Rotation Measures of Extragalactic Sources behind the Southern Galactic Plane: New Insights into the Large-Scale Magnetic Field of the Inner Milky Way

By Jc Brown, M. Haverkorn, B. Gaensler, A. Taylor, N. Bizunok, N. McClure-Griffiths, J. Dickey, A. Green. 2007

197 citations recorded by the source corpus.

We present new Faraday rotation measures (RMs) for 148 extragalactic radio sources behind the southern Galactic plane (253° ≤ l ≤ 356°, |b| ≤ 1.5°), and use these data in combination with published data to probe the large-scale structure of the Milky Way's magnetic field. We show that the magnitudes of these RMs oscillate with longitude in a manner that correlates with the locations of the Galactic spiral arms. The observed pattern in RMs requires the presence of at least one large-scale magnetic reversal in the fourth Galactic quadrant, located between the Sagittarius-Carina and Scutum-Crux spiral arms. To quantitatively compare our measurements to other recent studies, we consider all available extragalactic and pulsar RMs in the region we have surveyed, and jointly fit these data to simple models in which the large-scale field follows the spiral arms. In the best-fitting model, the magnetic field in the fourth Galactic quadrant is directed clockwise in the Sagittarius-Carina spiral arm (as viewed from the north Galactic pole), but is oriented counterclockwise in the Scutum-Crux arm. This contrasts with recent analyses of pulsar RMs alone, in which the fourth-quadrant field was presumed to be directed counterclockwise in the Sagittarius-Carina arm. Also in contrast to recent pulsar RM studies, our joint modeling of pulsar and extragalactic RMs demonstrates that large numbers of large-scale magnetic field reversals are not required to account for observations.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/39d362e875f580edbb87dcaad7169196e40316e9

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In Astronomy and Astrophysics

1. A. Strong
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Citations in the corpus

• Science with the Australian Square Kilometre Array Pathfinder (2007, background): “Until recently (Brown et al. 2003, 2007) there had been comparatively few EGS RMs available, while studies utilising pulsar RMs alone have been limited both by the comparatively sparse sampling of pulsars on the sky and by uncertainties in pulsar distances.”
• DERIVING THE GLOBAL STRUCTURE OF THE GALACTIC MAGNETIC FIELD FROM FARADAY ROTATION MEASURES OF EXTRAGALACTIC SOURCES (2011, methodology): “The remaining RM’s are taken from the Canadian Galactic Plane Survey (Brown et al. 2003), the Southern Galactic Plane Survey (Brown et al. 2007), and two smaller published lists from Klein et al. (2003) (108 RMs) and (Mao et al. 2008) (68 RMs).”
• Complex Faraday depth structure of active galactic nuclei as revealed by broad‐band radio polarimetry (2012, background): “Many studies have used these extragalactic background sources to study the strength and structure of magnetic fields in our Galaxy (e.g. Brown et al. 2007; Taylor, Stil & Sunstrum 2009; Mao et al. 2010; Harvey-Smith, Madsen & Gaensler 2011; Van Eck et al. 2011), other galaxies (e.g. Gaensler et al.…”
• A NEW MODEL OF THE GALACTIC MAGNETIC FIELD (2012, methodology): “We also note that Brown et al. (2007) reported a counterclockwise field in the molecular ring, while we find a very weak field that is mostly present in the model via the superimposed halo and X-field.”
• The 511 keV emission from positron annihilation in the Galaxy (2010, background): “It is now widely accepted that Bu reverses several times with decreasing radius, but the number and radial locations of the reversals are still highly controversial (Brown et al., 2007; Han et al., 2006, 1999; Rand and Lyne, 1994; Vallée, 2005).”
• Radio and millimeter continuum surveys and their astrophysical implications (2009, methodology): “(Subsequent to surveys, thousands of measurements of polarization on individual sources have been carried out at different frequencies, with the rotation measures thus derived used to map the details of the Galactic magnetic field – see e.g. Brown et al. (2007)).”
• Magnetic Fields in Galaxies (2010, background): “The azimuthal field reverses sign at least once with Galactocentric radius (Brown et al. 2007), possibly more (Han 2009).”
• The Australia Telescope Compact Array Broadband Backend (CABB): Description & First Results ⋆ (2011, methodology): “In particular Faraday rotation, an effect where the plane of polarization of a radio wave is rotated when the wave passes through an ionised region with an embedded magnetic field, has been a very popular method over many years (Gaensler et al. 2005; Brown et al. 2007).”
• Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust (2014, methodology): “Using the catalogues of Brown et al. (2003), Brown et al. (2007), Taylor et al. (2009), and Van Eck et al. (2011), in Fig.”
• Cosmological Magnetic Fields: Their Generation, Evolution and Observation (2013, background): “However, our knowledge of the Galactic magnetic field is rather limited (Han and Qiao 1994; Brown et al 2007; Pshirkov et al 2011; Jansson and Farrar 2012a,b; Oppermann et al 2012) and there still are large uncertainties in Galactic field models.”
• The Outer Scale of Turbulence in the Magnetoionized Galactic Interstellar Medium (2008, methodology): “The figure is similar to Figure 1 in Haverkorn et al. (2006b), except here we have used the finalized RM list in Brown et al. (2007) and discarded the 27 sources in Table 1.”
• Cosmic-ray propagation with DRAGON2: I. numerical solver and astrophysical ingredients (2016, background): “• The disk component is a generalisation of the model derived in [101].”
• Radio observational constraints on Galactic 3D-emission models (2007, methodology): “For the SGPS data the binning procedure is the same as used by Brown et al. (2007).”
• An improved map of the Galactic Faraday sky (2011, background): “…measures of extragalactic radio sources are those by Brown & Taylor (2001), Mao et al. (2010), Kronberg & Newton-McGee (2011), Pshirkov et al. (2011), and Brown et al. (2003b, 2007), Nota & Katgert (2010), and Van Eck et al. (2011), who supplemented extragalactic RMs with pulsar rotation measures.”