arXiv subjects

David T. Chuss

Publications and source records attributed to David T. Chuss.

At least 19 recordsLinked to original sources

arXiv2026

The Effects of Cosmic Ray Protons on Galactic Nonthermal Filaments

The Galactic Center (GC) contains a collection of filaments that are typically tens of parsecs in length, illuminated by synchrotron radiation from cosmic rays (CR). The origin of these nonthermal filaments (NTFs) is unclear. We aim to distinguish two injection mechanisms: the first mechanism posits that NTFs are fueled either by jets from pulsar wind nebulae and are lepton-dominated; the second mechanism posits that NTFs are fueled by accelerated particles from interstellar shocks and are proton-dominated. We explore these mechanisms using the magnetohydrodynamics (MHD) code Athena++, modified to account for radiative and collisional losses, to simulate CR propagation with lepton and proton CR species. We vary parameters such as magnetic field strength, plasma density, and the CR diffusion coefficient to determine how the range of conditions present in the GC can affect CRs' propagation, heating, plasma flow, and the observed synchrotron emission. We find few observable differences between the proton- and lepton-dominated cases, but comparing the models with observed filament properties motivates consideration of a third formation mechanism: the generation of NTFs arise from intermittent structures in Galactic Center turbulence.

astro-ph.HE↗

arXiv2026

Analyzing PAHs as a Tracer of Anomalous Microwave Emission Near the Galactic Plane Using the COSMOGLOBE DIRBE Reduction

The physical mechanism producing Anomalous Microwave Emission (AME) has been an unresolved puzzle for close to 30 years. One candidate mechanism is rotational emission from polycyclic aromatic hydrocarbons (PAHs) which can have the necessary electric dipole moment and size distribution to account for the AME in representative interstellar environments. However, previous investigations have found that AME is better correlated with the far-infrared dust emission rather than the PAH emission. In this work we analyze the correlations between the AME and the PAH and far-infrared dust emission using the 3.3 $μ$m PAH emission feature as observed by band 3 of the Diffuse Infrared Background Experiment (DIRBE). This analysis builds on previous work conducted in individual molecular clouds and extends it into fainter, more diffuse structures. In addition, we utilize the COSMOGLOBE DIRBE reduction for this work, building on previous studies that used the original DIRBE data set. We find that the AME is better correlated with far-infrared dust emission ($ρ\sim$0.9) than the PAH emission ($ρ\sim$0.7) in the central $|b|\leq$ 10\degree\ region of the sky. This could indicate either that non-PAH dust grains or an alternative physical emission mechanism is primarily responsible for the AME in the Galactic Plane, or that the excitation conditions for mid-infrared emission and for AME from PAHs differ substantially.

astro-ph.GA↗

arXiv2025

SOFIA Polarization Spectrum of Three Star-Forming Clouds

The dust emission polarization spectrum -- how the polarization percentage changes with wavelength -- serves as a probe of dust grain properties in star-forming regions. In this paper, we present 89 $μ$m - 214 $μ$m polarization spectrum measurements obtained from SOFIA/HAWC+ for three star-forming clouds -- OMC1, M17, and W3. We find that all three clouds have an overall decreasing polarization percentage with increasing wavelength (i.e., a ``falling polarization spectrum''). We use SOFIA and Herschel data to create column density and temperature maps for each cloud. We fit for the slope of the polarization spectrum at each sky position in each cloud, and using the Pearson $r$ coefficient we probe each cloud for possible correlations of slope with column density and slope with temperature. We also create plots of slope vs. column density and slope vs. temperature for each cloud. For the case of OMC1, our results are consistent with those presented by J. Michail et al., who carried out a similar analysis for that cloud. Our plots of polarization spectrum slope vs. column density reveal that for each cloud there exists a critical column density below which a falling polarization spectrum is not observed. For these more diffuse sightlines, the polarization spectrum is instead flat or slightly rising. This finding is consistent with a hypothesis presented 25 years ago in a paper led by R. Hildebrand based on Kuiper Airborne Observatory data. This hypothesis is that regions shielded from near-IR radiation are required to produce a sharply falling polarization spectrum.

