μK Arcmin Research Articles

Constraints on the Optical Depth to Reionization from Balloon-borne Cosmic Microwave Background Measurements

We assess the uncertainty with which a balloon-borne experiment, nominally called Tau Surveyor (τS), can measure the optical depth to reionization σ(τ) with given realistic constraints of instrument noise and foreground emissions. Using a τS fiducial design with six frequency bands between 150 and 380 GHz, with white and uniform map noise of 7 μK arcmin, achievable with a single midlatitude flight, and including Planck's 30 and 44 GHz data, we assess the error σ(τ) obtained with three foreground models and as a function of sky fraction f sky between 40% and 54%. We carry out the analysis using both parametric and blind foreground separation techniques. We compare the σ(τ) values to those obtained with low-frequency and high-frequency versions of the experiment called τS-lf and τS-hf, which have only four and up to eight frequency bands with narrower and wider frequency coverage, respectively. We find that with τS, the lowest constraint is σ(τ) = 0.0034, obtained for one of the foreground models with f sky = 54%. σ(τ) is larger, in some cases by more than a factor of 2, for smaller sky fractions, with τS-lf, or as a function of foreground model. The τS-hf configuration does not lead to significantly tighter constraints. The exclusion of the 30 and 44 GHz data, which give information about synchrotron emission, leads to significant τ misestimates. Decreasing noise by an ambitious factor of 10, while keeping f sky = 40%, gives σ(τ) = 0.0031. The combination of σ(τ) = 0.0034, baryon acoustic oscillation data from DESI, and future cosmic microwave background B-mode lensing data from the CMB-S3/CMB-S4 experiments could give σ(∑m ν ) = 17 meV.

Bicep/Keck XV: The Bicep3 Cosmic Microwave Background Polarimeter and the First Three-year Data Set

Abstract We report on the design and performance of the Bicep3 instrument and its first three-year data set collected from 2016 to 2018. Bicep3 is a 52 cm aperture refracting telescope designed to observe the polarization of the cosmic microwave background (CMB) on degree angular scales at 95 GHz. It started science observation at the South Pole in 2016 with 2400 antenna-coupled transition-edge sensor bolometers. The receiver first demonstrated new technologies such as large-diameter alumina optics, Zotefoam infrared filters, and flux-activated SQUIDs, allowing ∼10× higher optical throughput compared to the Keck design. Bicep3 achieved instrument noise equivalent temperatures of 9.2, 6.8, and 7.1 μ K CMB s and reached Stokes Q and U map depths of 5.9, 4.4, and 4.4 μK arcmin in 2016, 2017, and 2018, respectively. The combined three-year data set achieved a polarization map depth of 2.8 μK arcmin over an effective area of 585 square degrees, which is the deepest CMB polarization map made to date at 95 GHz.

Optimal Cosmic Microwave Background Lensing Reconstruction and Parameter Estimation with SPTpol Data

Abstract We perform the first simultaneous Bayesian parameter inference and optimal reconstruction of the gravitational lensing of the cosmic microwave background (CMB), using 100 deg2 of polarization observations from the SPTpol receiver on the South Pole Telescope. These data reach noise levels as low as 5.8 μK arcmin in polarization, which are low enough that the typically used quadratic estimator (QE) technique for analyzing CMB lensing is significantly suboptimal. Conversely, the Bayesian procedure extracts all lensing information from the data and is optimal at any noise level. We infer the amplitude of the gravitational lensing potential to be A ϕ = 0.949 ± 0.122 using the Bayesian pipeline, consistent with our QE pipeline result, but with 17% smaller error bars. The Bayesian analysis also provides a simple way to account for systematic uncertainties, performing a similar job as frequentist “bias hardening” or linear bias correction, and reducing the systematic uncertainty on A ϕ due to polarization calibration from almost half of the statistical error to effectively zero. Finally, we jointly constrain A ϕ along with A L, the amplitude of lensing-like effects on the CMB power spectra, demonstrating that the Bayesian method can be used to easily infer parameters both from an optimal lensing reconstruction and from the delensed CMB, while exactly accounting for the correlation between the two. These results demonstrate the feasibility of the Bayesian approach on real data, and pave the way for future analysis of deep CMB polarization measurements with SPT-3G, Simons Observatory, and CMB-S4, where improvements relative to the QE can reach 1.5 times tighter constraints on A ϕ and seven times lower effective lensing reconstruction noise.

A Measurement of the Degree-scale CMB B-mode Angular Power Spectrum with Polarbear

Abstract We present a measurement of the B-mode polarization power spectrum of the cosmic microwave background (CMB) using data taken from 2014 July to 2016 December with the Polarbear experiment. The CMB power spectra are measured using observations at 150 GHz with an instantaneous array sensitivity of on a 670 square degree patch of sky centered at (R.A., decl.) = (+0h12m0s, −59°18′). A continuously rotating half-wave plate is used to modulate polarization and to suppress low-frequency noise. We achieve 32 μK arcmin effective polarization map noise with a knee in sensitivity of ℓ = 90, where the inflationary gravitational-wave signal is expected to peak. The measured B-mode power spectrum is consistent with a ΛCDM lensing and single dust component foreground model over a range of multipoles 50 ≤ ℓ ≤ 600. The data disfavor zero at 2.2σ using this ℓ range of Polarbear data alone. We cross-correlate our data with Planck full mission 143, 217, and 353 GHz frequency maps and find the low-ℓ B-mode power in the combined data set to be consistent with thermal dust emission. We place an upper limit on the tensor-to-scalar ratio r < 0.90 at the 95% confidence level after marginalizing over foregrounds.

