Sky Polarization Research Articles

Probing the magnetized gas distribution in galaxy groups and the cosmic web with POSSUM Faraday rotation measures

ABSTRACT We present initial results from the Polarization Sky Survey of the Universe’s Magnetism (POSSUM), analysing 22 817 Faraday rotation measures (RMs) with median uncertainties of 1.2 rad m$^{-2}$ across 1520 deg2 to study magnetized gas associated with 55 nearby galaxy groups ($z\lesssim 0.025$) with halo masses between $10^{12.5}$ and $10^{14.0}$ M$_\odot$. We identify two distinct gas phases: the intragroup medium (IGrM) within 0–2 splashback radii and the warm-hot intergalactic medium (WHIM) extending from 2 to 7 splashback radii. These phases enhance the standard deviation of residual (i.e. Galactic foreground RM-subtracted) RMs by $6.9\pm 1.8$ rad m$^{-2}$ and $4.2 \pm 1.2$ rad m$^{-2}$, respectively. Estimated magnetic field strengths are several μG within the IGrM and 0.1–1 μG in the WHIM. We estimate the plasma $\beta$ in both phases, and show that magnetic pressure might be more dynamically important than in the ICM of more massive clusters or sparse cosmic web filaments. Our findings indicate that ‘missing baryons’ in the WHIM likely extend beyond the gravitational radii of group-mass haloes to Mpc scales, consistent with large-scale, outflow-driven ‘magnetized bubbles’ seen in cosmological simulations. We demonstrate that RM grids are an effective method for detecting magnetized thermal gas at galaxy group interfaces and within the cosmic web. This approach complements X-ray and Sunyaev-Zel’dovich effect methods, and when combined with fast radio burst dispersion measures, data from the full POSSUM survey – comprising approximately a million RMs – will allow direct magnetic field measurements to further our understanding of baryon circulation in these environments and the magnetized universe.

Night sky polarization model for a cloud-free atmosphere illuminated by ground-based light sources

ABSTRACT Skyglow from sources of artificial light at night poses a significant challenge to ground-based astronomical research and discovery. Although astronomers, conservationists, and light-pollution researchers have measured skyglow for decades, their data on diffuse night-time light fields are incomplete as they lacks information about the polarization state of the light. Here, we present the first successful theoretical model that predicts the degree and angle of linear polarization of scattered night sky light and accounts for complex, real-world distributions of ground light sources. The model proceeds from an analytical solution to the polarized radiative transfer equation that is validated by field experiments. We discuss several use cases of the model and demonstrate its practical consequences, such as the ability to more reliably determine which ground sources in the area around an observer contribute the most scattered light in a given sky element.

Planck data revisited: Low-noise synchrotron polarization maps from the WMAP and Planck space missions

Observations of cosmic microwave background (CMB) polarization, essential for probing a potential phase of inflation in the early Universe, suffer from contamination by polarized emission from the Galactic interstellar medium. This work combines existing observations from the WMAP and space missions to make a low-noise map of polarized synchrotron emission that can be used to clean forthcoming CMB observations. We combine DR5 K, Ka and Q WMAP maps with PR4 30 GHz and 44 GHz LFI maps and WMAP K, Ka and Q maps with LFI 30 GHz and 44 GHz maps, using weights that near-optimally combine the observations as a function of sky direction, angular scale, and polarization orientation. We publish well-characterized maps of synchrotron $Q$ and $U$ Stokes parameters at $ = 30$ GHz and an angular resolution of 1 degree. A statistical description of uncertainties is provided with Monte-Carlo simulations of additive and multiplicative errors. Our maps are the most sensitive full-sky maps of synchrotron polarization to date, and are made available to the scientific community on a dedicated website.

Solution of light vector superposition heading in zenith region of underwater sky polarization image

Solution of light vector superposition heading in zenith region of underwater sky polarization image

Effect of Foggy Environments on Sky Polarization Distribution

Effect of Foggy Environments on Sky Polarization Distribution

Speedy bearings to slacked steering: Mapping the navigation patterns and motions of Viking voyages.

