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Register a new userEvidence of Galaxy Cluster Motions with the Kinematic Sunyaev-Zeldovich Effect
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Using high-resolution microwave sky maps made by the Atacama Cosmology Telescope, we for the first time present strong evidence for motions of galaxy clusters and groups via microwave background temperature distortions due to the kinematic Sunyaev-Zeldovich effect. Galaxy clusters are identified by their constituent luminous galaxies observed by the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. We measure the mean pairwise momentum of clusters, with a probability of the signal being due to random errors of 0.002, and the signal is consistent with the growth of cosmic structure in the standard model of cosmology.
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Studying galaxy clusters through their Sunyaev-Zeldovich (SZ) imprint on the Cosmic Microwave Background has many important advantages. The total SZ signal is an accurate and precise tracer of the total pressure in the intra-cluster medium and of cluster mass, the key observable for using clusters as cosmological probes. Band 5 observations with SKA-MID towards cluster surveys from the next generation of X-ray telescopes such as e-ROSITA and from Euclid will provide the robust mass estimates required to exploit these samples. This will be especially important for high redshift systems, arising from the SZs unique independence to redshift. In addition, galaxy clusters are very interesting astrophysical systems in their own right, and the SKAs excellent surface brightness sensitivity down to small angular scales will allow us to explore the detailed gas physics of the intra-cluster medium.
We detect the kinematic Sunyaev-Zeldovich (kSZ) effect with a statistical significance of $4.2 sigma$ by combining a cluster catalogue derived from the first year data of the Dark Energy Survey (DES) with CMB temperature maps from the South Pole Telescope Sunyaev-Zeldovich (SPT-SZ) Survey. This measurement is performed with a differential statistic that isolates the pairwise kSZ signal, providing the first detection of the large-scale, pairwise motion of clusters using redshifts derived from photometric data. By fitting the pairwise kSZ signal to a theoretical template we measure the average central optical depth of the cluster sample, $bar{tau}_e = (3.75 pm 0.89)cdot 10^{-3}$. We compare the extracted signal to realistic simulations and find good agreement with respect to the signal-to-noise, the constraint on $bar{tau}_e$, and the corresponding gas fraction. High-precision measurements of the pairwise kSZ signal with future data will be able to place constraints on the baryonic physics of galaxy clusters, and could be used to probe gravity on scales $ gtrsim 100$ Mpc.
We present a new measurement of the kinetic Sunyaev-Zeldovich effect (kSZ) using Planck cosmic microwave background (CMB) and Baryon Oscillation Spectroscopic Survey (BOSS) data. Using the `LowZ North/South galaxy catalogue from BOSS DR12, and the group catalogue from BOSS DR13, we evaluate the mean pairwise kSZ temperature associated with BOSS galaxies. We construct a `Central Galaxies Catalogue (CGC) which consists of isolated galaxies from the original BOSS data set, and apply the aperture photometry (AP) filter to suppress the primary CMB contribution. By constructing a halo model to fit the pairwise kSZ function, we constrain the mean optical depth to be $bar{tau}=(0.53pm0.32)times10^{-4}(1.65,sigma)$ for `LowZ North CGC, $bar{tau}=(0.30pm0.57)times10^{-4}(0.53,sigma)$ for `LowZ South CGC, and $bar{tau}=(0.43pm0.28)times10^{-4}(1.53,sigma)$ for `DR13 Group. In addition, we vary the radius of the AP filter and find that the AP size of $7,{rm arcmin}$ gives the maximum detection for $bar{tau}$. We also investigate the dependence of the signal with halo mass and find $bar{tau}=(0.32pm0.36)times10^{-4}(0.8,sigma)$ and $bar{tau}=(0.67pm0.46)times10^{-4}(1.4,sigma)$ for `DR13 Group with halo mass restricted to, respectively, less and greater than its median halo mass, $10^{12}, h^{-1}{rm M}_{odot}$. For the `LowZ North CGC sample restricted to $M_{rm h} gtrsim 10^{14}, h^{-1}{rm M}_odot$ there is no detection of the kSZ signal because these high mass halos are associated with the high-redshift galaxies of the LowZ North catalogue, which have limited contribution to the pairwise kSZ signals.
We present measurements of the thermal Sunyaev-Zeldovich effect (SZE) toward SPT-CL J2334-4243 (the Phoenix galaxy cluster) at z=0.597 by the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 3. The SZE is imaged at 5 resolution (corresponding to the physical scale of 23kpc/h) within 200kpc/h from the central galaxy with the peak signal-to-noise ratio exceeding 11. Combined with the Chandra X-ray image, the ALMA SZE data further allow for non-parametric deprojection of electron temperature, density, and entropy. Our method can minimize contamination by the central AGN and the X-ray absorbing gas within the cluster, both of which largely affect the X-ray spectrum. We find no significant asymmetry or disturbance in the SZE image within the current measurement errors. The detected SZE signal agrees well with the average pressure profile of local cool-core clusters. Unlike any other known clusters, however, gas temperature drops by at least a factor of 5 toward the center. We identify ~6x10^{11} M_sun cool gas with temperature ~3keV in the inner 20kpc/h. Taken together, our results imply that the gas is indeed cooling efficiently and nearly isobarically down to this radius in the Phoenix cluster.
We used the APEX-SZ and LABOCA bolometer cameras on the APEX telescope to map the decrement of the Sunyaev-Zeldovich effect at 150 GHz and the increment at 345 GHz toward the galaxy cluster Abell 2163. The SZE images were used to model the radial density and temperature distribution of the ICM, and to derive the gas mass fraction in the cluster under the assumption of hydrostatic equilibrium. We used the isothermal beta model to fit the SZE decrement/increment radial profiles. We performed a simple, non-parametric de-projection of the radial density and temperature profiles, in conjunction with XMM-Newton X-ray data, under the simplifying assumption of spherical symmetry. We combined the peak SZE signals derived in this paper with published SZE measurements of this cluster to derive the cluster line-of-sight bulk velocity and the central Comptonization, using priors on the ICM temperature. We find that the best-fit isothermal model to the SZE data is consistent with the ICM properties implied by the X-ray data, particularly inside the central 1 Mpc radius. Although the assumptions of hydrostatic equilibrium and spherical symmetry may not be optimal for this complex system, the results obtained under these assumptions are consistent with X-ray and weak-lensing measurements. This shows the applicability of the simple joint SZE and X-ray de-projection technique described in this paper for clusters with a wide range of dynamical states. (Abridged)
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