Angular Scale Cosmic Microwave Background Research Articles

Cosmology Large Angular Scale Surveyor (CLASS): 90 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background (CMB) over ∼75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the large angular scale CMB polarization to constrain the tensor-to-scalar ratio and the optical depth to last scattering. This paper presents the optical characterization of the 90 GHz telescope. Observations of the Moon establish the pointing while dedicated observations of Jupiter are used for beam calibration. The standard deviations of the pointing error in azimuth, elevation, and boresight angle are 1.′3, 2.′1, and 2.′0, respectively, over the first 3 yr of observations. This corresponds to a pointing uncertainty ∼7% of the beam’s full width at half-maximum (FWHM). The effective azimuthally symmetrized instrument 1D beam estimated at 90 GHz has an FWHM of 0.°620 ± 0.°003 and a solid angle of 138.7 ± 0.6(stats.) ± 1.1(sys.) μsr integrated to a radius of 4°. The corresponding beam window function drops to bℓ2=0.93,0.71,0.14 at ℓ = 30, 100, 300, respectively. Far-sidelobes are studied using detector-centered intensity maps of the Moon and measured to be at a level of 10−3 or below relative to the peak. The polarization angle of Tau A estimated from preliminary survey maps is 149°.6 ± 0°.2(stats.) in equatorial coordinates. The instrumental temperature-to-polarization (T → P) leakage fraction, inferred from per-detector demodulated Jupiter scan data, has a monopole component at the level of 1.7 × 10−3, a dipole component with an amplitude of 4.3 × 10−3, with no evidence of quadrupolar leakage.

QUBIC VI: Cryogenic half wave plate rotator, design and performance

Setting an upper limit or detection of B-mode polarization imprinted by gravitational waves from Inflation is one goal of modern large angular scale cosmic microwave background (CMB) experiments around the world. A great effort is being made in the deployment of many ground-based, balloon-borne and satellite experiments, using different methods to separate this faint polarized component from the incoming radiation. QUBIC exploits one of the most widely-used techniques to extract the input Stokes parameters, consisting in a rotating half-wave plate (HWP) and a linear polarizer to separate and modulate polarization components. QUBIC uses a step-by-step rotating HWP, with 15° steps, combined with a 0.4°s-1 azimuth sky scan speed. The rotation is driven by a stepper motor mounted on the cryostat outer shell to avoid heat load at internal cryogenic stages. The design of this optical element is an engineering challenge due to its large 370 mm diameter and the 8 K operation temperature that are unique features of the QUBIC experiment. We present the design for a modulator mechanism for up to 370 mm, and the first optical tests by using the prototype of QUBIC HWP (180 mm diameter). The tests and results presented in this work show that the QUBIC HWP rotator can achieve a precision of 0.15° in position by using the stepper motor and custom-made optical encoder. The rotation induces <5.0 mW (95% C.L) of power load on the 4 K stage, resulting in no thermal issues on this stage during measurements. We measure a temperature settle-down characteristic time of 28 s after a rotation through a 15° step, compatible with the scanning strategy, and we estimate a maximum temperature gradient within the HWP of ≤ 10 mK. This was calculated by setting up finite element thermal simulations that include the temperature profiles measured during the rotator operations. We report polarization modulation measurements performed at 150 GHz, showing a polarization efficiency >99% (68% C.L.) and a median cross-polarization χPol of 0.12%, with 71% of detectors showing a χPol + 2σ upper limit <1%, measured using selected detectors that had the best signal-to-noise ratio.

Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: 40 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

Abstract The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background (CMB) over 75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the large angular scale (1° ≲ θ 90°) CMB polarization to constrain the tensor-to-scalar ratio at the r ∼ 0.01 level and the optical depth to last scattering to the sample variance limit. This paper presents the optical characterization of the 40 GHz telescope during its first observation era, from 2016 September to 2018 February. High signal-to-noise observations of the Moon establish the pointing and beam calibration. The telescope boresight pointing variation is &lt;0.°023 (&lt;1.6% of the beam’s full width at half maximum (FWHM)). We estimate beam parameters per detector and in aggregate, as in the CMB survey maps. The aggregate beam has an FWHM of 1.°579 ± 0.°001 and a solid angle of 838 ± 6 μsr, consistent with physical optics simulations. The corresponding beam window function has a sub-percent error per multipole at ℓ &lt; 200. An extended 90° beam map reveals no significant far sidelobes. The observed Moon polarization shows that the instrument polarization angles are consistent with the optical model and that the temperature-to-polarization leakage fraction is &lt;10−4 (95% C.L.). We find that the Moon-based results are consistent with measurements of M42, RCW 38, and Tau A from CLASS’s CMB survey data. In particular, Tau A measurements establish degree-level precision for instrument polarization angles.