Viking sailors ruled the North Atlantic Ocean for about three hundred years. Their main sailing route was the 60° 21' 55'' latitude between Norway and Greenland. Although they did not have a magnetic compass, in sunshine they used a sun-compass to determine the geographical north (solar Viking navigation: SVN). It has been hypothesized that when the Sun was invisible, Viking navigators determined the direction of polarization of skylight with sunstones (dichroic/birefringent crystals), and then estimated the geographical north using the sun-compass (sky-polarimetric Viking navigation: SPVN). Many details of the hypothetical SPVN have been thoroughly revealed in psychophysical laboratory and planetarium experiments. Combining these results with measured celestial polarization patterns, the success of SPVN was obtained as functions of sailing, meteorological and navigation parameters (sunstone type, sailing date, navigation periodicity, night sailing, cloudiness conditions). What was so far lacking in this experimental and computational archeological approach is the study of the success of SVN and a combined navigation using solar cues in sunshine (SVN) and sky polarization at invisible Sun (SPVN), the latter being the most realistic method. In this work we determine the success of the sole SVN and the combined SVN-SPVN relative to the mere SPVN for three navigator types (determining the intended sailing direction with large, medium or small frequencies) at spring equinox and summer solstice, with and without night sailing. We found that to maximize the sailing success, navigators had to choose different navigation methods depending on the navigation frequency. Using sky polarization with very frequent navigation, resulted in the highest chance to survive a three-week voyage from Norway to Greenland.

Exploration of actual sky polarization patterns: From influencing factor analyses to polarized light-aided navigation

The polarized light scattered by the sunlight and atmosphere is a general natural property of the atmospheric space of Earth. This study is devoted to an exploration of actual sky polarization pattern-oriented navigation. For the polarized light-aided VINS (abbreviated ‘visual-inertial navigation system’), one of our major concerns is to prove the heading (orientation) reference stays stable under the actual complex atmospheric environments. The influencing factors that contribute to the variation of the polarization pattern symmetry have been taken into account. The analytic AOP (abbreviated ‘angle of polarization’) and DOP (abbreviated ‘degree of polarization’) maps and quantitative analyses that concern spectrum character, cloudage, and aerosol optical depth relevant to light scattering effects are simultaneously presented. Given the globally referenced heading, one intuitive way of modeling multi-sensor fusion is to use a graph structure. Following the pipeline design of VINS Fusion, a polarization imaging factor constraint (expressed by the polarization measurement residual-encoded edges) is added in the state estimator and the cost function to be minimized during optimization is formulated. Via campus road experiments on the built robot platform, our proposal is compared against VINS Fusion under different weather conditions, revealing that over the entire closed path, our polarized light-aided VINS achieves high rate of both locally and globally consistent estimates. To our best knowledge, this is the first work to illuminate the insights into a practical, polarization imager-integrated navigating application in which the localization results can be optically explained, evaluated, and optimized.

COSMOGLOBE DR1 results

We present COSMOGLOBEData Release 1, which implements the first joint analysis of WMAP andPlanckLFI time-ordered data, processed within a single Bayesian end-to-end framework. This framework directly builds on a similar analysis of the LFI measurements by the BEYONDPLANCKcollaboration, and approaches the cosmic microwave background (CMB) analysis challenge through Gibbs sampling of a global posterior distribution, simultaneously accounting for calibration, mapmaking, and component separation. The computational cost of producing one complete WMAP+LFI Gibbs sample is 812 CPU-h, of which 603 CPU-h are spent on WMAP low-level processing; this demonstrates that end-to-end Bayesian analysis of the WMAP data is computationally feasible. We find that our WMAP posterior mean temperature sky maps and CMB temperature power spectrum are largely consistent with the official WMAP9 results. Perhaps the most notable difference is that our CMB dipole amplitude is 3366.2 ± 1.4 μK, which is 11 μK higher than the WMAP9 estimate and 2.5σhigher than BEYONDPLANCK; however, it is in perfect agreement with the HFI-dominatedPlanckPR4 result. In contrast, our WMAP polarization maps differ more notably from the WMAP9 results, and in general exhibit significantly lower large-scale residuals. We attribute this to a better constrained gain and transmission imbalance model. It is particularly noteworthy that theW-band polarization sky map, which was excluded from the official WMAP cosmological analysis, for the first time appears visually consistent with theV-band sky map. Similarly, the long standing discrepancy between the WMAPK-band and LFI 30 GHz maps is finally resolved, and the difference between the two maps appears consistent with instrumental noise at high Galactic latitudes. Relatedly, these updated maps allowed us for the first time to combine WMAP and LFI polarization data into a single coherent model of large-scale polarized synchrotron emission. Still, we identified a few issues that require additional work, including (1) low-level noise modeling; (2) large-scale temperature residuals at the 1–2 μK level; and (3) a strong degeneracy between the absoluteK-band calibration and the dipole of the anomalous microwave emission component. We conclude that leveraging the complementary strengths of WMAP and LFI has allowed the mitigation of both experiments’ weaknesses, and resulted in new state-of-the-art WMAP sky maps. All maps and the associated code are made publicly available through the COSMOGLOBEweb page.

