arXiv subjects

E. Ellingson

Publications and source records attributed to E. Ellingson.

At least 37 records · Page 2Linked to original sources

arXiv2006

Near-Infrared Properties of Moderate-Redshift Galaxy Clusters: Luminosity Functions and Density Profiles

We present K-band imaging for 15 of the Canadian Network for Observational Cosmology (CNOC1) clusters. The cluster luminosity density and number density profiles can be described by NFW models with concentration parameters of c_{l} = 4.28 \pm 0.70 and c_{g} = 4.13 \pm 0.57 respectively. Comparing these to the dynamical mass analysis of the same clusters shows that the galaxy luminosity and number density profiles are similar to the dark matter profile, and are not less concentrated like in local clusters. The luminosity functions show that the evolution of K^{*} over the redshift range 0.2 < z < 0.5 is consistent with a scenario where the majority of stars in cluster galaxies form at high-redshift (z_{f} > 1.5) and evolve passively thereafter. The best-fit for the faint-end slope of the luminosity function is alpha = -0.84 pm 0.08, which indicates that it does not evolve between z = 0 and z = 0.3. Using Principal Component Analysis of the spectra we classify cluster galaxies as either star-forming/recently-star-forming (EM+BAL) or non-starforming (ELL) and compute their respective luminosity functions. The faint-end slope of the ELL luminosity function is much shallower than for the EM+BAL galaxies at z = 0.3, and suggests the number of faint ELL galaxies in clusters decreases by a factor of ~3 from z = 0 to z = 0.3. The redshift evolution of K^{*} for both EM+BAL and ELL types is consistent with a passively evolving stellar population formed at high-redshift. Passive evolution in both classes, as well as the total cluster luminosity function, demonstrates that the bulk of the stellar population in all bright cluster galaxies is formed at high-redshift and subsequent transformations in morphology/color/spectral-type have little effect on the total stellar mass.

astro-ph↗

arXiv2005

The Low-Redshift Lyman Alpha Forest toward PKS 0405-123

We present STIS 7km/s resolution data of the Ly-a forest toward PKS0405-123 (z=0.574). We make two samples. The strong sample (60 systems) has column density logNHI>13.3 over 0.002 13.1 at 0.020 =47+-22km/s; for the weak, =44+-21km/s. Line blending and s/n effects likely inflate b. The redshift density dN/dz is consistent with previous, lower resolution results for logNHI>14.0. For 13.1 13.3, consistent with a numerical model. There is a void in the strong sample at 0.0320 13.5-14.0. The strength is similar to that of the galaxy-galaxy correlation for our sample, implying that such Ly-a systems have mass log M/Msun= 11.3+1.0-0.6. Including lower column density systems in the sample shows correlations only out to Delta v <125km/s, as would be expected for smaller density perturbations. Galaxy counts and local HI column density appear correlated, peaking at ~5000km/s. We also give column densities for Galactic species. (Abridged)

astro-ph↗

arXiv2004

Dynamical Masses of RCS Galaxy Clusters

A multi-object spectroscopy follow-up survey of galaxy clusters selected from the Red-sequence Cluster Survey (RCS) is being completed. About forty clusters were chosen with redshifts from 0.15 to 0.6, and in a wide range of richnesses. One of the main science drivers of this survey is a study of internal dynamics of clusters. We present some preliminary results for a subset of the clusters, including the correlation of optical richness with mass, and the mass-to-light ratio as a function of cluster mass.

astro-ph↗

arXiv2002

Correlations of Richness and Global Properties in Galaxy Clusters

We measure the optical richness of galaxy clusters from the CNOC1 cluster redshift survey using the galaxy-cluster center correlation amplitude B_gc. We show that the B_gc 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 Mpc of rho~r^{-1.8}. The excellent correlations between B_gc 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 B_gc parameter can be used to estimate the velocity dispersion of a cluster to a precision of approximately 15% (~+/-100 km/s), 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 B_gc, T_x, and L_x 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, T_x and L_x 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.

astro-ph↗

arXiv2001

A Study of 3CR Radio Galaxies from z = 0.15 to 0.65. I. Evidence for an Evolutionary Relationship Between Quasars and Radio Galaxies

