Multifrequency Cosmic Microwave Background Research Articles

A hybrid map-Cℓ component separation method for primordial CMB B-mode searches

The observation of the polarised emission from the Cosmic Microwave Background (CMB) from future ground-based and satellite-borne experiments holds the promise of indirectly detecting the elusive signal from primordial tensor fluctuations in the form of large-scale B-mode polarisation. Doing so, however, requires an accurate and robust separation of the signal from polarised Galactic foregrounds. We present a component separation method for multi-frequency CMB observations that combines some of the advantages of map-based and power-spectrum-based techniques, and which is direcly applicable to data in the presence of realistic foregrounds and instrumental noise. We demonstrate that the method is able to reduce the contamination from Galactic foregrounds below an equivalent tensor-to-scalar ratio r FG ≲ 5 × 10-4, as required for next-generation observatories, for a wide range of foreground models with varying degrees of complexity. This bias reduction is associated with a mild ∼20–30% increase in the final statistical uncertainties, and holds for large sky areas, and for experiments targeting both the reionisation and recombination bumps in the B-mode power spectrum.

The correlation of high-redshift galaxies with the thermal Sunyaev–Zel’dovich effect traces reionization

ABSTRACT We explore a potential new probe of reionization: the cross-correlation of high-redshift galaxies with maps of the thermal Sunyaev–Zel’dovich (tSZ) effect. We consider two types of high-redshift galaxies: Lyman break galaxies (LBGs) and Lyman-α emitters (LAEs). LBGs and LAEs will be detected in large numbers at high redshift (z ≈ 4–7) by ongoing and future surveys. We consider a future LBG sample from The Rubin Observatory Legacy Survey of Space and Time, and a selection of LAEs modelled after the Subaru SILVERRUSH programme, but covering a much larger sky fraction. The tSZ effect is sensitive to a line-of-sight integral of the ionized gas pressure, and is measured across large patches of sky using multifrequency cosmic microwave background (CMB) surveys. We consider forecast tSZ maps from CMB Stage 4 and more futuristic observations. Using a suite of hydrodynamical simulations, we show that LBGs and LAEs are correlated with the tSZ signal from reionization. The cross-spectra between LBGs/LAEs with tSZ maps contain information about the reionization history of the Universe, such as the distribution of bubble sizes, and could be used to directly measure the timing of reionization. The amplitude of the signal is small, however, and its detectability is hindered by low-redshift contributions to tSZ maps and by instrumental noise. If the low-redshift contribution to the observed tSZ signal is suppressed by masking of massive haloes, a combination of overlapping futuristic CMB and galaxy surveys could probe this signal.

Requirements for future CMB satellite missions: photometric and band-pass response calibration

Current and future Cosmic Microwave Background (CMB) Radiation experiments are targeting the polarized B-mode signal. The small amplitude of this signal makes a successful measurement challenging for current technologies. Therefore, very accurate studies to mitigate and control possible systematic effects are vital to achieve a successful observation. An additional challenge is coming from the presence of polarized Galactic foreground signals that contaminate the CMB signal. When they are combined, the foreground signals dominate the polarized CMB signal at almost every relevant frequency. Future experiments, like the LiteBIRD space-borne mission, aim at measuring the CMB B-mode signal with high accuracy to measure the tensor-to-scalar ratio r at the 10−3 level. We present a method to study the photometric calibration requirement needed to minimize the leakage of polarized Galactic foreground signals into CMB polarization maps for a multi-frequency CMB experiment. We applied this method to the LiteBIRD case, and we found precision requirements for the photometric calibration in the range ∼10−4–2.5×10−3 depending on the frequency band. Under the assumption that the detectors are uncorrelated, we found requirements per detector in the range ∼0.18×10−2–2.0×10−2. Finally, we relate the calibration requirements to the band-pass resolution to define constraints for a few representative band-pass responses: Δν∼0.2–2 GHz.

