High-resolution Cosmic Microwave Background Research Articles

On minimally parametric primordial power spectrum reconstruction and the evidence for ared tilt

The latest cosmological data seem to indicate a significant deviation from scaleinvariance of the primordial power spectrum when parameterized either by apower law or by a spectral index with non-zero ‘running’. This deviation, byitself, serves as a powerful tool for discriminating among theories for the origin ofcosmological structures such as inflationary models. Here, we use a minimally parametricsmoothing spline technique to reconstruct the shape of the primordial power spectrum.This technique is well suited to searching for smooth features in the primordialpower spectrum such as deviations from scale invariance or a running spectralindex, although it would recover sharp features of high statistical significance.We use the WMAP three-year results in combination with data from a suiteof higher resolution cosmic microwave background experiments (including thelatest ACBAR 2008 release), as well as large-scale structure data from SDSS and2dFGRS. We employ cross-validation to assess, using the data themselves, theoptimal amount of smoothness in the primordial power spectrum consistent withthe data. This minimally parametric reconstruction supports the evidence fora power law primordial power spectrum with a red tilt, but not for deviationsfrom a power law power spectrum. Smooth variations in the primordial powerspectrum are not significantly degenerate with the other cosmological parameters.

WMAP 3-yr primordial power spectrum

We constrain the form of the primordial power spectrum using Wilkinson Microwave Anisotropy Probe (WMAP) 3-yr cosmic microwave background (CMB) data (plus other high resolution CMB experiments) in addition to complementary large-scale structure (LSS) data: 2dF, Sloan Digital Sky Survey (SDSS), Ly α forest and luminous red galaxy (LRG) data from the SDSS catalogue. We extend the work of the WMAP team to that of a fully Bayesian approach whereby we compute the comparative Bayesian evidence in addition to parameter estimates for a collection of seven models: (i) a scale-invariant Harrison ‐Zel’dovich (HZ) spectrum; (ii) a power law; (iii) a running spectral index; (iv) a broken spectrum; (v) a power law with an abrupt cut-off on large scales; (vi) a reconstruction of the spectrum in eight bins in wavenumber and (vii) a spectrum resulting from a cosmological model proposed by Lasenby & Doran (LD). Using a basic data set of WMAP3 + other CMB + 2dF + SDSS, our analysis confirms that a scale-invariant spectrum is disfavoured by between 0.7 and 1.7 units of log evidence (depending on priors chosen) when compared with a power-law tilt. Moreover, a running spectrum is now significantly preferred, but only when using the most constraining set of priors. The addition of both Lyα and LRG data independently suggests much lower values of the running index than with basic data set alone, and interestingly the inclusion of Lyα significantly disfavours a running parametrization by more than a unit in log evidence. Overall, the highest evidences, over all data sets, were obtained with a power-law spectrum containing a cut-off with a significant log evidence difference of roughly 2 units. The natural tilt and exponential cut-off present in the LD spectrum is found to be favoured decisively by a log evidence difference of over 5 units, but only for a limited study within the best-fitting concordance cosmology.

21-cm Background Anisotropies Can Discern Primordial Non-Gaussianity

The non-Gaussianity of initial perturbations provides information on the mechanism that generated primordial density fluctuations. We find that 21-cm background anisotropies due to inhomogeneous neutral hydrogen distribution prior to reionization captures information on primordial non-Gaussianity better than a high-resolution cosmic microwave background anisotropy map. An all-sky 21-cm experiment over the frequency range from 14 to 40 MHz with angular information out to a multipole of 10(5) can limit the primordial non-Gaussianity parameter f(NL) <, similar 0.01.

PRIMORDIAL GRAVITATIONAL WAVES AND INFLATION: POSSIBILITIES FOR DETECTION

The curl-modes of Cosmic Microwave Background (CMB) polarization probe horizon-scale primordial gravitational waves related to inflation. A significant source of confusion is expected from a lensing conversion of polarization related to density perturbations to the curl mode, during the propagation of photons through the large scale structure. Either high resolution CMB anisotropy observations or 21 cm fluctuations at redshifts 30 and higher can be used to delens polarization data and to separate gravitational-wave polarization signature from that of cosmic-shear related signal. Separations based on proposed lensing reconstruction techniques for reasonable future experiments allow the possibility to probe inflationary energy scales down to 1015GeV . Beyond CMB polarization, at frequencies between 0.01 Hz to 1 Hz, space-based laser interferometers can also be used to probe the inflationary gravitational wave background. The confusion here is related to the removal of merging neutron star binaries at cosmological distances. Given the low merger rate and the rapid evolution of the gravitational wave frequency across this band, reliable removal techniques can be constructed. We discuss issues related to joint constraints that can be placed on the inflationary models based on CMB polarization information and space-based interferometers such as the Big Bang Observer.

