Low-Frequency Observations of Linearly Polarized Structures in the Interstellar Medium Near the South Galactic Pole

Lenc, E.; Gaensler, B. M.; Sun, Xiaohui; Sadler, E. M.; Willis, A.; Barry, N.; Beardsley, Adam P.; Bell, M. E.; Bernardi, G.; Bowman, Judd D.; Briggs, F.; Callingham, J. R.; Cappallo, R. J.; Carroll, P.; Corey, B. E.; Oliveira-Costa, A. de; Deshpande, A. A.; Dillon, Joshua S.; Dwarkanath, K. S.; Emrich, D.; Ewall‐Wice, Aaron; Lü, Feng; For, Bi-Qing; Goeke, R.; Greenhill, L. J.; Hancock, P. J.; Hazelton, B. J.; Hewitt, Jacqueline N.; Hindson, L.; Hurley‐Walker, N.; Johnston‐Hollitt, M.; Jacobs, Daniel; Kapińska, A. D.; Kaplan, D. L.; Kasper, J. C.; Kim, Han-Seek; Kratzenberg, E.; Line, J.; Loeb, Abraham; Lonsdale, Colin J.; Lynch, M. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Morgan, John S.; Murphy, Tara; Neben, Abraham R.; Oberoi, D.; Offringa, A. R.; Ord, S. M.; Paul, S.; Pindor, B.; Pober, Jonathan C.; Prabu, T.; Procopio, P.; Riding, J.; Rogers, A. E. E.; Roshi, A.; Shankar, N. Udaya; Sethi, Shiv K.; Srivani, K. S.; Staveley‐Smith, L.; Subrahmanyan, R.; Sullivan, M.; Tegmark, Max; Thyagarajan, Nithyanandan; Tingay, S. J.; Trott, Cathryn M.; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.; Williams, Anne; Williams, Christopher; Wu, Chen; Wyithe, J. Stuart B.; Zheng, Qian

doi:10.3847/0004-637x/830/1/38

Cited by 79 publications

(107 citation statements)

References 94 publications

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“…The motivation behind this choice is to create a more realistic model in the LF band. Observations indicate that Galactic polarized emission has a more local origin with decreasing frequency (e.g., Haverkorn et al 2004;Bernardi et al 2009;Lenc et al 2016) and, therefore, very little emission at high Faraday depth values. We will refer to this simulation as the "low φ" case (i.e.…”

Section: Polarized Foreground Modelmentioning

confidence: 99%

On the contamination of the global 21 cm signal from polarized foregrounds

Spinelli

Bernardi

Santos

2019

Monthly Notices of the Royal Astronomical Society

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Global (i.e. sky-averaged) 21 cm signal experiments can measure the evolution of the universe from the Cosmic Dawn to the Epoch of Reionization. These measurements are challenged by the presence of bright foreground emission that can be separated from the cosmological signal if its spectrum is smooth. This assumption fails in the case of single polarization antennas as they measure linearly polarized foreground emission -which is inevitably Faraday rotated through the interstellar medium. We investigate the impact of Galactic polarized foregrounds on the extraction of the global 21 cm signal through realistic sky and dipole simulations both in a low frequency band from 50 to 100 MHz, where a 21 cm absorption profile is expected, and in a higher frequency band (100 − 200 MHz). We find that the presence of a polarized contaminant with complex frequency structure can bias the amplitude and the shape of the reconstructed signal parameters in both bands. We investigate if polarized foregrounds can explain the unexpected 21 cm Cosmic Dawn signal recently reported by the EDGES collaboration. We find that unaccounted polarized foreground contamination can produce an enhanced and distorted 21 cm absorption trough similar to the anomalous profile reported by Bowman et al. (2018), and whose amplitude is in mild tension with the assumed input Gaussian profile (at ∼ 1.5σ level). Moreover, we note that, under the hypothesis of contamination from polarized foreground, the amplitude of the reconstructed EDGES signal can be overestimated by around 30%, mitigating the requirement for an explanation based on exotic physics.

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Section: Polarized Foreground Modelmentioning

confidence: 99%

On the contamination of the global 21 cm signal from polarized foregrounds

Spinelli

Bernardi

Santos

2019

Monthly Notices of the Royal Astronomical Society

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“…5) in that R.A. range, with the brightest being 28 Jy at 180 MHz. While it is not impossible that a source could be >10% polarized, the typical polarization fraction at these frequencies is much lower (Lenc et al 2016). In addition to the point sources of Hurley-Walker et al…”

Section: Features Of the Power Spectramentioning

confidence: 99%

Limits on Polarized Leakage for the PAPER Epoch of Reionization Measurements at 126 and 164 MHz

Moore

Aguirre

Kohn

et al. 2017

ApJ

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Polarized foreground emission is a potential contaminant of attempts to measure the fluctuation power spectrum of highly redshifted 21 cm H I emission from the epoch of reionization. Using the Donald C. Backer Precision Array for Probing the Epoch of Reionization, we present limits on the observed power spectra of all four Stokes parameters in two frequency bands, centered at 126 MHz (z=10.3) and 164 MHz (z=7.66), for a three-month observing campaign of a deployment involving 32 antennas, for which results on the unpolarized power spectrum have been reported at z=7.7 (by Parsons et al.) and at < < z 7.5 10.5 (by Jacobs et al.). The power spectra in this paper are processed in the same way as by those authors, and show no definitive detection of polarized power. This nondetection is consistent with what is known about polarized sources, combined with the suppression of polarized power by fluctuations in the ionospheric rotation measure, which can strongly affect Stokes Q and U. We are able to show that the net effect of polarized leakage is a negligible contribution at the levels of the limits reported by Parsons et al. and Jacobs et al.

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“…The LOFAR observation of the North Celestial Pole [117] also clearly shows diffuse emission on scales larger than a degree, while slightly higher levels are found on scales greater than 54 arcmin in the MWA observations at 154 MHz of the fields near the South Galactic Pole [76].…”

Section: Galactic Foregrounds In Total Intensitymentioning

confidence: 86%

Foregrounds and Their Mitigation

Chapman¹,

Jelić²

2019

The Cosmic 21-Cm Revolution

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The low-frequency radio sky is dominated by the diffuse synchrotron emission of our Galaxy and extragalactic radio sources related to Active Galactic Nuclei and star-forming galaxies. This foreground emission is much brighter than the cosmological 21 cm emission from the Cosmic Dawn and Epoch of Reionization. Studying the physical properties of the foregrounds is therefore of fundamental importance for their mitigation in the cosmological 21 cm experiments. This chapter gives a comprehensive overview of the foregrounds and our current state-of-the-art knowledge about their mitigation.

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Low-Frequency Observations of Linearly Polarized Structures in the Interstellar Medium Near the South Galactic Pole

Cited by 79 publications

References 94 publications

On the contamination of the global 21 cm signal from polarized foregrounds

On the contamination of the global 21 cm signal from polarized foregrounds

Limits on Polarized Leakage for the PAPER Epoch of Reionization Measurements at 126 and 164 MHz

Foregrounds and Their Mitigation

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