LOW-FREQUENCY OBSERVATIONS of LINEARLY POLARIZED STRUCTURES in the INTERSTELLAR MEDIUM NEAR the SOUTH GALACTIC POLE

E. Lenc, B. M. Gaensler, X. H. Sun, E. M. Sadler, A. G. Willis, N. Barry, A. P. Beardsley, M. E. Bell, G. Bernardi, Judd Bowman, F. Briggs, J. R. Callingham, R. J. Cappallo, P. Carroll, B. E. Corey, A. De Oliveira-Costa, A. A. Deshpande, J. S. Dillon, K. S. Dwarkanath, D. EmrichA. Ewall-Wice, L. Feng, B. Q. For, R. Goeke, L. J. Greenhill, P. Hancock, B. J. Hazelton, J. N. Hewitt, L. Hindson, N. Hurley-Walker, M. Johnston-Hollitt, Daniel Jacobs, A. D. Kapińska, D. L. Kaplan, J. C. Kasper, H. S. Kim, E. Kratzenberg, J. Line, A. Loeb, C. J. Lonsdale, M. J. Lynch, B. McKinley, S. R. McWhirter, D. A. Mitchell, M. F. Morales, E. Morgan, J. Morgan, T. Murphy, A. R. Neben, D. Oberoi, A. R. Offringa, S. M. Ord, S. Paul, B. Pindor, J. C. Pober, T. Prabu, P. Procopio, J. Riding, A. E E Rogers, A. Roshi, N. Udaya Shankar, S. K. Sethi, K. S. Srivani, L. Staveley-Smith, R. Subrahmanyan, I. S. Sullivan, M. Tegmark, Nithyanandan Thyagarajan, S. J. Tingay, C. Trott, M. Waterson, R. B. Wayth, R. L. Webster, A. R. Whitney, A. Williams, C. L. Williams, C. Wu, J. S B Wyithe, Q. Zheng

Research output: Contribution to journalArticle

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Abstract

We present deep polarimetric observations at 154 MHz with the Murchison Widefield Array (MWA), covering 625 deg2 centered on α = 0hand δ = -27°. The sensitivity available in our deep observations allows an in-band, frequency-dependent analysis of polarized structure for the first time at long wavelengths. Our analysis suggests that the polarized structures are dominated by intrinsic emission but may also have a foreground Faraday screen component. At these wavelengths, the compactness of the MWA baseline distribution provides excellent snapshot sensitivity to large-scale structure. The observations are sensitive to diffuse polarized emission at ∼54′ resolution with a sensitivity of 5.9 mJy beam-1 and compact polarized sources at ∼2.′4 resolution with a sensitivity of 2.3 mJy beam-1 for a subset (400 deg2) of this field. The sensitivity allows the effect of ionospheric Faraday rotation to be spatially and temporally measured directly from the diffuse polarized background. Our observations reveal large-scale structures (∼1°-8° in extent) in linear polarization clearly detectable in ∼2 minute snapshots, which would remain undetectable by interferometers with minimum baseline lengths of >110 m at 154 MHz. The brightness temperature of these structures is on average 4 K in polarized intensity, peaking at 11 K. Rotation measure synthesis reveals that the structures have Faraday depths ranging from -2 to 10 rad m-2 with a large fraction peaking at approximately +1 rad m-2. We estimate a distance of 51 20 pc to the polarized emission based on measurements of the in-field pulsar J2330-2005. We detect four extragalactic linearly polarized point sources within the field in our compact source survey. Based on the known polarized source population at 1.4 GHz and non-detections at 154 MHz, we estimate an upper limit on the depolarization ratio of 0.08 from 1.4 GHz to 154 MHz.

Original languageEnglish (US)
Article number38
JournalAstrophysical Journal
Volume830
Issue number1
DOIs
StatePublished - Oct 10 2016

Fingerprint

sensitivity
wavelength
interferometer
brightness temperature
point source
polarization
void ratio
estimates
Faraday effect
linear polarization
wavelengths
depolarization
pulsars
ionospherics
point sources
set theory
coverings
interferometers
synthesis
analysis

Keywords

  • ISM: magnetic fields
  • ISM: structure
  • magnetic fields
  • polarization
  • radio continuum: ISM
  • techniques: polarimetric

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Lenc, E., Gaensler, B. M., Sun, X. H., Sadler, E. M., Willis, A. G., Barry, N., ... Zheng, Q. (2016). LOW-FREQUENCY OBSERVATIONS of LINEARLY POLARIZED STRUCTURES in the INTERSTELLAR MEDIUM NEAR the SOUTH GALACTIC POLE. Astrophysical Journal, 830(1), [38]. https://doi.org/10.3847/0004-637X/830/1/38