Radio emission from early-type galaxies and cosmic microwave background experiments

We investigate the possible contribution from the emission of accretion flows around supermassive black holes in early-type galaxies to current measurements of the cosmic microwave background (CMB) at radio frequencies. We consider a range of luminosities suggested by targeted radio observations and accretion models, and compute the residual contribution of these sources to the spectrum and bispectrum of the observed CMB maps. As for high-resolution CMB experiments, we find that the unresolved component of these sources could make up to ∼40-50 per cent of the observed Cosmic Background Imager (CBI) and Berkeley Illinois Maryland Association (BIMA) array power spectrum at l > 2000. As a consequence, the inferred σ SZ 8 value could be biased high by up to 6-7 per cent. As for all-sky experiments, we find that the contribution of accretion-flow sources to the Wilkinson Microwave Anisotropy Probe (WMAP) bispectrum is at the 2-3 per cent level at most. At the flux limit that Planck will achieve, however, these sources may contribute up to 15 per cent of the bispectrum in the 60-100 GHz frequency range. Moreover, Planck should detect hundreds of these sources in the 30-300 GHz frequency window. These detections, possibly coupled with galaxy type confirmation from optical surveys, will allow number counts to put tighter constraints on the radio luminosity and accretion-flow properties of early-type galaxies. These sources may also contribute up to the 30 per cent level to the residual radio sources power spectrum in future high-resolution Sunyaev-Zeldovich (SZ) surveys (like the Atacama Cosmology Telescope or the Atacama Pathfinder Experiment) reaching mJy flux limits.

Beyond the Damping Tail: Cross‐Correlating the Kinetic Sunyaev‐Zel’dovich Effect with Cosmic Shear

Secondary anisotropies of the cosmic microwave background (CMB) have the potential to reveal intricate details about the history of our universe between the present and recombination epochs. However, because the CMB we observe is the projected sum of a multitude of effects, the interpretation of small-scale anisotropies by future high-resolution experiments will be marred by uncertainty and speculation without the handles provided by other observations. The recent controversy over the excess small-scale anisotropy detected by CBI and the BIMA array is a foretaste of potential challenges that will be faced when interpreting future experiments. In this paper we show that cross-correlating the CMB with an overlapping weak-lensing survey will isolate the elusive kinetic Sunyaev-Zel'dovich (kSZ) effect from secondary anisotropies generated at higher redshifts. We show that if upcoming high angular resolution CMB experiments, like Planck/ACT/SPT, cover the same area of sky as current and future weak-lensing surveys, like CFTHLS/SNAP/LSST, the cross-correlation of cosmic shear with the kSZ effect will be detected with high signal-to-noise ratio, increasing the potential science accessible to both sets of surveys. For example, if ACT and a CFHTLS-like survey were to overlap, this cross-correlation would be detected with a total signal-to-noise ratio greater than 220, reaching 1.8 per individual multipole around l ~ 5000. Furthermore, this cross-correlation probes the three-point coupling between the underlying dark matter and the momentum of the ionized baryons in the densest regions of the universe at intermediate redshifts. Similar to the thermal Sunyaev-Zel'dovich (tSZ) power spectrum, its strength is extremely sensitive to the power spectrum normalization parameter, σ8, scaling roughly as σ. It provides an effective mechanism to isolate any component of anisotropy due to patchy reionization and rule out primordial small-scale anisotropy.

Cosmic Microwave Background as a Gravity Probe

We show that cosmic microwave background (CMB) observations have a strong potentiality not only as a test of cosmic kinematics but also as a gravity probe. We compare the recent high-resolution CMB data to models with a direct coupling of dark energy to dark matter. This extra interaction violates the equivalence principle, acts as an additional scalar gravity on dark matter fluctuations, and imprints a characteristic signature on the CMB spectra. Defining the ratio β of the dark energy interaction to gravity, we that β < 0.16 (95% confidence level [c.l.]) from the current CMB data set, regardless of the potential. This implies that the effective equation of state between equivalence and tracking has been close to the pure matter equation of state within 1% and that scalar gravity is at least 40 times weaker than tensor gravity. Furthermore, we show that an ideal CMB experiment limited by cosmic variance only can put an upper bound β < 0.05 (95% c.l.), comparable to the best limits provided by local gravity experiments on the coupling to baryons.

