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Register a new userThe Contribution of Radio Galaxy Contamination to Measurements of the Sunyaev-Zeldovich Decrement in Massive Galaxy Clusters at 140 GHz with Bolocam
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We describe in detail our characterization of the compact radio source population in 140 GHz Bolocam observations of a set of 45 massive galaxy clusters. We use a combination of 1.4 and 30 GHz data to select a total of 28 probable cluster-member radio galaxies and also to predict their 140 GHz flux densities. All of these galaxies are steep-spectrum radio sources and they are found preferentially in the cool-core clusters within our sample. In particular, 11 of the 12 brightest cluster member radio sources are associated with cool-core systems. Although none of the individual galaxies are robustly detected in the Bolocam data, the ensemble-average flux density at 140 GHz is consistent with, but slightly lower than, the extrapolation from lower frequencies assuming a constant spectral index. In addition, our data indicate an intrinsic scatter of 30 percent around the power-law extrapolated flux densities at 140 GHz, although our data do not tightly constrain this scatter. For our cluster sample, which is composed of high-mass and moderate-redshift systems, we find that the maximum fractional change in the Sunyaev-Zeldovich signal integrated over any single cluster due to the presence of these radio sources is 20 percent, and only 1/4 of the clusters show a fractional change of more than 1 percent. The amount of contamination is strongly dependent on cluster morphology, and nearly all of the clusters with more than 1 percent contamination are cool-core systems. This result indicates that radio contamination is not significant compared to current noise levels in 140 GHz images of massive clusters and is in good agreement with the level of radio contamination found in previous results based on lower frequency data or simulations.
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We report on twenty-three clusters detected blindly as Sunyaev-Zeldovich (SZ) decrements in a 148 GHz, 455 square-degree map of the southern sky made with data from the Atacama Cosmology Telescope 2008 observing season. All SZ detections announced in this work have confirmed optical counterparts. Ten of the clusters are new discoveries. One newly discovered cluster, ACT-CL J0102-4915, with a redshift of 0.75 (photometric), has an SZ decrement comparable to the most massive systems at lower redshifts. Simulations of the cluster recovery method reproduce the sample purity measured by optical follow-up. In particular, for clusters detected with a signal-to-noise ratio greater than six, simulations are consistent with optical follow-up that demonstrated this subsample is 100% pure. The simulations further imply that the total sample is 80% complete for clusters with mass in excess of 6x10^14 solar masses referenced to the cluster volume characterized by five hundred times the critical density. The Compton y -- X-ray luminosity mass comparison for the eleven best detected clusters visually agrees with both self-similar and non-adiabatic, simulation-derived scaling laws.
We investigate the contamination of the Sunyaev--Zeldovich (SZ) effect for six galaxy clusters, A1689, A1995, A2142, A2163, A2261, and A2390, observed by the Y. T. Lee Array for Microwave Background Anisotropy during 2007. With the range of baselines used, we find that the largest effect (of order 13%-50% of the central SZ flux density) comes from primary anisotropies in the cosmic microwave background and exceeds the thermal noise in all six cases. Contamination from discrete radio sources is estimated to be at a level of (3%-60%) of the central SZ flux density. We use the statistics of these contaminating sources to estimate and correct the errors in the measured SZ effects of these clusters.
We present scaling relations between the integrated Sunyaev-Zeldovich Effect (SZE) signal, $Y_{rm SZ}$, its X-ray analogue, $Y_{rm X}equiv M_{rm gas}T_{rm X}$, and total mass, $M_{rm tot}$, for the 45 galaxy clusters in the Bolocam X-ray-SZ (BOXSZ) sample. All parameters are integrated within $r_{2500}$. $Y_{2500}$ values are measured using SZE data collected with Bolocam, operating at 140 GHz at the Caltech Submillimeter Observatory (CSO). The temperature, $T_{rm X}$, and mass, $M_{rm gas,2500}$, of the intracluster medium are determined using X-ray data collected with Chandra, and $M_{rm tot}$ is derived from $M_{rm gas}$ assuming a constant gas mass fraction. Our analysis accounts for several potential sources of bias, including: selection effects, contamination from radio point sources, and the loss of SZE signal due to noise filtering and beam-smoothing effects. We measure the $Y_{2500}$--$Y_{rm X}$ scaling to have a power-law index of $0.84pm0.07$, and a fractional intrinsic scatter in $Y_{2500}$ of $(21pm7)%$ at fixed $Y_{rm X}$, both of which are consistent with previous analyses. We also measure the scaling between $Y_{2500}$ and $M_{2500}$, finding a power-law index of $1.06pm0.12$ and a fractional intrinsic scatter in $Y_{2500}$ at fixed mass of $(25pm9)%$. While recent SZE scaling relations using X-ray mass proxies have found power-law indices consistent with the self-similar prediction of 5/3, our measurement stands apart by differing from the self-similar prediction by approximately 5$sigma$. Given the good agreement between the measured $Y_{2500}$--$Y_{rm X}$ scalings, much of this discrepancy appears to be caused by differences in the calibration of the X-ray mass proxies adopted for each particular analysis.
[Abridged] We present a catalog of 68 galaxy clusters, of which 19 are new discoveries, detected via the Sunyaev-Zeldovich effect (SZ) at 148 GHz in the Atacama Cosmology Telescope (ACT) survey of 504 square degrees on the celestial equator. A subsample of 48 clusters within the 270 square degree region overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14 Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters, the sample is studied further through a Profile Based Amplitude Analysis using a single filter at a fixed theta_500 = 5.9 angular scale. This new approach takes advantage of the Universal Pressure Profile (UPP) to fix the relationship between the cluster characteristic size (R_500) and the integrated Compton parameter (Y_500). The UPP scalings are found to be nearly identical to an adiabatic model, while a model incorporating non-thermal pressure better matches dynamical mass measurements and masses from the South Pole Telescope. A high signal to noise ratio subsample of 15 ACT clusters is used to obtain cosmological constraints. We first confirm that constraints from SZ data are limited by uncertainty in the scaling relation parameters rather than sample size or measurement uncertainty. We next add in seven clusters from the ACT Southern survey, including their dynamical mass measurements based on galaxy velocity dispersions. In combination with WMAP7 these data simultaneously constrain the scaling relation and cosmological parameters, yielding sigma_8 = 0.829 pm 0.024 and Omega_m = 0.292 pm 0.025. The results include marginalization over a 15% bias in dynamical mass relative to the true halo mass. In an extension to LCDM that incorporates non-zero neutrino mass density, we combine our data with WMAP7+BAO+Hubble constant measurements to constrain Sigma m_ u < 0.29 eV (95% C. L.).
We present CARMA 30 GHz Sunyaev-Zeldovich (SZ) observations of five high-redshift ($z gtrsim 1$), infrared-selected galaxy clusters discovered as part of the all-sky Massive and Distant Clusters of WISE Survey (MaDCoWS). The SZ decrements measured toward these clusters demonstrate that the MaDCoWS selection is discovering evolved, massive galaxy clusters with hot intracluster gas. Using the SZ scaling relation calibrated with South Pole Telescope clusters at similar masses and redshifts, we find these MaDCoWS clusters have masses in the range $M_{200} approx 2-6 times 10^{14}$ $M_odot$. Three of these are among the most massive clusters found to date at $zgtrsim 1$, demonstrating that MaDCoWS is sensitive to the most massive clusters to at least $z = 1.3$. The added depth of the AllWISE data release will allow all-sky infrared cluster detection to $z approx 1.5$ and beyond.
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