LOW-FREQUENCY OBSERVATIONS of LINEARLY POLARIZED STRUCTURES in the INTERSTELLAR MEDIUM NEAR the SOUTH GALACTIC POLE. / Lenc, E.; Gaensler, B. M.; Sun, X. H.; Sadler, E. M.; Willis, A. G.; Barry, N.; Beardsley, A. P.; Bell, M. E.; Bernardi, G.; Bowman, Judd; Briggs, F.; Callingham, J. R.; Cappallo, R. J.; Carroll, P.; Corey, B. E.; Oliveira-Costa, A. De; Deshpande, A. A.; Dillon, J. S.; Dwarkanath, K. S.; Emrich, D.; Ewall-Wice, A.; Feng, L.; For, B. Q.; Goeke, R.; Greenhill, L. J.; Hancock, P.; Hazelton, B. J.; Hewitt, J. N.; Hindson, L.; Hurley-Walker, N.; Johnston-Hollitt, M.; Jacobs, Daniel; Kapińska, A. D.; Kaplan, D. L.; Kasper, J. C.; Kim, H. S.; Kratzenberg, E.; Line, J.; Loeb, A.; Lonsdale, C. J.; Lynch, M. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Morgan, J.; Murphy, T.; Neben, A. R.; Oberoi, D.; Offringa, A. R.; Ord, S. M.; Paul, S.; Pindor, B.; Pober, J. C.; Prabu, T.; Procopio, P.; Riding, J.; Rogers, A. E E; Roshi, A.; Shankar, N. Udaya; Sethi, S. K.; Srivani, K. S.; Staveley-Smith, L.; Subrahmanyan, R.; Sullivan, I. S.; Tegmark, M.; Thyagarajan, Nithyanandan; Tingay, S. J.; Trott, C.; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.; Wu, C.; Wyithe, J. S B; Zheng, Q.

In: Astrophysical Journal, Vol. 830, No. 1, 38, 10.10.2016.

Research output: Contribution to journalArticle

Lenc, E, Gaensler, BM, Sun, XH, Sadler, EM, Willis, AG, Barry, N, Beardsley, AP, Bell, ME, Bernardi, G, Bowman, J, Briggs, F, Callingham, JR, Cappallo, RJ, Carroll, P, Corey, BE, Oliveira-Costa, AD, Deshpande, AA, Dillon, JS, Dwarkanath, KS, Emrich, D, Ewall-Wice, A, Feng, L, For, BQ, Goeke, R, Greenhill, LJ, Hancock, P, Hazelton, BJ, Hewitt, JN, Hindson, L, Hurley-Walker, N, Johnston-Hollitt, M, Jacobs, D, Kapińska, AD, Kaplan, DL, Kasper, JC, Kim, HS, Kratzenberg, E, Line, J, Loeb, A, Lonsdale, CJ, Lynch, MJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Morgan, J, Murphy, T, Neben, AR, Oberoi, D, Offringa, AR, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Rogers, AEE, Roshi, A, Shankar, NU, Sethi, SK, Srivani, KS, Staveley-Smith, L, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Thyagarajan, N, Tingay, SJ, Trott, C, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Wu, C, Wyithe, JSB & Zheng, Q 2016, 'LOW-FREQUENCY OBSERVATIONS of LINEARLY POLARIZED STRUCTURES in the INTERSTELLAR MEDIUM NEAR the SOUTH GALACTIC POLE', Astrophysical Journal, vol. 830, no. 1, 38. https://doi.org/10.3847/0004-637X/830/1/38
Lenc, E. ; Gaensler, B. M. ; Sun, X. H. ; Sadler, E. M. ; Willis, A. G. ; Barry, N. ; Beardsley, A. P. ; Bell, M. E. ; Bernardi, G. ; Bowman, Judd ; Briggs, F. ; Callingham, J. R. ; Cappallo, R. J. ; Carroll, P. ; Corey, B. E. ; Oliveira-Costa, A. De ; Deshpande, A. A. ; Dillon, J. S. ; Dwarkanath, K. S. ; Emrich, D. ; Ewall-Wice, A. ; Feng, L. ; For, B. Q. ; Goeke, R. ; Greenhill, L. J. ; Hancock, P. ; Hazelton, B. J. ; Hewitt, J. N. ; Hindson, L. ; Hurley-Walker, N. ; Johnston-Hollitt, M. ; Jacobs, Daniel ; Kapińska, A. D. ; Kaplan, D. L. ; Kasper, J. C. ; Kim, H. S. ; Kratzenberg, E. ; Line, J. ; Loeb, A. ; Lonsdale, C. J. ; Lynch, M. J. ; McKinley, B. ; McWhirter, S. R. ; Mitchell, D. A. ; Morales, M. F. ; Morgan, E. ; Morgan, J. ; Murphy, T. ; Neben, A. R. ; Oberoi, D. ; Offringa, A. R. ; Ord, S. M. ; Paul, S. ; Pindor, B. ; Pober, J. C. ; Prabu, T. ; Procopio, P. ; Riding, J. ; Rogers, A. E E ; Roshi, A. ; Shankar, N. Udaya ; Sethi, S. K. ; Srivani, K. S. ; Staveley-Smith, L. ; Subrahmanyan, R. ; Sullivan, I. S. ; Tegmark, M. ; Thyagarajan, Nithyanandan ; Tingay, S. J. ; Trott, C. ; Waterson, M. ; Wayth, R. B. ; Webster, R. L. ; Whitney, A. R. ; Williams, A. ; Williams, C. L. ; Wu, C. ; Wyithe, J. S B ; Zheng, Q. / LOW-FREQUENCY OBSERVATIONS of LINEARLY POLARIZED STRUCTURES in the INTERSTELLAR MEDIUM NEAR the SOUTH GALACTIC POLE. In: Astrophysical Journal. 2016 ; Vol. 830, No. 1.
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title = "LOW-FREQUENCY OBSERVATIONS of LINEARLY POLARIZED STRUCTURES in the INTERSTELLAR MEDIUM NEAR the SOUTH GALACTIC POLE",
abstract = "We present deep polarimetric observations at 154 MHz with the Murchison Widefield Array (MWA), covering 625 deg2 centered on α = 0hand δ = -27°. The sensitivity available in our deep observations allows an in-band, frequency-dependent analysis of polarized structure for the first time at long wavelengths. Our analysis suggests that the polarized structures are dominated by intrinsic emission but may also have a foreground Faraday screen component. At these wavelengths, the compactness of the MWA baseline distribution provides excellent snapshot sensitivity to large-scale structure. The observations are sensitive to diffuse polarized emission at ∼54′ resolution with a sensitivity of 5.9 mJy beam-1 and compact polarized sources at ∼2.′4 resolution with a sensitivity of 2.3 mJy beam-1 for a subset (400 deg2) of this field. The sensitivity allows the effect of ionospheric Faraday rotation to be spatially and temporally measured directly from the diffuse polarized background. Our observations reveal large-scale structures (∼1°-8° in extent) in linear polarization clearly detectable in ∼2 minute snapshots, which would remain undetectable by interferometers with minimum baseline lengths of >110 m at 154 MHz. The brightness temperature of these structures is on average 4 K in polarized intensity, peaking at 11 K. Rotation measure synthesis reveals that the structures have Faraday depths ranging from -2 to 10 rad m-2 with a large fraction peaking at approximately +1 rad m-2. We estimate a distance of 51 20 pc to the polarized emission based on measurements of the in-field pulsar J2330-2005. We detect four extragalactic linearly polarized point sources within the field in our compact source survey. Based on the known polarized source population at 1.4 GHz and non-detections at 154 MHz, we estimate an upper limit on the depolarization ratio of 0.08 from 1.4 GHz to 154 MHz.",
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TY - JOUR