astro-ph.SR↗

arXiv2025

Statistical Analysis of PAHs as a Tracer of Anomalous Microwave Emission Using DIRBE Data

We use archival data from the Diffuse Infrared Background Experiment (DIRBE) to map the polycyclic aromatic hydrocarbon (PAH) 3.3 $μ$m emission feature and analyze its correlation with AME in 98 compact sources identified by the Planck collaboration. We find that while FIR thermal dust emission continues to be a better tracer of AME in most of the considered regions, 17% of the AME sources are better correlated with emission from small PAHs as traced by DIRBE. Furthermore, of the 27 sources which were identified as highly significant AME detections in the Planck analysis, 37% prefer PAHs as an AME tracer. Further work is required to understand to what extent local interstellar conditions are affecting PAH emission mechanisms and to reveal the underlying carriers of AME.

astro-ph.CO↗

arXiv2025

The Complex Magnetic Field of the Extreme Galactic Center: PRIMA Science Potential

The Central Molecular Zone (CMZ) of the Galactic Center (GC) region of the Milky Way contains a substantial fraction of the molecular mass of the Galaxy >10e7 solar masses yet exhibits an order of magnitude lower star formation efficiency (SFE) than expected given the high densities found in this region. There are multiple possible explanations for the depressed SFE in the CMZ, like feedback, strong turbulence, longer free-fall timescales, and high magnetic field strengths. It is currently unclear which of these mechanisms is the dominant inhibitor of star formation in the CMZ. It is important to understand the star formation process in the extreme environment of the CMZ because it is the only Galactic nuclear region we are able to study at high spatial resolutions with current observatories. One way to determine the relative importance of the different SFE inhibiting mechanisms is through multi-spatial and multi-frequency polarimetric observations of the CMZ. Such observations will provide insight into the behavior of the magnetic field in this unique environment. These observations will complement radio observations of non-thermal structures revealing the magnetic field morphology and polarization. The PRobe far--Infrared Mission for Astrophysics (PRIMA) will be uniquely capable of contributing to such explorations by providing unique resolutions and frequencies for polarimetric observations. The PRIMAger instrument will yield polarimetric observations covering the wavelength range 80 -- 261 um with beam sizes ranging from 11 -- 28'', capabilities that complement existing and upcoming observatories.

astro-ph.GA↗

arXiv2025

High-Efficiency and Low-Noise Detectors for the Upgraded CLASS 90 GHz Focal Plane

We present the in-lab and on-sky performance for the upgraded 90 GHz focal plane of the Cosmology Large Angular Scale Surveyor (CLASS), which had four of its seven detector wafers updated during the austral winter of 2022. The update aimed to improve the transition-edge-sensor (TES) stability and bias range and to realize the high optical efficiency of the sensor design. Modifications included revised circuit terminations, electrical contact between the TES superconductor and the normal metal providing the bulk of the bolometer's heat capacity, and additional filtering on the TES bias lines. The upgrade was successful: 94% of detectors are stable down to 15% of the normal resistance, providing a wide overlapping range of bias voltages for all TESs on a wafer. The median telescope efficiency improved from $0.42^{+0.15}_{-0.22}$ to $0.60^{+0.10}_{-0.32}$ (68% quantiles). For the four upgraded wafers alone, median telescope efficiency increased to $0.65^{+0.06}_{-0.06}$. Given our efficiency estimate for the receiver optics, this telescope efficiency implies a detector efficiency exceeding $0.90$. The overall noise-equivalent temperature of the 90 GHz focal plane improved from 19 $μ$K$\sqrt{s}$ to 9.7 $μ$K$\sqrt{s}$.

astro-ph.IM↗

arXiv2025

SOFIA/HAWC+ Far-Infrared Polarimetric Large Area CMZ Exploration Survey. V. The Magnetic Field Strength and Morphology in the Sagittarius C Complex

