Initial LOFAR observations of epoch of reionization windows: Diffuse polarized emission in the ELAIS-N1 field

V. Jelic, A.G. de Bruyn, M. Mevius, F.B. Abdalla, K.M.B. Asad, G. Bernardi, M.A. Brentjens, S. Bus, E. Chapman, B. Ciardi, S. Daiboo, E.R. Fernandez, A. Ghosh, G. Harker, H. Jensen, S. Kazemi, L.V.E Koopmans, P. Labropoulos, Marinus Jan Bentum, P. Best & 1 others H. Falcke

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Abstract

Aims: This study aims to characterise the polarized foreground emission in the ELAIS-N1 field and to address its possible implications for extracting of the cosmological 21 cm signal from the LOw-Frequency ARray – Epoch of Reionization (LOFAR-EoR) data. Methods: We used the high band antennas of LOFAR to image this region and RM-synthesis to unravel structures of polarized emission at high Galactic latitudes.

Results: The brightness temperature of the detected Galactic emission is on average ~4 K in polarized intensity and covers the range from –10 to + 13 rad m-2 in Faraday depth. The total polarized intensity and polarization angle show a wide range of morphological features. We have also used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. The LOFAR and WSRT images show a similar complex morphology at comparable brightness levels, but their spatial correlation is very low. The fractional polarization at 150 MHz, expressed as a percentage of the total intensity, amounts to ≈1.5%. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies.

Conclusions: The wide frequency range, high angular resolution, and high sensitivity make LOFAR an exquisite instrument for studying Galactic polarized emission at a resolution of ~1–2 rad m-2 in Faraday depth. The different polarized patterns observed at 150 MHz and 350 MHz are consistent with different source distributions along the line of sight wring in a variety of Faraday thin regions of emission. The presence of polarized foregrounds is a serious complication for epoch of reionization experiments. To avoid the leakage of polarized emission into total intensity, which can depend on frequency, we need to calibrate the instrumental polarization across the field of view to a small fraction of 1%.
Original languageEnglish
Pages (from-to)1-12
Number of pages12
JournalAstronomy & astrophysics
Volume568
Issue numberA101
DOIs
Publication statusPublished - 7 Jul 2014

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LOFAR
time measurement
polarization
radio telescopes
synthesis
radio
brightness temperature
field of view
angular resolution
line of sight
leakage
antenna
brightness
indication
antennas
frequency ranges
sensitivity
high resolution

Keywords

  • EWI-25428
  • IR-93232
  • METIS-309730

Cite this

Jelic, V., de Bruyn, A. G., Mevius, M., Abdalla, F. B., Asad, K. M. B., Bernardi, G., ... Falcke, H. (2014). Initial LOFAR observations of epoch of reionization windows: Diffuse polarized emission in the ELAIS-N1 field. Astronomy & astrophysics, 568(A101), 1-12. https://doi.org/10.1051/0004-6361/201423998
Jelic, V. ; de Bruyn, A.G. ; Mevius, M. ; Abdalla, F.B. ; Asad, K.M.B. ; Bernardi, G. ; Brentjens, M.A. ; Bus, S. ; Chapman, E. ; Ciardi, B. ; Daiboo, S. ; Fernandez, E.R. ; Ghosh, A. ; Harker, G. ; Jensen, H. ; Kazemi, S. ; Koopmans, L.V.E ; Labropoulos, P. ; Bentum, Marinus Jan ; Best, P. ; Falcke, H. / Initial LOFAR observations of epoch of reionization windows: Diffuse polarized emission in the ELAIS-N1 field. In: Astronomy & astrophysics. 2014 ; Vol. 568, No. A101. pp. 1-12.
@article{b72070b829b84bef9b376452120fb373,
title = "Initial LOFAR observations of epoch of reionization windows: Diffuse polarized emission in the ELAIS-N1 field",
abstract = "Aims: This study aims to characterise the polarized foreground emission in the ELAIS-N1 field and to address its possible implications for extracting of the cosmological 21 cm signal from the LOw-Frequency ARray – Epoch of Reionization (LOFAR-EoR) data. Methods: We used the high band antennas of LOFAR to image this region and RM-synthesis to unravel structures of polarized emission at high Galactic latitudes. Results: The brightness temperature of the detected Galactic emission is on average ~4 K in polarized intensity and covers the range from –10 to + 13 rad m-2 in Faraday depth. The total polarized intensity and polarization angle show a wide range of morphological features. We have also used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. The LOFAR and WSRT images show a similar complex morphology at comparable brightness levels, but their spatial correlation is very low. The fractional polarization at 150 MHz, expressed as a percentage of the total intensity, amounts to ≈1.5{\%}. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies.Conclusions: The wide frequency range, high angular resolution, and high sensitivity make LOFAR an exquisite instrument for studying Galactic polarized emission at a resolution of ~1–2 rad m-2 in Faraday depth. The different polarized patterns observed at 150 MHz and 350 MHz are consistent with different source distributions along the line of sight wring in a variety of Faraday thin regions of emission. The presence of polarized foregrounds is a serious complication for epoch of reionization experiments. To avoid the leakage of polarized emission into total intensity, which can depend on frequency, we need to calibrate the instrumental polarization across the field of view to a small fraction of 1{\%}.",
keywords = "EWI-25428, IR-93232, METIS-309730",
author = "V. Jelic and {de Bruyn}, A.G. and M. Mevius and F.B. Abdalla and K.M.B. Asad and G. Bernardi and M.A. Brentjens and S. Bus and E. Chapman and B. Ciardi and S. Daiboo and E.R. Fernandez and A. Ghosh and G. Harker and H. Jensen and S. Kazemi and L.V.E Koopmans and P. Labropoulos and Bentum, {Marinus Jan} and P. Best and H. Falcke",
note = "eemcs-eprint-25428",
year = "2014",
month = "7",
day = "7",
doi = "10.1051/0004-6361/201423998",
language = "English",
volume = "568",
pages = "1--12",
journal = "Astronomy & astrophysics",
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Jelic, V, de Bruyn, AG, Mevius, M, Abdalla, FB, Asad, KMB, Bernardi, G, Brentjens, MA, Bus, S, Chapman, E, Ciardi, B, Daiboo, S, Fernandez, ER, Ghosh, A, Harker, G, Jensen, H, Kazemi, S, Koopmans, LVE, Labropoulos, P, Bentum, MJ, Best, P & Falcke, H 2014, 'Initial LOFAR observations of epoch of reionization windows: Diffuse polarized emission in the ELAIS-N1 field' Astronomy & astrophysics, vol. 568, no. A101, pp. 1-12. https://doi.org/10.1051/0004-6361/201423998