Natural inflation: consistency with cosmic microwave background observations of Planck and BICEP2

Natural inflation is a good fit to all cosmic microwave background (CMB) data and may be the correct description of an early inflationary expansion of the Universe. The large angular scale CMB polarization experiment BICEP2 has announced a major discovery, which can be explained as the gravitational wave signature of inflation, at a level that matches predictions by natural inflation models. The natural inflation (NI) potential is theoretically exceptionally well motivated in that it is naturally flat due to shift symmetries, and in the simplest version takes the form V(ϕ) = Λ4 [1 ± cos(Nϕ/f)]. A tensor-to-scalar ratio r > 0.1 as seen by BICEP2 requires the height of any inflationary potential to be comparable to the scale of grand unification and the width to be comparable to the Planck scale. The Cosine Natural Inflation model agrees with all cosmic microwave background measurements as long as f ⩾ mPl (where mPl = 1.22 × 1019 GeV) and Λ ∼ mGUT ∼ 1016 GeV. This paper also discusses other variants of the natural inflation scenario: we show that axion monodromy with potential V∝ ϕ2/3 is inconsistent with the BICEP2 limits at the 95% confidence level, and low-scale inflation is strongly ruled out. Linear potentials V ∝ ϕ are inconsistent with the BICEP2 limit at the 95% confidence level, but are marginally consistent with a joint Planck/BICEP2 limit at 95%. We discuss the pseudo-Nambu Goldstone model proposed by Kinney and Mahanthappa as a concrete realization of low-scale inflation. While the low-scale limit of the model is inconsistent with the data, the large-field limit of the model is marginally consistent with BICEP2. All of the models considered predict negligible running of the scalar spectral index, and would be ruled out by a detection of running.

Local Voids as the Origin of Large‐Angle Cosmic Microwave Background Anomalies. I.

We explore the large angular scale temperature anisotropies in the cosmic microwave background due to expanding homogeneous local voids at redshift z ≲ 1. A compensated spherically symmetric homogeneous dust-filled void with radius ~3 × 102 h-1 Mpc and density contrast δ ~ -0.3 can be observed as a cold spot with a temperature anisotropy ΔT/T ~ -1 × 10-5 surrounded by a slightly hotter ring. We find that a pair of these circular cold spots separated by ~50° can account both for the planarity of the octopole and for the alignment between the quadrupole and the octopole in the cosmic microwave background (CMB) anisotropy. The cold spot in the Galactic southern hemisphere, which is anomalous at the ~3 σ level, can be explained by such a large void at z ~ 1. The observed north-south asymmetry in the large-angle CMB power can be attributed to the asymmetric distribution of these local voids between the two hemispheres. The statistical significance of the low quadrupole is further reduced in this interpretation of the large angular scale CMB anomalies.

Searching for integrated Sachs–Wolfe effect beyond temperature anisotropies: CMB E-modepolarization–galaxy cross-correlation

