Las Campanas Distant Cluster Survey Research Articles

Galaxy Cluster Correlation Function to z ~ 1.5 in the IRAC Shallow Cluster Survey

We present the galaxy cluster autocorrelation function of 277 galaxy cluster candidates with 0.25 \le z \le 1.5 in a 7 deg^2 area of the IRAC Shallow Cluster Survey. We find strong clustering throughout our galaxy cluster sample, as expected for these massive structures. Specifically, at <z> = 0.5 we find a correlation length of r_0 = 17.40^{+3.98}_{-3.10} h^-1 Mpc, in excellent agreement with the Las Campanas Distant Cluster Survey, the only other non-local measurement. At higher redshift, <z> = 1, we find that strong clustering persists, with a correlation length of r_0=19.14^{+5.65}_{-4.56} h^-1 Mpc. A comparison with high resolution cosmological simulations indicates these are clusters with halo masses of \sim 10^{14} Msun, a result supported by estimates of dynamical mass for a subset of the sample. In a stable clustering picture, these clusters will evolve into massive (10^{15} Msun) clusters by the present day.

The X-ray properties of optically selected z &gt; 0.6 clusters in the European Southern Observatory Distant Cluster Survey

We present XMM-Newton observations of three optically selected z > 0.6 clusters from the European Southern Observatory (ESO) Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find that the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and - unlike other high-redshift, optically selected clusters - are consistent with the T$-\sigma$ and L$_{X-\sigma}$ relations determined from X-ray-selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak-lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalogue may, like selection by X-ray luminosity, be well suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by z ~ 0.8.

EDisCS – the ESO distant cluster survey

We present the ESO Distant Cluster Survey (EDisCS) a survey of 20 fields containing distant galaxy clusters with redshifts ranging from 0.4 to almost 1.0. Candidate clusters were chosen from among the brightest objects identified in the Las Campanas Distant Cluster Survey, half with estimated redshift z_est~0.5 and half with z_est~0.8. They were confirmed by identifying red sequences in moderately deep two colour data from VLT/FORS2. For confirmed candidates we have assembled deep three-band optical photometry using VLT/FORS2, deep near-infrared photometry in one or two bands using NTT/SOFI, deep optical spectroscopy using VLT/FORS2, wide field imaging in two or three bands using the ESO Wide Field Imager, and HST/ACS mosaic images for 10 of the most distant clusters. This first paper presents our sample and the VLT photometry we have obtained. We present images, colour-magnitude diagrams and richness estimates for our clusters, as well as giving redshifts and positions for the brightest cluster members. Subsequent papers will present our infrared photometry, spectroscopy, HST and wide-field imaging, as well as a wealth of further analysis and science results. Our reduced data become publicly available as these papers are accepted.

Galaxy Cluster Assembly at z = 0.37

We present X-ray and spectroscopic confirmation of a cluster assembling from multiple, distinct galaxy groups at z = 0.371. Initially detected in the Las Campanas Distant Cluster Survey, the structure contains at least four X-ray-detected groups that lie within a maximum projected separation of 4 Mpc and within Δv = 550 km s-1 of one another. Using Chandra imaging and wide-field optical spectroscopy, we show that the individual groups lie on the local σ-T relation and derive a total mass of M ≥ 5 × 1014 M☉ for the entire structure. We demonstrate that the groups are gravitationally bound to one another and will merge into a single cluster with about one-third or more the mass of Coma. We also find that although the cluster is in the process of forming, the individual groups already have a higher fraction of passive members than the field. This result indicates that galaxy evolution on group scales is key to developing the early-type galaxies that dominate the cluster population by z ~ 0.

On the Incidence of Strong Gravitational Lensing by Clusters in the Las Campanas Distant Cluster Survey

The observed incidence of strongly lensing clusters exceeds the predictions of a Lambda-CDM model by about a factor of 10. We revisit the observational side of this discrepancy by measuring the incidence of strong lensing in a subsample of clusters drawn from the Las Campanas Distant Cluster Survey (LCDCS). Among clusters with 0.5<= z <= 0.7, the redshift range in which we focus our search, we find two strongly lensed systems within an effective search area of 69 sq. deg. There is at least one other strongly lensed system in the LCDCS outside of this redshift range, where we are less complete. Over all redshifts, the Lambda-CDM model produces one large arc every 146 sq. degrees. Assuming Poisson statistics, the probability of finding 3 or more strongly lensing clusters in 69 sq. degrees is 0.012. The lensing incidence within the LCDCS is in agreement with that derived from an X-ray selected sample and what has been preliminarily presented from an independent optical cluster survey. The origin of the disagreement between theory and observations, which remains at least at the order of magnitude scale for the Lambda-CDM model, lies either in the concordance cosmological model, in the characteristics of the resulting cluster potentials, or in the adopted source population.