A catalogue of radio supernova remnants and candidate supernova remnants in the EMU/POSSUM Galactic pilot field

ABSTRACT We use data from the pilot observations of the EMU/POSSUM surveys to study the ‘missing supernova remnant (SNR) problem’, the discrepancy between the number of Galactic SNRs that have been observed, and the number that are estimated to exist. The Evolutionary Map of the Universe (EMU) and the Polarization Sky Survey of the Universe’s Magnetism (POSSUM) are radio sky surveys that are conducted using the Australian Square Kilometre Array Pathfinder (ASKAP). We report on the properties of seven known SNRs in the joint Galactic pilot field, with an approximate longitude and latitude of 323° ≤ l ≤ 330° and −4° ≤ b ≤ 2°, respectively, and identify 21 SNR candidates. Of these, four have been previously identified as SNR candidates, three were previously listed as a single SNR, 13 have not been previously studied, and one has been studied in the infrared. These are the first discoveries of Galactic SNR candidates with EMU/POSSUM and, if confirmed, they will increase the SNR density in this field by a factor of 4. By comparing our SNR candidates to the known Galactic SNR population, we demonstrate that many of these sources were likely missed in previous surveys due to their small angular size and/or low surface brightness. We suspect that there are SNRs in this field that remain undetected due to limitations set by the local background and confusion with other radio sources. The results of this paper demonstrate the potential of the full EMU/POSSUM surveys to uncover more of the missing Galactic SNR population.

Sky Polarization Pattern Reconstruction and Neutral Line Detection Based on Adversarial Learning

Sky Polarization Pattern Reconstruction and Neutral Line Detection Based on Adversarial Learning

Sky polarization pattern under multi-layer environment of atmosphere and sea fog

The vertical polarization distribution pattern of sea fog multilayer media and skylight in the atmosphere is explored. To change the complicated maritime environment, the simplified double layer structure of the atmosphere and sea fog is employed, and the scattering coefficients of the uniform atmosphere and sea fog medium are derived using the Rayleigh and Mie scattering methods, respectively. Using the adding-doubling method (RT3) based on the vector radiation transmission equation, the transmission of radiation between the two layers of the medium is calculated to obtain the polarization distribution conditions of skylight, and the variation tendency of the polarization characteristics observed from the ground is studied for the downwelling radiation of sea fog on the meridian of the Sun. An indoor sea fog setting was employed to perform the polarization transmission test, and the relationship between humidity, light intensity transmittance, and polarization degree was explored. The data suggest that the Sun’s position gives the lowest degree of polarization (DOP), and that the maximum value is obtained when the angle between the solar altitude angle and the observed altitude angle is 90°. Short wavelength lasers have a higher influence on optical transmittance than long wavelength lasers do when humidity levels increase. The circular polarization effect of long wavelength laser is better in damp surroundings.

