On the Statistical Significance of the Bulk Flow Measured by the PLANCK Satellite

A recent analysis of data collected by the Planck satellite detected a net dipole at the location of X-ray selected galaxy clusters, corresponding to a large-scale bulk flow extending at least to $z\sim 0.18$, the median redshift of the cluster sample. The amplitude of this flow, as measured with Planck, is consistent with earlier findings based on data from the Wilkinson Microwave Anisotropy Probe (WMAP). However, the uncertainty assigned to the dipole by the Planck team is much larger than that found in the WMAP studies, leading the authors of the Planck study to conclude that the observed bulk flow is not statistically significant. We here show that two of the three implementations of random sampling used in the error analysis of the Planck study lead to systematic overestimates in the uncertainty of the measured dipole. Random simulations of the sky do not take into account that the actual realization of the sky leads to filtered data that have a 12% lower root-mean-square dispersion than the average simulation. Using rotations around the Galactic pole (the Z axis), increases the uncertainty of the X and Y components of the dipole and artificially reduces the significance of the dipole detection from 98-99% to less than 90% confidence. When either effect is taken into account, the corrected errors agree with those obtained using random distributions of clusters on Planck data, and the resulting statistical significance of the dipole measured by Planck is consistent with that of the WMAP results.Comment: A & A, in pres

A measurement of large-scale peculiar velocities of clusters of galaxies: results and cosmological implications

Peculiar velocities of clusters of galaxies can be measured by studying the fluctuations in the cosmic microwave background (CMB) generated by the scattering of the microwave photons by the hot X-ray emitting gas inside clusters. While for individual clusters such measurements result in large errors, a large statistical sample of clusters allows one to study cumulative quantities dominated by the overall bulk flow of the sample with the statistical errors integrating down. We present results from such a measurement using the largest all-sky X-ray cluster catalog combined to date and the 3-year WMAP CMB data. We find a strong and coherent bulk flow on scales out to at least > 300 h^{-1} Mpc, the limit of our catalog. This flow is difficult to explain by gravitational evolution within the framework of the concordance LCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities.Comment: Ap.J. (Letters), in press. 20 Oct issue (Vol. 686

Intermittence of the Map of Kinetic Sunyaev-Zel'dovich Effect and Turbulence of IGM

We investigate the possibility of detecting the turbulent state of the IGM with the kinetic Sunyaev-Zel'dovich (kSZ) effect. Being sensitive to the divergence-free component of the momentum field of the IGM, the kSZ effect might be used to probe the vorticity of the turbulent IGM. With cosmological hydrodynamical simulation in the concordance $\Lambda$CDM universe, we find that the structure functions of 2D kSZ maps show strong intermittence, and the intermittent exponents follow a law similar to the She-Leveque scaling formula of fully developed turbulence. We also find that the intermittence is weak in the maps of thermal Sunyaev-Zel'dovich (tSZ) effect. Nevertheless, the superposition of the kSZ and tSZ effects still contain significant intermittence. We conclude that the turbulent behavior of the IGM may be revealed by the observation of SZ effect on angular scales equal to or less than 0.5 arcminute, corresponding to the multipole parameter $l\geq 2 \times10^4$.Comment: 10 pages, 4 figures, accepted for publication in ApJ

Temperature Anisotropies and Distortions Induced by Hot Intracluster Gas on the Cosmic Microwave Background

The power spectrum of temperature anisotropies induced by hot intracluster gas on the cosmic background radiation is calculated. For low multipoles it remains constant while at multipoles above $l>2000$ it is exponentially damped. The shape of the radiation power spectrum is almost independent of the average intracluster gas density profile, gas evolution history or clusters virial radii; but the amplitude depends strongly on those parameters and could be as large as 20% that of intrinsic contribution. The exact value depends on the global properties of the cluster population and the evolution of the intracluster gas. The distortion on the Cosmic Microwave Background black body spectra varies in a similar manner. The ratio of the temperature anisotropy to the mean Comptonization parameters is shown to be almost independent of the cluster model and, in first approximation, depends only on the number density of clusters.Comment: 10 pages, Latex, 3 figures; to be published in Ap

Measuring the dark flow with public X-ray cluster data

We present new results on the "dark flow" from a measurement of the dipole in the distribution of peculiar velocities of galaxy clusters, applying the methodology proposed and developed by us earlier. Our latest measurement is conducted using new, low-noise 7-yr WMAP data as well as an all-sky sample of X-ray selected galaxy clusters compiled exclusively from published catalogs. Our analysis of the CMB signature of the kinematic Sunyaev-Zeldovich (SZ) effect finds a statistically significant dipole at the location of galaxy clusters. The residual dipole outside the cluster regions is small, rendering our overall measurement 3-4 sigma significant. The amplitude of the dipole correlates with cluster properties, being larger for the most X-ray luminous clusters, as required if the signal is produced by the SZ effect. Since it is measured at zero monopole, the dipole can not be due to the thermal SZ effect. Our results are consistent with those obtained earlier by us from 5-yr WMAP data and using a proprietary cluster catalog. In addition, they are robust to quadrupole removal, demonstrating that quadrupole leakage contributes negligibly to the signal. The lower noise of the 7-yr WMAP also allows us, for the first time, to obtain tentative empirical confirmation of our earlier conjecture that the adopted filtering flips the sign of the KSZ effect for realistic clusters and thus of the deduced direction of the flow. The latter is consistent with our earlier measurement in both the amplitude and direction. Assuming the filtering indeed flips the sign of the KSZ effect from the clusters, the direction agrees well also with the results of independent work using galaxies as tracers at lower distances. We make all maps and cluster templates derived by us from public data available to the scientific community to allow independent tests of our method and findings.Comment: ApJ, in press. Replaced with accepted version. The data needed for these results are at http://www.kashlinsky.info/bulkflows/data_publi