Tests of the Las Campanas Distant Cluster Survey from Confirmation Observations for the ESO Distant Cluster Survey

The ESO Distant Cluster Survey (EDisCS) is a photometric and spectroscopic study of the galaxy cluster population at two epochs, z~0.5 and z~0.8, drawn from the Las Campanas Distant Cluster Survey (LCDCS). We report results from the initial candidate confirmation stage of the program and use these results to probe the properties of the LCDCS. Of the 30 candidates targeted, we find statistically significant overdensities of red galaxies near 28. Of the ten additional candidates serendipitously observed within the fields of the targeted 30, we detect red galaxy overdensities near six. We test the robustness of the published LCDCS estimated redshifts to misidentification of the brighest cluster galaxy (BCG) in the survey data, and measure the spatial alignment of the published cluster coordinates, the peak red galaxy overdensity, and the brightest cluster galaxy. We conclude that for LCDCS clusters out to z~0.8, 1) the LCDCS coordinates agree with the centroid of the red galaxy overdensity to within 25'' (~150 h^{-1} kpc) for 34 out of 37 candidates with 3\sigma galaxy overdensities, 2) BCGs are typically coincident with the centroid of the red galaxy population to within a projected separation of 200 h^{-1} kpc (32 out of 34 confirmed candidates), 3) the red galaxy population is strongly concentrated, and 4) the misidentification of the BCG in the LCDCS causes a redshift error >0.1 in 15-20% of the LCDCS candidates. These findings together help explain the success of the surface brightness fluctuations detection method.

Cluster detection from surface-brightness fluctuations in SDSS data

Galaxy clusters can be detected as surface brightness enhancements in smoothed optical surveys. This method does not require individual galaxies to be identiable, and enables clusters to be detected out to surpris- ingly high redshifts, as recently demonstrated by the Las Campanas Distant Cluster Survey (LCDCS). Here, we investigate redshift limits for cluster detection in the Sloan Digital Sky Survey (SDSS). Calibrating assumptions about the surface brightness prole, the mass-to-light ratio, and the spectral energy distribution of galaxy clusters using available observational data, we show that it should be possible to detect galaxy groups out to redshifts of 0.5, and massive galaxy clusters out to redshifts of1:2 in summed r 0 +i 0 +z 0 SDSS data. Redshift estimates can be derived from the SDSS magnitudes of brightest cluster members out to redshifts near unity. Over the area of sky it covers, SDSS should nd >98% of the clusters detectable by the Planck satellite through the thermal Sunyaev-Zel'dovich eect. The few Planck clusters not detected in SDSS will almost all be at z > 1:2.

The Las Campanas Distant Cluster Survey Correlation Function

We present the first nonlocal (z > 0.2) measurement of the cluster-cluster spatial correlation length, using data from the Las Campanas Distant Cluster Survey (LCDCS). We measure the angular correlation function for velocity dispersion-limited subsamples of the catalog at estimated redshifts of 0.35 ≤ zest < 0.575 and derive spatial correlation lengths for these clusters via the cosmological Limber equation. The correlation lengths that we measure for clusters in the LCDCS are consistent both with local results for the APM cluster catalog and with theoretical expectations based upon the Virgo Consortium Hubble Volume simulations and the analytic predictions. Despite samples containing over 100 clusters, our ability to discriminate between cosmological models is limited because of statistical uncertainty.

