F. Atrio-Barandela

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 yr 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 ΛCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities.

Dark Matter and Dark Energy Interactions: Theoretical Challenges, Cosmological Implications and Observational Signatures

Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.

A Measurement of Large-Scale Peculiar Velocities of Clusters of Galaxies: Technical Details

This paper presents detailed analysis of large-scale peculiar motions derived from a sample of ~700 X-ray clusters and cosmic microwave background (CMB) data obtained with WMAP. We use the kinematic Sunyaev-Zeldovich (KSZ) effect combining it into a cumulative statistic that preserves the bulk motion component with the noise integrated down. Such statistic is the dipole of CMB temperature fluctuations evaluated over the pixels of the cluster catalog. To remove the cosmological CMB fluctuations the maps are filtered with a Wiener-type filter in each of the eight WMAP channels (Q, V, W) that have negligible foreground component. Our findings are as follows. The thermal SZ (TSZ) component of the clusters is described well by the Navarro-Frenk-White profile expected if the hot gas traces the dark matter in the cluster potential wells. Such gas has X-ray temperature decreasing rapidly toward the cluster outskirts, which we demonstrate results in the decrease of the TSZ component as the aperture is increased to encompass the cluster outskirts. We then detect a statistically significant dipole in the CMB pixels at cluster positions. Arising exclusively at the cluster pixels, this dipole cannot originate from the foreground or instrument noise emissions and must be produced by the CMB photons that interacted with the hot intracluster gas via the SZ effect. The dipole remains as the monopole component, due to the TSZ effect, vanishes within the small statistical noise out to the maximal aperture where we still detect the TSZ component. We demonstrate with simulations that the mask and cross-talk effects are small for our catalog and contribute negligibly to the measurements. The measured dipole thus arises from the KSZ effect produced by the coherent large-scale bulk flow motion. The cosmological implications of the measurements are discussed by us in the 2008 work of Kashlinsky et al.

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 cluster core radii, but the amplitude depends strongly on those parameters. Its 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 blackbody 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 parameters of the cluster model, and at first approximation depends only on the number density of clusters. An independent determination of the contribution of clusters to the distortion of the blackbody spectrum and the temperature fluctuations of the cosmic microwave background would determine the number density of clusters that contribute to the Sunyaev-Zeldovich effect.

Measuring Cosmological Bulk Flows via the Kinematic Sunyaev-Zeldovich Effect in the Upcoming Cosmic Microwave Background Maps

We propose a new method for measuring the possible large-scale bulk flows in the universe from the cosmic microwave background (CMB) maps from the upcoming missions of the Microwave Anistropy Probe (MAP) and Planck. This can be done by studying the statistical properties of the CMB temperature field at many X-ray cluster positions. At each cluster position, the CMB temperature fluctuation will be a combination of the Sunyaev-Zeldovich (SZ) kinematic and thermal components, the cosmological fluctuations, and the instrument noise term. When averaged over many such clusters, the last three will integrate down, whereas the first one will be dominated by a possible bulk flow component. In particular, we propose to use all-sky X-ray cluster catalogs that should (or could) be available soon from X-ray satellites and then to evaluate the dipole component of the CMB field at the cluster positions. We show that for the MAP and Planck mission parameters, the dominant contributions to the dipole will be from the terms that are due to the SZ kinematic effect produced by the bulk flow (the signal we seek) and the instrument noise (the noise in our signal). Then, by computing the expected signal-to-noise ratio for such measurement, we find that at the 95% confidence level, the bulk flows on scales >/=100 h(-1) Mpc can be probed down to the amplitude of less than 200 km s(-1) with the MAP data and down to only approximately 30 km s(-1) with the Planck mission.

MEASUREMENT OF THE ELECTRON-PRESSURE PROFILE OF GALAXY CLUSTERS IN 3 YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) DATA

Using 3 year WMAP data at the locations of ~700 X-ray-selected clusters, we have detected the amplitude of the thermal Sunyaev-Zeldovich (TSZ) effect at the 15 ? level, the highest statistical significance reported so far. Owing to the large size of our cluster sample, we are able to detect the corresponding cosmic microwave background distortions out to large cluster-centric radii. The region over which the TSZ signal is detected is, on average, 4 times larger in radius than the X-ray-emitting region, extending to ~3 -->h?170 Mpc. We show that an isothermal ?-model does not fit the electron pressure at large radii; instead, the baryon profile is consistent with the Navarro-Frenk-White profile, which is expected for dark matter in the concordance ?CDM model. The X-ray temperature at the virial radius of the clusters falls by a factor ~3-4 from the central value, depending on the cluster concentration parameter. Our results suggest that cluster dynamics at large radii is dominated by dark matter and is well described by Newtonian gravity.

