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

Karhunen-Loeve eigenvalue problems in cosmology: how should we tackle large data sets?

Since cosmology is no longer "the data-starved science", the problem of how to best analyze large data sets has recently received considerable attention, and Karhunen-Loeve eigenvalue methods have been applied to both galaxy redshift surveys and Cosmic Microwave Background (CMB) maps. We present a comprehensive discussion of methods for estimating cosmological parameters from large data sets, which includes the previously published techniques as special cases. We show that both the problem of estimating several parameters jointly and the problem of not knowing the parameters a priori can be readily solved by adding an extra singular value decomposition step. It has recently been argued that the information content in a sky map from a next generation CMB satellite is sufficient to measure key cosmological parameters (h, Omega, Lambda, etc) to an accuracy of a few percent or better - in principle. In practice, the data set is so large that both a brute force likelihood analysis and a direct expansion in signal-to-noise eigenmodes will be computationally unfeasible. We argue that it is likely that a Karhunen-Loeve approach can nonetheless measure the parameters with close to maximal accuracy, if preceded by an appropriate form of quadratic "pre-compression". We also discuss practical issues regarding parameter estimation from present and future galaxy redshift surveys, and illustrate this with a generalized eigenmode analysis of the IRAS 1.2 Jy survey optimized for measuring beta=Omega^{0.6}/b using redshift space distortions.Comment: 15 pages, with 5 figures included. Substantially expanded with worked COBE examples for e.g. the multiparameter case. Available from http://www.sns.ias.edu/~max/karhunen.html (faster from the US), from http://www.mpa-garching.mpg.de/~max/karhunen.html (faster from Europe) or from [email protected]

Galaxy redshift surveys selected by neutral hydrogen using FAST

We discuss the possibility of performing a substantial spectroscopic galaxy redshift survey selected via the 21cm emission from neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope (FAST) to be built in China. We consider issues related to the estimation of the source counts and optimizations of the survey, and discuss the constraints on cosmological models that such a survey could provide. We find that a survey taking around two years could detect ~10^7 galaxies with an average redshift of ~0.15 making the survey complementary to those already carried out at optical wavelengths. These conservative estimates have used the z=0 HI mass function and have ignored the possibility of evolution. The results could be used to constrain Gamma = (Omega_m h) to 5 per cent and the spectral index, n_s, to 7 per cent independent of cosmic microwave background data. If we also use simulated power spectra from the Planck satellite, we can constrain w to be within 5 per cent of -1.Comment: 13 pages, 15 figures, Accepted by MNRAS, minor correction

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

New constraints on Parity Symmetry from a re-analysis of the WMAP-7 low resolution power spectra

The Parity symmetry of the Cosmic Microwave Background (CMB) pattern as seen by WMAP 7 is tested jointly in temperature and polarization at large angular scale. A Quadratic Maximum Likelihood (QML) estimator is applied to the WMAP 7 year low resolution maps to compute all polarized CMB angular power spectra. The analysis is supported by 10000 realistic Monte-Carlo realizations. We confirm the previously reported Parity anomaly for TT in the range $\delta \ell=[2,22]$ at $> 99.5$ C.L.. No anomalies have been detected in TT for a wider $\ell$ range (up to $\ell_{max}=40$). No violations have been found for EE, TE and BB which we test here for the first time. The cross-spectra TB and EB are found to be consistent with zero. We also forecast {\sc Planck} capabilities in probing Parity violations on low resolution maps.Comment: 8 pages, 6 figures, 4 tables. Accepted for publication in MNRA

Testing Standard Cosmology with Large Scale Structure

The galaxy power spectrum contains information on the growth of structure, the growth rate through redshift space distortions, and the cosmic expansion through baryon acoustic oscillation features. We study the ability of two proposed experiments, BigBOSS and JDEM-PS, to test the cosmological model and general relativity. We quantify the latter result in terms of the gravitational growth index \gamma, whose value in general relativity is \gamma\approx 0.55. Significant deviations from this value could indicate new physics beyond the standard model of cosmology. The results show that BigBOSS (JDEM-PS) would be capable of measuring \gamma with an uncertainty \sigma(\gamma) = 0.043 (0.054), which tightens to \sigma(\gamma) = 0.031 (0.038) if we include Stage III data priors, marginalizing over neutrino mass, time varying dark energy equation of state, and other parameters. For all dark energy parameters and related figures of merit the two experiments give comparable results. We also carry out some studies of the influence of redshift range, resolution, treatment of nonlinearities, and bias evolution to enable further improvement.Comment: 9 pages, 12 tables, 1 figure; v3 matches MNRAS accepted versio

