A. Kashlinsky

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.

SEDS: The Spitzer Extended Deep Survey: survey design, photometry, and deep IRAC source counts

The Spitzer Extended Deep Survey (SEDS) is a very deep infrared survey within five well-known extragalactic science fields: the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, COSMOS, the Hubble Deep Field North, and the Extended Groth Strip. SEDS covers a total area of 1.46 deg(2) to a depth of 26 AB mag (3s) in both of the warm Infrared Array Camera (IRAC) bands at 3.6 and 4.5 mu m. Because of its uniform depth of coverage in so many widely-separated fields, SEDS is subject to roughly 25% smaller errors due to cosmic variance than a single-field survey of the same size. SEDS was designed to detect and characterize galaxies from intermediate to high redshifts (z = 2-7) with a built-in means of assessing the impact of cosmic variance on the individual fields. Because the full SEDS depth was accumulated in at least three separate visits to each field, typically with six- month intervals between visits, SEDS also furnishes an opportunity to assess the infrared variability of faint objects. This paper describes the SEDS survey design, processing, and publicly-available data products. Deep IRAC counts for the more than 300,000 galaxies detected by SEDS are consistent with models based on known galaxy populations. Discrete IRAC sources contribute 5.6 +/- 1.0 and 4.4 +/- 0.8 nW m(-2) sr(-1) at 3.6 and 4.5 mu m to the diffuse cosmic infrared background (CIB). IRAC sources cannot contribute more than half of the total CIB flux estimated from DIRBE data. Barring an unexpected error in the DIRBE flux estimates, half the CIB flux must therefore come from a diffuse component.

Tracing the first stars with fluctuations of the cosmic infrared background

The deepest space- and ground-based observations find metal-enriched galaxies at cosmic times when the Universe was less than 1 Gyr old. These stellar populations had to be preceded by the metal-free first stars, known as ‘population III’. Recent cosmic microwave background polarization measurements indicate that stars started forming early—when the Universe was ≤200 Myr old. It is now thought that population III stars were significantly more massive than the present metal-rich stellar populations. Although such sources will not be individually detectable by existing or planned telescopes, they would have produced significant cosmic infrared background radiation in the near-infrared, whose fluctuations reflect the conditions in the primordial density field. Here we report a measurement of diffuse flux fluctuations after removing foreground stars and galaxies. The anisotropies exceed the instrument noise and the more local foregrounds; they can be attributed to emission from population III stars, at an era dominated by these objects.

Cosmic Infrared Background and Early Galaxy Evolution

The cosmic infrared background (CIB) reflects the sum total of galactic luminosities integrated over the entire age of the universe. From its measurement the red-shifted starlight and dust-absorbed and re-radiated starlight of the CIB can be used to determine (or constrain) the rates of star formation and metal production as a function of time and deduce information about objects at epochs currently inaccessible to telescopic studies. This review discusses the state of current CIB measurements and the (mostly space-based) instruments with which these measurements have been made, the obstacles (the various foreground emissions) and the physics behind the CIB and its structure. Theoretical discussion of the CIB levels can now be normalized to the standard cosmological model narrowing down theoretical uncertainties. We review the information behind and theoretical modeling of both the mean (isotropic) levels of the CIB and their fluctuations. The CIB is divided into three broad bands: near-IR (NIR), mid-IR (MIR) and far-IR (FIR). For each of the bands we review the main contributors to the CIB flux and the epochs at which the bulk of the flux originates. We also discuss the data on the various quantities relevant for correct interpretation of the CIB levels: the star-formation history, the present-day luminosity function measurements, resolving the various galaxy contributors to the CIB, etc. The integrated light of all galaxies in the deepest NIR galaxy counts to date fails to match the observed mean level of the CIB, probably indicating a significant high-redshift contribution to the CIB. Additionally, Population III stars should have left a strong and measurable signature via their contribution to the CIB anisotropies for a wide range of their formation scenarios, and measuring the excess CIB anisotropies coming from high z would provide direct information on the epoch of the first stars.

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.

Clustering of the Diffuse Infrared Light from the COBE DIRBE maps. III. Power spectrum analysis and excess isotropic component of fluctuations.