Beyond Optical Depth: Future Determination of Ionization History from the Cosmic Microwave Background.

We explore the fundamental limits to which reionization histories can be constrained using only large-scale cosmic microwave background (CMB) anisotropy measurements. The redshift distribution of the fractional ionization x e (z) affects the angular distribution of CMB polarization. We project constraints on the reionization history of the universe using low-noise full-sky temperature and E-mode measurements of the CMB. We show that the measured TE power spectrum, , has roughly one quarter of the constraining power of on the reionization optical depth τ, and its addition improves the precision on τ by 20% over using only. We also use a two-step reionization model with an additional high-redshift step, parameterized by an early ionization fraction , and a late reionization step at z re. We find that future high signal-to-noise measurements of the multipoles 10 ⩽ ℓ < 20 are especially important for breaking the degeneracy between and z re. In addition, we show that the uncertainties on these parameters determined from a map with sensitivity 10 μK arcmin are less than 5% larger than the uncertainties in the noiseless case, making this noise level a natural target for future large sky area E-mode measurements.

Impact of post-Born lensing on the CMB

Lensing of the CMB is affected by post-Born lensing, producing corrections to the convergence power spectrum and introducing field rotation. We show numerically that the lensing convergence power spectrum is affected at the ≲ 0.2% level on accessible scales, and that this correction and the field rotation are negligible for observations with arcminute beam and noise levels ≳ 1 μK arcmin. The field rotation generates ∼ 2.5% of the total lensing B-mode polarization amplitude (0.2% in power on small scales), but has a blue spectrum on large scales, making it highly subdominant to the convergence B modes on scales where they are a source of confusion for the signal from primordial gravitational waves. Since the post-Born signal is non-linear, it also generates a bispectrum with the convergence. We show that the post-Born contributions to the bispectrum substantially change the shape predicted from large-scale structure non-linearities alone, and hence must be included to estimate the expected total signal and impact of bispectrum biases on CMB lensing reconstruction quadratic estimators and other observables. The field-rotation power spectrum only becomes potentially detectable for noise levels ≪ 1 μK arcmin, but its bispectrum with the convergence may be observable at ∼ 3σ with Stage IV observations. Rotation-induced and convergence-induced B modes are slightly correlated by the bispectrum, and the bispectrum also produces additional contributions to the lensed BB power spectrum.

PROSPECTS FOR DELENSING THE COSMIC MICROWAVE BACKGROUND FOR STUDYING INFLATION

A detection of excess cosmic microwave background (CMB) B-mode polarization on large scales allows the possibility of measuring not only the amplitude of these fluctuations but also their scale dependence, which can be parametrized as the tensor tilt nT. Measurements of this scale dependence will be hindered by the secondary B-mode polarization anisotropy induced by gravitational lensing. Fortunately, these contaminating B modes can be estimated and removed with a sufficiently good estimate of the intervening gravitational potential and a good map of CMB E-mode polarization. We present forecasts for how well these gravitational lensing B modes can be removed, assuming that the lensing potential can be estimated either internally from CMB data or using maps of the cosmic infrared background (CIB) as a tracer. We find that CIB maps are as effective as CMB maps for delensing at the noise levels of the current generation of CMB experiments, while the CMB maps themselves will ultimately be best for delensing at polarization noise below = 1 μK arcmin. At this sensitivity level, CMB delensing will be able to measure nT to an accuracy of 0.02 or better, which corresponds to the tensor tilt predicted by the consistency relation for single-field slow-roll models of inflation with r = 0.2. However, CIB-based delensing will not be sufficient for constraining nT in simple inflationary models.

The local B-polarization of the CMB: A very sensitive probe of cosmic defects

We present a new and especially powerful signature of cosmic strings and other topological or non-topological defects in the polarization of the cosmic microwave background (CMB). We show that even if defects contribute 1% or less in the CMB temperature anisotropy spectrum, their signature in the local B˜-polarization correlation function at angular scales of tens of arc-minutes is much larger than that due to gravitational waves from inflation, even if the latter contribute with a ratio as big as r≃0.1 to the temperature anisotropies. We show that when going from non-local to local B˜-polarization, the ratio of the defect signal-to-noise with respect to the inflationary value increases by about an order of magnitude. Proposed B-polarization experiments, with a good sensitivity on arc-minute scales, may either detect a contribution from topological defects produced after inflation or place stringent limits on them. Already Planck should be able to improve present constraints on defect models by about an order of magnitude, to the level of ϵ=Gv2<10−7. A future full-sky experiment like CMBpol, with polarization sensitivities of the order of 1 μK arcmin, will be able to constrain the defect parameter ϵ to less than a few×10−9, depending on the defect model.

Mapping the Dark Matter through the Cosmic Microwave Background Damping Tail

The lensing of cosmic microwave background (CMB) photons by intervening large-scale structure leaves a characteristic imprint on its arcminute-scale anisotropy that can be used to map the dark matter distribution in projection on degree scales or ~100 h-1 Mpc comoving. We introduce a new algorithm for mass reconstruction that optimally utilizes information from the weak lensing of CMB anisotropies in the damping tail. Individual degree-scale mass structures can be recovered with a high signal-to-noise ratio from a foreground-free CMB map of arcminute-scale resolution, specifically with an FWHM beam less than 5' and a noise level less than 15 (10-6 arcmin) or 41 (μK arcmin).