Signals of Inflation in a Friendly String Landscape

Following Freivogel {\it et al} we consider inflation in a predictive (or `friendly') region of the landscape of string vacua, as modeled by Arkani-Hamed, Dimopoulos and Kachru. In such a region the dimensionful coefficients of super-renormalizable operators unprotected by symmetries, such as the vacuum energy and scalar mass-squareds are freely scanned over, and the objects of study are anthropically or `environmentally' conditioned probability distributions for observables. In this context we study the statistical predictions of (inverted) hybrid inflation models, where the properties of the inflaton are probabilistically distributed. We derive the resulting distributions of observables, including the deviation from flatness $|1-\Omega|$, the spectral index of scalar cosmological perturbations $n_s$ (and its scale dependence $dn_s/d\log k$), and the ratio of tensor to scalar perturbations $r$. The environmental bound on the curvature implies a solution to the $\eta$-problem of inflation with the predicted distribution of $(1-n_s)$ indicating values close to current observations. We find a relatively low probability ($<3$) of `just-so' inflation with measurable deviations from flatness. Intermediate scales of inflation are preferred in these models.Comment: 20 pages, 11 figure

Multiple universes, cosmic coincidences, and other dark matters

Even when completely and consistently formulated, a fundamental theory of physics and cosmological boundary conditions may not give unambiguous and unique predictions for the universe we observe; indeed inflation, string/M theory, and quantum cosmology all arguably suggest that we can observe only one member of an ensemble with diverse properties. How, then, can such theories be tested? It has been variously asserted that in a future measurement we should observe the a priori most probable set of predicted properties (the ``bottom-up'' approach), or the most probable set compatible with all current observations (the ``top-down'' approach), or the most probable set consistent with the existence of observers (the ``anthropic'' approach). These inhabit a spectrum of levels of conditionalization and can lead to qualitatively different predictions. For example, in a context in which the densities of various species of dark matter vary among members of an ensemble of otherwise similar regions, from the top-down or anthropic viewpoints -- but not the bottom-up -- it would be natural for us to observe multiple types of dark matter with similar contributions to the observed dark matter density. In the anthropic approach it is also possible in principle to strengthen this argument and the limit the number of likely dark matter sub-components. In both cases the argument may be extendible to dark energy or primordial density perturbations. This implies that the anthropic approach to cosmology, introduced in part to explain "coincidences" between unrelated constituents of our universe, predicts that more, as-yet-unobserved coincidences should come to light.Comment: 18 JCAP-style pages, accepted by JCAP. Revised version adds references and some clarification

Separation of foregrounds from cosmic microwave background observations with the MAP satellite

Simulated observations of a 10\dg \times 10\dg field by the Microwave Anisotropy Probe (MAP) are analysed in order to separate cosmic microwave background (CMB) emission from foreground contaminants and instrumental noise and thereby determine how accurately the CMB emission can be recovered. The simulations include emission from the CMB, the kinetic and thermal Sunyaev-Zel'dovich (SZ) effects from galaxy clusters, as well as Galactic dust, free-free and synchrotron. We find that, even in the presence of these contaminating foregrounds, the CMB map is reconstructed with an rms accuracy of about 20 $\mu$K per 12.6 arcmin pixel, which represents a substantial improvement as compared to the individual temperature sensitivities of the raw data channels. We also find, for the single 10\dg \times 10\dg field, that the CMB power spectrum is accurately recovered for \ell \la 600.Comment: 7 pages, 7 figures, MNRAS submitte

On measuring the covariance matrix of the nonlinear power spectrum from simulations

We show how to estimate the covariance of the power spectrum of a statistically homogeneous and isotropic density field from a single periodic simulation, by applying a set of weightings to the density field, and by measuring the scatter in power spectra between different weightings. We recommend a specific set of 52 weightings containing only combinations of fundamental modes, constructed to yield a minimum variance estimate of the covariance of power. Numerical tests reveal that at nonlinear scales the variance of power estimated by the weightings method substantially exceeds that estimated from a simple ensemble method. We argue that the discrepancy is caused by beat-coupling, in which products of closely spaced Fourier modes couple by nonlinear gravitational growth to the beat mode between them. Beat-coupling appears whenever nonlinear power is measured from Fourier modes with a finite spread of wavevector, and is therefore present in the weightings method but not the ensemble method. Beat-coupling inevitably affects real galaxy surveys, whose Fourier modes have finite width. Surprisingly, the beat-coupling contribution dominates the covariance of power at nonlinear scales, so that, counter-intuitively, it is expected that the covariance of nonlinear power in galaxy surveys is dominated not by small scale structure, but rather by beat-coupling to the largest scales of the survey.Comment: 19 pages, 4 figures. To appear in Monthly Notices of the Royal Astronomical Society. Revised to match accepted versio