A Wide Spectral Range Sky Radiance Model

AbstractPre‐computed models of sky radiance are a tool to rapidly determine incident solar irradiance in applications as diverse as movie VFX, lighting simulation for architecture, experimental biology, and flight simulators. Several such models exist, but most provide data only for the visible range and, in some cases, for the near‐UV. But for accurate simulations of photovoltaic plant yield and the thermal properties of buildings, a pre‐computed reference sky model which covers the entire spectral range of terrestrial solar irradiance is needed: and this range is considerably larger than what extant models provide. We deliver this, and for a ground‐based observer provide the three components of sky dome radiance, atmospheric transmittance, and polarisation. We also discuss the additional aspects that need to be taken into consideration when including the near‐infrared in such a model. Additionally, we provide a simple standalone C++ implementation as well as an implementation with a GUI.

Temporal and Spatial Characteristics of the Global Skylight Polarization Vector Field

There are two widely recognized global fields in nature: the gravity field and the geomagnetic field. Universal gravitation and Earth rotation are important sources of the Earth’s gravity and geomagnetic fields, which are well known to us. After years of long-term observation, global research, and analysis, it was discovered that we have neglected a direct incident energy of the universe on the Earth. Solar radiation, leading to energy exchange from the atmosphere 100 km above the land surface, is the energy source of the Earth. Polarization is one of the four basic physical properties of solar radiation. After the solar radiation reaches the surface of these media, it reflects, scatters or refracts, and exhibits different degrees of polarization. The polarized solar light forms the Earth–sky polarization vector field. The polarized light dispersion is expected to become a new method for global analysis of the human environment. Polarization detection is the best way to accurately explore the atmospheric effects. Local polarized skylight distribution was found in different sites in the world; however, the global distribution of the polarized sunlight radiation has never been explored. In this paper, we investigate the Global Skylight Polarization Field. This study aimed at providing new insight into the laws of polarization over our Earth. We use a Rayleigh scattering model to obtain the simulation results of the sky polarization field. Rayleigh scattering occurs when the particle size is much smaller than the wavelength of the incident electromagnetic wave. We also use a polarized fisheye camera to collect the sky polarization image and calculate the distribution pattern of the DOLP (degree of linear polarization) and AOLP (azimuth of linear polarization) of the skylight. The stability and gradual change in the degree of polarization in the zenith direction are verified, and the distribution law and daily change law of the degree of polarization in the sky are obtained. With the increase in the solar altitude angle, the degree of polarization will decrease. We also observed the skylight polarization in different weather conditions. Our results demonstrate the physical basis, characteristics, and usability of the polarization field. They show an inevitable trend from optical remote sensing to polarization remote sensing.

Sensitivity and robustness of sky-polarimetric Viking navigation: Sailing success is most sensitive to night sailing, navigation periodicity and sailing date, but robust against weather conditions.

Although Viking sailors did not have a magnetic compass, they could successfully navigate with a sun-compass under a sunny sky. Under cloudy/foggy conditions, they might have applied the sky-polarimetric Viking navigation (SPVN), the high success of which has been demonstrated with computer simulations using the following input data: sky polarization patterns measured with full-sky imaging polarimetry, and error functions of the navigation steps measured in psychophysical laboratory and planetarium experiments. As a continuation of the earlier studies, in this work we investigate the sensitivity of the success of SPVN to the following relevant sailing, meteorological and navigational parameters: sunstone type, sailing date, navigation periodicity, night sailing, dominance of strongly, medium or weakly cloudy skies, and changeability of cloudiness. Randomly varying these parameters in the simulation of Viking voyages along the latitude 60° 21' 55'' N from Norway to Greenland, we determined those parameters which had strong and weak influences on the success of SPVN. The following intrinsic parameters of the simulation were also randomly changed: sailing speed, visibility distance of Greenland's southeast coastline and start time of diurnal sailing. Our results show that the sailing success is sensitive to the night sailing, navigation periodicity and sailing date, while it is robust against the sunstone type, dominance of strongly, medium or weakly cloudy skies, and changing cloudiness.