A radio catalog of Galactic HII regions for applications from decimeter to millimeter wavelengths

By collecting the information from 24 previously published lists and catalogs, we produce a comprehensive catalog (Master Catalog) of 1442 Galactic HII regions. For each object, we quote the original fluxes and diameters as well as the available information on radio line velocities, line widths and line temperatures and the errors on these quantitities. References to the original works are also reported. By exploiting all these data we produce a Synthetic Catalog of fluxes and diameters (with corresponding errors) at 2.7 GHz. This choice is motivated by the extensive, although not complete, information available at this frequency, widely spread among many different catalogs, and by its relevance for both detailed studies on Galactic HII regions and the extrapolation up to millimetric wavelengths. The catalog can be used for detailed studies of Galactic HII regions and, by extrapolation, for investigations of HII regions up to millimetric wavelengths. In particular, we discuss the study of the effects of microwave emission from HII regions on the new generation of Cosmic Microwave Background (CMB) experiments. We present simulations of the detection of HII regions in the Planck high resolution CMB survey, and briefly analize some of the typical applications of our catalog to the evaluation of CMB anisotropy experiments such as calibration, beam reconstruction and straylight effects. The Master Catalog and the Synthetic Catalog are available via ftp at: cdsarc.u-strasbg.fr. This work is related to Planck-LFI activities.

Small angular scale CMB anisotropies from CBI and BIMA experiments: Early universe or local structures?

The advent of high-resolution cosmic microwave background (CMB) experiments now allows studies on the temperature fluctuations at scales corresponding to a few arcminutes and below. Though the reported excess power at $l\ensuremath{\sim}2000\ensuremath{-}6000$ by CBI and BIMA is roughly consistent with a secondary contribution resulting from the Sunyaev-Zeldovich effect, this requires a higher normalization for the matter power spectrum than measured by other means. In addition to a local redshift contribution, another strong possibility for anisotropies at very small scales involves nonstandard aspects of inflationary models. To distinguish between contributions from early universe and local structures, including a potential point source contribution, and to understand the extent to which structures at low redshifts contribute to small-scale temperature anisotropies, it may be necessary to perform a combined study involving CMB and the large-scale structure. We suggest a cross correlation of the temperature data with a map of the large-scale structure, such as the galaxy distribution. For next generation small angular scale CMB experiments, multifrequency observations may be a necessary aspect to allow an additional possibility to distinguish between these different scenarios.

All-sky astrophysical component separation with Fast Independent Component Analysis (FASTICA)

We present a new, fast, algorithm for the separation of astrophysical components superposed in maps of the sky. The algorithm, based on the Independent Component Analysis (ICA) technique, is aimed at recovering both the spatial pattern and the frequency scalings of the emissions from statistically independent astrophysical processes, present along the line-of-sight, from multi-frequency observations, without any a priori assumption on properties of the components to be separated, except that all of them, except possibly one, must have non-Gaussian distributions. The analysis starts from very simple toy-models of the sky emission in order to assess the quality of the reconstruction when inputs are well known and controlled. In particular, we study the dependence of the results of separation conducted on and off the Galactic plane independently, showing that optimal separation is achieved for sky regions where components are smoothly distributed. Then we consider simulated observations of the microwave sky with angular resolution and instrumental noise, supposed to be white and stationary, at the mean nominal levels for the Planck satellite. The angular response function is assumed to be identical at each frequency since this is, up to now, one of the Fast Independent Component Analysis (FastICA) limitations. We consider several Planck observation channels containing the most important known diffuse signals: the cosmic microwave background (CMB), Galactic synchrotron, dust and free–free emissions. A method for calibrating the reconstructed maps of each component at each frequency has been devised. The spatial patterns of all the components have been recovered on all scales probed by the instrument. In particular, the CMB angular power spectra is recovered at the per cent level up to ℓmax≃2000. Frequency scalings and normalization have been recovered with better than 1 per cent precision for all the components at frequencies and in sky regions where their signal-to-noise ratio ≳1.5; the error increases at ∼10 per cent level for signal-to-noise ratios ≃1. Runs have been performed on a Pentium III 600-MHz computer; although the computing time slightly depends on the number of channels and components to be recovered, FastICA typically took about 10 min for all-sky simulations with 3.5-arcmin pixel size. Although the quoted results have been obtained under a number of simplifying assumptions, we conclude that FastICA is an extremely promising technique for analysing the maps that will be obtained by the forthcoming high-resolution CMB experiments.