On the Impact of Random Residual Calibration Error on the Gibbs ILC CMB Estimates over Large Angular Scales

Abstract Residual errors in calibration coefficients corresponding to observed cosmic microwave background (CMB) maps are an important issue when estimating a pure CMB signal. These errors in the input-foreground-contaminated CMB maps, if not properly taken into account in a component separation method, may lead to bias in the cleaned CMB map and estimated CMB angular power spectrum. But the inability to exactly determine the calibration coefficients corresponding to each observed CMB map from a multifrequency CMB experiment makes it very difficult to incorporate their exact and actual values during the component separation method. Hence, the effect of any random and residual calibration error in the cleaned CMB map and its angular power spectrum of a component separation problem can only be understood by performing detailed Monte Carlo simulations. In this paper, we investigate the impact of using input-observed CMB maps with random calibration errors on the posterior density of a cleaned CMB map and theoretical CMB angular power spectrum over large angular scales of the sky following the Gibbs Internal-Linear-Combination (ILC) method. By performing detailed Monte Carlo simulations of WMAP and Planck temperature anisotropy observations, including their estimate on calibration errors, we show that the best-fit map corresponding to the posterior maximum is minimally biased in the Gibbs ILC method by a CMB normalization bias and residual foreground bias. The residual calibration-induced error in the best-fit power spectrum causes an overall 6% increase of the net error when added in quadrature with the cosmic-variance-induced error.

A new probe of axion-like particles: CMB polarization distortions due to cluster magnetic fields

We propose using the upcoming Cosmic Microwave Background (CMB) ground based experiments to detect the signal of ALPs (Axion like particles) interacting with magnetic fields in galaxy clusters. The conversion between CMB photons and ALPs in the presence of the cluster magnetic field can cause a polarized spectral distortion in the CMB around a galaxy cluster. The strength of the signal depends upon the redshift of the galaxy cluster and will exhibit a distinctive spatial profile around it depending upon the structure of electron density and magnetic field. This distortion produces a different shape from the other known spectral distortions like y-type and μ-type and hence are separable from the multi-frequency CMB observation. The spectrum is close to Kinematic Sunyaev-Zeldovich (kSZ) signal but can be separated from it using the polarization information. For the future ground-based CMB experiments such as Simons Observatory and CMB-S4, we estimate the measurability of this signal in the presence of foreground contamination, instrument noise and CMB anisotropies. This new avenue can probe the photon-ALP coupling over the ALP mass range from 10−13 eV to 10−12 eV with two orders of magnitude better accuracy from CMB-S4 than the current existing bounds.

Forecasting performance of CMB experiments in the presence of complex foreground contaminations

We present a new, semi-analytic framework for estimating the level of residuals present in CMB maps derived from multi-frequency Cosmic Microwave Background (CMB) data and forecasting their impact on cosmological parameters. The data are assumed to contain non-negligible signals of astrophysical and/or Galactic origin, which we clean using parametric component separation technique. We account for discrepancies between the foreground model assumed during the separation procedure and the true one, allowing for differences in scaling laws and/or their spatial variations. Our estimates and their uncertainties include both systematic and statistical effects and are averaged over the instrumental noise and CMB signal realizations. The framework can be further extended to account self-consistently for existing uncertainties in the foreground models. We demonstrate and validate the framework on simple study cases which aim at estimating the tensor-to-scalar ratio, r. The proposed approach is computationally efficient permitting an investigation of hundreds of set-ups and foreground models on a single CPU.

Kinematic Sunyaev-Zel'dovich Effect with Projected Fields: A Novel Probe of the Baryon Distribution with Planck, WMAP, and WISE Data.