The cross-correlation between cosmic microwave background (CMB) temperatureanisotropies and the large-scale structure (LSS) traced by the galaxy distribution, orsources at different wavelengths, is now well known. This correlation results from theintegrated Sachs–Wolfe (ISW) effect in CMB anisotropies generated at late times due tothe dark energy component of the Universe. In a reionized universe, electron scattering atlow redshifts leads to a large-scale polarization contribution. In addition to theprimordial quadrupole, involving anisotropies at the last scattering surface, the ISWquadrupole rescatters and contributes to the large angular scale polarization signal.Thus, in principle, the low multipole polarization bump in the E-mode should becorrelated with the galaxy distribution. Unlike the CMB temperature–LSS correlationthat peaks for tracers at low redshifts, due to the increasing visibility function,while the fractional ISW quadrupole is decreasing, with increasing redshift, thepolarization–galaxy correlation peaks mostly at redshifts between 1 and 3. Under certainconditions, mostly involving a low optical depth to reionization if the Universereionized at a redshift around 6, the cross-polarization–source signal is marginallydetectable if all-sky maps of the large-scale structure at redshifts between 1 and 3 areavailable. If the Universe reionized at a redshift higher than 10, it is unlikely thatthis correlation will be detectable even with no instrumental noise all-sky maps.While our estimates do not guarantee a detection, unknown physics related tothe dark energy uncertain issues related to the large angular scale CMB andpolarization anisotropies, and uncertainties related to the reionization history of theUniverse may motivate attempts to measure this correlation using upcoming CMBpolarization E-mode maps and large-scale structure maps of the high-redshift universewith the Large Synoptic Survey Telescope and quasar catalogues, among others.

Cross-correlation studies with CMB polarization maps

The free-electron population during the reionized epoch rescatters the cosmic microwave background (CMB) temperature quadrupole and generates a now well-known polarization signal at large angular scales. While this contribution has been detected in the temperature-polarization cross power spectrum measured with Wilkinson Microwave Anisotropy Probe data, due to the large cosmic variance associated with anisotropy measurements at angular scales of tens of degrees only limited information related to reionization, such as the optical depth to electron scattering, can be extracted. The inhomogeneities in the free-electron population lead to an additional secondary polarization anisotropy contribution at arcminute scales. While the fluctuation amplitude, relative to dominant primordial fluctuations, is small, we suggest that a cross correlation between the arcminute scale CMB polarization data and a tracer field of the high redshift universe, such as through fluctuations captured by the 21 cm neutral hydrogen background or those in the infrared background related to the first protogalaxies, may allow one to study additional details related to reionization. For this purpose, we discuss an optimized higher order correlation measurement, in the form of a three-point function, including information from large angular scale CMB temperature anisotropies in addition to the arcminute scale polarization signal related to inhomogeneous reionization. We suggest that the proposed bispectrum can be measured with a substantial signal-to-noise ratio and does not require all-sky maps of CMB polarization or that of the tracer field. A measurement such as the one proposed may allow one to establish the epoch when CMB polarization related to reionization is generated and to address the question whether the universe was reionized once or twice.

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.

Gaussianity of Degree‐Scale Cosmic Microwave Background Anisotropy Observations

We present results from a first test of the Gaussianity of degree-scale cosmic microwave background (CMB) anisotropy. We investigate Gaussianity of the CMB anisotropy by studying the topology of CMB anisotropy maps from the QMAP and Saskatoon experiments. We also study the QMASK map, a combination map of the QMAP and Saskatoon data. We measure the genus from noise-suppressed Wiener-filtered maps at an angular scale of about 1.5 degrees. To test the Gaussianity of the observed anisotropy, we compare these results to those derived from a collection of simulated maps for each experiment in a Gaussian spatially-flat cosmological constant dominated cold dark matter model. The genus-threshold level relations of the QMAP and Saskatoon maps are consistent with Gaussianity. While the combination QMASK map has a mildly non-Gaussian genus curve which is not a consequence of known foreground contamination, this result is not statistically significant at the 2 sigma level. These results extend previous upper limits on the non-Gaussianity of the large angular scale (> 10 degrees) CMB anisotropy (measured by the COBE DMR experiment) down to degree angular scales.

Large scale pressure fluctuations and the Sunyaev-Zel’dovich effect

The Sunyaev-Zel'dovich (SZ) effect associated with pressure fluctuations of the large scale structure gas distribution will be probed with current and upcoming wide-field small angular scale cosmic microwave background experiments. We study the generation of pressure fluctuations by baryons which are present in virialized dark matter halos, with overdensities $\ensuremath{\gtrsim}200$ and by baryons present in overdensities $\ensuremath{\lesssim}10.$ For collapsed halos, assuming the gas distribution is in hydrostatic equilibrium with matter density distribution, we predict the pressure power spectrum and bispectrum associated with the large scale structure gas distribution by extending the dark matter halo approach which describes the density field in terms of correlations between and within halos. The projected pressure power spectrum allows a determination of the resulting SZ power spectrum due to virialized structures. The unshocked photoionized baryons present in smaller overdensities trace the Jeans-scale smoothed dark matter distribution. They provide a lower limit to the SZ effect due to large scale structure in the absence of massive collapsed halos. We extend our calculations to discuss higher order statistics, such as bispectrum and skewness in SZ data. The SZ-weak lensing cross correlation is suggested as a probe of correlations between dark matter and baryon density fields, while the probability distribution functions of peak statistics of SZ halos in wide field CMB data can be used as a probe of cosmology and non-Gaussian evolution of large scale pressure fluctuations.