T1 - LOW-FREQUENCY OBSERVATIONS of LINEARLY POLARIZED STRUCTURES in the INTERSTELLAR MEDIUM NEAR the SOUTH GALACTIC POLE

AU - Lenc, E.

AU - Gaensler, B. M.

AU - Sun, X. H.

AU - Sadler, E. M.

AU - Willis, A. G.

AU - Barry, N.

AU - Beardsley, A. P.

AU - Bell, M. E.

AU - Bernardi, G.

AU - Bowman, Judd

AU - Briggs, F.

AU - Callingham, J. R.

AU - Cappallo, R. J.

AU - Carroll, P.

AU - Corey, B. E.

AU - Oliveira-Costa, A. De

AU - Deshpande, A. A.

AU - Dillon, J. S.

AU - Dwarkanath, K. S.

AU - Emrich, D.

AU - Ewall-Wice, A.

AU - Feng, L.

AU - For, B. Q.

AU - Goeke, R.

AU - Greenhill, L. J.

AU - Hancock, P.

AU - Hazelton, B. J.

AU - Hewitt, J. N.

AU - Hindson, L.

AU - Hurley-Walker, N.

AU - Johnston-Hollitt, M.

AU - Jacobs, Daniel

AU - Kapińska, A. D.

AU - Kaplan, D. L.

AU - Kasper, J. C.

AU - Kim, H. S.

AU - Kratzenberg, E.

AU - Line, J.

AU - Loeb, A.

AU - Lonsdale, C. J.

AU - Lynch, M. J.

AU - McKinley, B.

AU - McWhirter, S. R.

AU - Mitchell, D. A.

AU - Morales, M. F.

AU - Morgan, E.

AU - Morgan, J.

AU - Murphy, T.

AU - Neben, A. R.

AU - Oberoi, D.

AU - Offringa, A. R.

AU - Ord, S. M.

AU - Paul, S.

