Peering into the Milky Way by FAST: III. Magnetic fields in the Galactic halo and farther spiral arms revealed by the Faraday effect of faint pulsars

Abstract

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the most sensitive radio telescope for pulsar observations. We make polarimetric measurements of a large number of faint and distant pulsars using the FAST. We present the new measurements of Faraday rotation for 134 faint pulsars in the Galactic halo. Significant improvements are also made for some basic pulsar parameters for 15 of them. We analyse the newly determined rotation measures (RMs) for the Galactic magnetic fields by using these 134 halo pulsars, together with previously available RMs for pulsars and extragalactic radio sources and also the newly determined RMs for another 311 faint pulsars which are either newly discovered in the project of the Galactic Plane Pulsar Snapshot (GPPS) survey or previously known pulsars without RMs. The RM tomographic analysis in the first Galactic quadrant gives roughly the same field strength of around 2 µG for the large-scale toroidal halo magnetic fields. The scale height of the halo magnetic fields is found to be at least 2.7±0.3 kpc. The RM differentiation of a large number of pulsars in the Galactic disk in the Galactic longitude range of 26 • < l < 90 • gives evidence for the clockwise magnetic fields (viewed from the north Galactic pole) in two interarm regions inside the Scutum arm and between the Scutum and Sagittarius arm, and the clockwise fields in the Local-Perseus interarm region and field reversals in the Perseus arm and beyond.

FAST Pulsar Database. I. Polarization Profiles of 682 Pulsars

“…The degrees of linear, circular and absolute circular polarization and their uncertainties are listed in columns (10)-( 12) respectively. We obtain new RMs (i.e., RM = RM obs − RM ion ) for 402 pulsars as given in column (13), which have been employed to investigate the magnetic fields in the Galaxy by Xu et al (2022). The figure number for polarization profile, and the short notes as well as references for profile comparison are given in columns ( 14)-( 16) respectively.…”

The Huge Magnetic Toroids in the Milky Way Halo

“…We obtain a sample of the RMs of 59,233 background radio sources, with the overall mean number density of 1.5 deg −2 (see Figure 1). For pulsars, except for the RMs collected from radio observations all over the world (Manchester et al 2005), we have also got our own pulsar RM data for faint pulsars (Xu et al 2022;Wang et al 2023), observed by using the Five-hundred-meter Aperture Spherical radio Telescope (FAST; Nan 2008). In total, we have the RMs of 634 pulsars at Galactic latitudes greater than 8°(see Figure 1).…”

“…The remaining pulsars are too faint to be measured efficiently for RMs by other radio telescopes. We carried out the FAST polarization observations by two projects (PT2020_0164 and PT2021_0051) from 2020 October to 2021 November, and we determined new RM values for 134 faint halo pulsars (Xu et al 2022). The pulsar data density is improved in the left-sky part (i.e., the first and the second quadrants of our Galaxy).…”

“…e us Source At present, the Galactic distribution of the electron density in the Milky Way has been modeled from pulsar DMs and independently measured distances (Cordes & Lazio 2002;Yao et al 2017). Based on the RMs and DMs of a large number of pulsars, as well as the RMs of background radio sources at the lower Galactic latitudes, e.g., within 8°from the Galactic plane, the large-scale magnetic fields 3 in the Galactic disk have been revealed to follow spiral arms, with reversals between the arms and interarm regions (Han et al 2006(Han et al , 2018Xu et al 2022).…”

The GPPS HI survey—A deeper view of the Milky Way galaxy

“…The Five-hundred-meter Aperture Spherical radio Telescope, FAST, has done this survey as part of the Galactic Plane Pulsar Snapshot (GPPS) Survey [2]. The primary goal is to find pulsars in the Galactic plane, 500 have been found already, but the survey has secondary applications to mapping the neutral atomic interstellar medium with the HI line [1], the ionized medium using recombination lines [3], and the magnetic field through measurement of Faraday rotation of pulsars [4]. This special edition includes papers describing results of all these projects; the background and significance of the HI data are considered in this News & Views piece.…”