Deep optical images have been gathered for a nearly complete sample of radio galaxies from the Revised 3rd Cambridge (3CR) Catalog in the redshift range 0.15 < z < 0.65. Total and nuclear magnitudes and colors have been extracted. The richness of the galaxy clustering environment has also been quantified by calculating the amplitude of the galaxy-galaxy spatial covariance function (B_gg), showing overdensities ranging up to Abell class 0-1 clusters. These optical data are compared to similar data from an existing sample of radio-loud quasars in the same redshift range for the purpose of determining the relationship between radio galaxies and quasars. In the range 0.15 < z < 0.4, we find that quasars and radio galaxies have significantly different environments in that only radio galaxies are found in rich cluster environments. This comparison appears to rule out the hypothesis that all quasars are radio galaxies viewed from a particular angle at the 97% confidence level (99.6% confidence level if N-galaxies are considered quasars). The existence of quasars in clusters at z > 0.4 supports the hypothesis that some radio-loud quasars may dim with time and evolve into radio galaxies with an e-folding time of ~0.9 Gyr. A compatible scenario is presented for this evolution in which the quasar dims due to the absence of low velocity interactions between the quasar host and companion galaxies which trigger quasar activity and/or a diminishing fuel supply caused by the more effective gas ``sweeping'' of a growing intracluster medium.

astro-ph↗

arXiv2001

New X-ray Clusters in the EMSS II: Optical Properties

We present optical images for 9 new clusters of galaxies we have found in a reanalysis of the Einstein IPC images comprising the Extended Medium Sensitivity Survey (EMSS). Based on the presence of a red sequence of galaxies in a color-magnitude (CM) diagram, a redshift is estimated for each cluster. Galaxy overdensities (cluster richnesses) are measured in each field using the B_gc statistic which allows their plausible identification with the X-ray emission. The nature of our X-ray detection algorithm suggests that most of these clusters have low X-ray surface brightness (LSB) compared to the previously known EMSS clusters. We compare the optical and X-ray observations of these clusters with the well-studied Canadian Network for Observational Cosmology (CNOC) subsample of the EMSS, and conclude that the new clusters exhibit a similar range of optical richnesses, X-ray luminosities, and, somewhat surprisingly, galaxy populations as the predominantly rich, relaxed EMSS/CNOC clusters.

astro-ph↗

arXiv2001

New X-ray Clusters in the EMSS I: Modifications to the XLF

The complete ensemble of Einstein Imaging Proportional Counter (IPC) X-ray images has been re-processed and re-analyzed using a multi-aperture source detection algorithm. A catalog of 772 new source candidates detected within the central regions of the 1435 IPC fields comprising the Extended Medium Sensitivity Survey (EMSS) has been compiled. By comparison, 478 EMSS sources fall within the same area of sky. A randomly-selected subsample of 133 fields was first examined. We found that most of these sources are either the summation of two or more lower count rate point sources that fall within the larger detection apertures or are single point sources, while \leq 2.3% of the full catalog of sources are extrapolated to be actual distant (z > 0.14) clusters whose extended X-ray structure kept them from being detected in the EMSS despite having sufficient total flux. We then constructed other subsamples specifically selected to contain those X-ray sources most likely to be clusters. Both a database search and an optical imaging campaign have found several new distant clusters, setting a firm lower limit on the number of new clusters in the entire catalog. We estimate that the original EMSS cluster sample is 72-83% complete. We update the Henry et al. 1992 EMSS distant cluster sample with more recent information, and use the redshifts and X-ray luminosities for these new EMSS clusters to compute a revised X-ray Luminosity Function (XLF). The addition of these new high-z, high-L_X clusters to the EMSS is sufficient to remove the requirement for ``negative'' evolution at high-L_X out to z~0.5. We conclude that the EMSS has systematically missed clusters of low surface brightness.

astro-ph↗

arXiv2000

The Evolution of Population Gradients in Galaxy Clusters: the Butcher-Oemler Effect and Cluster Infall

