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 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.
Keywords
Cite
@article{arxiv.1607.05779,
title = {Low frequency observations of linearly polarized structures in the interstellar medium near the south Galactic pole},
author = {Emil Lenc and B. M. Gaensler and X. H. Sun and E. M. Sadler and A. G. Willis and N. Barry and A. P. Beardsley and M. E. Bell and G. Bernardi and J. D. Bowman and F. Briggs and J. R. Callingham and R. J. Cappallo and P. Carroll and B. E. Corey and A. de Oliveira-Costa and A. A. Deshpande and J. S. Dillon and K. S. Dwarkanath and D. Emrich and A. Ewall-Wice and L. Feng and B. -Q. For and R. Goeke and L. J. Greenhill and P. Hancock and B. J. Hazelton and J. N. Hewitt and L. Hindson and N. Hurley-Walker and M. Johnston-Hollitt and D. C. Jacobs and A. D. Kapinska and D. L. Kaplan and J. C. Kasper and H. -S. Kim and E. Kratzenberg and J. Line and A. Loeb and C. J. Lonsdale and M. J. Lynch and B. McKinley and S. R. McWhirter and D. A. Mitchell and M. F. Morales and E. Morgan and J. Morgan and T. Murphy and A. R. Neben and D. Oberoi and A. R. Offringa and S. M. Ord and S. Paul and B. Pindor and J. C. Pober and T. Prabu and P. Procopio and J. Riding and A. E. E. Rogers and A. Roshi and N. Udaya Shankar and S. K. Sethi and K. S. Srivani and L. Staveley-Smith and R. Subrahmanyan and I. S. Sullivan and M. Tegmark and Nithyanandan Thyagarajan and S. J. Tingay and C. Trott and M. Waterson and R. B. Wayth and R. L. Webster and A. R. Whitney and A. Williams and C. L. Williams and C. Wu and J. S. B. Wyithe and Q. Zheng},
journal= {arXiv preprint arXiv:1607.05779},
year = {2016}
}
Comments
32 pages, 20 figures, accepted to ApJ