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1. BICEP/Keck. XVI. Characterizing Dust Polarization through Correlations with Neutral Hydrogen

   https://doi.org/10.3847/1538-4357/acb64c  

   Ade, P. A. R. ; Ahmed, Z. ; Amiri, M. ; Barkats, D. ; Thakur, R. Basu ; Bischoff, C. A. ; Beck, D. ; Bock, J. J. ; Boenish, H. ; Bullock, E. ; et al ( March 2023 , The Astrophysical Journal)

   We characterize Galactic dust filaments by correlating BICEP/Keck and Planck data with polarization templates based on neutral hydrogen (Hi) observations. Dust polarization is important for both our understanding of astrophysical processes in the interstellar medium (ISM) and the search for primordial gravitational waves in the cosmic microwave background (CMB). In the diffuse ISM, Hiis strongly correlated with the dust and partly organized into filaments that are aligned with the local magnetic field. We analyze the deep BICEP/Keck data at 95, 150, and 220 GHz, over the low-column-density region of sky where BICEP/Keck has set the best limits on primordial gravitational waves. We separate the Hiemission into distinct velocity components and detect dust polarization correlated with the local Galactic Hibut not with the Hiassociated with Magellanic Streami. We present a robust, multifrequency detection of polarized dust emission correlated with the filamentary Himorphology template down to 95 GHz. For assessing its utility for foreground cleaning, we report that the Himorphology template correlates inBmodes at a ∼10%–65% level over the multipole range 20 <ℓ< 200 with the BICEP/Keck maps, which contain contributions from dust, CMB, and noise components. We measure the spectral index of the filamentary dust component spectral energy distribution to beβ= 1.54 ± 0.13. We find no evidence for decorrelation in this region between the filaments and the rest of the dust field or from the inclusion of dust associated with the intermediate velocity Hi. Finally, we explore the morphological parameter space in the Hi-based filamentary model.

    

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2. The Latest Constraints on Inflationary B-modes from the BICEP/Keck Telescopes

   https://doi.org/10.48550/arxiv.2203.16556  

   Ade, P. A. ; Ahmed, Z. ; Amiri, M. ; Barkats, D. ; Basu Thakur, R. ; Beck, D. ; Bischoff, C. ; Bock, J. J. ; Boenish, H. ; Bullock, E. ; et al ( March 2022 , 2022 Cosmology session of the 56th Rencontres de Moriond)

   For the past decade, the BICEP/Keck collaboration has been operating a series of telescopes at the Amundsen-Scott South Pole Station measuring degree-scale B-mode polarization imprinted in the Cosmic Microwave Background (CMB) by primordial gravitational waves (PGWs). These telescopes are compact refracting polarimeters mapping about 2% of the sky, observing at a broad range of frequencies to account for the polarized foreground from Galactic synchrotron and thermal dust emission. Our latest publication "BK18" utilizes the data collected up to the 2018 observing season, in conjunction with the publicly available WMAP and Planck data, to constrain the tensor-to-scalar ratio r. It particularly includes (1) the 3-year BICEP3 data which is the current deepest CMB polarization map at the foreground-minimum 95 GHz; and (2) the Keck 220 GHz map with a higher signal-to-noise ratio on the dust foreground than the Planck 353 GHz map. We fit the auto- and cross-spectra of these maps to a multicomponent likelihood model (ΛCDM+dust+synchrotron+noise+r) and find it to be an adequate description of the data at the current noise level. The likelihood analysis yields σ(r)=0.009. The inference of r from our baseline model is tightened to r0.05=0.014+0.010−0.011 and r0.05<0.036 at 95% confidence, meaning that the BICEP/Keck B-mode data is the most powerful existing dataset for the constraint of PGWs. The up-coming BICEP Array telescope is projected to reach σ(r)≲0.003 using data up to 2027. 

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3. Full-sky, Arcminute-scale, 3D Models of Galactic Microwave Foreground Dust Emission Based on Filaments

   https://doi.org/10.3847/1538-4357/ac54b2  

   Hervías-Caimapo, Carlos ; Huffenberger, Kevin M. ( March 2022 , The Astrophysical Journal)

