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Morgan, James

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Morgan, James
Author's Publications: search.filters.isAuthorOfPublication.70301571-c583-462f-a598-0c641575680e

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    Low frequency observations of linearly polarized structures in the interstellar medium near the south Galactic pole
    (American Astronomical Society, 2016) Lenc, E.; Gaensler, Bryan; Sun, X; Sadler, Evan; Willis, A. G.; Barry, Nicholas; Beardsley, A. P.; Bell, Marjorie; Bernardi, G.; Bowman, Jason; Briggs, Florence; 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, Lincoln; Hancock, P.; Hazelton, B. J.; Hewitt, Justina; Hindson, L.; Hurley-Walker, N.; Johnston-Hollitt, M.; Jacobs, Daniel; Kapińska, A. D.; Kaplan, Daniel; Kasper, Justin; Kim, Andrew Hyung-Do; Kratzenberg, E.; Line, J.; Loeb, Abraham; Lonsdale, C. J.; Lynch, M. J.; McKinley, B.; McWhirter, Sarah; Mitchell, Daniel; Morales, M. F.; Morgan, E.; Morgan, James; Murphy, Teresa; Neben, A. R.; Oberoi, D.; Offringa, A. R.; Ord, Stephen; Paul, S.; Pindor, B.; Pober, J. C.; Prabu, T.; Procopio, P.; Riding, J.; Rogers, Adrianne; Roshi, A.
    We present deep polarimetric observations at 154 MHz with the Murchison Widefield Array (MWA), covering 625 deg^2 centered on RA=0 h, Dec=-27 deg. 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 deg^2) 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 deg - 8 deg in extent) in linear polarization clearly detectable in ~2 minute snapshots, which would remain undetectable by interferometers with minimum baseline lengths >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 rad m^-2 to 10 rad m^-2 with a large fraction peaking at ~+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.