We present photometric and spectroscopic measurements of the galaxy populations in clusters from the CNOC1 sample of rich, X-ray luminous clusters at $0.18 < z < 0.55$. A classical measure of the galaxy blue fraction for spectroscopically confirmed cluster members shows a significant Butcher-Oemler effect for the sample, but only when radii larger than 0.5$r_{200}$ are considered. We perform a principal component analysis of galaxy spectra to divide the total cluster light into contributions from stellar populations of different ages. Composite radial distributions of different stellar populations show strong gradients as a function of cluster-centric radius. The composite population is dominated by evolved populations in the core, and gradually changes at radii greater than the virial radius to one which is similar to coeval field galaxies. We do not see evidence at any radius within the clusters for an excess of star formation over that seen in the coeval field. Within this redshift range, significant evolution in the fractional population gradient is seen. Both low and high redshift clusters have similar populations in the cluster cores, but higher redshift clusters have steeper gradients and more star forming galaxies at radii outside of the core region~-- in effect, a restatement of the Butcher-Oemler effect. Luminosity density profiles are consistent with a scenario where this phenomenon is due to a decline over time in the infall rate of field galaxies into clusters. Depending on how long galaxies reside in clusters before their star formation rates are diminished, this suggests a decrease in the infall into clusters of a factor of $\sim 3$ between $z > 0.8$ and $z \sim 0.5$. We also discuss alternative scenarios for the evolution of cluster populations.

astro-ph↗

arXiv2000

The X-ray Size-Temperature Relation for Intermediate Redshift Galaxy Clusters

We present the first measurements of the X-ray size-temperature (ST) relation in intermediate redshift (z~0.30) galaxy clusters. We interpret the local ST relation (z~0.06) in terms of underlying scaling relations in the cluster dark matter properties, and then we use standard models for the redshift evolution of those dark matter properties to show that the ST relation does not evolve with redshift. We then use ROSAT HRI observations of 11 clusters to examine the intermediate redshift ST relation; for currently favored cosmological parameters, the intermediate redshift ST relation is consistent with that of local clusters. Finally, we use the ST relation and our evolution model to measure angular diameter distances; with these 11 distances we evaluate constraints on Omega_M and Omega_L which are consistent with those derived from studies of Type Ia supernovae. The data rule out a model with Omega_M=1 and Omega_L=0 with 2.5 sigma confidence. When limited to models where Omega_M+Omega_L=1, these data are inconsistent with Omega_M=1 with 3 sigma confidence.

astro-ph↗

arXiv2000

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.

astro-ph↗

arXiv2000

The velocity and mass distribution of clusters of galaxies from the CNOC1 cluster redshift survey

In the context of the CNOC1 cluster survey, redshifts were obtained for galaxies in 16 clusters. The resulting sample is ideally suited for an analysis of the internal velocity and mass distribution of clusters. Previous analyses of this dataset used the Jeans equation to model the projected velocity dispersion profile. However, the results of such an analysis always yield a strong degeneracy between the mass density profile and the velocity dispersion anisotropy profile. Here we analyze the full (R,v) dataset of galaxy positions and velocities in an attempt to break this degeneracy. We build an `ensemble cluster' from the individual clusters under the assumption that they form a homologous sequence. To interpret the data we study a one-parameter family of spherical models with different constant velocity dispersion anisotropy. The best-fit model is sought using a variety of statistics, including the overall likelihood of the dataset. Although the results of our analysis depend slightly on which statistic is used to judge the models, all statistics agree that the best-fit model is close to isotropic. This result derives primarily from the fact that the observed grand-total velocity histogram is close to Gaussian, which is not expected to be the case for a strongly anisotropic model. The best-fitting models have a mass-to-number-density ratio that is approximately independent of radius over the range constrained by the data. They also have a mass-density profile that is consistent with the dark matter halo profile advocated by Navarro, Frenk & White, in terms of both the profile shape and the characteristic scale length. This adds important new weight to the evidence that clusters do indeed follow this proposed universal mass density profile. [Abridged]

astro-ph↗

arXiv1999

Population Gradients in Galaxy Clusters at 0.2 < Z < 0.6

We present a principal component analysis of galaxy spectra from the CNOC sample of rich X-ray luminous clusters at 0.18 < z < 0.55. Composite radial distributions of different stellar populations show strong gradients as a function of cluster-centric redshift. The composite population is dominated by evolved populations in the core, and gradually changes to one which is similar to coeval field galaxies at radii greater than the virial radius. We do not see evidence in the clusters for an excess of star formation over that seen in the coeval field. Within this redshift range, significant evolution in the gradient shape is seen, with higher redshift clusters showing steeper gradients. This results in larger numbers of younger galaxies seen towards the inner regions of the clusters-- in effect, a restatement of the Butcher-Oemler effect. Luminosity density profiles are consistent with a scenario where this phenomenon is due to a decline over time in the infall rate of field galaxies into clusters. Depending on how long galaxies reside in clusters before their star formation rates are diminished, this suggests an epoch for maximal infall into clusters at z > 0.7. We also discuss alternative scenarios for the evolution of cluster populations.