   We present theDustFilamentscode, a full-sky model for the millimeter Galactic emission of thermal dust. Our model, composed of millions of filaments that are imperfectly aligned with the magnetic field, is able to reproduce the main features of the dust angular power spectra at 353 GHz as measured by the Planck mission. Our model is made up of a population of filaments with sizes following a Pareto distribution$\propto L_a^{-2.445}$, with an axis ratio between short and long semiaxesϵ∼ 0.16 and an angle of magnetic field misalignment with a dispersion rms(θ_LH) = 10°. On large scales, our model follows a Planck-based template. On small scales, our model produces spectra that behave like power laws up toℓ∼ 4000 or smaller scales by considering even smaller filaments, limited only by computing power. We can produce any number of Monte Carlo realizations of small-scale Galactic dust. Our model will allow tests of how the small-scale non-Gaussianity affects CMB weak lensing and the consequences for the measurement of primordial gravitational waves or relativistic light relic species. Our model also can generate frequency decorrelation on the modified blackbody spectrum of dust and is freely adjustable to different levels of decorrelation. This can be used to test the performance of component separation methods and the impact of frequency spectrum residuals on primordialB-mode surveys. The filament density we paint in the sky is also able to reproduce the general level of non-Gaussianities measured by Minkowski functionals in the Planck 353 GHz channel map.

    

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4. Magnetic Misalignment of Interstellar Dust Filaments

   https://doi.org/10.3847/1538-4357/acb0c4  

   Cukierman, Ari J. ; Clark, S. E. ; Halal, George ( April 2023 , The Astrophysical Journal)

   We present evidence for scale-independent misalignment of interstellar dust filaments and magnetic fields. We estimate the misalignment by comparing millimeter-wave dust-polarization measurements from Planck with filamentary structures identified in neutral-hydrogen (Hi) measurements from Hi4PI. We find that the misalignment angle displays a scale independence (harmonic coherence) for features larger than the Hi4PI beamwidth (16.′2). We additionally find a spatial coherence on angular scales of$\mathit{}(1°)$. We present several misalignment estimators formed from the auto- and cross-spectra of dust-polarization and Hi-based maps, and we also introduce a map-space estimator. Applied to large regions of the high-Galactic-latitude sky, we find a global misalignment angle of ∼2°, which is robust to a variety of masking choices. By dividing the sky into small regions, we show that the misalignment angle correlates with the parity-violatingTBcross-spectrum measured in the Planck dust maps. The misalignment paradigm also predicts a dustEBsignal, which is of relevance in the search for cosmic birefringence but as yet undetected; the measurements ofEBare noisier than those ofTB, and our correlations ofEBwith misalignment angle are found to be weaker and less robust to masking choices. We also introduce an Hi-based dust-polarization template constructed from the Hessian matrix of the Hiintensity, which is found to correlate more strongly than previous templates with Planck dustBmodes.

    

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5. CLASS Angular Power Spectra and Map-component Analysis for 40 GHz Observations through 2022

   https://doi.org/10.3847/1538-4357/ad1abf  

   Eimer, Joseph R. ; Li 李, Yunyang 云炀 ; Brewer, Michael K. ; Shi 时, Rui 瑞. ; Ali, Aamir ; Appel, John W. ; Bennett, Charles L. ; Bruno, Sarah Marie ; Bustos, Ricardo ; Chuss, David T. ; et al ( March 2024 , The Astrophysical Journal)

   Measurement of the largest angular scale (ℓ< 30) features of the cosmic microwave background (CMB) polarization is a powerful way to constrain the optical depth to reionization and search for the signature of inflation through the detection of primordialB-modes. We present an analysis of maps covering 73.6% of the sky made from the 40 GHz channel of the Cosmology Large Angular Scale Surveyor (CLASS) from 2016 August to 2022 May. Taking advantage of the measurement stability enabled by front-end polarization modulation and excellent conditions from the Atacama Desert, we show this channel achieves higher sensitivity than the analogous frequencies from satellite measurements in the range 10 <ℓ< 100. Simulations show the CLASS linear (circular) polarization maps have a white noise level of$125(130)\mu \mathrm{K}\mathrm{arcmin}$. We measure the Galaxy-maskedEEandBBspectra of diffuse synchrotron radiation and compare to space-based measurements at similar frequencies. In combination with external data, we expand measurements of the spatial variations of the synchrotron spectral energy density (SED) to include new sky regions and measure the diffuse SED in the harmonic domain. We place a new upper limit on a background of circular polarization in the range 5 <ℓ< 125 with the first bin showingD_ℓ< 0.023$\mu {\mathrm{K}}_{\mathrm{CMB}}^2$at 95% confidence. These results establish a new standard for recovery of the largest-scale CMB polarization from the ground and signal exciting possibilities when the higher sensitivity and higher-frequency CLASS channels are included in the analysis.

    

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