The kinematic Sunyaev-Zel'dovich (KSZ) effect-the Doppler boosting of cosmic microwave background (CMB) photons due to Compton scattering off free electrons with nonzero bulk velocity-probes the abundance and the distribution of baryons in the Universe. All KSZ measurements to date have explicitly required spectroscopic redshifts. Here, we implement a novel estimator for the KSZ-large-scale structure cross-correlation based on projected fields: it does not require redshift estimates for individual objects, allowing KSZ measurements from large-scale imaging surveys. We apply this estimator to cleaned CMB temperature maps constructed from Planck and WMAP data and a galaxy sample from the Wide-field Infrared Survey Explorer (WISE). We measure the KSZ effect at 3.8σ-4.5σ significance, depending on the use of additional WISE galaxy bias constraints. We verify that our measurements are robust to possible dust emission from the WISE galaxies. Assuming the standard Λ cold dark matter cosmology, we directly constrain (f_{b}/0.158)(f_{free}/1.0)=1.48±0.19 (statistical error only) at redshift z≈0.4, where f_{b} is the fraction of matter in baryonic form and f_{free} is the free electron fraction. This is the tightest KSZ-derived constraint reported to date on these parameters. Astronomers have long known that baryons do not trace dark matter on ∼ kiloparsec scales and there has been strong evidence that galaxies are baryon poor. The consistency between the f_{b} value found here and the values inferred from analyses of the primordial CMB and big bang nucleosynthesis verifies that baryons approximately trace the dark matter distribution down to ∼ megaparsec scales. While our projected-field estimator is already competitive with other KSZ approaches when applied to current data sets (because we are able to use the full-sky WISE photometric survey), it will yield enormous signal-to-noise ratios when applied to upcoming high-resolution, multifrequency CMB surveys.

Linearized iterative least-squares (LIL): a parameter-fitting algorithm for component separation in multifrequency cosmic microwave background experiments such asPlanck

We present an efficient algorithm for the least squares parameter fitting optimized for component separation in multi-frequency CMB experiments. We sidestep some of the problems associated with non-linear optimization by taking advantage of the quasi-linear nature of the foreground model. We demonstrate our algorithm, linearized iterative least-squares (LIL), on the publicly available Planck sky model FFP6 simulations and compare our result with the other algorithms. We work at full Planck resolution and show that degrading the resolution of all channels to that of the lowest frequency channel is not necessary. Finally we present results for the publicly available Planck data. Our algorithm is extremely fast, fitting 6 parameters to 7 lowest Planck channels at full resolution (50 million pixels) in less than 160 CPU-minutes (or few minutes running in parallel on few tens of cores). LIL is therefore easily scalable to future experiments which may have even higher resolution and more frequency channels. We also naturally propagate the uncertainties in different parameters due to noise in the maps as well as degeneracies between the parameters to the final errors on the parameters using Fisher matrix. One indirect application of LIL could be a front-end for Bayesian parameter fitting to find the maximum of the likelihood to be used as the starting point for the Gibbs sampling. We show for rare components, such as the carbon-monoxide emission, present in small fraction of sky, the optimal approach should combine parameter fitting with model selection. LIL may also be useful in other astrophysical applications which satisfy the quasi-linearity criteria.

Searching for primordial magnetism with multifrequency cosmic microwave background experiments

Bounds on the amplitude of a scale-invariant stochastic primordial magnetic field (PMF) can be significantly improved by measurements of the Faraday rotation (FR) of cosmic microwave background polarization. The mode-coupling correlations induced by FR make it possible to extract it from cross-correlations of the B-mode polarization with the E-mode and the temperature anisotropy. In this paper, we construct an estimator of the rotation measure that appropriately combines measurements of the FR from multiple frequency channels. We study the dependence of the signal-to-noise ratio in the PMF detection on the resolution and the noise of the detectors, as well as the removal of the weak lensing contribution and the Galactic FR. We show that a recently proposed space-based experiment Polarized Radiation Imaging and Spectroscopy Mission can detect magnetic fields of 0.1 nG strength at a 2σ level. Higher detection levels can be achieved by reducing the detector noise and improving the resolution or increasing the number of channels in the 30–70 GHz frequency range.

An optimal and model-independent measurement of the intracluster pressure profile – I. Methodology and first applications

We present a statistically-optimal and model-independent method to extract the pressure profile of hot gas in the intracluster medium (ICM). Using the thermal Sunyaev-Zeldovich effect, we constrain the mean pressure profile of the ICM by appropriately considering all primary cosmic microwave background (CMB) and instrumental noise correlations, while using the maximum resolution and sensitivity of all frequency channels. As a first application, we analyze CMB maps of WMAP 9-year data through a study of the Meta-Catalogue of X-ray detected Clusters of galaxies (MCXC). We constrain the universal pressure profile out to 4R_500 with 15-sigma confidence, though our measurements are only significant out to R_200. Using a temperature profile constrained from X-ray observations, we measure the mean gas mass fraction out to R_200. Within statistical and systematic uncertainties, our constraints are compatible with the cosmic baryon fraction and the expected gas fraction in halos. While Planck multi-frequency CMB data are expected to reduce statistical uncertainties by a factor of 20, we argue that systematic errors in determining mass of clusters dominate the uncertainty in gas mass fraction measurements at the level of 20 percent.

