Faraday Tomography with CHIME: The “Tadpole” Feature G137+7

Abstract A direct consequence of Faraday rotation is that the polarized radio sky does not resemble the total intensity sky at long wavelengths. We analyze G137+7, which is undetectable in total intensity but appears as a depolarization feature. We use the first polarization maps from the Canadian Hydrogen Intensity Mapping Experiment. Our 400–729 MHz bandwidth and angular resolution, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>17</mml:mn> <mml:mo accent="false">′</mml:mo> </mml:math> – <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>30</mml:mn> <mml:mo accent="false">′</mml:mo> </mml:math> , allow us to use Faraday synthesis to analyze the polarization structure. In polarized intensity and polarization angle maps, we find a tail extending 10° from the head and designate the combined object, the tadpole . Similar polarization angles, distinct from the background, indicate that the head and tail are physically associated. The head appears as a depolarized ring in single channels, but wideband observations show that it is a Faraday rotation feature. Our investigations of H i and H α find no connections to the tadpole. The tail suggests motion of either the gas or an ionizing star through the interstellar medium; the B2(e) star HD 20336 is a candidate. While the head features a coherent, ∼ −8 rad m −2 Faraday depth, Faraday synthesis also identifies multiple components in both the head and tail. We verify the locations of the components in the spectra using QU fitting. Our results show that approximately octave-bandwidth Faraday rotation observations at ∼600 MHz are sensitive to low-density ionized or partially ionized gas, which is undetectable in other tracers.

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Publication Details

Journal
The Astrophysical Journal
Published
2024-08-01
DOI
https://doi.org/10.3847/1538-4357/ad5099
Citations
3
Primary Topic
Advanced Frequency and Time Standards
Type
article
Field-Weighted Citation Impact
1.01

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article

Faraday Tomography with CHIME: The “Tadpole” Feature G137+7

Dallas Wulf, T. L. Landecker, Rebecca A. Booth, Kiyoshi W. Masui et al.
3 citations
The Astrophysical Journal
Advanced Frequency and Time Standards
1.01
article

Faraday Tomography with CHIME: The “Tadpole” Feature G137+7

Dallas Wulf, T. L. Landecker, Rebecca A. Booth, Kiyoshi W. Masui, R. R. Ransom, G. Hinshaw, A. J. M. Thomson, W. Reich, M. Halpern, J. C. Brown, E. Carretti, Tristan Pinsonneault-Marotte, Anna Ordog, M. Wolleben, A. Bracco, Simon Foreman, John M. Dickey, R. Kothes, Jennifer West, Joseph Kania, Seth R. Siegel, J. Richard Shaw, Haochen Wang, Joshua MacEachern, P. Reich, Alex S. Hill, M. Haverkorn, Mehrnoosh Tahani, Nasser Mohammed, Aimee Menard
article en
3 citations

Abstract

Abstract A direct consequence of Faraday rotation is that the polarized radio sky does not resemble the total intensity sky at long wavelengths. We analyze G137+7, which is undetectable in total intensity but appears as a depolarization feature. We use the first polarization maps from the Canadian Hydrogen Intensity Mapping Experiment. Our 400–729 MHz bandwidth and angular resolution, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>17</mml:mn> <mml:mo accent="false">′</mml:mo> </mml:math> – <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>30</mml:mn> <mml:mo accent="false">′</mml:mo> </mml:math> , allow us to use Faraday synthesis to analyze the polarization structure. In polarized intensity and polarization angle maps, we find a tail extending 10° from the head and designate the combined object, the tadpole . Similar polarization angles, distinct from the background, indicate that the head and tail are physically associated. The head appears as a depolarized ring in single channels, but wideband observations show that it is a Faraday rotation feature. Our investigations of H i and H α find no connections to the tadpole. The tail suggests motion of either the gas or an ionizing star through the interstellar medium; the B2(e) star HD 20336 is a candidate. While the head features a coherent, ∼ −8 rad m −2 Faraday depth, Faraday synthesis also identifies multiple components in both the head and tail. We verify the locations of the components in the spectra using QU fitting. Our results show that approximately octave-bandwidth Faraday rotation observations at ∼600 MHz are sensitive to low-density ionized or partially ionized gas, which is undetectable in other tracers.

The Astrophysical JournalVol. 971(1)
West Virginia University (US), Herzberg Institute of Astrophysics (CA), Commonwealth Scientific and Industrial Research Organisation (AU), Centre National de la Recherche Scientifique (FR), University of Tasmania (AU), University of British Columbia (CA), Radboud University Nijmegen (NL), University of Calgary (CA), Perimeter Institute (CA), Okanagan College (CA), Université Paris Cité (FR), Université Paris Sciences et Lettres (FR), Dominion Astrophysical Observatory (CA), Arcetri Astrophysical Observatory (IT), École Normale Supérieure - PSL (FR), Sorbonne Université (FR), Kavli Institute for Particle Astrophysics and Cosmology (US), Istituto di Radioastronomia di Bologna (IT), Astronomy and Space (AU), Max Planck Institute for Radio Astronomy (DE), McGill University (CA), Arizona State University (US), Massachusetts Institute of Technology (US), Okanagan University College (CA)
Canada Foundation for Innovation, Smithsonian Astrophysical Observatory, Natural Sciences and Engineering Research Council of Canada, National Research Council Canada, Division of Astronomical Sciences, HORIZON EUROPE European Research Council
Openalex Percentile: Top 25%
Advanced Frequency and Time Standards
1.01
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