Integrated Sachs-Wolfe effect in interacting dark energy models

Models with dark energy decaying into dark matter have been proposed in cosmology to solve the coincidence problem. We study the effect of such coupling on the cosmic microwave background temperature anisotropies. The interaction changes the rate of evolution of the metric potentials and the growth rate of matter density perturbations and modifies the integrated Sachs-Wolfe component of cosmic microwave background temperature anisotropies, enhancing the effect. Cross correlation of galaxy catalogs with cosmic microwave background maps provides a model-independent test to constrain the interaction. We particularize our analysis for a specific interacting model and show that galaxy catalogs with median redshifts z{sub m}=0.1-0.9 can rule out models with an interaction parameter strength of c{sup 2}{approx_equal}0.1 better than 99.95% confidence level. Values of c{sup 2}{<=}0.01 are compatible with the data and may account for the possible discrepancy between the fraction of dark energy derived from Wilkinson microwave anisotropy probe 3 yr data and the fraction obtained from the integrated Sachs-Wolfe effect. Measuring the fraction of dark energy by these two methods could provide evidence of an interaction.

Steps toward the power spectrum of matter. I.the mean spectrum of galaxies

We calculate the mean power spectrum of all galaxies using published power spectra of galaxies and clusters of galaxies. On small scales we use the power spectrum derived from the two-dimensional distribution of Automatic Plate Measuring Facility (APM) galaxies, since this sample is not influenced by redshift distortions and is the largest and deepest sample of galaxies available. On large scales we use power spectra derived from three-dimensional data for various galaxy and cluster samples which are reduced to real space and in amplitude to the power spectrum of APM galaxies. We find that available data indicate the presence of two different populations in the nearby universe. Clusters of galaxies sample a relatively large region in the universe where rich, medium, and poor superclusters are well represented. Their mean power spectrum has a spike at wavenumber k = 0.05 ± 0.01 h Mpc-1, followed by an approximate power-law spectrum of index n ≈ -1.9 toward small scales. Some galaxy surveys (APM three-dimensional, IRAS QDOT, and SSRS+CfA2 130 Mpc) have similar spectra. The power spectrum found from the Las Campanas Redshift Survey and IRAS 1.2 Jy surveys is flatter around the maximum, which may represent regions of the universe with medium-rich and poor superclusters. Differences in power spectra for these populations may partly be due to the survey geometries of the data sets in question and/or to features of the original data analysis.

Steps toward the Power Spectrum of Matter. II. The Biasing Correction with σ8 Normalization

We suggest a new method to determine the bias parameter of galaxies relative to matter. The method is based on the assumption that gravity is the dominating force which determines the formation of the structure in the universe. Because of gravitational instability, matter flows out of underdense regions toward overdense regions. To form a galaxy, the density of matter within a certain radius must exceed a critical value (Press-Schechter limit); thus galaxy formation is a threshold process. In low-density environments (voids) galaxies do not form and matter remains in primordial form. We estimate the value of the threshold density which divides the matter into two populations, a low-density population in voids and a clustered population in high-density regions. We investigate the influence of the presence of these two populations on the power spectrum of matter and galaxies. We find that the power spectrum of clustered particles (galaxies) is similar to the power spectrum of matter. We show that the fraction of total matter in the clustered population determines the difference between amplitudes of fluctuations of matter and galaxies, i.e., the bias factor. To determine the fraction of matter in voids and clustered population we perform numerical simulations. The fraction of matter in galaxies at the present epoch is found using a calibration through the σ8 parameter. We find σ8 = 0.89 ± 0.09 for galaxies, σ8 = 0.68 ± 0.09 for matter, and bgal = 1.3 ± 0.13, the biasing factor of the clustered matter (galaxies) relative to all matter.

Constraining

Models of