Initial LOFAR observations of epoch of reionization windows: Diffuse polarized emission in the ELAIS-N1 field. / Jelic, V.; de Bruyn, A.G.; Mevius, M.; Abdalla, F.B.; Asad, K.M.B.; Bernardi, G.; Brentjens, M.A.; Bus, S.; Chapman, E.; Ciardi, B.; Daiboo, S.; Fernandez, E.R.; Ghosh, A.; Harker, G.; Jensen, H.; Kazemi, S.; Koopmans, L.V.E; Labropoulos, P.; Bentum, Marinus Jan; Best, P.; Falcke, H.

In: Astronomy & astrophysics, Vol. 568, No. A101, 07.07.2014, p. 1-12.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Initial LOFAR observations of epoch of reionization windows: Diffuse polarized emission in the ELAIS-N1 field

AU - Jelic, V.

AU - de Bruyn, A.G.

AU - Mevius, M.

AU - Abdalla, F.B.

AU - Asad, K.M.B.

AU - Bernardi, G.

AU - Brentjens, M.A.

AU - Bus, S.

AU - Chapman, E.

AU - Ciardi, B.

AU - Daiboo, S.

AU - Fernandez, E.R.

AU - Ghosh, A.

AU - Harker, G.

AU - Jensen, H.

AU - Kazemi, S.

AU - Koopmans, L.V.E

AU - Labropoulos, P.

AU - Bentum, Marinus Jan

AU - Best, P.

AU - Falcke, H.

N1 - eemcs-eprint-25428

PY - 2014/7/7

Y1 - 2014/7/7

N2 - Aims: This study aims to characterise the polarized foreground emission in the ELAIS-N1 field and to address its possible implications for extracting of the cosmological 21 cm signal from the LOw-Frequency ARray – Epoch of Reionization (LOFAR-EoR) data. Methods: We used the high band antennas of LOFAR to image this region and RM-synthesis to unravel structures of polarized emission at high Galactic latitudes. Results: The brightness temperature of the detected Galactic emission is on average ~4 K in polarized intensity and covers the range from –10 to + 13 rad m-2 in Faraday depth. The total polarized intensity and polarization angle show a wide range of morphological features. We have also used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. The LOFAR and WSRT images show a similar complex morphology at comparable brightness levels, but their spatial correlation is very low. The fractional polarization at 150 MHz, expressed as a percentage of the total intensity, amounts to ≈1.5%. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies.Conclusions: The wide frequency range, high angular resolution, and high sensitivity make LOFAR an exquisite instrument for studying Galactic polarized emission at a resolution of ~1–2 rad m-2 in Faraday depth. The different polarized patterns observed at 150 MHz and 350 MHz are consistent with different source distributions along the line of sight wring in a variety of Faraday thin regions of emission. The presence of polarized foregrounds is a serious complication for epoch of reionization experiments. To avoid the leakage of polarized emission into total intensity, which can depend on frequency, we need to calibrate the instrumental polarization across the field of view to a small fraction of 1%.

AB - Aims: This study aims to characterise the polarized foreground emission in the ELAIS-N1 field and to address its possible implications for extracting of the cosmological 21 cm signal from the LOw-Frequency ARray – Epoch of Reionization (LOFAR-EoR) data. Methods: We used the high band antennas of LOFAR to image this region and RM-synthesis to unravel structures of polarized emission at high Galactic latitudes. Results: The brightness temperature of the detected Galactic emission is on average ~4 K in polarized intensity and covers the range from –10 to + 13 rad m-2 in Faraday depth. The total polarized intensity and polarization angle show a wide range of morphological features. We have also used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. The LOFAR and WSRT images show a similar complex morphology at comparable brightness levels, but their spatial correlation is very low. The fractional polarization at 150 MHz, expressed as a percentage of the total intensity, amounts to ≈1.5%. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies.Conclusions: The wide frequency range, high angular resolution, and high sensitivity make LOFAR an exquisite instrument for studying Galactic polarized emission at a resolution of ~1–2 rad m-2 in Faraday depth. The different polarized patterns observed at 150 MHz and 350 MHz are consistent with different source distributions along the line of sight wring in a variety of Faraday thin regions of emission. The presence of polarized foregrounds is a serious complication for epoch of reionization experiments. To avoid the leakage of polarized emission into total intensity, which can depend on frequency, we need to calibrate the instrumental polarization across the field of view to a small fraction of 1%.

KW - EWI-25428

KW - IR-93232

KW - METIS-309730

U2 - 10.1051/0004-6361/201423998

DO - 10.1051/0004-6361/201423998

M3 - Article

VL - 568

SP - 1

EP - 12

JO - Astronomy & astrophysics

JF - Astronomy & astrophysics

SN - 0004-6361

IS - A101

ER -