The effect of cosmic variance on the characteristics of dust polarization power spectra

In the context of cosmic microwave background polarization studies and the characterization of the Galactic foregrounds, the power spectrum analysis of the thermal dust polarization sky has led to intriguing evidence of an E∕B asymmetry and a positive TE correlation. In this work, we produce synthesized dust polarization maps from a set of global magneto-hydrodynamic (MHD) simulations of Milky-Way-sized galaxies, and analyze their power spectra at intermediate angular scales (intermediate angular multipoles ℓ∈[60, 140]). We study the role of the initial configuration of the large-scale magnetic field, its strength, and the feedback on the power spectrum characteristics. Using full-galaxy MHD simulations, we were able to estimate the variance induced by the peculiar location of the observer in the galaxy. We find that the polarization power spectra sensitively depend on the observer’s location, impeding a distinction between different simulation setups. In particular, there is a clear statistical difference between the power spectra measured from within the spiral arms and those measured from the inter-arm regions. Also, power spectra from within supernova-driven bubbles share common characteristics, regardless of the underlying model. However, no correlation was found between the statistical properties of the polarization power spectra and the local (with respect to the observer) mean values of physical quantities such as the density and the strength of the magnetic field. Finally, we find some indications that the global strength of the magnetic field may play a role in shaping the power spectrum characteristics; as the global magnetic field strength increases, the E∕B asymmetry and the TE correlation increase, whereas the viewpoint-induced variance decreases. However, we find no direct correlation with the strength of the local magnetic field that permeates the mapped region of the interstellar medium.

Alternative LISA-TAIJI networks

The spaceborne gravitational wave (GW) detectors LISA and TAIJI are planned to be launched in the 2030s. The dual detectors with comparable sensitivities will form a network observing GWs with significant advantages. In this work, we investigate the three possible LISA-TAIJI networks for the different location and orientation compositions of the LISA orbit ($+60\ifmmode^\circ\else\textdegree\fi{}$ inclination and trailing the Earth by 20\ifmmode^\circ\else\textdegree\fi{}) and alternative TAIJI orbit configurations, including TAIJIp ($+60\ifmmode^\circ\else\textdegree\fi{}$ inclination and leading the Earth by 20\ifmmode^\circ\else\textdegree\fi{}), TAIJIc ($+60\ifmmode^\circ\else\textdegree\fi{}$ inclination and colocated with LISA), and TAIJIm ($\ensuremath{-}60\ifmmode^\circ\else\textdegree\fi{}$ inclination and leading the Earth by 20\ifmmode^\circ\else\textdegree\fi{}). Of the three LISA-TAIJI configurations, the LISA-TAIJIm network shows the best performance in the sky localization and polarization determination for massive binary systems due to its better complementary antenna pattern, and LISA-TAIJIc could achieve the best cross-correlation and observe the stochastic GW background with optimal sensitivity.

The Global Magneto-Ionic Medium Survey (GMIMS): the brightest polarized region in the southern sky at 75 cm and its implications for Radio Loop II

ABSTRACT Using the Global Magneto-Ionic Medium Survey (GMIMS) Low-Band South (LBS) southern sky polarization survey, covering 300–480 MHz at 81 arcmin resolution, we reveal the brightest region in the southern polarized sky at these frequencies. The region, G150−50, covers nearly 20 $\deg ^2$, near (l, b) ≈ (150○, −50○). Using GMIMS-LBS and complementary data at higher frequencies (∼0.6–30 GHz), we apply Faraday tomography and Stokes QU-fitting techniques. We find that the magnetic field associated with G150−50 is both coherent and primarily in the plane of the sky, and indicates that the region is associated with Radio Loop II. The Faraday depth spectra across G150−50 are broad and contain a large-scale spatial gradient. We model the magnetic field in the region as an expanding shell, and we can reproduce both the observed Faraday rotation and the synchrotron emission in the GMIMS-LBS band. Using QU fitting, we find that the Faraday spectra are produced by several Faraday dispersive sources along the line of sight. Alternatively, polarization horizon effects that we cannot model are adding complexity to the high-frequency polarized spectra. The magnetic field structure of Loop II dominates a large fraction of the sky, and studies of the large-scale polarized sky will need to account for this object. Studies of G150−50 with high angular resolution could mitigate polarization horizon effects, and clarify the nature of G150−50.