Peculiar velocity effects in high-resolution microwave background experiments

We investigate the impact of peculiar velocity effects due to the motion of the solar system relative to the cosmic microwave background (CMB) on high resolution CMB experiments. It is well known that on the largest angular scales the combined effects of Doppler shifts and aberration are important; the lowest Legendre multipoles of total intensity receive power from the large CMB monopole in transforming from the CMB frame. On small angular scales aberration dominates and is shown here to lead to significant distortions of the total intensity and polarization multipoles in transforming from the rest frame of the CMB to the frame of the solar system. We provide convenient analytic results for the distortions as series expansions in the relative velocity of the two frames, but at the highest resolutions a numerical quadrature is required. Although many of the high resolution multipoles themselves are severely distorted by the frame transformations, we show that their statistical properties distort by only an insignificant amount. Therefore, the cosmological parameter estimation is insensitive to the transformation from the CMB frame (where theoretical predictions are calculated) to the rest frame of the experiment.

PLANCK: Systematic effects induced by periodic fluctuations of arbitrary shape

A fundamental requirement in the new generation of high resolution Cosmic Microwave Background imaging experiments is a strict control of systematic errors that must be kept at K level in the nal maps. Some of these errors are of celestial origin, while others will be generated by periodic fluctuations of the satellite environment. These environment instabilities will cause fluctuations in the measured signal output thus generating correlated eects in the reconstructed maps. In this paper we present an analytical study of the impact of periodic signal fluctuations on the measured sky maps produced by the Planck survey. In particular we show how it is possible to estimate analytically the damping factor of the peak-to-peak amplitude of the fluctuation at the instrument output after the projection in the nal maps.

Early-universe constraints on a time-varying fine structure constant

Higher-dimensional theories have the remarkable feature of predicting a time (and hence redshift) dependence of the ``fundamental'' four dimensional constants on cosmological time scales. In this paper, we update the bounds on a possible variation of the fine structure constant $\ensuremath{\alpha}$ at the time of big bang nucleosynthesis $(z\ensuremath{\sim}{10}^{10})$ and cosmic microwave background (CMB) $(z\ensuremath{\sim}{10}^{3}).$ Using the recently released high-resolution CMB anisotropy data and the latest estimates of primordial abundances of ${}^{4}\mathrm{He}$ and D, we do not find evidence for a varying \ensuremath{\alpha} at more than a one-sigma level at either epoch.

In-Flight Main Beam Reconstruction for Planck-LFI

In-flight measurements of the shape of the antenna main beam is a crucial input to the data analysis pipeline of each high resolution Cosmic Microwave Background (CMB) anisotropy experiment. We study the main beam reconstruction achievable by the PLANCK Low Frequency Instrument (LFI) through the observation of external planets. Although were strict our analysis to the 30 GHz LFI channel, the method can be easily extended to all the PLANCK frequency channels and to other CMB anisotropy experiments. We show that it is possible to fit the time ordered data from the external planets (mainly Jupiter and Saturn) to obtain an accurate, robust, simple and fast reconstruction of the main beam properties under very general conditions, almost independently of the calibration accuracy. In addition, we find that a bivariate Gaussian approximation of main beam shapes represents a significant improvement with respect to asymmetric representation. The impact of the most relevant systematic effects is also addressed. We demonstrate that by combining the recovery of the maximum signal at the planet transit with accurate in-flight calibration, it is possible to measure the intrinsic planet temperatures at millimetric wavelengths with < 1% accuracy. This work is based on PLANCK-LFI activities.