SUBDEGREE SUNYAEV-ZEL'DOVICH SIGNAL FROM MULTIFREQUENCY BOOMERANG OBSERVATIONS

The Sunyaev-Zel'dovich (SZ) effect is the inverse Compton-scattering of cosmic microwave background (CMB) photons by hot electrons in the intervening gas throughout the universe. The effect has a distinct spectral signature that allows its separation from other signals in multifrequency CMB data sets. Using CMB anisotropies measured at three frequencies by the BOOMERANG 2003 flight we constrain SZ fluctuations in the 10 arcmin to 1 deg angular range. Propagating errors and potential systematic effects through simulations, we obtain an overall upper limit of 15.3 μK (2σ) for rms SZ fluctuations in a broad bin between multipoles of 250 and 1200 at the Rayleigh-Jeans (RJ) end of the spectrum. The resulting upper limit on the local universe normalization of the density perturbations with BOOMERANG SZ data alone is σSZ 8 < 1.14 at the 95% confidence level. When combined with other CMB anisotropy and SZ measurements, we find σSZ 8 < 0.92 (95% c.l.).

Tomography of the Reionization Epoch with Multifrequency CMB Observations

We study the constraints that future multifrequency cosmic microwave background (CMB) experiments will be able to set on the metal enrichment history of the intergalactic medium at the epoch of reionization. We forecast the signal-to-noise ratio for the detection of the signal introduced into the CMB by resonant scattering off metals at the end of the cosmic dark ages. We take into account systematics associated with cross-channel calibration, errors in reconstruction of the point-spread function, and inaccurate foreground removal. We develop an algorithm to optimally extract the signal generated by metals during reionization and to accurately remove the contamination due to the thermal Sunyaev-Zel'dovich effect. Although demanding levels of foreground characterization and control of systematics are required, they are very distinct from those encountered in H I 21 cm studies and CMB polarization, and this fact encourages the study of resonant scattering off metals as an alternative way of conducting tomography of the reionization epoch. A realistic experiment, looking at clean regions of the sky, can detect changes of 3%-12% (95% confidence level) in the O III abundance (with respect to its solar value) in the redshift range z = 12-22 for reionization redshift zre > 10. However, for zre < 10 one can only set upper limits on N II abundance increments of ~60% solar in the redshift range z = 5.5-9 (95% c.l.). These constraints assume that cross-channel calibration is accurate to 1 part in 104, which constitutes the most critical technical requirement of this method but is still achievable with current technology.

All-sky component separation in the presence of anisotropic noise and dust temperature variations

We present an extension of the harmonic-space maximum-entropy component separation method (MEM) for multifrequency cosmic microwave background observations that allows one to perform the separation with more plausible assumptions about the receiver noise and foreground astrophysical components. Component separation is considered in the presence of spatially varying noise variance and spectral properties of the foreground components. It is shown that, if not taken properly into account, the presence of spatially varying foreground spectra, in particular, can severely reduce the accuracy of the component separation. Nevertheless, by extending the basic method to accommodate such behaviour and the presence of anisotropic noise, we find that the accuracy of the component separation can be improved to a level comparable with previous investigations in which these effects were not present.

Distances and Cosmology from Galaxy Cluster Cosmic Microwave Background Data

The measurement of the angular diameter distance to galaxy clusters, through combined Sunyaev-Zel'dovich (SZ) effect data with X-ray emission observations, is now a well-known probe of cosmology. Using a combination of SZ data and a map of the lensed cosmic microwave background (CMB) anisotropies by the galaxy cluster potential, we propose an alternative geometric technique to measure distance information primarily through cluster-related multifrequency CMB measurements. We discuss the necessary requirements to implement this measurement, potential errors including systematic biases, and the extent to which cosmological parameters can be extracted. While individual cluster distances are not likely to be precise, with upcoming subarcminute-resolution wide-area CMB observations, useful information on cosmology, such as on the dark energy equation of state, can be obtained from a large sample of galaxy clusters. Alternatively, the proposed study provides a much needed method to calibrate and to understand evolutionary effects and systematics internally within cluster catalogs from wide-field blind SZ surveys.

