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Register a new userSunyaev Zeldovich Effect Observations of Strong Lensing Galaxy Clusters: Probing the Over-Concentration Problem
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We have measured the Sunyaev Zeldovich (SZ) effect for a sample of ten strong lensing selected galaxy clusters using the Sunyaev Zeldovich Array (SZA). The SZA is sensitive to structures on spatial scales of a few arcminutes, while the strong lensing mass modeling constrains the mass at small scales (typically < 30). Combining the two provides information about the projected concentrations of the strong lensing clusters. The Einstein radii we measure are twice as large as expected given the masses inferred from SZ scaling relations. A Monte Carlo simulation indicates that a sample randomly drawn from the expected distribution would have a larger median Einstein radius than the observed clusters about 3% of the time. The implied overconcentration has been noted in previous studies with smaller samples of lensing clusters. It persists for this sample, with the caveat that this could result from a systematic effect such as if the gas fractions of the strong lensing clusters are substantially below what is expected.
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The use of galaxy clusters as precision cosmological probes relies on an accurate determination of their masses. However, inferring the relationship between cluster mass and observables from direct observations is difficult and prone to sample selection biases. In this work, we use weak lensing as the best possible proxy for cluster mass to calibrate the Sunyaev-Zeldovich (SZ) effect measurements from the APEX-SZ experiment. For a well-defined (ROSAT) X-ray complete cluster sample, we calibrate the integrated Comptonization parameter, $Y_{rm SZ}$, to the weak-lensing derived total cluster mass, $M_{500}$. We employ a novel Bayesian approach to account for the selection effects by jointly fitting both the SZ Comptonization, $Y_{rm SZ}text{--}M_{500}$, and the X-ray luminosity, $L_{rm x}text{--}M_{500}$, scaling relations. We also account for a possible correlation between the intrinsic (log-normal) scatter of $L_{rm x}$ and $Y_{rm SZ}$ at fixed mass. We find the corresponding correlation coefficient to be $r= 0.47_{-0.35}^{+0.24}$, and at the current precision level our constraints on the scaling relations are consistent with previous works. For our APEX-SZ sample, we find that ignoring the covariance between the SZ and X-ray observables biases the normalization of the $Y_{rm SZ}text{--}M_{500}$ scaling high by $1text{--}2sigma$ and the slope low by $sim 1sigma$, even when the SZ effect plays no role in the sample selection. We conclude that for higher-precision data and larger cluster samples, as anticipated from on-going and near-future cluster cosmology experiments, similar biases (due to intrinsic covariances of cluster observables) in the scaling relations will dominate the cosmological error budget if not accounted for correctly.
We present the first measurement of the relationship between the Sunyaev-Zeldovich effect signal and the mass of galaxy clusters that uses gravitational lensing to measure cluster mass, based on 14 X-ray luminous clusters at z~0.2 from the Local Cluster Substructure Survey. We measure the integrated Compton y-parameter, Y, and total projected mass of the clusters (M_GL) within a projected clustercentric radius of 350 kpc, corresponding to mean overdensities of 4000-8000 relative to the critical density. We find self-similar scaling between M_GL and Y, with a scatter in mass at fixed Y of 32%. This scatter exceeds that predicted from numerical cluster simulations, however, it is smaller than comparable measurements of the scatter in mass at fixed T_X. We also find no evidence of segregation in Y between disturbed and undisturbed clusters, as had been seen with T_X on the same physical scales. We compare our scaling relation to the Bonamente et al. relation based on mass measurements that assume hydrostatic equilibrium, finding no evidence for a hydrostatic mass bias in cluster cores (M_GL = 0.98+/-0.13 M_HSE), consistent with both predictions from numerical simulations and lensing/X-ray-based measurements of mass-observable scaling relations at larger radii. Overall our results suggest that the Sunyaev-Zeldovich effect may be less sensitive than X-ray observations to the details of cluster physics in cluster cores.
