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1. A Constraint on Primordial B-modes from the First Flight of the Spider Balloon-borne Telescope

   https://doi.org/10.3847/1538-4357/ac20df  

   Ade, P. A. R. ; Amiri, M. ; Benton, S. J. ; Bergman, A. S. ; Bihary, R. ; Bock, J. J. ; Bond, J. R. ; Bonetti, J. A. ; Bryan, S. A. ; Chiang, H. C. ; et al ( March 2022 , The Astrophysical Journal)

   We present the first linear polarization measurements from the 2015 long-duration balloon flight ofSpider, which is an experiment that is designed to map the polarization of the cosmic microwave background (CMB) on degree angular scales. The results from these measurements include maps and angular power spectra from observations of 4.8% of the sky at 95 and 150 GHz, along with the results of internal consistency tests on these data. While the polarized CMB anisotropy from primordial density perturbations is the dominant signal in this region of sky, Galactic dust emission is also detected with high significance. Galactic synchrotron emission is found to be negligible in theSpiderbands. We employ two independent foreground-removal techniques to explore the sensitivity of the cosmological result to the assumptions made by each. The primary method uses a dust template derived fromPlanckdata to subtract the Galactic dust signal. A second approach, which constitutes a joint analysis ofSpiderandPlanckdata in the harmonic domain, assumes a modified-blackbody model for the spectral energy distribution of the dust with no constraint on its spatial morphology. Using a likelihood that jointly samples the template amplitude andrparameter space, we derive 95% upper limits on the primordial tensor-to-scalar ratio from Feldman–Cousins and Bayesian constructions, findingr< 0.11 andr< 0.19, respectively. Roughly half the uncertainty inrderives from noise associated with the template subtraction. New data at 280 GHz fromSpider’s second flight will complement thePlanckpolarization maps, providing powerful measurements of the polarized Galactic dust emission.

    

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2. 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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3. Polarization from Aligned Dust Grains in the β Pic Debris Disk

   https://doi.org/10.3847/1538-4357/ac6023  

   Hull, Charles L. H. ; Yang 杨, Haifeng 海峰 ; Cortés, Paulo C. ; Dent, William R. F. ; Kral, Quentin ; Li, Zhi-Yun ; Le Gouellec, Valentin J. M. ; Hughes, A. Meredith ; Milli, Julien ; Teague, Richard ; et al ( May 2022 , The Astrophysical Journal)

   We present 870μm Atacama Large Millimeter/submillimeter Array polarization observations of thermal dust emission from the iconic, edge-on debris diskβPic. While the spatially resolved map does not exhibit detectable polarized dust emission, we detect polarization at the ∼3σlevel when averaging the emission across the entire disk. The corresponding polarization fraction isP_frac= 0.51% ± 0.19%. The polarization position angleχis aligned with the minor axis of the disk, as expected from models of dust grains aligned via radiative alignment torques (RAT) with respect to a toroidal magnetic field (B-RAT) or with respect to the anisotropy in the radiation field (k-RAT). When averaging the polarized emission across the outer versus inner thirds of the disk, we find that the polarization arises primarily from the SW third. We perform synthetic observations assuming grain alignment via bothk-RAT andB-RAT. Both models produce polarization fractions close to our observed value when the emission is averaged across the entire disk. When we average the models in the inner versus outer thirds of the disk, we find thatk-RAT is the likely mechanism producing the polarized emission inβPic. A comparison of timescales relevant to grain alignment also yields the same conclusion. For dust grains with realistic aspect ratios (i.e.,s> 1.1), our models imply low grain-alignment efficiencies.

    

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4. The Simons Observatory: Galactic Science Goals and Forecasts

   https://doi.org/10.3847/1538-4357/ac5e36  

   Hensley, Brandon S. ; Clark, Susan E. ; Fanfani, Valentina ; Krachmalnicoff, Nicoletta ; Fabbian, Giulio ; Poletti, Davide ; Puglisi, Giuseppe ; Coppi, Gabriele ; Nibauer, Jacob ; Gerasimov, Roman ; et al ( April 2022 , The Astrophysical Journal)

   Observing in six frequency bands from 27 to 280 GHz over a large sky area, the Simons Observatory (SO) is poised to address many questions in Galactic astrophysics in addition to its principal cosmological goals. In this work, we provide quantitative forecasts on astrophysical parameters of interest for a range of Galactic science cases. We find that SO can: constrain the frequency spectrum of polarized dust emission at a level of Δβ_d≲ 0.01 and thus test models of dust composition that predict thatβ_din polarization differs from that measured in total intensity; measure the correlation coefficient between polarized dust and synchrotron emission with a factor of two greater precision than current constraints; exclude the nonexistence of exo-Oort clouds at roughly 2.9σif the true fraction is similar to the detection rate of giant planets; map more than 850 molecular clouds with at least 50 independent polarization measurements at 1 pc resolution; detect or place upper limits on the polarization fractions of CO(2–1) emission and anomalous microwave emission at the 0.1% level in select regions; and measure the correlation coefficient between optical starlight polarization and microwave polarized dust emission in 1° patches for all lines of sight withN_H≳ 2 × 10²⁰cm⁻². The goals and forecasts outlined here provide a roadmap for other microwave polarization experiments to expand their scientific scope via Milky Way astrophysics.³⁷³⁷

   A supplement describing author contributions to this paper can be found athttps://simonsobservatory.org/wp-content/uploads/2022/02/SO_GS_Contributions.pdf.

    

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5. A New Constraint on the Relative Disorder of Magnetic Fields between Neutral Interstellar Medium Phases

   https://doi.org/10.3847/1538-4357/ad5ade  

   Lei, Minjie ; Clark, S_E ( August 2024 , The Astrophysical Journal)

   Utilizing Planck polarized dust emission maps at 353 GHz and large-area maps of the neutral hydrogen (Hi) cold neutral medium (CNM) fraction (f_CNM), we investigate the relationship between dust polarization fraction (p₃₅₃) andf_CNMin the diffuse high latitude ($∣b∣>30°$) sky. We find that the correlation betweenp₃₅₃andf_CNMis qualitatively distinct from thep₃₅₃–Hicolumn density (N_Hi) relationship. At low column densities (N_Hi< 4 × 10²⁰cm⁻²) wherep₃₅₃andN_Hiare uncorrelated, there is a strong positivep₃₅₃–f_CNMcorrelation. We fit thep₃₅₃–f_CNMcorrelation with data-driven models to constrain the degree of magnetic field disorder between phases along the line of sight. We argue that an increased magnetic field disorder in the warm neutral medium (WNM) relative to the CNM best explains the positivep₃₅₃–f_CNMcorrelation in diffuse regions. Modeling the CNM-associated dust column as being maximally polarized, with a polarization fractionp_CNM∼ 0.2, we find that the best-fit mean polarization fraction in the WNM-associated dust column is 0.22p_CNM. The model further suggests that a significantf_CNM-correlated fraction of the non-CNM column (an additional 18.4% of the Himass on average) is also more magnetically ordered, and we speculate that the additional column is associated with the unstable medium. Our results constitute a new large-area constraint on the average relative disorder of magnetic fields between the neutral phases of the interstellar medium, and are consistent with the physical picture of a more magnetically aligned CNM column forming out of a disordered WNM.

    

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