Faraday moments of the Southern Twenty-centimeter All-sky Polarization Survey (STAPS)

¹ Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL, The Netherlands
² National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³ Department of Physics and Astronomy, The University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
⁴ School of Physics and Astronomy, Yunnan University, Kunming 650500, PR China
⁵ National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, PR China
⁶ School of Astronomy, University of Chinese Academy of Sciences, Beijing 100049, PR China
⁷ INAF Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
⁸ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁹ Department of Physics, Stanford University, Stanford, CA 94305, USA
¹⁰ Kavli Institute for Particle Astrophysics & Cosmology, PO Box 2450, Stanford University, Stanford, CA 94305, USA
¹¹ School of Natural Sciences, Private Bag 37, University of Tasmania, Hobart, TAS, Australia
¹² Dunlap Institute for Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
¹³ David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
¹⁴ Division of Physical and Biological Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
¹⁵ Dominion Radio Astrophysical Observatory, Herzberg Astronomy and Astrophysics Research Centre, National Research Council Canada, PO Box 248, Penticton, BC V2A 6J9 Canada
¹⁶ Department of Computer Science, Math, Physics, & Statistics, The University of British Columbia, Okanagan Campus, Kelowna, BC V1V 1V7, Canada
¹⁷ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
¹⁸ Banting and KIPAC Fellowships: Kavli Institute for Particle Astrophysics & Cosmology (KIPAC), Stanford University, Stanford, CA 94305, USA
¹⁹ Skaha Remote Sensing Ltd., 3165 Juniper Drive, Naramata, BC V0H 1N0, Canada

^★ Corresponding author; nergis.raycheva@ru.nl

Received: 9 February 2024
Accepted: 20 May 2024

Abstract

Context. Faraday tomography of broadband radio polarization surveys enables us to study magnetic fields and their interaction with the interstellar medium (ISM). Such surveys include the Global Magneto-Ionic Medium Survey (GMIMS), which covers the northern and southern hemispheres at ~300–1800 MHz.

Aims. In this work, we used the GMIMS High Band South (1328–1768 MHz), also named the Southern Twenty-centimeter All-sky Polarization Survey (STAPS), which observes the southern sky at a resolution of 18′.

Methods. To extract the key parameters of the magnetized ISM from STAPS, we computed the Faraday moments of the tomographic data cubes. These moments include the total polarized intensity, the mean Faraday depth weighted by the polarized intensity, the weighted dispersion of the Faraday spectrum, and its skewness. We compared the Faraday moments to those calculated over the same frequency range in the northern sky (using the Dominion Radio Astrophysical Observatory, DRAO), in a strip of 360°× 30° that overlaps with STAPS coverage.

Results. We find that the total polarized intensity is generally dominated by diffuse emission that decreases at longitudes of l ≤ 300°. The Faraday moments reveal a variety of polarization structures. Low-intensity regions at high latitudes usually have a single Faraday depth component. Due to its insufficiently large frequency coverage, STAPS cannot detect Faraday thick structures. Comparing the Faraday depths from STAPS to total rotation measures from extragalactic sources suggests that STAPS frequencies are high enough that the intervening ISM causes depolarization to background emission at intermediate and high Galactic latitudes. Where they overlap, the STAPS and DRAO surveys exhibit broad correspondence but differ in polarized intensity by a factor of ~1.8.