We present an analysis of the magnetic field strength and morphology in the Sagittarius C complex (Sgr C; G359.43-0.09) in the Milky Way Galaxy's Central Molecular Zone (CMZ), using the 214 $μ$m polarimetry data acquired with the High-resolution Airborne Wide-band Camera (HAWC+) instrument aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). We conduct a modified Davis-Chandrasekhar-Fermi (DCF) analysis of individual clouds and find that the sky-plane magnetic field strength varies from highly turbulent regions having inferred strengths of $\sim30~μ{\rm G}$ to regions of relatively uniform field orientation having strengths of $\sim 300~μ{\rm G}$. Several hundred magnetic field pseudovectors in the Sgr C region were measured to trace the projected magnetic field orientation within cold molecular clouds, and as is the trend throughout the CMZ, they show a higher polarization fraction toward the periphery of the clouds. The magnetic field orientations suggest that outflows from active star-forming regions, such as the G359.43-0.10 extended green object (EGO) and the protostellar source FIR-4 (G359.43+0.02), cause high turbulence in their vicinity. The magnetic field direction is found to be tangential to the surface of the Sgr C HII region, which displays spatial correspondence with two [CII] emission cavities reported in the HII region, signifying a compression front between the HII region and the surrounding dense clouds. Several other features in the vicinity of Sgr C, especially numerous non-thermal radio filaments (NTFs) and a diffuse source of X-ray emission to the immediate southwest of the HII region, are discussed with regard to the magnetic field measurements.

astro-ph.GA↗

arXiv2025

Systematic error mitigation for the PIXIE Fourier transform spectrometer

The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission concept to measure the spectrum and polarization of the cosmic microwave background. Cosmological signals are small compared to the instantaneous instrument noise, requiring strict control of instrumental signals. The instrument design provides multiple levels of null operation, signal modulation, and signal differences, with only few-percent systematic error suppression required at each level. Jackknife tests based on discrete instrument symmetries provide an independent means to identify, model, and remove remaining instrumental signals. We use detailed time-ordered simulations, including realistic performance and tolerance parameters, to evaluate the instrument response to broad classes of systematic errors for both spectral distortions and polarization. The largest systematic errors contribute additional white noise at the few-percent level compared to the dominant photon noise. Coherent instrumental effects which do not integrate down are smaller still, and remain several orders of magnitude below the targeted cosmological signals.

astro-ph.CO↗

arXiv2024

SOFIA/HAWC+ Far-Infrared Polarimetric Large-Area CMZ Exploration Survey. IV. Relative Magnetic Field Orientation Throughout the CMZ

The nature of the magnetic field structure throughout the Galactic Center (GC) has long been of interest. The recent Far-InfraREd Polarimetric Large-Area CMZ Exploration (FIREPLACE) Survey reveals preliminary connections between the seemingly distinct vertical and horizontal magnetic field distributions previously observed in the GC. We use the statistical techniques of the Histogram of Relative Orientation (HRO) and the Projected Rayleigh Statistic (PRS) to assess whether the CMZ magnetic field preferentially aligns with the structure of the CMZ molecular clouds or the morphology of the non-thermal emission of the GC NTF population. We find that there is a range of magnetic field orientations throughout the population of CMZ molecular clouds, ranging from parallel to perpendicular orientation. We posit these orientations depend on the prevalence of gravitational shear in the GC in contrast with what is observed in Galactic Disk star-forming regions. We also compare the magnetic field orientation from dust polarimetry with individual prominent NTFs, finding a preferred perpendicular relative orientation. This perpendicular orientation indicates that the vertical field component found in the FIREPLACE observations is not spatially confined to the NTFs, providing evidence for a more pervasive vertical field in the GC. From dynamical arguments, we estimate an upper limit on the magnetic field strength for this vertical field, finding B less than or equal to 4 mG. A field close to this upper limit would indicate that the NTFs are not local enhancements of a weaker background field and that the locations of the NTFs depend on proximity to sites of cosmic ray production.