The cosmic infrared background (CIB) radiation is the cosmic repository for energy release throughout the history of the universe. The spatial fluctuations of the CIB resulting from galaxy clustering are expected to be at least a few percent on scales of a degree, depending on the luminosity and clustering history of the early universe. Using the all-sky data from the COBE DIRBE instrument at wavelengths 1.25-100 μm, we attempt to measure the CIB fluctuations. In the near-IR, foreground emission is dominated by small-scale structure due to stars in the Galaxy. There we find a strong correlation between the amplitude of the fluctuations and Galactic latitude after removing bright foreground stars. Using data outside the Galactic plane (|b| > 20°) and away from the center (90° < l < 270°), we extrapolate the amplitude of the fluctuations to csc |b| = 0. We find positive intercepts of δFrms = 15.5, 5.9, 2.4, and 2.0 nW m-2 sr-1 at 1.25, 2.2, 3.5, and 4.9 μm, respectively, where the errors are the range of 92% confidence limits. For color subtracted maps between band 1 and 2 we find the isotropic part of the fluctuations at 7.6 nW m-2 sr-1. Based on detailed numerical and analytic models, this residual is not likely to originate from the Galaxy, our clipping algorithm, or instrumental noise. We demonstrate that the residuals from the fit used in the extrapolation are distributed isotropically and suggest that this extra variance may result from structure in the CIB. We also obtain a positive intercept from a linear combination of maps at 1.25 and 2.2 μm. For 2° < θ < 15°, a power-spectrum analysis yields firm upper limits of (θ/5°) × δFrms(θ) < 6, 2.5, 0.8, and 0.5 nW m-2 sr-1 at 1.25, 2.2, 3.5, and 4.9 μm, respectively. From 10 to 100 μm, the dominant foregrounds are emission by dust in the solar system and the Galaxy. The upper limits on the CIB fluctuations are below 1 nW m-2 sr-1 there and are lowest (≤0.5 nW m-2 sr-1) at 25 μm.

RECONSTRUCTING THE NEAR-INFRARED BACKGROUND FLUCTUATIONS FROM KNOWN GALAXY POPULATIONS USING MULTIBAND MEASUREMENTS OF LUMINOSITY FUNCTIONS

We model fluctuations in the cosmic infrared background (CIB) arising from known galaxy populations using 233 measured UV, optical, and near-IR luminosity functions (LFs) from a variety of surveys spanning a wide range of redshifts. We compare best-fit Schechter parameters across the literature and find clear indication of evolution with redshift. Providing fitting formulae for the multi-band evolution of the LFs out to z ~ 5, we calculate the total emission redshifted into the near-IR bands in the observer frame and recover the observed optical and near-IR galaxy counts to good accuracy. Our empirical approach, in conjunction with a halo model describing the clustering of galaxies, allows us to compute the fluctuations of the unresolved CIB and compare the models to current measurements. We find that fluctuations from known galaxy populations are unable to account for the large-scale CIB clustering signal seen by Spitzer/IRAC and AKARI/IRC and continue to diverge out to larger angular scales. This holds true even if the LFs are extrapolated out to faint magnitudes with a steep faint-end slope all the way to z = 8. We also show that removing resolved sources to progressively fainter magnitude limits isolates CIB fluctuations to increasingly higher redshifts. Our empirical approach suggests that known galaxy populations are not responsible for the bulk of the fluctuation signal seen in the measurements and favors a very faint population of highly clustered sources.

Detection of Small-Scale Fluctuations in the Near-Infrared Cosmic Infrared Background from Long-Exposure 2MASS Fields

We report first results for the cosmic infrared background (CIB) fluctuations at 1.25, 1.65, and 2.17 μm obtained from long exposures constructed from Two Micron All Sky Survey standard star fields. We have co-added and analyzed scans from one such field with a total exposure time greater than 1 hr and removed sources and other artifacts. The stars and galaxies were clipped out to Ks 19 mag, leaving only high-z galaxies (or possibly local low surface brightness systems). The angular power spectrum of the remaining diffuse emission on scales from a few arcseconds to a few arcminutes has a power-law slope consistent with emission produced by clustered galaxies. The noise (and residual artifacts) contribution to the signal is small, and the colors of the signal are very different from Galactic stars or airglow. We therefore identify the signal as CIB fluctuations from the faint unresolved galaxies. We show that the present-day galaxies with no evolution would produce a significant deficit in the observed CIB fluctuations. Thus, the dominant contribution to the observed signal must come from high z and may indicate high rates of star formation at those epochs.

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.