Constraints on the Size Evolution of Brightest Cluster Galaxies

We measure the luminosity profiles of 16 brightest cluster galaxies (BCGs) at 0.4 < z < 0.8 using high-resolution F160W NICMOS and F814W WFPC2 Hubble Space Telescope imaging. The heterogeneous sample is drawn from a variety of surveys: seven from clusters in the Einstein Medium Sensitivity Survey, five from the Las Campanas Distant Cluster Survey and its Northern Hemisphere precursor, and the remaining four from traditional optical surveys. We find that the surface brightness profiles of all but three of these BCGs are well described by a standard de Vaucouleurs (r1/4) profile out to at least ~2re and that the biweight-estimated NICMOS effective radius of our high-redshift BCGs (re = 8.3 ± 1.4 kpc for H0 = 80 km s-1 Mpc-1, Ωm = 0.2, ΩΛ = 0.0) is ~2 times smaller than that measured for a local BCG sample. If high-redshift BCGs are in dynamical equilibrium and satisfy the same scaling relations as low-redshift ones, this change in size would correspond to a mass growth of a factor of 2 since z ~ 0.5. However, the biweight-estimated WFPC2 effective radius of our sample is 18 ± 5.1 kpc, which is fully consistent with the local sample. While we can rule out mass accretion rates higher than a factor of 2 in our sample, the discrepancy between our NICMOS and WFPC2 results, which after various tests we describe appears to be physical, does not yet allow us to place strong constraints on accretion rates below that level.

Revisiting Brightest Cluster Galaxy Evolution with the Las Campanas Distant Cluster Survey

We investigate the influence of environment on brightest cluster galaxy (BCG) evolution using a sample of 63 clusters at 0.3 ≤ z ≤ 0.9 drawn primarily from the Las Campanas Distant Cluster Survey and follow-up V, I, and K' photometry. The luminosity evolution of the entire BCG sample is not adequately described by a single evolutionary model. Using the integrated light from the cluster detection as a proxy for cluster LX and the suggestion by Burke, Collins, & Mann, we set LX = 2 × 1044 ergs s-1 to be the division between high- and low-luminosity clusters. At high redshift (z > 0.6) BCGs from low-LX clusters are fainter, on average, than those from high-LX clusters and are best modeled as having constant luminosity with redshift. The BCGs from high-LX clusters are best modeled as having a stellar population that formed at large redshift (zform > 5) and is passively evolving. However, for the entire BCG population, the observed V-I and I-K' colors are well described by a single evolutionary model in which the stellar populations have zform > 5 and subsequently passively evolve. We conclude that accretion is proportionally more significant for BCGs in lower mass clusters at these redshifts (a factor of 2-4 increase in mass since z ~ 1 for the low-LX systems; Aragon-Salamanca and coworkers) and that the accreted matter is in the form of systems with evolved stellar populations.

Cluster Galaxy Evolution from a New Sample of Galaxy Clusters at 0.3 &lt;z&lt; 0.9

We analyze photometry and spectroscopy of a sample of 63 clusters at 0.3 ≤ z ≤ 0.9 drawn from the Las Campanas Distant Cluster Survey to empirically constrain models of cluster galaxy evolution. Specifically, (1) by combining I-band photometry of 44 of our clusters with that of 19 clusters from the literature, we parameterize the redshift dependence of M in the observed frame as M = (-21.74 ± 0.12) - (0.88 ± 0.24)z - 5 log h (rms deviation = 0.34) for 0.3 ≤ z ≤ 0.9 (Ω0 = 0.2, ΩΛ = 0); (2) by combining 30 of our clusters and 14 clusters from the literature with V and I data, we parameterize the redshift dependence of the V-I color of the E/S0 red sequence in the observed frames as V-I = (-0.24 ± 0.28) + (7.42 ± 1.03)z - (4.61 ± 0.91)z2 (rms deviation = 0.16) for 0.3 ≤ z ≤ 0.9; and (3) by combining 13 of our clusters with 15 clusters from the literature with I and K' data, we parameterize the redshift dependence of the I-K' color of the E/S0 red sequence in the observed frames as I-K' = (0.66 ± 0.65) + (9.50 ± 3.72)z - (14.72 ± 7.01)z2 + (8.72 ± 4.29)z3 (rms deviation = 0.18) for 0.3 ≤ z ≤ 0.9. Using the peak surface brightness of the cluster detection, Σ, as a proxy for cluster mass, we find no correlation between Σ and M or the location of the red envelope in V-I. We suggest that these observations can be explained with a model in which luminous early-type galaxies (or more precisely, the progenitors of current-day luminous early-type galaxies) form the bulk of their stellar populations at high redshifts (5) and in which many of these galaxies, if not all, accrete mass either in the form of evolved stellar populations or gas that causes only a short-term episode of star formation at lower redshifts (1.5 < z < 2). Our data are too crude to reach conclusions regarding the evolutionary state of any particular cluster or to investigate whether the morphological evolution of galaxies matches the simple scenario that we discuss, but the statistical nature of this study suggests that the observed evolutionary trends are universal in massive clusters.