H. K. C. Yee

The Average Mass and Light Profiles of Galaxy Clusters

The systematic errors in the virial mass-to-light ratio, Mv/L, of galaxy clusters as an estimator of the field M/L value are assessed. We overlay 14 clusters in redshift space to create an ensemble cluster that averages over substructure and asymmetries. The combined sample, including background, contains about 1150 galaxies, extending to a projected radius of about twice r200. The radius r200, defined as where the mean interior density is 200 times the critical density, is expected to contain the bulk of the virialized cluster mass. The dynamically derived M(r200)/L(r200) of the ensemble is (0.82 ? 0.14)Mv/L. The Mv/L overestimate is attributed to not taking into account the surface pressure term in the virial equation. Under the assumption that the velocity anisotropy parameter is in the range 0 ? ? ? 2/3, the galaxy distribution accurately traces the mass profile beyond about the central 0.3r200. There are no color or luminosity gradients in the galaxy population beyond 2r200, but there is 0.11 ? 0.05 mag fading in the r-band luminosities between the field and cluster galaxies. We correct the cluster virial mass-to-light ratio, Mv/L = 289 ? 50 h M?/L? (calculated assuming q0 = 0.1), for the biases in Mv and mean luminosity to estimate the field M/L = 213 ? 59 h M?/L?. With our self-consistently derived field luminosity density, j/?c = 1136 ? 138 h M?/L? (at z 1/3), the corrected M/L indicates ?0 = 0.19 ? 0.06 ? 0.04 (formal 1 ? random error and estimated potential systematic errors) for those components of the mass field in rich clusters.

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.

Galaxy evolution in Abell 2390

The galaxy population in the intermediate-redshift (z = 0.228) rich cluster Abell 2390 is investigated. We present velocities, colors, and morphological information for an exceptionally large sample of 323 galaxies (216 cluster members) in a 46 ? 7 (6 h?1 Mpc ? 1 h?1 Mpc) strip centered on the cD galaxy. This sample of confirmed cluster members is second only to that for the Coma cluster in terms of sample size and spatial coverage in the cluster rest frame and it is the first to trace the transition between a rich cluster and the field at intermediate redshift. The galaxy population in the cluster changes gradually from a very evolved, early-type population in the inner 0.4 h?1 Mpc of the cluster to a progressively later type population in the extensive outer envelope of the cluster from 1 to 3 h?1 Mpc in radius. Radial gradients in galaxy g - r color, 4000 ? break, H? and [O II] line strengths, and morphology are seen in the cluster and are investigated by comparing the data to models computed with the GISSEL spectral synthesis package. The results suggest that the cluster has been built up gradually by the infall of field galaxies over ~8 Gyr and that star formation has been truncated in infalling galaxies during the accretion process. The morphological composition of the cluster is shown to be consistent with such a scenario. If true for other clusters, infall-truncated star formation as seen in Abell 2390 may explain both the Butcher-Oemler effect and the large fraction of S0 galaxies in clusters. Only 5% of the galaxies observed in Abell 2390 exhibit evidence for star formation at levels stronger than those seen in typical late-type systems. This suggests that starbursts do not play a major role in driving cluster galaxy evolution at the redshift of Abell 2390, although infall-induced starbursts leading to truncated star formation may have played a role in the earlier history of the cluster. Evidence is found for at least one subcomponent on the west side of the cluster, which is likely to be infalling at the epoch of observation.

Star Formation in Cluster Galaxies at 0.2 < z < 0.55

The rest-frame equivalent width of the [OII] λ3727 emission line, W0(O II), has been measured for cluster and field galaxies in the Canadian Network for Observational Cosmology redshift survey of rich clusters at 0.2 10 A, as expected in a model of cluster formation in which star formation is truncated on infall. Evidence of suppressed star formation relative to the field is present in the whole cluster sample, out to 2R200, so the mechanism responsible for the differential evolution must be acting at a large distance from the cluster center and not just in the core. The mean star formation rate in the cluster galaxies with the strongest emission corresponds to an increase in the total stellar mass of less than about 4% if the star formation is due to a secondary burst lasting 0.1 Gyr.

The WiggleZ Dark Energy Survey: Final data release and cosmological results

This paper presents cosmological results from the final data release of the WiggleZ Dark Energy Survey. We perform full analyses of different cosmological models using the WiggleZ power spectra measured at z=0.22, 0.41, 0.60, and 0.78, combined with other cosmological data sets. The limiting factor in this analysis is the theoretical modeling of the galaxy power spectrum, including nonlinearities, galaxy bias, and redshift-space distortions. In this paper we assess several different methods for modeling the theoretical power spectrum, testing them against the Gigaparsec WiggleZ simulations (GiggleZ). We fit for a base set of six cosmological parameters, {Ω_(b)h^2,Ω_(CDM)h^2,H_0,τ,A_s,n_s}, and five supplementary parameters {n_(run),r,w,Ω_k,∑m_ν}. In combination with the cosmic microwave background, our results are consistent with the ΛCDM concordance cosmology, with a measurement of the matter density of Ωm=0.29±0.016 and amplitude of fluctuations σ_8=0.825±0.017. Using WiggleZ data with cosmic microwave background and other distance and matter power spectra data, we find no evidence for any of the extension parameters being inconsistent with their ΛCDM model values. The power spectra data and theoretical modeling tools are available for use as a module for CosmoMC, which we here make publicly available at http://smp.uq.edu.au/wigglez-data. We also release the data and random catalogs used to construct the baryon acoustic oscillation correlation function.