We present a detection-significance-limited catalog of 21 Sunyaev-Zeldovich selected galaxy clusters. These clusters, along with 1 unconfirmed candidate, were identified in 178 deg^2 of sky surveyed in 2008 by the South Pole Telescope to a depth of 18 uK-arcmin at 150 GHz. Optical imaging from the Blanco Cosmology Survey (BCS) and Magellan telescopes provided photometric (and in some cases spectroscopic) redshift estimates, with catalog redshifts ranging from z=0.15 to z>1, with a median z = 0.74. Of the 21 confirmed galaxy clusters, three were previously identified as Abell clusters, three were presented as SPT discoveries in Staniszewski et al, 2009, and three were first identified in a recent analysis of BCS data by Menanteau et al, 2010; the remaining 12 clusters are presented for the first time in this work. Simulated observations of the SPT fields predict the sample to be nearly 100% complete above a mass threshold of M_200 ~ 5x10^14 M_sun/h at z = 0.6. This completeness threshold pushes to lower mass with increasing redshift, dropping to ~4x10^14 M_sun/h at z=1. The size and redshift distribution of this catalog are in good agreement with expectations based on our current understanding of galaxy clusters and cosmology. In combination with other cosmological probes, we use the cluster catalog to improve estimates of cosmological parameters. Assuming a standard spatially flat wCDM cosmological model, the addition of our catalog to the WMAP 7-year analysis yields sigma_8 = 0.81 +- 0.09 and w = -1.07 +- 0.29, a ~50% improvement in precision on both parameters over WMAP7 alone.
We report the direct detection of the kinetic Sunyaev-Zeldovich (kSZ) effect in galaxy clusters with a 3.5 sigma significance level. The measurement was performed by stacking the Planck map at 217 GHz at the positions of galaxy clusters from the Wen-Han-Liu (WHL) catalog. To avoid the cancelation of positive and negative kSZ signals, we used the large-scale distribution of the Sloan Digital Sky Survey (SDSS) galaxies to estimate the peculiar velocities of the galaxy clusters along the line of sight and incorporated the sign in the velocity-weighted stacking of the kSZ signals. Using this technique, we were able to measure the kSZ signal around galaxy clusters beyond 3R500. Assuming a standard beta-model, we also found that the gas fraction within R500 is fgas,500 = 0.12 +- 0.04 for the clusters with the mass of M500 ~ 1e14 Msun/h. We compared this result to predictions from the Magneticum cosmological hydrodynamic simulations as well as other kSZ and X-ray measurements, most of which show a lower gas fraction than the universal baryon fraction for the same mass of clusters. Our value is statistically consistent with results from the measurements and simulations and also with the universal value within our measurement uncertainty.
A recent stacking analysis of Planck HFI data of galaxy clusters (Hurier 2016) allowed to derive the cluster temperatures by using the relativistic corrections to the Sunyaev-Zeldovich effect (SZE). However, the temperatures of high-temperature clusters, as derived from this analysis, resulted to be basically higher than the temperatures derived from X-ray measurements, at a moderate statistical significance of $1.5sigma$. This discrepancy has been attributed by Hurier (2016) to calibration issues. In this paper we discuss an alternative explanation for this discrepancy in terms of a non-thermal SZE astrophysical component. We find that this explanation can work if non-thermal electrons in galaxy clusters have a low value of their minimum momentum ($p_1sim0.5-1$), and if their pressure is of the order of $20-30%$ of the thermal gas pressure. Both these conditions are hard to obtain if the non-thermal electrons are mixed with the hot gas in the intra cluster medium, but can be possibly obtained if the non-thermal electrons are mainly confined in bubbles with high content of non-thermal plasma and low content of thermal plasma, or in giant radio lobes/relics located in the outskirts of clusters. In order to derive more precise results on the properties of non-thermal electrons in clusters, and in view of more solid detections of a discrepancy between X-rays and SZE derived clusters temperatures that cannot be explained in other ways, it would be necessary to reproduce the full analysis done by Hurier (2016) by adding systematically the non-thermal component of the SZE.
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