astro-ph↗

arXiv1999

Velocity Dispersions of CNOC Clusters and the Evolution of the Cluster Abundance

We present the results of the analysis of the internal velocity dispersions, σ_v, for the CNOC sample of distant galaxy clusters, based on an interlopers removal algorithm, which is different from that originally applied by Carlberg et al. (1996, C96). We find that the resulting σ_v values are consistent within <10% with the original C96 estimates. This result points in favor of a substantial robustness of currently applied methods for optical studies of the internal cluster dynamics. The resulting distribution of velocity dispersions is used to trace the redshift evolution of the cluster abundance with the aim of constraining the matter density parameter, Ω_m. We find that constraints on Ω_m are very sensitive to the adopted value of σ_8, as obtainable from the local cluster abundance: as σ_8 varies from 0.5 to 0.6 (for Omega_m=1), the best fitting Omega_m varies in the range 0.3-1.0.

astro-ph↗

arXiv1999

Differential Galaxy Evolution in Cluster and Field Galaxies at z=0.3

(abridged) We measure spectral indices for 1823 galaxies in the CNOC1 sample of fifteen X-ray luminous clusters at 0.18<z<0.55, to investigate the mechanisms responsible for differential evolution between the galaxy cluster and field environments. The radial trends of D4000, Hdelta and [OII] are all consistent with an age sequence, in the sense that the last episode of star formation occurred more recently in galaxies farthest from the cluster center. Throughout the cluster environment, galaxies show evidence for older mean stellar populations than field galaxies. From the subsample of galaxies more luminous than M_r=-18.8 + 5log h, we identify a sample of K+A galaxies, which may result from recently terminated star formation. Corrected for a systematic effect which results from the large uncertainties on individual spectral index measurements, we estimate that K+A galaxies make up only 1.5 +/- 0.8 % of the cluster sample, and 1.2 +/- 0.8 % of the field. We compare our data with spectrophotometric models and conclude that up to 1.9 +/- 0.8 % of the cluster population may have had its star formation recently truncated without a starburst. However, this is still not significantly greater than the fraction of such galaxies in the field, 3.1 +/- 1.0 %. Furthermore, we do not detect an excess of cluster galaxies that have unambiguously undergone a starburst within the last 1 Gyr. Our results imply that these cluster environments are not responsible for inducing starbursts; thus, the increase in cluster blue galaxy fraction with redshift may not be a strictly cluster--specific phenomenon. We suggest that the truncation of star formation in clusters may largely be a gradual process, perhaps due to the exhaustion of gas in the galactic disk over fairly long timescales.

astro-ph↗

arXiv1999

X-ray Mass Estimates at $z\sim0.3$ for the CNOC Cluster Sample

Results are presented from the analysis of ROSAT HRI and PSPC observations of the CNOC subsample of the EMSS high redshift galaxy clusters. X-ray surface brightness profiles of 14 clusters with $0.17 < z < 0.55$ are constructed and fit to isothermal $β$ models. Where possible, we use both the HRI and PSPC data to constrain the fit. Under the assumptions of isothermality, hydrostatic equilibrium, and spherical symmetry, we derive total X-ray masses within a range of radii from 141 to $526 h^{-1}_{100}$ kpc. These masses are compared with both the dynamical masses obtained from galaxy velocities and the projected masses from published gravitational lensing studies. We find no systematic bias between X-ray and dynamical methods across the sample, with an average $M_{Dyn}/M_X=1.04\pm0.07$, although individual clusters exhibit mass discrepancies up to a factor of 2. We estimate that the systematic effects due to cooling flows, non-equilibrium systems and temperature gradients affect the average mass ratio by no more than $15-20%$. Weak gravitational lensing masses appear to be systematically higher than X-ray results by factors of $\sim50%$, while strong lensing estimates show larger discrepancies (factors of $\sim2.5$). However, these comparisons are complicated by the need to extrapolate the X-ray data to larger or smaller radii. X-ray derived cluster gas masses are calculated, from which we obtain a cluster baryon fraction of $\sim5%h^{-3/2}_{100}$, yielding $Ω_0 \sim0.3h^{-1/2}_{100}$.