Cosmic strings in an open universe: Quantitative evolution and observational consequences

The cosmic string scenario in an open universe is developed---including the equations of motion, a model of network evolution, the large angular scale cosmic microwave background (CMB) anisotropy, and the power spectrum of density fluctuations produced by cosmic strings with dark matter. We first derive the equations of motion for a cosmic string in an open Friedmann-Robertson-Walker (FRW) space-time. With these equations and the cosmic string stress-energy conservation law, we construct a quantitative model of the evolution of the gross features of a cosmic string network in a dust-dominated, $\ensuremath{\Omega}&lt;1$ FRW space-time. Second, we apply this model of network evolution to the results of a numerical simulation of cosmic strings in a dust-dominated, $\ensuremath{\Omega}=1$ FRW space-time, in order to estimate the rms temperature anisotropy induced by cosmic strings in the CMB. By comparing to the COBE-DMR observations, we obtain the normalization for the cosmic string mass per unit length $\ensuremath{\mu}$ as a function of $\ensuremath{\Omega}$. Third, we consider the effects of the network evolution and normalization in an open universe on the large scale structure formation scenarios with either cold or hot dark matter (CDM, HDM). The string+HDM scenario for $\ensuremath{\Omega}&lt;1$ appears to produce too little power on scales $k\ensuremath{\gtrsim}1$ $\ensuremath{\Omega}{h}^{2}/$Mpc. In a low density universe the string+CDM scenario is a better model for structure formation. We find that for cosmological parameters $\ensuremath{\Gamma}=\ensuremath{\Omega}h\ensuremath{\sim}0.1$--0.2 in an open universe the string+CDM power spectrum fits the shape of the linear power spectrum inferred from various galaxy surveys. For $\ensuremath{\Omega}\ensuremath{\sim}0.2$--0.4, the model requires a bias $b\ensuremath{\gtrsim}2$ in the variance of the mass fluctuation on scales $8{h}^{\ensuremath{-}1}$ Mpc. In the presence of a cosmological constant, the spatially flat string+CDM power spectrum requires a slightly lower bias than for an open universe of the same matter density.

Large-scale cosmic microwave background anisotropies in isocurvature baryon open universe models

view Abstract Citations (29) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Large-Scale Cosmic Microwave Background Anisotropies in Isocurvature Baryon Open Universe Models Gorski, Krzysztof M. ; Silk, Joseph Abstract We calculate the large angular scale cosmic microwave background anisotropy in a low-density baryon-dominated universe with isocurvature primordial inhomogeneities. In models in which the initial power spectra of perturbations are steeper than white noise, P(k) is proportional to k^n^, n < 0, predictions for the quadrupole moment of the anisotropy are found to be in conflict with existing observational limits, if the universe remained fully ionized and Compton drag inhibited growth of inhomogeneities until z ~ 100. In order to lower the amplitude of the anisotropy, one has to substantially prolong the duration of the growth phase of density perturbations, while smearing out fine-scale anisotropies, thereby requiring reionization to occur at a redshift smaller than 100, but larger than the redshift of the last scattering surface (in a reionized model). A definitive test will require measurement of large angular scale anisotropy to a level σT/T ~ 3 x 10^-6^. Publication: The Astrophysical Journal Pub Date: November 1989 DOI: 10.1086/185564 Bibcode: 1989ApJ...346L...1G Keywords: Anisotropy; Baryons; Perturbation Theory; Relic Radiation; Compton Effect; Computational Astrophysics; Universe; White Noise; Astrophysics; COSMIC BACKGROUND RADIATION; COSMOLOGY full text sources ADS |