Polarization neutral point pairs of the solar corona and the lunar disc observed during the total solar eclipse on 11 August 1999 in Hungary.

During the total solar eclipses on 11 August 1999 in Kecel (Hungary) and on 29 March 2006 in Side (Turkey), two Hungarian groups performed full-sky imaging polarimetric measurements of the eclipsed sky. They observed the spatiotemporal change of the celestial polarization pattern and detected three polarization neutral points as well as two points with maximal polarization of the sky. Parallel to these studies, the polarization pattern in front of the lunar disc, the solar corona, and the surrounding sky have also been measured. During the total solar eclipse on 21 August 2017 in the USA (Rexburg-Idaho, Madras-Oregon), three American/international groups have measured the polarization characteristics of the full sky and the solar corona. The first group observed the spatiotemporal variation of the celestial polarization pattern, and the second group detected three polarization neutral points of the sky and observed two neutral points of the solar corona. The latter were named as Minnaert and van de Hulst neutral points. The third group observed two neutral points of the lunar disc. We have reanalyzed the earlier polarization patterns of the lunar disc, solar corona, and the surrounding sky measured during the Hungarian total eclipse on 11 August 1999. In these reanalyzed polarization patterns, all four neutral points observed during the eclipse on 21 August 2017 in the USA occur: the Minnaert/van de Hulst neutral point pair above/below the eclipsed Sun, where coronal polarization is canceled by sky polarization, and the northern and southern (unnamed) neutral points of the lunar disc, where the directions of polarization of coronal light and foreground skylight are perpendicular to each other with the same polarized intensity. We name the latter two polarization neutral points after Coulson and Vorobiev.

Error Analysis and Optimization of a Sky Full-Polarization Imaging Detection System

An accurate sky polarization field map is a prerequisite for polarization navigation applications. In this article, a detector for sky full-polarization imaging detection is described, the major error-influencing factors (MEIFS ) are obtained, and the error propagation is modeled and analyzed. We reveal the relationship between the error of the inversed Stokes vector and the condition number of the detector matrix, which shows that the error of the inversed Stokes vector is affected by the Stokes vector of the incident light itself and the MEIFS together, with the MEIFS playing a decisive role. With the MEIFS optimized, the impact of detector error on the inversed Stokes vector is attenuated. A control equation for system calibration is also deduced which can establish the connection between the detector matrix design and calibration process. The work in this article provides a reference for optimization and calibration of sky full-polarization imaging detectors.

Towards ending the partial sky E-B ambiguity in CMB observations

A crucial problem for partial sky analysis of CMB polarization is the E-B leakage problem. Such leakage arises from the presence of `ambiguous' modes that satisfy properties of both E and B modes. Solving this problem is critical for primordial polarization B mode detection in partial sky CMB polarization experiments. In this work we introduce a new method for reducing the leakage. We demonstrate that if we complement the E-mode information outside the observation patch with ancillary data from full-sky CMB observations, we can reduce and even effectively remove the E-to-B leakage. For this objective, we produce E-mode Stokes QU maps from Wiener filtered full-sky intensity and polarization CMB observations. We use these maps to fill the sky region that is not observed by the ground-based experiment of interest, and thus complement the partial sky Stokes QU maps. Since the E-mode information is now available on the full sky we see a significant reduction in the E-to-B leakage. We evaluate on simulated data sets the performance of our method for a `shallow' fsky = 8%, and a `deep' fsky = 2% northern hemisphere sky patch, with AliCPT-like properties, and a LSPE-like fsky = 30% sky patch, by combining those observations with Planck-like full sky polarization maps. We find that our method outperforms the standard and the pure-B method pseudo-Cℓ estimators for all of our simulations. Our new method gives unbiased estimates of the B-mode power spectrum through-out the entire multipole range with near-optimal pseudo-Cℓ errors for ℓ > 20. We also study the application of our method to the CMB-S4 experiment combined with LiteBIRD-like full sky data, and show that using signal-dominated full sky E-mode data we can eliminate the E-to-B leakage problem.