A Radio-Polarization and Rotation Measure Study of the Gum Nebula and Its Environment

Purcell, Cormac; Gaensler, B. M.; Sun, Xiaohui; Carretti, E.; Bernardi, G.; Haverkorn, M.; Kesteven, Michael; Poppi, S.; Schnitzeler, Dominic; Staveley‐Smith, L.

doi:10.1088/0004-637x/804/1/22

Cited by 50 publications

(46 citation statements)

References 129 publications

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“…Our highest RM values exceed those published for sources behind Galactic H II regions. Vallée & Bignell (1983), Purcell et al (2015), and Ma et al (2019) reported |RM | up to 633 rad m −2 behind the Gum nebula. Harvey-Smith et al (2011) found |RM | 300 rad m −2 behind a sample of large-diameter, high-latitude, H II regions.…”

Section: Resultsmentioning

confidence: 94%

Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm

Shanahan

Lemmer

Stil

et al. 2019

ApJL

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We present first results for Faraday rotation of compact polarized sources (1 to 2 GHz continuum) in The HI/OH/Recombination line (THOR) survey of the inner Galaxy. In the Galactic longitude range 39 • < < 52 • , we find rotation measures in the range −310 rad m −2 ≤ RM ≤ +4219 rad m −2 , with the highest values concentrated within a degree of = 48 • at the Sagittarius arm tangent. Most of the high RM s arise in diffuse plasma, along lines of sight that do not intersect H II regions. For > 49 • , RM drops off rapidly, while at < 47 • , the mean RM is higher with a larger standard deviation than at > 49 • . We attribute the RM structure to the compressed diffuse Warm Ionized Medium in the spiral arm, upstream of the major star formation regions. The Sagittarius arm acts as a significant Faraday screen inside the Galaxy. This has implications for models of the Galactic magnetic field and the expected amount of Faraday rotation of Fast Radio Bursts from their host galaxies. We emphasize the importance of sensitivity to high Faraday depth in future polarization surveys.

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Section: Resultsmentioning

confidence: 94%

Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm

Shanahan

Lemmer

Stil

et al. 2019

ApJL

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“…Chanot & Sivan 1983). Its origin is still debated, although most authors suggest that the nebula is likely an old supernova remnant (Woermann et al 2001;Purcell et al 2015). The Gum nebula is located about 500 pc from us, straddles the plane of the Milky Way (extending from l ∼-15 • to l ∼+15 • ), and our line of sight in its direction overlaps with a number of different objects (Fig.…”

Section: The Large-scale Structure and The Iras Vela Shellmentioning

confidence: 89%

A ring in a shell: the large-scale 6D structure of the Vela OB2 complex

Cantat-Gaudin

Mapelli

Balaguer-Núñez

et al. 2019

A&A

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Context. The Vela OB2 association is a group of ∼10 Myr stars exhibiting a complex spatial and kinematic substructure. The all-sky Gaia DR2 catalogue contains proper motions, parallaxes (a proxy for distance), and photometry that allow us to separate the various components of Vela OB2. Aims. We characterise the distribution of the Vela OB2 stars on a large spatial scale, and study its internal kinematics and dynamic history. Methods. We make use of Gaia DR2 astrometry and published Gaia-ESO Survey data. We apply an unsupervised classification algorithm to determine groups of stars with common proper motions and parallaxes. Results. We find that the association is made up of a number of small groups, with a total current mass over 2330 M . The threedimensional distribution of these young stars trace the edge of the gas and dust structure known as the IRAS Vela Shell across ∼180 pc and shows clear signs of expansion. Conclusions. We propose a common history for Vela OB2 and the IRAS Vela Shell. The event that caused the expansion of the shell happened before the Vela OB2 stars formed, imprinted the expansion in the gas the stars formed from, and most likely triggered star formation.

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“…Vallee & Bignell (1983) modelled the Gum nebula as a magnetic bubble close to the Sun, using 32 RMs that lie within 30 • of the centre of the Gum nebula. More recently, Purcell et al (2015) modelled the Gum nebula as an H ii region around a wind-blown bubble. RMs in the top part of the Gum nebula, which Purcell et al used in their analysis, show a clear transition from inside the edge of the bubble (strong Hα emission) to outside, over a very small distance (see fig.…”

Section: Resultsmentioning

confidence: 99%

S-PASS/ATCA: a window on the magnetic universe in the Southern hemisphere

Schnitzeler

Carretti

Wieringa

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present S-PASS/ATCA, the first wide-band radio polarimetry survey of compact sources in the southern sky. We describe how we selected targets for observations with the Australia Telescope Compact Array (ATCA) in the 16 cm band (1.3 -3.1 GHz), our observing and calibration strategy, how we analysed the data, and how we tested the quality of the data. The data are made publicly available. The survey contains on average one source per five square degrees and has an angular resolution at 2.2 GHz of ∼ 2 ′ ×1 ′ . Sources with |RM|s > 150 rad m −2 are seen towards the Galactic plane and bright H ii regions, but are rare elsewhere on the sky. Sightlines that are separated by up to 3 ′ show very similar RMs. Based on this observation, we argue that the Galactic foreground is the dominant contributor to RM, confirming previous results, and that the sources must have very simple distributions of Faraday-rotating and synchrotronemitting media. Many sources that emit at a single RM have a spectral index in linear polarization that is (very) different from the spectral index in Stokes I. Analysing ratios of flux densities Q/I and U/I (to correct for spectral index effects) then leads to erroneous results. About 80 per cent of sightlines in our survey are dominated by emission at only one RM. Therefore, RMs that were determined previously from narrow-band observations at these frequencies are still safe to use.

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A Radio-Polarization and Rotation Measure Study of the Gum Nebula and Its Environment

Cited by 50 publications

References 129 publications

Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm

Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm

A ring in a shell: the large-scale 6D structure of the Vela OB2 complex

S-PASS/ATCA: a window on the magnetic universe in the Southern hemisphere

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