Determining Ω\Omega from cluster correlation function

It is shown how data on the cluster correlation function can be used in order to reconstruct the density of the pregalactic density field on the cluster mass scale. The method is applied to the data on the cluster correlation amplitude -- richness dependence. The spectrum of the recovered density field has the same shape as the density field derived from data on the galaxy correlation function which is measured as function of linear scales. Matching the two amplitudes relates the mass to the comoving scale it contains and thereby leads to a direct determination of $\Omega$. The resultant density parameter turns out to be $\Omega$=0.25.Comment: to appear in Physics Reports, "Dark Matter 98", vol.30

Cosmic Infrared Background from Early Epochs - Searching for Signatures of the First Stars

Cosmic infrared background (CIB) contains emission from epochs inaccessible to current telescopic studies, such as the era of the first stars. We discuss theoretical expectations for the CIB contributions from the early population of massive stars. We then present the latest results from the ongoing project by our team (Kashlinsky, Arendt, Mather & Moseley 2005,2007a,b,c,) to measure CIB fluctuations from early epochs using deep Spitzer data. The results show the existence of significant CIB fluctuations at the IRAC wavelengths (3.6 to 8 mic) which remain after removing galaxies down to very faint levels. These fluctuations must arise from populations that have a significant clustering component, but only low levels of the shot noise. Furthermore, there are no correlations between the source-subtracted IRAC maps and the corresponding fields observed with the HST ACS at optical wavelengths. Taken together, these data imply that 1) the sources producing the CIB fluctuations are individually faint with flux < a few nJy at 3.6 and 4.5 mic; 2) are located within the first 0.7 Gyr (unless these fluctuations can somehow be produced by - so far unobserved - local galaxies of extremely low luminosity and with the unusual for local populations clustering pattern), 3) they produce contribution to the net CIB flux of at least 1-2 nW/m^2/sr at 3.6 and 4.5 mic and must have mass-to-light ratio significantly below the present-day populations, and 4) they have angular density of ~ a few per arcsec^2 and are in the confusion of the present day instruments, but can be individually observable with JWST.Comment: To appear in "First Stars III", eds. B. O'Shea, A. Heger & T. Abe

Probing the Universe's Tilt with the Cosmic Infrared Background Dipole

Conventional interpretation of the observed cosmic microwave background (CMB) dipole is that all of it is produced by local peculiar motions. Alternative explanations requiring part of the dipole to be primordial have received support from measurements of large-scale bulk flows. A test of the two hypothesis is whether other cosmic dipoles produced by collapsed structures later than last scattering coincide with the CMB dipole. One background is the cosmic infrared background (CIB) whose absolute spectrum was measured to ~30% by the COBE satellite. Over the 100 to 500 {\mu}m wavelength range its spectral energy distribution can provide a probe of its alignment with CMB. This is tested with the COBE FIRAS dataset which is available for such a measurement because of its low noise and frequency resolution important for Galaxy subtraction. Although the FIRAS instrument noise is in principle low enough to determine the CIB dipole, the Galactic foreground is sufficiently close spectrally to keep the CIB dipole hidden. A similar analysis is performed with DIRBE, which - because of the limited frequency coverage - provides a poorer a dataset. We discuss strategies for measuring the CIB dipole with future instruments to probe the tilt and apply it to the Planck, Herschel and the proposed Pixie missions. We demonstrate that a future FIRAS-like instrument with instrument noise a factor of ~10 lower than FIRAS would make a statistically significant measurement of the CIB dipole. We find that the Planck and Herschel data sets will not allow a robust CIB dipole measurement. The Pixie instrument promises a determination of the CIB dipole and its alignment with either the CMB dipole or the dipole galaxy acceleration vector.Comment: 9 pages 9 figure

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

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