Extreme starlight polarization in a region with highly polarized dust emission

Panopoulou, G. V.; Hensley, Brandon; Skalidis, R.; Blinov, D.; Tassis, Konstantinos

doi:10.1051/0004-6361/201935266

Cited by 44 publications

(53 citation statements)

References 44 publications

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“…This discrepancy may be pointing to systematic offsets between the two data sets, which are constructed from entirely different tracers and methods. In fact, at high latitude, existing dust maps show significant systematic variations even among maps created using Planck data alone (see, e.g., Panopoulou et al 2019). A detailed comparison between the 3D dust map of Leike et al (2020) and the far-IR-inferred extinction from Planck, though warranted, is beyond the scope of this paper.…”

Section: Loop Imentioning

confidence: 94%

Revisiting the Distance to Radio Loops I and IV Using Gaia and Radio/Optical Polarization Data

Panopoulou

Dickinson

Readhead

et al. 2021

ApJ

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Galactic synchrotron emission exhibits large angular scale features known as radio spurs and loops. Determining the physical size of these structures is important for understanding the local interstellar structure and for modeling the Galactic magnetic field. However, the distance to these structures is either under debate or entirely unknown. We revisit a classical method of finding the location of radio spurs by comparing optical polarization angles with those of synchrotron emission as a function of distance. We consider three tracers of the magnetic field: stellar polarization, polarized synchrotron radio emission, and polarized thermal dust emission. We employ archival measurements of optical starlight polarization and Gaia distances and construct a new map of polarized synchrotron emission from WMAP and Planck data. We confirm that synchrotron, dust emission, and stellar polarization angles all show a statistically significant alignment at high Galactic latitude. We obtain distance limits to three regions toward Loop I of 112 ± 17 pc, 135 ± 20 pc, and <105 pc. Our results strongly suggest that the polarized synchrotron emission toward the North Polar Spur at b > 30° is local. This is consistent with the conclusions of earlier work based on stellar polarization and extinction, but in stark contrast with the Galactic center origin recently revisited on the basis of X-ray data. We also obtain a distance measurement toward part of Loop IV (180 ± 15 pc) and find evidence that its synchrotron emission arises from chance overlap of structures located at different distances. Future optical polarization surveys will allow the expansion of this analysis to other radio spurs.

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Section: Loop Imentioning

confidence: 94%

Revisiting the Distance to Radio Loops I and IV Using Gaia and Radio/Optical Polarization Data

Panopoulou

Dickinson

Readhead

et al. 2021

ApJ

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“…The maximal value of p max /E(B−V) was long considered to be 9% (Serkowski et al 1975). It was recently reevaluated to be at least 13% (Planck Collaboration XII 2020; Panopoulou et al 2019), corresponding to a polarization fraction of p V /τ V 4.5%, with τ V = 1.086 A V .…”

Section: Fitting Extinction and Polarization Curves In The Opticalmentioning

confidence: 99%

A systematic study of radiative torque grain alignment in the diffuse interstellar medium

Reißl

Guillet

Brauer

et al. 2020

A&A

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Context. Analyses of Planck data have demonstrated that the grain alignment efficiency is almost constant in the diffuse and translucent interstellar medium (ISM). Aims. We aim to test whether the radiative torque (RAT) theory is compatible with these new observational constraints on grain alignment. Methods. We combine a numerical magnetohydrodynamical simulation with a state-of-the-art radiative transfer post-processing code POLARIS which incorporates a physical dust model and the detailed physics of grain alignment by RATs. A dust model based on two distinct power-law-sized distributions of spherical graphite grains and oblate silicate grains was designed to reproduce the mean spectral dependence of extinction and polarization observed in the diffuse ISM. From a simulation of interstellar turbulence obtained with the adaptive-mesh-refinement code RAMSES, we extracted a data cube with physical conditions representative of the diffuse ISM. We post-process the RAMSES cube with POLARIS to compute the grain temperature and alignment efficiency in each cell of the cube. Finally, we simulate synthetic dust emission and polarization observations. Results. In our simulation, the grain alignment efficiency is well-correlated with the gas pressure, but not with the radiative torque intensity. Because of the low dust extinction in our simulation, the magnitude of the radiative torque varies little, decreasing only for column densities larger than 1022 cm−2. In comparing our synthetic maps with those obtained assuming a uniform alignment efficiency, we find no systematic difference and very small random differences. The dependencies of the polarization fraction p with the column density NH or with the dispersion in polarization angle S are also similar in both cases. The drop of grain alignment produced by the RAT model in the denser cells of the data cube does not significantly affect the patterns of the synthetic polarization maps, the polarization signal being dominated by the line-of-sight and beam integration of the geometry of the magnetic field. If a star is artificially inserted at the center of the simulation, the polarization fraction is increased everywhere, with no specific pattern around the star. The angle-dependence of the RAT efficiency is not observed in simulated maps and where the magnetic field is artificially set to a uniform configuration in the plane of the sky, it is only seen to be very weak in the optimal configuration. Conclusions. The RAT alignment theory is found to be compatible with the Planck polarization data for the diffuse and translucent ISM in the sense that both uniform alignment and RAT alignment lead to very similar simulated maps. To further test the predictions of the RAT theory in an environment where an important drop of grain alignment is expected, high-resolution polarization observations of dense regions must be confronted with numerical simulations sampling high-column densities (NH > 1022 cm−2) through dense clouds, given a sufficient statistical basis.

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“…The RoboPol monitoring program (Pavlidou et al 2014) provided R-band polarimetry (for details on the data reduction see King et al 2014;Panopoulou et al 2015).…”

Section: Introductionmentioning

confidence: 99%