Non-Gaussian aspects of thermal and kinetic Sunyaev-Zel’dovich effects

We discuss non-Gaussian effects associated with the local large-scale structure contributions to the cosmic microwave background (CMB) anisotropies through the thermal Sunyaev-Zel'dovich (SZ) effect. The non-Gaussianities associated with the SZ effect arise from the existence of a significant four-point correlation function in large scale pressure fluctuations. Using the pressure trispectrum calculated under the recently popular halo model, we discuss the full covariance of the SZ thermal power spectrum. We use this full covariance matrix to study the astrophysical uses of the SZ effect and discuss the extent to which gas properties can be derived from a measurement of the SZ power spectrum. With the SZ thermal effect separated in temperature fluctuations using its frequency information, the kinetic SZ effect, also known as the Ostriker-Vishniac effect, is expected to dominate the CMB temperature fluctuations at small angular scales. This effect arises from the baryon modulation of the first order Doppler effect resulting from the relative motion of scatterers. The presence of the SZ kinetic effect can be determined through a cross-correlation between the SZ thermal and a CMB map at small scales. Since the SZ kinetic effect is second order, however, contributions to such a cross-correlation arise to lower order in the form of a three-point correlation function, or a bispectrum in Fourier space. We suggest an additional statistic that can be used to study the correlation between pressure traced by the SZ thermal effect and the baryons traced by the SZ kinetic effect involving the cross-power spectrum constructed through squared temperatures instead of the usual temperature itself. Through a signal-to-noise calculation, we show that future small angular scale multifrequency CMB experiments, sensitive to multipoles of a few thousand, will be able to measure the cross-correlation of SZ thermal and SZ kinetic effects through a temperature squared power spectrum.

Large‐Scale Sunyaev‐Zeldovich Effect: Measuring Statistical Properties with Multifrequency Maps

We study the prospects for extracting detailed statistical properties of the Sunyaev-Zeldovich (SZ) eUect associated with large-scale structure using upcoming multifrequency cosmic microwave background (CMB) experiments. The greatest obstacle to detecting the large-angle signal is the confusion noise pro- vided by the primary anisotropies themselves, and to a lesser degree Galactic and extragalactic fore- grounds. We employ multifrequency subtraction techniques and the latest foregrounds models to determine the detection threshold for the Boomerang, Microwave Anisotropy Probe (MAP; several kK), and Planck CMB (sub-kK) experiments. Calibrating a simpli—ed biased-tracer model of the gas pressure from 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 eUect 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 eUect in the CMB. Detection of these eUects will help determine the properties of the as yet undetected gas, including the manner in which the gas pressure traces the dark matter. Subject headings: cosmic microwave backgroundcosmology: theory ¨ large-scale structure of universe

A method for subtracting foregrounds from multifrequency CMB sky maps

An improved method for subtracting contaminants from cosmic microwave background (CMB) sky maps is presented, and used to estimate how well future experiments will be able to recover the primordial CMB fluctuations. We find that the naive method of subtracting foregrounds (such as dust emission, synchrotron radiation, free-free emission, unresolved point sources, etc.) on a pixel-by-pixel basis can be improved by more than an order of magnitude by taking advantage of the correlation of the emission in neighbouring pixels. The optimal multifrequency subtraction method improves on simple pixel-by-pixel subtraction, both by taking noise levels into account and by exploiting the fact that most contaminants have angular power spectra that differ substantially from that of the CMB. The results arenatural to visualize in the two-dimensional plane with axes defined by multipole ℓ and frequency v. We present a brief overview of the geography of this plane, showing the regions probed by various experiments and where we expect contaminants to dominate. We illustrate the method by estimating how well the proposed ESA COBRAS/SAMBA mission will be able to recover the CMB fluctuations against contaminating foregrounds.