strong evolution has occurred in the correlation function; if the observed correlation function is modeled as ξ(r, z) = ξ(r, 0)(1 + z)-(3+e) with ξ(r, 0) = (r/5.1 h-1 Mpc)-1.7, then e ≈ 1.5. Comparison of the redshift space and real space correlation functions indicates that the one-dimensional pairwise peculiar velocity dispersion σ at z ≈ 0.37 is weakly inconsistent with 720 km s-1, the value predicted by the cosmic virial theorem if Ω0 = 1. The observed correlation functions are, however, consistent with σ ≈ 360 km s-1, the value expected if Ω0 = 0.2.

The CNOC2 field galaxy redshift survey

The second Canadian Network for Observational Cosmology ( CNOC) galaxy redshift survey, CNOC2, is designed to investigate the relations between the dramatic evolution of field galaxies and their clustering over the redshift range 0 to 0.7. The sample of about 6000 galaxies with accurate velocities is spread over four sky patches with a total area of about 1.5deg2. Here we report preliminary results based on two of the sky patches and within the redshift range of 0.12 to 0.55. After classifying the galaxy spectral energy distributions relative to non–evolving references, we find that the early and intermediate–type populations can be described with nearly pure luminosity evolution, whereas the late–type population requires nearly pure density evolution. The spatial two–point correlation functions have a strong colour dependence with scale, and a weaker, apparently scale–free, luminosity dependence. The population most likely to be conserved with redshift is the high–luminosity galaxies. In particular, we choose galaxies with MRke ⩽−20 mag as our tracer population. We find that the evolution of the clustered density in proper co–ordinates at r ≲ 10h−1 Mpc, ρgg ∝ r0γ(1+z)3, is best described as a ‘de–clustering’, proportional to (1+z)0.6±0.4); or equivalently, there is a weak growth of clustering in co–moving co–ordinates, x0 ∝(1+z)(−0.3±0.2). This conclusion is supported by the pairwise peculiar velocities, which show no significant change with redshift. The cosmic virial theorem applied to the CNOC2 data gives Q3ΩM/b = 0.11 ± 0.04, where Q3 is the three–point correlation parameter and b the bias.

Spectroscopic Gravitational Lens Candidates in the CNOC2 Field Galaxy Redshift Survey

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 followup observations. Each has a secure redshift based on several features, plus a discrepant emission line which does not match any known or plausible feature and is visible in multiple direct spectral images. We identify these lines as Lyman-alpha or [OII] 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 [OII] from projected z 3 galaxies. We estimate that only 1.9+-0.7 [OII]-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.

Active Galactic Nuclei in the CNOC2 Field Galaxy Redshift Survey

We present a sample of 47 confirmed and 14 candidate active galactic nuclei (AGNs) discovered in the Canadian Network for Observational Cosmology field galaxy redshift survey (CNOC2). The sample consists of 38 objects identified from broad emission lines, eight from narrow [Ne V] emission, and 15 candidates from Fe II or Mg II absorption lines, one of which has been confirmed as a broad-line AGN via infrared spectroscopy. Redshifts of these AGNs range from z = 0.27 to z = 4.67, and the average absolute magnitude is MB -22.25, below the quasar/Seyfert division at MB = -23. Only two of the AGNs are detected at radio wavelengths. We find that only 0.3%?0.1% of galaxies brighter than ~M* + 1 at 0.281 < z < 0.685 contain broad-line or [Ne V] AGNs. We find a total surface density of 270?400 AGNs deg-2 to R = 22.09, comparable to previously published estimates. About 20% of these AGNs are classified as resolved or probably resolved in CFHT seeing and might be missed in surveys that target unresolved objects only. The sample includes several unusual objects: one with a very strong double-peaked Mg II emission line, several with unusual emission-line properties, one with an O III ?3133 broad absorption line, at least one with an optical absorption-line spectrum but broad H? emission in the near-IR. No color selection criteria were involved in selecting this spectroscopically discovered sample. The sample is also unbiased against objects with luminous host galaxies, since the spectroscopy preferentially targeted extended objects. Simple color-color diagram selection criteria can recover ~81% ? 6% of the CNOC2 AGNs, but several of the most unusual objects would be missing from such a color-selected sample. In the subsample of broad emission line?selected AGNs, the average equivalent widths for Mg II and C III] agree with the predictions of previous studies of the Baldwin effect. However, the average equivalent widths for C IV and Ly? are smaller than predicted by previous studies of the Baldwin effect at lower redshift. This may imply that the slopes of the C IV and Ly? Baldwin effects evolve with redshift, steepening with cosmic time. The broad emission line subsample also shows a higher incidence of associated Mg II ?2798 absorption than in most previous surveys and an incidence of associated C IV ?1549 absorption that may be more similar to that of radio-selected quasar samples than optically selected ones. This may arise from strong absorption being anticorrelated with optical luminosity or becoming less frequent with cosmic time or possibly because our selection method is not biased against objects with resolved spatial structure or reddened by dust associated with the absorbing gas.

The CNOC Cluster Survey

The CNOC cluster survey was designed to measure the cluster mass to light ratio and the luminosity density of the Universe in the same range of redshifts for the purpose of estimating the parameter Ω. We find that the clusters at z ≃ 1/3 have a mean ratio of virial mass to k-corrected Gunn r luminosity of M v /L = 288 ± 49h M⊙/L⊙, where quantities are estimated with H 0 = 100h kms-1 Mpc-1 and q 0 = 0.1. The radially resolved profiles of galaxy density and velocity dispersion support the hypothesis that the clusters are effectively in equilibrium and that the galaxies are distributed similarly to the total mass. However, the virial mass needs to be reduced by a factor of 0.70 ± 0.06, on the average, to account for background contamination, which increases the virial radius, and the oft-neglected “surface term” of the virial mass estimate. In the same photometric system the mean co-moving luminosity density has a closure mass-to-light ratio of 1017±144h M⊙/L⊙. After correcting for the virial mass overestimate and the small differential evolution of galaxy luminosities in and out of clusters, we find that Ω 0 = 0.18 ± 0.05 for those components of the mass field that fall into clusters.

The ΩM‐ΩΛDependence of the Apparent Cluster Ω

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.