astro-ph.GA↗

arXiv2024

Sensitivity-Improved Polarization Maps at 40 GHz with CLASS and WMAP data

Improved polarization measurements at frequencies below 70 GHz with degree-level angular resolution are crucial for advancing our understanding of the Galactic synchrotron radiation and the potential polarized anomalous microwave emission and ultimately benefiting the detection of primordial $B$ modes. In this study, we present sensitivity-improved 40 GHz polarization maps obtained by combining the CLASS 40 GHz and WMAP $Q$-band data through a weighted average in the harmonic domain. The decision to include WMAP $Q$-band data stems from similarities in the bandpasses. Leveraging the accurate large-scale measurements from WMAP $Q$ band and the high-sensitivity information from CLASS 40 GHz band at intermediate scales, the noise level at $\ell\in[30, 100]$ is reduced by a factor of $2-3$ in the map space. A pixel domain analysis of the polarized synchrotron spectral index ($β_s$) using WMAP $K$ band and the combined maps (mean and 16/84th percentile across the $β_s$ map: $-3.08_{-0.20}^{+0.20}$) reveals a stronger preference for spatial variation (PTE for a uniform $β_s$ hypothesis smaller than 0.001) than the results obtained using WMAP $K$ and $Ka$ bands ($-3.08_{-0.14}^{+0.14}$). The cross-power spectra of the combined maps follow the same trend as other low-frequency data, and validation through simulations indicates negligible bias introduced by the combination method (sub-percent level in the power spectra). The products of this work are publicly available on $\mathtt{LAMBDA}$.

astro-ph.CO↗

arXiv2024

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 90GHz telescope, which has been observing since July 2018. 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 arcminutes, respectively, over the first 3 years 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 deg and a solid angle of 138.7+/-0.6(stats.)+/-1.1(sys.) usr integrated to a radius of 4 deg. The corresponding beam window function drops to b_ell^2 = 0.93, 0.71, 0.14 at ell = 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.) deg in equatorial coordinates. The instrumental temperature-to-polarization (T-to-P) leakage fraction, inferred from per-detector demodulated Jupiter scan data, has a monopole component at the level of 1.7 x 10^-3, a dipole component with an amplitude of 4.3 x 10^-3, with no evidence of quadrupolar leakage.

astro-ph.IM↗

arXiv2024

Modeling the Far-Infrared Polarization Spectrum of a High-Mass Star Forming Cloud

The polarization spectrum, or wavelength dependence of the polarization fraction, of interstellar dust emission provides important insights into the grain alignment mechanism of interstellar dust grains. We investigate the far-infrared polarization spectrum of a realistic simulated high-mass star forming cloud under various models of grain alignment and emission. We find that neither a homogeneous grain alignment model nor a grain alignment model that includes collisional dealignment is able to produce the falling spectrum seen in observations. On the other hand, we find that a grain alignment model with grain alignment efficiency dependent on local temperature is capable of producing a falling spectrum that is in qualitative agreement with observations of OMC-1. For the model most in agreement with OMC-1, we find no correlation between temperature and the slope of the polarization spectrum. However, we do find a positive correlation between column density and the slope of the polarization spectrum. We suggest this latter correlation to be the result of wavelength-dependent polarization by absorption.

astro-ph.GA↗

arXiv2024

Design and characterization of a 60-cm reflective half-wave plate for the CLASS 90 GHz band telescope

