Table of Links
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Dara & Instruments
3.1. CHIME and GMIMS surveys and 3.2. CHIME/GMIMS Low Band North
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Features of the Tadpole
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The Origin of the Tadpole
5.1. Neutral Hydrogen Structure
5.2. Ionized Hydrogen Structure
APPENDIX
A. RESOLVED AND UNRESOLVED FARADAY COMPONENTS IN FARADAY SYNTHESIS
4.1. Morphology in single-frequency images
We show images of the tadpole region in Q and U at 614 MHz in Figure 2, image products derived from Faraday synthesis with CHIME in Figure 3, and pI and χ from the polarization data sets described above, covering 150 − 1420 MHz, in Figure 5. The tadpole is immediately apparent in the single-channel CHIME Q and U images in Figure 2 with a circular feature we call the “head” near (ℓ, b) = (137◦ , +7◦ ) and a “tail” extending to the right as far as (127◦ , +6◦ ), most clearly in U. The structure as a whole strongly resembles the larval stage of amphibians, leading us to nickname it the tadpole. We use the name ‘G137+7’ to refer to the circular region first identified by Verschuur (1968), and the name ‘tadpole’ to describe the entire feature, including the tail. The head (G137+7) is the feature which has been studied since Verschuur (1968); it is visible in all channels in Figure 5.
At 150 MHz (Fig. 5ab), the head is evident as a large, diffuse structure in pI. There is a circular pattern to the polarization angles, suggesting rapid wrapping through π radians as one moves outward radially from the center of the head.
At 410 MHz in the CHIME pI data, the clearest signature of the head is a narrow ring of low polarized intensity which extends in a nearly-complete circle. At 614 MHz, there is a similar ring of low polarized intensity, but only in a semicircle on the left (east) side of the head. This feature is one beam wide, a clear signature of beam depolarization, with the polarization angle changing within the beam such that there is destructive interference, reducing the polarized intensity (Sokoloff et al. 1998; Gaensler et al. 2001). The same feature is evident in pI from the Faraday synthesis products in Figure 3, but it does not stand out as much: by using information at a wide range of λ2, the Faraday synthesis product is less sensitive to beam depolarization than single-frequency images. Furthermore, if the depolarized ring arises from beam depolarization, we would not expect to see it in the ST+EMLS data due to the signficantly smaller beam (1′ compared to 30′). This is in fact
the case in Figure 5i: none of the head, the depolarized ring, or the tail is evident in pI.
In polarization angle, the 410 MHz CHIME data show a clear wrap through π radians moving radially from the center of the head to outside the ring (Fig. 5f). The tail of the tadpole stands out clearly, especially as a polarization angle feature in Figure 3c and Figure 5fh. The tadpole, both head and tail, is also visible at 1420 MHz in the ST+EMLS polarization angle image (Fig. 5j), despite not being evident in pI. The large-scale structure at 1420 MHz is similar to that observed in CHIME 614 MHz polarization angle (Fig. 5h), where the χ values agree in sign with that of ST+EMLS. The values of |χ| are smaller at 1420 MHz than at 614 MHz, which is consistent with the expected reduction in Faraday rotation at higher frequencies. We note some smaller structures on sub-tadpole scales in ST+EMLS data not present in CHIME which may arise from probing larger physical depths at a higher frequency and with a much smaller beam, combining to yield a more-distant polarization horizon (Uyaniker et al. 2003). In contrast, although the WSRT data have an angular resolution on the order of magnitude of the ST+EMLS data, the larger λ 2 means we expect the polarization horizon to be closer, possibly probing physical depths more similar to CHIME than to the ST+EMLS.
Authors:
(1) Nasser Mohammed, Department of Computer Science, Math, Physics, & Statistics, University of British Columbia, Okanagan Campus, Kelowna, BC V1V 1V7, Canada and Dominion Radio Astrophysical Observatory, Herzberg Research Centre for Astronomy and Astrophysics, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada;
(2) Anna Ordog, Department of Computer Science, Math, Physics, & Statistics, University of British Columbia, Okanagan Campus, Kelowna, BC V1V 1V7, Canada and Dominion Radio Astrophysical Observatory, Herzberg Research Centre for Astronomy and Astrophysics, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada;
(3) Rebecca A. Booth, Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada;
(4) Andrea Bracco, INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy and Laboratoire de Physique de l’Ecole Normale Superieure, ENS, Universit´e PSL, CNRS, Sorbonne Universite, Universite de Paris, F-75005 Paris, France;
(5) Jo-Anne C. Brown, Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada;
(6) Ettore Carretti, INAF-Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy;
(7) John M. Dickey, School of Natural Sciences, University of Tasmania, Hobart, Tas 7000 Australia;
(8) Simon Foreman, Department of Physics, Arizona State University, Tempe, AZ 85287, USA;
(9) Mark Halpern, Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 Canada;
(10) Marijke Haverkorn, Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands;
(11) Alex S. Hill, Department of Computer Science, Math, Physics, & Statistics, University of British Columbia, Okanagan Campus, Kelowna, BC V1V 1V7, Canada and Dominion Radio Astrophysical Observatory, Herzberg Research Centre for Astronomy and Astrophysics, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada;
(12) Gary Hinshaw, Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 Canada;
(13) Joseph W. Kania, Department of Physics and Astronomy, West Virginia University, P.O. Box 6315, Morgantown, WV 26506, USA and Center for Gravitational Waves and Cosmology, West Virginia University, Chestnut Ridge Research Building, Morgantown, WV 26505, USA;
(14) Roland Kothes, Dominion Radio Astrophysical Observatory, Herzberg Research Centre for Astronomy and Astrophysics, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada;
(15) T.L. Landecker, Dominion Radio Astrophysical Observatory, Herzberg Research Centre for Astronomy and Astrophysics, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada;
(16) Joshua MacEachern, Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 Canada;
(17) Kiyoshi W. Masui, MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA and Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA;
(18) Aimee Menard, Department of Computer Science, Math, Physics, & Statistics, University of British Columbia, Okanagan Campus, Kelowna, BC V1V 1V7, Canada and Dominion Radio Astrophysical Observatory, Herzberg Research Centre for Astronomy and Astrophysics, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada;
(19) Ryan R. Ransom, Dominion Radio Astrophysical Observatory, Herzberg Research Centre for Astronomy and Astrophysics, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada and Department of Physics and Astronomy, Okanagan College, Kelowna, BC V1Y 4X8, Canada;
(20) Wolfgang Reich, Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany;(21) Patricia Reich, 16
(22) J. Richard Shaw, Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 Canada
(23) Seth R. Siegel, Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo, ON N25 2YL, Canada, Department of Physics, McGill University, 3600 rue University, Montreal, QC H3A 2T8, Canada, and Trottier Space Institute, McGill University, 3550 rue University, Montreal, QC H3A 2A7, Canada;
(24) Mehrnoosh Tahani, Banting and KIPAC Fellowships: Kavli Institute for Particle Astrophysics & Cosmology (KIPAC), Stanford University, Stanford, CA 94305, USA;
(25) Alec J. M. Thomson, ATNF, CSIRO Space & Astronomy, Bentley, WA, Australia;
(26) Tristan Pinsonneault-Marotte, Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 Canada;
(27) Haochen Wang, MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA and Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA;
(28) Jennifer L. West, Dominion Radio Astrophysical Observatory, Herzberg Research Centre for Astronomy and Astrophysics, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9, Canada;
(29) Maik Wolleben, Skaha Remote Sensing Ltd., 3165 Juniper Drive, Naramata, BC V0H 1N0, Canada.
This paper is