astro-ph↗

arXiv1998

Galaxy Evolution in the z=0.4274 Cluster MS1621.5+2640

We discuss the galaxy population of the rich cluster MS1621.5+2640 at z=0.4274, based on spectra and imaging in a field of size 9 arcmin by 23 arcmin (~2 by 5 h**-1 Mpc). The sample comprises 277 galaxies, of which 112 are cluster members, 7 are `near-members', and 47 are field galaxies in the redshift range 0.37<=z<=0.50. The results are analyzed and compared with the z=0.2279 rich cluster Abell 2390. MS1621.5+2640 has a higher blue fraction, a younger stellar population, and is a less evolved cluster. We do not find strong evidence of significant excess star formation compared with the field, although there is a small population of outlying near-members that is unusually blue and that may be affected by the cluster. There is a substantial population of red galaxies with significant Hdelta absorption, which are not easily explained by any simple form of modeled star formation history. We detect two distinct populations of cluster galaxies: those where star formation ceased some time ago, and those with a gradual decrease over many Gyr. Our data suggests that the cluster formed by accretion from the field, with truncation of the star formation beginning at very large radii (>2 times the virial radius). The truncation process does not seem to be a sharp one though, in that lower-luminosity early-type galaxies in the inner core of the cluster are seen with significant Hdelta absorption, indicating some star formation within the last 1-2 Gyr. Some combination of stripping of gas from the outer parts of the galaxy, together with gradual exhaustion of the gas in the inner parts would be consistent with our data.

astro-ph↗

arXiv1998

The CNOC2 Field Galaxy Redshift Survey

The CNOC2 field galaxy redshift survey is designed to provide measurements of the evolution of galaxies and their clustering over the redshift range 0 to 0.7. The sample is spread over four sky patches with a total area of about 1.5 square degrees. Here we report preliminary results based on two of the sky patches, and the redshift range of 0.15 to 0.55. We find that galaxy evolution can be statistically described as nearly pure luminosity evolution of early and intermediate SED types, and nearly pure density evolution of the late SED types. The correlation of blue galaxies relative to red galaxies is similar on large scales but drops by a factor of three on scales less than about 0.3/h mpc, approximately the mean scale of virialization. There is a clear, but small, 60%, change in clustering with 1.4 mag of luminosity. To minimize these population effects in our measurement of clustering evolution, we choose galaxies with M_r^{k,e}<= -20 mag as a population whose members are most likely to be conserved with redshift. Remarkably, the evolution of the clustered density in proper co-ordinates at r < 10/h Mpc, proportional to r_0^gamma (1+z)^3, is best described as a ``de-clustering'', (1+z)^{0.6+/-0.4}. Or equivalently, there is a weak growth of clustering in co-moving co-ordinates, x_0~ (1+z)^{-0.3 +/- 0.2}. This conclusion is supported by the pairwise peculiar velocities which rise slightly, but not significantly, into the past. The Cosmic Virial Theorem applied to the CNOC2 data gives Q Omega_M/b=0.11 +/- 0.04$, where Q is the three point correlation parameter and b the bias. Similarly, galaxy groups have a virial mass-to-light ratio (evolution corrected) of M_{virial}/L_R^{k,e} = 215h Lsun/Msun, or Omega_M=0.15 +/- 0.05.

astro-ph↗

arXiv1998

The Omega_M-Omega_Lambda Constraint from CNOC Clusters

The CNOC redshift survey of galaxy clusters measures Omega_M from Omega_e(z)= M/L x j/ρ_c which can be applied on a cluster-by-cluster basis. The mass-to-light ratios, M/L, are estimated from rich galaxy clusters, corrected to the field population over the 0.18 to 0.55 redshift range. Since the luminosity density depends on cosmological volumes, the resulting Omega_e(z) has a strong dependence on cosmology which allows us to place the results in the Omega_M-Omega_Lambda plane. The resulting Omega_M declines if Omega_Lambda>0 and we find that Omega_Lambda<1.5.

astro-ph↗