Front-end polarization modulation enables improved polarization measurement stability by modulating the targeted signal above the low-frequency $1/f$ drifts associated with atmospheric and instrumental instabilities and diminishes the impact of instrumental polarization. In this work, we present the design and characterization of a new 60-cm diameter Reflective Half-Wave Plate (RHWP) polarization modulator for the 90 GHz band telescope of the Cosmology Large Angular Scale Surveyor (CLASS) project. The RHWP consists of an array of parallel wires (diameter $50~\mathrm{μm}$, $175~\mathrm{μm}$ pitch) positioned $0.88~\mathrm{mm}$ from an aluminum mirror. In lab tests, it was confirmed that the wire resonance frequency ($f_\mathrm{res}$) profile is consistent with the target, $139~\mathrm{Hz}<f_\mathrm{res}<154~\mathrm{Hz}$ in the optically active region (diameter smaller than $150~\mathrm{mm}$), preventing the wire vibration during operation and reducing the RHWP deformation under the wire tension. The mirror tilt relative to the rotating axis was controlled to be $<15''$, corresponding to an increase in beam width due to beam smearing of $<0.6''$, negligible compared to the beam's full-width half-maximum of $36'$. The median and 16/84th percentile of the wire--mirror separation residual was $0.048^{+0.013}_{-0.014}~\mathrm{mm}$ in the optically active region, achieving a modulation efficiency $ε=96.2_{+0.5}^{-0.4}\%$ with an estimated bandpass of 34 GHz. The angular velocity of the RHWP was maintained to an accuracy of within $0.005\%$ at the nominal rotation frequency ($2.5~\mathrm{Hz}$). The RHWP has been successfully integrated into the CLASS 90 GHz telescope and started taking data in June 2024, replacing the previous modulator that has been in operation since June 2018.

astro-ph.IM↗

arXiv2024

SOFIA/HAWC+ Far-Infrared Polarimetric Large Area CMZ Exploration (FIREPLACE) II: Detection of a Magnetized Dust Ring in the Galactic Center

We present the detection of a magnetized dust ring (M0.8-0.2) in the Central Molecular Zone (CMZ) of the Galactic Center. The results presented in this paper utilize the first data release (DR1) of the Far-Infrared Polarimetric Large Area CMZ Exploration (FIREPLACE) survey (i.e., FIREPLACE I; Butterfield et al. 2023). The FIREPLACE survey is a 214 $μ$m polarimetic survey of the Galactic Center using the SOFIA/HAWC+ telescope. The M0.8-0.2 ring is a region of gas and dust that has a circular morphology with a central depression. The dust polarization in the M0.8-0.2 ring implies a curved magnetic field that traces the ring-like structure of the cloud. We posit an interpretation in which an expanding shell compresses and concentrates the ambient gas and magnetic field. We argue that this compression results in the strengthening of the magnetic field, as we infer from the observations toward the interior of the ring.

astro-ph.GA↗

arXiv2024

SOFIA/HAWC+ Far-Infrared Polarimetric Large-Area CMZ Exploration (FIREPLACE) Survey III: Full Survey Data Set

We present the second data release (DR2) of the Far-Infrared Polarimetric Large-Area CMZ Exploration (FIREPLACE) survey. This survey utilized the Stratospheric Observatory for Infrared Astronomy (SOFIA) High-resolution Airborne Wideband Camera plus (HAWC+) instrument at 214 $μ$m (E-band) to observe dust polarization throughout the Central Molecular Zone (CMZ) of the Milky Way. DR2 consists of observations that were obtained in 2022 covering the region of the CMZ extending roughly from the Brick to the Sgr C molecular clouds (corresponding to a roughly 1$^{\circ}$ $\times$ 0.75$^{\circ}$ region of the sky). We combine DR2 with the first FIREPLACE data release to obtain full coverage of the CMZ (a 1.5$^{\circ}$ $\times$0.75$^{\circ}$ region of the sky). After applying total and polarized intensity significance cuts on the full FIREPLACE data set we obtain $\rm\sim$65,000 Nyquist-sampled polarization pseudovectors. The distribution of polarization pseudovectors confirms a bimodal distribution in the CMZ magnetic field orientations, recovering field components that are oriented predominantly parallel or perpendicular to the Galactic plane. These magnetic field orientations indicate possible connections between the previously observed parallel and perpendicular distributions. We also inspect the magnetic fields toward a set of prominent CMZ molecular clouds (the Brick, Three Little Pigs, 50 km s$\rm^{-1}$, Circum-nuclear Disk, CO 0.02-0.02, 20 km s$\rm^{-1}$, and Sgr C), revealing spatially varying magnetic fields that generally trace the morphologies of the clouds. We find evidence that compression from stellar winds and shear from tidal forces are prominent mechanisms influencing the structure of the magnetic fields observed within the clouds.

