On the detectability of non-trivial topologies

We explore the main physical processes which potentially affect the topological signal in the Cosmic Microwave Background (CMB) for a range of toroidal universes. We consider specifically reionisation, the integrated Sachs-Wolfe (ISW) effect, the size of the causal horizon, topological defects and primordial gravitational waves. We use three estimators: the information content, the S/N statistic and the Bayesian evidence. While reionisation has nearly no effect on the estimators, we show that taking into account the ISW strongly decreases our ability to detect the topological signal. We also study the impact of varying the relevant cosmological parameters within the 2 sigma ranges allowed by present data. We find that only Omega_Lambda, which influences both ISW and the size of the causal horizon, significantly alters the detection for all three estimators considered here.Comment: 11 pages, 9 figure

The Sunyaev-Zel'dovich Effect by Cocoons of Radio Galaxies

We estimate the deformation of the cosmic microwave background radiation by the hot region (``cocoon'') around a radio galaxy. A simple model is adopted for cocoon evolution while the jet is on, and a model of evolution is constructed after the jet is off. It is found that at low redshift the phase after the jet is off is longer than the lifetime of the jets. The Compton y-parameter generated by cocoons is calculated with a Press-Schechter number density evolution. The resultant value of y is of the same order as the COBE constraint. The Sunyaev-Zeldovich effect due to cocoons could therefore be a significant foreground source of small angular scale anisotropies in the cosmic microwave background radiation.Comment: Published version, 23 pages with 5 figure

The X-ray surface brightness profiles of hot galaxy clusters up to z~0.8: evidence for self-similarity and constraints on Omega_0

We study the ROSAT surface brightness profiles of a sample of 25 distant (0.33.5keV) clusters. For both open and flat cosmological models, the derived emission measure profiles are scaled according to the self-similar model of cluster formation. We use the standard scaling relations of cluster properties with z and temperature, with the empirical slope of the Mgas-T relation derived by Neumann & Arnaud (2001). Using a \chi^2 test, we perform a quantitative comparison of the scaled emission measure profiles of distant clusters with a reference profile derived from the sample of 15 hot nearby clusters compiled by Neumann & Arnaud (1999), which were found to obey self-similarity. For a low density flat universe, the distant cluster scaled data were found to be consistent, both in shape and normalisation, with the reference local profile.It indicates that hot clusters constitute a homologous family up to high z, and supports the standard picture of structure formation for the dark matter component. Because of the intrinsic regularity in the hot cluster population, the scaled profiles can be used as distance indicators, the correct cosmology being the one for which the profiles at different redshifts coincide. The present data allow us to put a tight constraint on Omega0 for a flat Universe: Omega0=0.40^{+0.15}_{-0.12} (90% confidence level). The critical model was excluded at the 98% confidence level. Consistently, the observed evolution of the normalisation of the Lx-T relation was found to comply with the self-similar model for Omega0=0.4, Lambda=0.6. The constraint derived on Omega0 is in remarkable agreement with the constraint obtained from SNI (Perlmutter etal, 1999) or from combined analysis of the power spectrum of the 2dFGRS and the CMB anisotropy (Efstathiou etal, 2001). ABRIDGE

Unusually Large Fluctuations in the Statistics of Galaxy Formation at High Redshift

We show that various milestones of high-redshift galaxy formation, such as the formation of the first stars or the complete reionization of the intergalactic medium, occurred at different times in different regions of the universe. The predicted spread in redshift, caused by large-scale fluctuations in the number density of galaxies, is at least an order of magnitude larger than previous expectations that argued for a sharp end to reionization. This cosmic scatter in the abundance of galaxies introduces new features that affect the nature of reionization and the expectations for future probes of reionization, and may help explain the present properties of dwarf galaxies in different environments. The predictions can be tested by future numerical simulations and may be verified by upcoming observations. Current simulations, limited to relatively small volumes and periodic boundary conditions, largely omit cosmic scatter and its consequences. In particular, they artificially produce a sudden end to reionization, and they underestimate the number of galaxies by up to an order of magnitude at redshift 20.Comment: 8 ApJ pages, 4 figures, ApJ. Minor changes in revised version. Originally first submitted for publication on Aug. 29, 200