AU - Pindor, B.

AU - Pober, J. C.

AU - Prabu, T.

AU - Procopio, P.

AU - Riding, J.

AU - Rogers, A. E E

AU - Roshi, A.

AU - Shankar, N. Udaya

AU - Sethi, S. K.

AU - Srivani, K. S.

AU - Staveley-Smith, L.

AU - Subrahmanyan, R.

AU - Sullivan, I. S.

AU - Tegmark, M.

AU - Thyagarajan, Nithyanandan

AU - Tingay, S. J.

AU - Trott, C.

AU - Waterson, M.

AU - Wayth, R. B.

AU - Webster, R. L.

AU - Whitney, A. R.

AU - Williams, A.

AU - Williams, C. L.

AU - Wu, C.

AU - Wyithe, J. S B

AU - Zheng, Q.

PY - 2016/10/10

Y1 - 2016/10/10

N2 - We present deep polarimetric observations at 154 MHz with the Murchison Widefield Array (MWA), covering 625 deg2 centered on α = 0hand δ = -27°. The sensitivity available in our deep observations allows an in-band, frequency-dependent analysis of polarized structure for the first time at long wavelengths. Our analysis suggests that the polarized structures are dominated by intrinsic emission but may also have a foreground Faraday screen component. At these wavelengths, the compactness of the MWA baseline distribution provides excellent snapshot sensitivity to large-scale structure. The observations are sensitive to diffuse polarized emission at ∼54′ resolution with a sensitivity of 5.9 mJy beam-1 and compact polarized sources at ∼2.′4 resolution with a sensitivity of 2.3 mJy beam-1 for a subset (400 deg2) of this field. The sensitivity allows the effect of ionospheric Faraday rotation to be spatially and temporally measured directly from the diffuse polarized background. Our observations reveal large-scale structures (∼1°-8° in extent) in linear polarization clearly detectable in ∼2 minute snapshots, which would remain undetectable by interferometers with minimum baseline lengths of >110 m at 154 MHz. The brightness temperature of these structures is on average 4 K in polarized intensity, peaking at 11 K. Rotation measure synthesis reveals that the structures have Faraday depths ranging from -2 to 10 rad m-2 with a large fraction peaking at approximately +1 rad m-2. We estimate a distance of 51 20 pc to the polarized emission based on measurements of the in-field pulsar J2330-2005. We detect four extragalactic linearly polarized point sources within the field in our compact source survey. Based on the known polarized source population at 1.4 GHz and non-detections at 154 MHz, we estimate an upper limit on the depolarization ratio of 0.08 from 1.4 GHz to 154 MHz.

AB - We present deep polarimetric observations at 154 MHz with the Murchison Widefield Array (MWA), covering 625 deg2 centered on α = 0hand δ = -27°. The sensitivity available in our deep observations allows an in-band, frequency-dependent analysis of polarized structure for the first time at long wavelengths. Our analysis suggests that the polarized structures are dominated by intrinsic emission but may also have a foreground Faraday screen component. At these wavelengths, the compactness of the MWA baseline distribution provides excellent snapshot sensitivity to large-scale structure. The observations are sensitive to diffuse polarized emission at ∼54′ resolution with a sensitivity of 5.9 mJy beam-1 and compact polarized sources at ∼2.′4 resolution with a sensitivity of 2.3 mJy beam-1 for a subset (400 deg2) of this field. The sensitivity allows the effect of ionospheric Faraday rotation to be spatially and temporally measured directly from the diffuse polarized background. Our observations reveal large-scale structures (∼1°-8° in extent) in linear polarization clearly detectable in ∼2 minute snapshots, which would remain undetectable by interferometers with minimum baseline lengths of >110 m at 154 MHz. The brightness temperature of these structures is on average 4 K in polarized intensity, peaking at 11 K. Rotation measure synthesis reveals that the structures have Faraday depths ranging from -2 to 10 rad m-2 with a large fraction peaking at approximately +1 rad m-2. We estimate a distance of 51 20 pc to the polarized emission based on measurements of the in-field pulsar J2330-2005. We detect four extragalactic linearly polarized point sources within the field in our compact source survey. Based on the known polarized source population at 1.4 GHz and non-detections at 154 MHz, we estimate an upper limit on the depolarization ratio of 0.08 from 1.4 GHz to 154 MHz.

KW - ISM: magnetic fields

KW - ISM: structure

KW - magnetic fields

KW - polarization

KW - radio continuum: ISM

KW - techniques: polarimetric

UR - http://www.scopus.com/inward/record.url?scp=84990984030&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84990984030&partnerID=8YFLogxK

U2 - 10.3847/0004-637X/830/1/38

DO - 10.3847/0004-637X/830/1/38

M3 - Article

AN - SCOPUS:84990984030

VL - 830

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

M1 - 38

ER -