astro-ph.GA↗

arXiv2024

CLASS Angular Power Spectra and Map-Component Analysis for 40 GHz Observations through 2022

Measurement of the largest angular scale ($\ell < 30$) 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 primordial $B$-modes. We present an analysis of maps covering 73.6\% of the sky made from the $40\,\mathrm{GHz}$ 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 $10 < \ell < 100$. Simulations show the CLASS linear (circular) polarization maps have a white noise level of $125 \,(130)\,\mathrm{μK\, arcmin}$. We measure the Galaxy-masked $EE$ and $BB$ spectra 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 $5 < \ell < 125$ with the first bin showing $D_\ell < 0.023$ $\mathrm{μK^2_{CMB}}$ 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.

astro-ph.CO↗

arXiv2023

SOFIA/HAWC+ Far-InfraRed Polarimetric Large Area CMZ Exploration (FIREPLACE) Survey I: General Results from the Pilot Program

We present the first data release (DR1) of the Far-Infrared Polarimetric Large Area CMZ Exploration (FIREPLACE) survey. The survey was taken using the 214-micron band of the HAWC+ instrument with the SOFIA telescope (19.6$'$ resolution; 0.7 pc). In this first data release we present dust polarization observations covering a ~0.5$°$ region of the Galactic Center's Central Molecular Zone (CMZ), approximately centered on the Sgr B2 complex. We detect ~25,000 Nyquist-sampled polarization pseudovectors, after applying the standard SOFIA cuts for minimum signal-to-noise in fractional polarization and total intensity of 3 and 200, respectively. Analysis of the magnetic field orientation suggests a bimodal distribution in the field direction. This bimodal distribution shows enhancements in the distribution of field directions for orientations parallel and perpendicular to the Galactic plane, which is suggestive of a CMZ magnetic field configuration with polodial and torodial components. Furthermore, a detailed analysis of individual clouds included in our survey (i.e., Sgr B2, Sgr B2-NW, Sgr B2-Halo, Sgr B1, and Clouds-E/F) shows these clouds have fractional polarization values of 1--10% at 214-micron, with most of the emission having values $<$5%. A few of these clouds (i.e., Sgr B2, Clouds-E/F) show relatively low fractional polarization values toward the cores of the cloud, with higher fractional polarization values toward the less dense periphery. We also observe higher fractional polarization towards compact HII regions which could indicate an enhancement in the grain alignment in the dust surrounding these sources.

astro-ph.GA↗

arXiv2023

CLASS Observations of Atmospheric Cloud Polarization at Millimeter Wavelengths

The dynamic atmosphere imposes challenges to ground-based cosmic microwave background observation, especially for measurements on large angular scales. The hydrometeors in the atmosphere, mostly in the form of clouds, scatter the ambient thermal radiation and are known to be the main linearly polarized source in the atmosphere. This scattering-induced polarization is significantly enhanced for ice clouds due to the alignment of ice crystals under gravity, which are also the most common clouds seen at the millimeter-astronomy sites at high altitudes. This work presents a multifrequency study of cloud polarization observed by the Cosmology Large Angular Scale Surveyor (CLASS) experiment on Cerro Toco in the Atacama Desert of northern Chile, from 2016 to 2022, at the frequency bands centered around 40, 90, 150, and 220 GHz. Using a machine-learning-assisted cloud classifier, we made connections between the transient polarized emission found in all four frequencies with the clouds imaged by monitoring cameras at the observing site. The polarization angles of the cloud events are found to be mostly $90^\circ$ from the local meridian, which is consistent with the presence of horizontally aligned ice crystals. The 90 and 150 GHz polarization data are consistent with a power law with a spectral index of $3.90\pm0.06$, while an excess/deficit of polarization amplitude is found at 40/220 GHz compared with a Rayleigh scattering spectrum. These results are consistent with Rayleigh-scattering-dominated cloud polarization, with possible effects from supercooled water absorption and/or Mie scattering from a population of large cloud particles that contribute to the 220 GHz polarization.

astro-ph.IM↗