Surveys of Galaxy Clusters with the Sunyaev Zel'dovich Effect

We have created mock Sunyaev-Zel'dovich effect (SZE) surveys of galaxy clusters using high resolution N-body simulations. To the pure surveys we add `noise' contributions appropriate to instrument and primary CMB anisotropies. Applying various cluster finding strategies to these mock surveys we generate catalogues which can be compared to the known positions and masses of the clusters in the simulations. We thus show that the completeness and efficiency that can be achieved depend strongly on the frequency coverage, noise and beam characteristics of the instruments, as well as on the candidate threshold. We study the effects of matched filtering techniques on completeness, and bias. We suggest a gentler filtering method than matched filtering in single frequency analyses. We summarize the complications that arise when analyzing the SZE signal at a single frequency, and assess the limitations of such an analysis. Our results suggest that some sophistication is required when searching for `clusters' within an SZE map.Comment: 8 pages, 7 figure

Removing point sources from CMB maps

For high-precision cosmic microwave background (CMB) experiments, contamination from extragalactic point sources is a major concern. It is therefore useful to be able to detect and discard point source contaminated pixels using the map itself. We show that the sensitivity with which this can be done can often be greatly improved (by factors between 2.5 and 18 for the upcoming Planck mission) by a customized hi-pass filtering that suppresses fluctuations due to CMB and diffuse galactic foregrounds. This means that point source contamination will not severely degrade the cleanest Planck channels unless current source count estimates are off by more than an order of magnitude. A catalog of around 40,000 far infra-red sources at 857 GHz may be a useful by-product of Planck.Comment: 4 pages, with 2 figures included. Minor revisions to match accepted version. Color figure and links at http://www.sns.ias.edu/~max/cleaning.html (faster from the US), from http://www.mpa-garching.mpg.de/~max/cleaning.html (faster from Europe) or from [email protected], and Angelica's foreground links at http://www.sns.ias.edu/~angelica/foreground.htm

Large-Scale Sunyaev-Zel'dovich Effect: Measuring Statistical Properties with Multifrequency Maps

We study the prospects for extracting detailed statistical properties of the Sunyaev-Zel'dovich (SZ) effect associated with large scale structure using upcoming multifrequency CMB experiments. The greatest obstacle to detecting the large-angle signal is the confusion noise provided by the primary anisotropies themselves, and to a lesser degree galactic and extragalactic foregrounds. We employ multifrequency subtraction techniques and the latest foregrounds models to determine the detection threshold for the Boomerang, MAP (several microK) and Planck CMB (sub microK) experiments. Calibrating a simplified biased-tracer model of the gas pressure off recent hydrodynamic simulations, we estimate the SZ power spectrum, skewness and bispectrum through analytic scalings and N-body simulations of the dark matter. We show that the Planck satellite should be able to measure the SZ effect with sufficient precision to determine its power spectrum and higher order correlations, e.g. the skewness and bispectrum. Planck should also be able to detect the cross correlation between the SZ and gravitational lensing effect in the CMB. Detection of these effects will help determine the properties of the as yet undetected gas, including the manner in which the gas pressure traces the dark matter.Comment: 13 ApJ pages, 11 figures; typos and figure 5 revised; submitted to Ap

Characterization of the non-Gaussianity of radio and IR point sources at CMB frequencies

This study, using publicly available simulations, focuses on the characterization of the non-Gaussianity produced by radio point sources and by infrared (IR) sources in the frequency range of the cosmic microwave background from 30 to 350 GHz. We propose a simple prescription to infer the angular bispectrum from the power spectrum of point sources considering independent populations of sources, with or without clustering. We test the accuracy of our prediction using publicly available all-sky simulations of radio and IR sources and find very good agreement. We further characterize the configuration dependence and the frequency behaviour of the IR and radio bispectra. We show that the IR angular bispectrum peaks for squeezed triangles and that the clustering of IR sources enhances the bispectrum values by several orders of magnitude at scales ℓ∼ 100. At 150 GHz the bispectrum of IR sources starts to dominate that of radio sources on large angular scales, and it dominates the whole multipole range at 350 GHz. Finally, we compute the bias on fNL induced by radio and IR sources. We show that the positive bias induced by radio sources is significantly reduced by masking the sources. We also show, for the first time, that the form of the IR bispectrum mimics a primordial ‘local' bispectrum fNL. The IR sources produce a negative bias which becomes important for Planck-like resolution and at high frequencies (ΔfNL∼−6 at 277 GHz and ΔfNL∼−60-70 at 350 GHz). Most of the signal being due to the clustering of faint IR sources, the bias is not reduced by masking sources above a flux limit and may, in some cases, even be increased due to the reduction of the shot-noise ter