Effects of inflationary bubbles on the polarization and temperature anisotropies of the cosmic microwave background

We predict the imprint of linear bubbly perturbations on the polarization and temperature anisotropies of the cosmic microwave background (CMB). We model analytically a bubbly density perturbation at the beginning of the radiation-dominated era and we apply the linear theory of cosmological perturbations to compute its time evolution. At decoupling, it uniquely marks the CMB polarization and temperature anisotropy sky. As predicted by recent general work regarding spatially limited cosmological seeds, during evolution the perturbation propagates beyond the size of the bubble and it reaches the CMB sound horizon in the time considered. Therefore, its signal appears as a series of concentric rings, each characterized by its own amplitude and sign, on the scale of the sound horizon at decoupling (1° on the sky). Polarization and temperature rings are strictly correlated; photons coming from the centre of the bubble are not polarized, because of the spherical symmetry of the present problem. As expected for linear perturbations with size L and density contrast δ at decoupling, δTT is roughly δ(LH−1)2; the polarization is about 10 per cent of the temperature anisotropy. We predict the impact of a distribution of bubbles on the CMB polarization and temperature power spectra. Considering models containing both cold dark matter (CDM) Gaussian and bubbly non-Gaussian fluctuations, we simulate and analyse 10°×10° sky patches with angular resolution of about 3.5 arcmin. The CMB power associated with the bubbles is entirely on subdegree angular scales (200l1000), which will be explored by the forthcoming high-resolution CMB experiments with per cent precision. Depending on the parameters of the bubbly distribution, we find extra power with respect to the ordinary CDM Gaussian fluctuations; we infer simple analytical scalings of the power induced by bubbly perturbations and we constrain our parameters with the existing data.

Impact of Inhomogeneous Reionization on Cosmic Microwave Background Anisotropy

It is likely that the reionization of the Universe did not occur homogeneously. Using a model that associates ionized patches with overdense regions, we find that the resulting cosmic microwave background (CMB) anisotropy power spectrum peaks at angular scales corresponding to the extent of the ionized regions, and has a width that reflects the correlations between them. There is considerable uncertainty in the amplitude. Neglecting inhomogeneous reionization in the determination of cosmological parameters from high resolution CMB maps may cause significant systematic error.

Subdegree Cosmic Microwave Background Anisotropies from Inflationary Bubbles

It is well known that processes of first-order phase transitions may have occurred in the inflationary era. If one or more occurred well before the end of inflation, the nucleated bubbles would have been stretched to large scales and the primordial power spectrum would contain a scale-dependent non-Gaussian component provided by the remnants of the bubbles. We predict the anisotropies in the cosmic microwave background (CMB) induced by inflationary bubbles. We build a general analytic model for describing a bubbly perturbation, evolve each Fourier mode using the linear theory of perturbations from reheating until decoupling, and get the CMB anisotropies by considering the bubbly perturbation intersecting the last scattering surface. The CMB image of an inflationary bubble is a series of concentric isothermal rings of different color (sign of δT/T) on the scale of the sound horizon at decoupling (≤1° in the sky); the resulting anisotropy is therefore strongly non-Gaussian. The mean amplitude of δT/T for a bubble of size L follows the known estimates for linear perturbations, δT/T δρ/ρ(L/H-1)2. In particular, bubbles with size corresponding to the seeds of the observed large-scale voids (tens of comoving Mpc) induce an interesting pattern of CMB anisotropies on the subdegree angular scale, to be further investigated and compared with the forthcoming high-resolution CMB maps provided by the Microwave Anisotropy Probe (MAP) and the Planck experiments.

How to measure CMB power spectra without losing information

A new method for estimating the angular power spectrum ${C}_{l}$ from cosmic microwave background (CMB) maps is presented, which has the following desirable properties. (1) It is unbeatable in the sense that no other method can measure ${C}_{l}$ with smaller error bars. (2) It is quadratic, which makes the statistical properties of the measurements easy to compute and use for estimation of cosmological parameters. (3) It is computationally faster than rival high-precision methods such as the nonlinear maximum-likelihood technique, with the crucial steps scaling as ${n}^{2}$ rather than ${n}^{3}$, where $n$ is the number of map pixels. (4) It is applicable to any survey geometry whatsoever, with arbitrary regions masked out and arbitrary noise behavior. (5) It is not a ``black-box'' method, but quite simple to understand intuitively: it corresponds to a high-pass filtering and edge softening of the original map followed by a straight expansion in truncated spherical harmonics. It is argued that this method is computationally feasible even for future high-resolution CMB experiments with $n\ensuremath{\sim}{10}^{6}$--${10}^{7}$. It is shown that ${C}_{l}$ computed with this method is useful not merely for graphical presentation purposes, but also as an intermediate (and arguably necessary) step in the data analysis pipeline, reducing the data set to a more manageable size before the final step of constraining Gaussian cosmological models and parameters --- while retaining all the cosmological information that was present in the original map.