The Incidence of Strong-Lensing Clusters in the Red-Sequence Cluster Survey*

The incidence of giant arcs due to strong-lensing clusters of galaxies is known to be discrepant with current theoretical expectations. This result derives from a comparison of several cluster samples with predictions in the framework of the currently favored ΛCDM cosmology, and one possible explanation for the discrepancy is that this cosmological model is not correct. In this paper we discuss the incidence of giant arcs in the Red-Sequence Cluster Survey (RCS), which again shows significant disagreement with theoretical predictions. We briefly describe a total of eight strong-lens systems, seven of which are discussed here for the first time. Based on the details of these systems, in particular on the ratio of single- to multiple-arc systems, we argue that it may be possible to explain this discrepancy in the currently favored cosmology by modifying the details of the lenses themselves. Specifically, the high incidence of multiple-arc systems and their overall high redshift suggests that a subpopulation of the global cluster population is responsible for much of the observed lensing. The lack of lensing clusters at z < 0.64 in the RCS indicates that a property associated with clusters at early times results in the boosted lensing cross sections; likely, a combination of ellipticity and elongation along the line of sight, substructure, and changes in the cluster-mass profiles is responsible. Cluster mass, which should evolve to globally higher values toward lower redshifts, is clearly not the most significant consideration for the formation of giant arcs.

Weak Lensing Study of Galaxy Biasing

We combine weak lensing measurements from the Red-Sequence Cluster Survey (RCS) and the VIRMOS-DESCART survey and present the first direct measurements of the bias parameter b and the galaxy-mass cross-correlation coefficient r on scales ranging from 0.2 to 9.3 h Mpc (which correspond to aperture radii of 15-45) at a lens redshift z 0.35. We find strong evidence that both b and r change with scale for our sample of lens galaxies (19.5 < RC < 21), which have luminosities around L*. For the currently favored cosmology (?m = 0.3, ?? = 0.7), we find b = 0.71 (68% confidence) on a scale of 1-2 h Mpc, increasing to ~1 on larger scales. The value of r has only minimal dependence on the assumed cosmology. The variation of r with scale is very similar to that of b and reaches a minimum value of r ~ 0.57 (at 1 h Mpc; 68% confidence). This suggests significant stochastic biasing and/or nonlinear biasing. On scales larger than ~ 4 h Mpc, the value of r is consistent with a value of r = 1. In addition, we use RCS data alone to measure the ratio b/r on scale ranging from 0.15 to 12.5 h Mpc (1-60) and find that the ratio varies somewhat with scale. We obtain an average value of b/r = 1.090 ? 0.035, in good agreement with previous estimates. A (future) careful comparison of our results with models of galaxy formation can provide unique constraints, as r is linked intimately to the details of galaxy formation.

Quasars and active galactic nuclei in rich environments. II, The evolution of radio-loud quasars

It is shown here that the environments of radio-loud quasars have a strong effect on the optical evolution of the quasars. Quasars in rich clusters of galaxies are found to fade at least four optical magnitudes between redshifts 0.65 and 0.3, corresponding to a statistical e-folding fading time of about 1.0 Gyr. This rapid decrease in quasar activity is about four times as fast as quasars in poor environments. Several physical mechanisms of this evolution are suggested, emphasizing dynamical evolution of the cluster core and evolution in the amount of gaseous fuel in the cluster environment. The environments of radio-loud and radio-quiet quasars are shown to be significantly different. Radio-quiet quasars are much less frequently situated in galaxy clusters as rich as Abell class I. This result is consistent with scenarios linking radio-loud quasars with elliptical host galaxies and radio-quiet quasars with spiral host galaxies. 49 refs.

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.

Correlations of Richness and Global Properties in Galaxy Clusters

Richness is a key defining characteristic of a galaxy cluster. We measure the optical richness of galaxy clusters from the Canadian Network for Observational Cosmology Cluster Redshift Survey using the galaxy cluster center correlation amplitude Bgc. We show that the Bgc values measured using photometric catalogs are consistent with those derived from redshift catalogs, indicating that richness can be measured reliably from photometric data alone, even at moderate redshifts of ~0.6. We establish the correlations between optical richness and other important attributes of a galaxy cluster, such as velocity dispersion, mass, radius, and X-ray temperature and luminosity. We find that the scaling relations of these quantities with richness are entirely consistent with those derived by assuming a simple mass density profile at 0.5 h Mpc of ρ ~ r-1.8. The excellent correlations between Bgc and velocity dispersion and X-ray temperature allow one to use richness, an easily measurable quantity using relatively shallow optical imaging data alone, as a predictor of these quantities at moderate redshifts. The Bgc parameter can be used to estimate the velocity dispersion of a cluster to a precision of approximately 15% (~±100 km s-1) and X-ray temperature to about 20%. Similar correlations, but with larger scatter, are also obtained between richness and the characteristic radius and mass of the clusters. We compare the relative merits of Bgc, TX, and LX as predictors of the dynamical mass and find that they are comparable, providing estimates at an accuracy of ~30%. We also perform similar analyses of correlations between richness and velocity dispersion, TX, and LX with a sample of low-redshift Abell clusters and find consistent results, but with larger scatter, which may be the result of a less homogeneous database or sample-dependent effects.